Natural Family Planning International, Inc. (NFPI)
Home NFP Resources Spiritual Resources Blogs Contact

NFP Research

Review of Breastfeeding Infertility Research up to 1972

By Sheila Kippley

[Note: Most of this research was conducted prior to 1970, was compiled by Sheila Kippley, and was published in the second edition of Breastfeeding and Natural Child Spacing by Harper & Row, 1974. This research, found in the 1974 Appendix, was deleted in later editions. This older research is included here for those who may find it interesting.

The research of the 1970s, 1980s, and 1990s on breastfeeding infertility complements or confirms that research done in earlier days. "Fully breastfeeding," "complete breastfeeding," and "total breastfeeding" in the old research all mean the same as "exclusive breastfeeding" in the recent research of our day. That is, the baby receives only his mother's milk, and directly from her breast. Amenorrhea means the woman is not having any menstrual periods.]

What follows is the Appendix I in the 1974 edition of Breastfeeding and Natural Child Spacing.

A Review of the Research
The following material summarizes most of the work that has been conducted on the subject of breastfeeding and infertility. This review has its limitation. In the first place, when breastfeeding was the accepted norm, say before 1920, medical research was not as well developed as it is today. On the other hand, as medical research became more popular, breastfeeding became less and less popular and therefore became less a subject of research. Furthermore, while research that might have been done before 1920 may have dealt with mothers who were breastfeeding 100 % or totally for a considerable length of time, present research is hampered by the fact that women who are included in a sample of nursing mothers are usually not nursing 100%. Many are using the bottle or solids. Sometimes the researcher does not clearly define how the mother is feeding the baby. Breastfeeding, then, is difficult to study in a culture where so few mothers nurse for a considerable length of time, and where artificial feeding of the infant is a common practice.

Research today becomes more difficult due to the heavy emphasis placed on contraceptive practices. The researcher should know the personal views of each mother to be certain that breastfeeding is the only method of family planning used for a certain period of time. In our country it is interesting to note that, regardless of our emphasis on bottles, early solids, and contraceptive practices, the studies show that breastfeeding still decreases the fertility rates. They also show that breastfeeding can be a very effective and natural way to space babies.

This review attempts to show the important role suckling plays in the maintenance of natural infertility. Hormones cannot be ignored in the total picture. However, since so little is known about the complex hormonal pattern involved in the maintenance of lactation infertility, no explanation will be attempted. The discussion instead will center around the suckling act-an external act we can see and understand, unlike the hormones themselves.

How does the suckling of an infant at the breast of his mother influence menstruation and ovulation? The following selections were taken from studies that sought to explain the absence of menstruation during lactation.

In 1951 Dr. Albert Sharman, of the Royal Samaritan Hospital for Women in Glasgow, noticed that menstruation occurred during lactation for some mothers and not for others. From this observation the doctor felt that lactation alone did not prevent a woman from having periods, but that there would have to be some other contributory cause.1

In 1954 a research team concluded from their work that the reappearance of the menstrual cycles in the early months after childbirth was normally brought about by a reduction in a suckling2 stimulus. This reduction is voluntary, or else is brought about by the use of artificial foods to supplement the mother's milk.3

In 1967 another research team found that follicular growth (development necessary before ovulation can occur) and ovulation were inhibited during suckling.4 In 1949 Dr. Isadore Udesky of the Northwestern University Medical School and Michael Reese Hospital had reported the same observation from his studies. He added that suckling is directly responsible for this inhibition of the ovarian cycle.5

It is interesting to note an endocrine study that was done in 1967. Dr. C. E. Grosvenor and his associates found that two things were necessary for efficient release of prolactin in response to suckling among suckled mother rats: 1) The suckling had to be periodic and 2) it had to occur at short intervals.6 Prolactin is one of the hormones said to be responsible for lactation. (I might add here that these quantitative characteristics of the suckling act-short intervals and periodic-also seem to influence the effectiveness of the spacing mechanism.)

In 1965 the World Health Organization reported that there are two obvious stimuli that interrupt the reproductive cycles in the adult female. These are coitus which results in pregnancy and suckling.7 In another report the WHO said that with lactation 1) there is a period of time after delivery when a woman does not menstruate or ovulate, 2) the first period often occurs without ovulation, 3) infertility remains for a longer period if lactation is prolonged, and 4) our knowledge of lactation with respect to infertility is still incomplete.8

The Inactivity of Ovaries during Lactation Studies also show that the ovaries are at rest or nonfunctioning during lactation.

  1. Albert Sharman, "Ovulation after Pregnancy," Fertility and Sterility 2 (1951), 387.
  2. "Suckling" and "sucking" are both used in the research terminology interchangeably. Suckling is broader; sometimes it means the individual acts; at other times, it refers to the breastfeeding process over a period of months. In this article, I used the word "suckling" as a preferred choice.
  3. Thomas McKeown and J. R. Gibson, "A Note on Menstruation and Conception During Lactation," Journal of Obstetrics and Gynecology of the British Empire 61 (1954), 825-6.
  4. Hiroshi Minaguchi and Joseph Meites, "Effects of Suckling on Hypothalamic LH-Releasing Factor and Prolactin Inhibiting Factor, and on Pituitary LH and Prolactin," Endocrinology 80 (1967), 604-6.
  5. Isadore Udesky, "Ovulation in Lactating Women," American Journal of Obstetrics and Gynecology 59 (1950), 847.
  6. C. E. Grosvenor, F. Mena, and D. A. Schaefgen, "Effect of Non-suckling Interval and Duration of Suckling on the Suckling-Induced Fall in Pituitary Prolactin Concentration in the Rat," Endocrinology 81(1967): 453.
  7. World Health Organization, "Neuroendocrinology and Reproduction in the Human," Technical Report Series 304 (Geneva, 1965), 11.
  8. World Health Organization, "Biology of Human Reproduction," Technical Report Series 280 (Geneva, 1964); idem., "Physiology of Lactation," Technical Report Series 305 (Geneva, 1965),10.

It was suggested in 1961 that the absence of menstruation during lactation is due to ovarian inactivity.9

In 1943 Dr. Paul Topkins concluded that the absence of menstruation during lactation is due to the suppression of the ovarian function. He stated that during lactation amenorrhea, the follicles in the ovaries failed to mature and rupture.10

When a doctor wrote to the Journal of the American Medical Association in 1958 asking why a woman does not become pregnant or ovulate when she is breastfeeding, the editor's reply was the following:

Ovarian function is suppressed but not completely inhibited during lactation. Recent evidence indicates that it is the stimulus of suckling of the infant rather than lactation which acts on the pituitary gland, probably by way of the midbrain. The decrease in the frequency of feedings and the cessation of nursing result in the reestablishment of ovarian function, the reappearance of menstruation, and, ultimately, ovulation. Complete breastfeeding in the early months of life is a fairly effective method of suppressing ovarian function and conception.11

Lactation and Conception
During the years 1938 to 1940, Dr. Margaret Robinson noted that pregnancies occurred while mothers were nursing their babies. The nursing mothers (number not given) conceived two to three months after delivery. The 1100 nursing cases in this study, however, were characterized by early weaning and "failing lactation" (the title of the research paper).12 Since the study involved only cases of unsuccessful nursing and "premature weaning" according to Dr. Robinson, we might assume that the breastfeeding was not complete nor the milk supply ample at the time of conception.

In 1943 Dr. Paul Topkins observed that during the non-menstrual phase among nursing mothers, conception rarely occurred. He questioned to what degree ovulation is inhibited among nursing mothers and performed 145 biopsies on 28 normal nursing mothers who had had regular menstrual cycles before delivery. Women who had four or more specimens taken were chosen for this study. Dr. Topkins concluded that ovulation is suppressed during lactation and that this inhibition of ovarian activity is complete when menstruation is absent and incomplete when menstruation is present.13

In 1946 Dr. J. W. B. Douglas of the University of London studied the different aspects of breastfeeding among 4,669 babies. Since in this study a breastfed baby was considered breastfed until he was entirely weaned off the breast, it is impossible to determine the duration of complete breastfeeding in these cases. Mothers in this study averaged about five and a half months of nursing.

9. W. C. Keettel and J. T. Bradbury, "Endocrine Studies of Lactation Amenorrhea," American Journal of Obstetrics and Gynecology 82 (1961), 995.

10. Paul Topkins, "The Histologic Appearance of the Endometrium During Lactation and Its Relationship to Ovarian Function," American Journal of Obstetrics and Gynecology 77 (1959), 57.

11. "Letters to the Editor," Journal of the American Medical Association 167 (1958), 144.

12. Margaret Robinson, "Failing Lactation," Lancet 1 (1943), 66.

13. Op. cit.,57.

One aspect that interested Dr. Douglas was the rate of pregnancies during the first year after childbirth among bottle-feeding and breastfeeding mothers. He found that during the first nine months after childbirth the number of pregnancies was considerably lower among those mothers who were nursing their babies, but that during the 10 to 12-month period the number of pregnancies was the same for both groups. He explained this conclusion by saying that in the latter months of this study mothers were only nursing their babies once or twice during the day. The doctor pointed out that it was impossible to determine two varying factors: the use of birth control and the frequency of coitus. However, he felt that the breastfeeding mothers were not practicing a more effective method of birth control because their fertility rate equaled that of the bottle-feeding mothers once breastfeeding ceased.14

In 1950 Dr. Isadore Udesky performed repeated endometrial biopsies on 121 nursing mothers during the non-menstrual phase to determine any evidence of ovulation before menstruation returned. The doctor said that all of the nursing mothers were nursing "regularly." The question arises as to whether a nursing mother can become pregnant before menstruation returns following childbirth. He answered yes, but only in a very few-about 3½ %. His primary conclusion was that, during lactation and the absence of menstruation, the suppression of the ovarian function is almost complete.15

In 1951 Dr. Albert Sharman presented a paper to the Seventh Annual Meeting of the American Society for the Study of Sterility outlining a follow-up study carried out on 834 women during the nine-month period following delivery. Dr. Sharman defines the type of feeding with reference to the liquid diet of the baby. Complete lactators (196) apparently were those who only offered the breast. No bottle would have been offered on a regular basis among these mothers, for he defines the next group of women as partial lactators (356), or those who eventually offered the breast and the bottle toward the end of the study. Non-lactators (282) were those who offered only the bottle. Out of the total 834 women, only 12 (approximately 1½ %) became pregnant during the nine-month period following childbirth, and all 12 had at least two menstrual periods before conception took place. A significant factor is that none of the "lactators" became pregnant during this time. Three women who became pregnant while partially nursing had all introduced the bottle at least a month or more before conception took place. Dr. Sharman concluded that there is a considerably lower risk of conception among nursing mothers.16

In a subsequent paper, written in 1954, Dr. Sharman was primarily interested in recording the menstrual periods of apparently these same 834 women. His recordings and tables indicated that menstruation did occur at a later date among the nursing mothers.17

In 1953 a study was conducted by a registered nurse, Rose Gioiosa, at the Catholic Maternity Institute in Santa Fe, New Mexico, where encouragement and instruction are offered to nursing mothers. Among the 148 nursing mothers selected, 500

14. J. W. B. Douglas, "The Extent of Breast Feeding in Great Britain in 1946, with Special Reference to the Health and Survival of Children," Journal of Obstetrics and Gynecology of the British Empire 57 (1950), 343.

15. Op. cit., 845.

16. Op. cit., 386.

17. Albert Sharman, "Menstruation after Childbirth," Journal of Obstetrics and Gynecology of the British Empire 58 (1954), 443. pregnancies were studied during the years. Only 46 of the 500 pregnancies occurred during the time of lactation, and these occurred during the weaning process in the latter months of breastfeeding. All other pregnancies occurred after the mothers had stopped nursing. The return of menstruation was not considered in this study.

From this study the nurse concluded that breastfeeding is a natural means of spacing children and that this protection lasts for about 9 months or more, providing no formula is given to the baby. She emphasized that early solids or early supplements decreased the amount of time in which a mother is unable to conceive. The natural-spacing mechanism is shortened by early weaning, and as a result the mother conceives at a much earlier date than she would if she had nursed her baby for 9 months or more without the use of bottles and had introduced supplementary solids only at about 6 months of age. She also strongly emphasized the need for educational programs to inform the youth and expectant parents of the advantages of breastfeeding and especially of natural spacing.18

Rose Gioiosa also wrote another article, "Breastfeeding and Child Spacing,"19 in which she showed that one of the most practical advantages of breastfeeding is that a mother can space babies naturally, that she does not need to use any other family-planning technique in order to space her children. She related doctors' experiences in other countries, where they found that mothers nurse for a long time because they believe that breastfeeding prevents the risk of another pregnancy. In certain countries (Africa, Ceylon, India, Iraq, Malaya, Syria) there are still places where breastfeeding is valued as a baby-spacer. She then analyzed the 1961 La Leche League Nationwide Survey and found once again that early weaning shortens the natural spacing interval afforded by breastfeeding.

In 1954 McKeown and Gibson studied 1,227 women for one year following childbirth. Of these mothers, 87 (7%) conceived during the year. No mother conceived while fully breastfeeding and before having periods. Two mothers who were nursing fully conceived after having one menstrual period. All the other mothers were using artificial feedings before conception occurred.20

In 1968 Dr. T. J. Cronin studied the basal temperature recordings of 174 mothers during the three months following childbirth. Among this group there were 93 who did not try to nurse their babies. For the mothers who did not nurse, the mean time up to the return of menstruation was 58.9 days, and the mean time up to the time of the first ovulation was 73.5 days after delivery.

There were 28 mothers who stopped nursing less than four weeks after delivery. In this small group the doctor found that menstruation returned on the average 15.4 days earlier than it had for the non-nursing group. Yet these mothers who quit nursing at any early date had a mean period of 70.7 days before ovulation returned, a median figure which is very close to the non-nursing group.

Of the remaining 53 mothers who were still nursing after the 28-day period following childbirth, 10 ovulated before the three-month period date following delivery. Five of the

18. Rose Gioiosa, "Incidence of Pregnancy During Lactation in 500 Cases," American Journal of Obstetrics and Gynecology 70 (1955), 162-174.

19. La Leche League reprint no. 121 (Franklin Park, Illinois, 1964).

20. Op. cit., 826.

mothers already had a return of menstruation, four had stopped nursing at the time of ovulation, and only one nursing mother ovulated before the return of her menstrual periods. Ovulation in her case occurred at Day 73; menstruation appeared on Day 84; and she supplemented on Day 99.

Observing other studies that had been done to determine the time of ovulation following childbirth and observing his own group of nursing mothers (many of whom supplemented in the early months or who stopped nursing during the three-month period following delivery), Dr. Cronin concluded that ovulation rarely occurs during the 10 weeks following childbirth if the mother is fully nursing and if menstruation is not present.21

In 1933 Dr. C. H. Peckham from the Department of Obstetrics at Johns Hopkins University and Hospital analyzed Dr. J. W. Williams' study conducted on 2,885 women. Almost all of these mothers were nursing when they left the hospital, and most continued to nurse even if they used the bottle. Fifty percent (50%) of the mothers were still nursing at 6 months; 28% were still nursing at the end of the year. The average duration of breastfeeding for this group was about 8½ months.

Of these 2,885 women, 30% conceived during the first year (about 877). Of the mothers who were nursing at the time of conception, over 50% menstruated four or more times before conception, but 10% conceived without menstruating.22

An Egyptian medical team studied the lactation patterns of 120 mothers by verbal questioning. The duration of breastfeeding among these women averaged 15.1 months. This study I found confusing; definitions were not clear. One-third of the mothers menstruated during the first three postpartum months and two-thirds during the first nine postpartum months with "full lactation" averaging nine months among these mothers. The incidence of pregnancy for nursing mothers during amenorrhea was given as 50% and during menstruation as 63%. The 50% risk factor during lactation amenorrhea is a much higher figure than those given in other studies. The doctors concluded that breastfeeding is an unsatisfactory method of birth control.23

In France Juliette Pascal [Sister Marie Christine] studied the postpartum periods among nursing and non-nursing mothers for three years (1965-1968). Here are some of the conclusions: 1) The 449 nursing mothers averaged 58 days of amenorrhea, although it is noted that menstruation returned most frequently in the 40- to 49-day period following childbirth; 2) one-third of the nursing mothers run a risk of conceiving before the first postpartum menses; 3) only 3% run the risk of conception prior to the first postpartum menses if completely nursing.24

It is interesting that the first two conclusions might be what you would expect among bottle-feeding mothers. Suffice it to say that only 7% of these mothers nursed past 6 months and over half of them had quit nursing by the 6th week. An interesting

21. T. J. Cronin, "The Influence of Lactation upon Ovulation," Lancet 2 (1968), 423-4.

22. C. H. Peckham, "An Investigation of Some Effects of Pregnancy Noted Six Weeks and One Year After Delivery," Bulletin of the Johns Hopkins Hospital 54 (1934), 204.

23. 23. I. Kamal et al., "Clinical, Biochemical, and Experimental Studies on Lactation," American Journal of Obstetrics and Gynecology 105:3 (October 1, 1969), 317, 321.

24. Juliette Pascal, "Some Aspects of Post-Partum Physiology" (Doctoral thesis presented at the University of Nancy, France, October 1969). Translation and summary by Dr. S. P. Carreau of Serena, Inc., and Dr. C. Lanctot of the Natural Family Planning Association of Connecticut.

comparison of Pascal's work and our survey is given later in the part of Appendix II dealing with the report on breastfeeding and amenorrhea by the author and her husband. [available at this website] The primary reason for selecting Pascal's work for such a comparison was that this work was publicized among some natural family planning groups as being a significant contribution.

Dr. Christopher Tietze of The Population Council sought to clarify the confusion as to whether or not a woman could conceive while nursing her baby and attempted to review all the available demographic medical work. In 1961 his work was presented before the International Population Conference; the paper was titled "The Effect of Breastfeeding on the Rate of Conception." In this paper he concluded the following points:

  1. that the prolonged absence of menstruation seems to be the major factor involved in the delay of conception among nursing mothers;
  2. that during breastfeeding, and with the absence of menstruation, "ovulation is suppressed and conception therefore impossible";
  3. that while ovulation is normally followed by a menstrual flow, "the first menstrual flow is preceded by ovulation in only a minority of [lactating] women";
  4. that a woman has about a 5% chance of conceiving before the return of her first menstrual period;
  5. that when menstruation returns, the first two periods are usually infertile;
  6. that the risk of conceiving "increases rapidly after menstruation has returned";
  7. and that since "breastfeeding tends to prolong the interval between pregnancies, it seems worthwhile to evaluate it as a method of child spacing."25

Dr. Konald Prem from the University of Minnesota Medical School is conducting a study on postpartum ovulation among nursing and non-nursing mothers with the aid of basal body temperature graphs. The non-nursing mother may experience ovulation as early as 27 days after childbirth, and ovulation usually occurs prior to menses after a natural spontaneous abortion. The incidence of early return of fertility is great among nursing mothers who supplement or wean early, whereas the incidence of a fertile ovulation before menstruation during the first 4 to 5 months of total breastfeeding is small. Of the 118 nursing mothers, 6 conceived without a return of menstruation. Dr. Prem concluded that the risk of pregnancy during lactation amenorrhea is about 5%- 1% less than the risk recorded by Remfry in 1895.26

The Duration of Amenorrhea
One table in Dr. Tietze's paper presented the works of various researchers, and here it was shown that in one group of 523 Indian women the mean duration of breastfeeding was 16½ months and the mean duration of amenorrhea was almost 12 months.27

In 1958, among a group of 272 nursing mothers in Bombay, it was found that a third of the mothers had a period by the 9th month, half of them had a period by the 12th month, and for those who continued to nurse most did not have a return of menstruation

25. Christopher Tietze, "The Effect of Breastfeeding on the Rate of Conception" (Paper presented at the International Population Conference, New York, September 1961), 131-134.

26. Konald Prem, "Post-Partum Ovulation" (Paper presented at La Leche League International Convention, Chicago, July 1971).

27. Op. cit.

until their baby was 18 months old. Amenorrhea of a year or more was quite common in India-unlike the nursing mothers in America and in Europe. When menstruation did finally return after many months following childbirth, the research team observed that fertility was by no means impaired and conception was still possible. This is a normal condition and cannot be said to be pathological, for the authors said the once menstruation became reestablished, the fertility rate in these nursing mothers was as high as those for whom menstruation returned within the twelve-month period following childbirth.28

The effectiveness of the non-menstrual phase in preventing pregnancy was studied among a group of 390 women and reported in the Journal of Obstetrics and Gynecology of India. The mean duration of lactation for 282 mothers was 13½ months; the mean duration of amenorrhea was 5¼ months. At the end of this study, the remaining 108 nursing mothers still had no return of their menstruation. The conclusions were that those who weaned early or used other milks early also had early menstruation; that the earlier artificial feeding began, the earlier menstruation began; and that menstruation began later among the fully lactating mothers.29

In Cairo a study of 145 nursing mothers found 86 of them experiencing amenorrhea. Among these 86, the duration of postpartum lactation amenorrhea ranged from 6 weeks to 26 months. Forty-six (46) mothers nursed for less than 6 months, 20 nursed from 6 to 12 months, and 20 nursed for a year or longer. Lactation amenorrhea lasted longer when the breastfeeding was not supplemented. The authors concluded that it is a fact that physiologic infertility is associated with postpartum lactation amenorrhea and should receive more attention as a result of population concerns.30

A study in Taiwan showed that the nursing mother averaged 10.6 months of amenorrhea as compared to 3.5 months of amenorrhea for the non-nursing mother. Thus, lactation provided on the average 7.1 more months of natural infertility. The researchers estimated that the prevalence of lactation with its additional 7.1 months of added infertility would prevent 20% of the births that would occur without lactation. They found that other factors influenced the duration of amenorrhea. Supplementation meant a shorter postpartum amenorrhea. In addition, city life and education reduced the period of lactation as well as the period of amenorrhea.31

While for some years it has been almost routine for some doctors to give a drug injection to most women after childbirth to dry up the milk supply, some new research is being done in the opposite direction. A medical team recently reported on their efforts to promote the production of breast milk and postpartum infertility through intravenous injections of thyrotropin-releasing hormone (TRH). They listed nausea, vomiting,

28. H. Peters, S. Israel, and S. Purshottam, "Lactation Period in Indian Women-Duration of Amenorrhea and Vaginal and Cervical Cytology," Fertility and Sterility 9 (1958), 134; Paul Topkins, Abstract on "Peters, Israel, and Purshottam: Lactation Period in Indian Women: Duration of Amenorrhea and Vaginal and Cervical Cytology," American Journal of Obstetrics and Gynecology 77 (1959), 921.

29. Stuart Silverberg, "Selected Abstracts," American Journal of Obstetrics and Gynecology 82 (1961), 1196.

30. M. F. El-Minawi and M. S. Foda, "Postpartum Lactation Amenorrhea," American Journal of Obstetrics and Gynecology 111 (September 1, 1971), 17, 21.

31. A. Jain et al., "Demographic Aspects of Lactation and Postpartum Amenorrhea," Demography, May 1970, 267, 269.

urinary urgency, and breast engorgement as side effects although their particular patients had only the latter.32

Such a drug may be helpful in the case where a mother wants to reestablish lactation, as for example, when wanting to nurse an adopted child or when an already weaned child needs breast milk. However, I hope that the use of such a drug will be confined to such rare cases and will not be used for birth control purposes. All that the normal woman needs for an ample milk supply is a suckling baby from childbirth onwards.

In 1966 Dr. Eva J. Salber and her associates from Harvard School of Public Health in Boston recorded the duration of amenorrhea after childbirth among 2,197 mothers. Non-nursing and nursing mothers had an overall mean of 68 days without menstruation. Of the bottle-feeding mothers, 91% had a return of menstruation within 3 months after childbirth. The other 9% had a return within the next 3 months. On the other hand, 26% of the nursing mothers had a return of menses 3 months after childbirth, and about 60% had a return by 6 months postpartum. Most nursing mothers (95%) had a return of their period within 6 weeks after they discontinued nursing.33

These figures resemble those given by McKeown and Gibson in 1954. They found that 40% of the breastfeeding mothers and 95% of the bottle-feeding mothers had a return of menses by 4 months after childbirth.34

On the other hand, Prem found in his study of 74 mothers who nursed longer than 6 months that 57 (77%) were without menses at 6 months postpartum. Of those 51 mothers who breastfed longer than 9 months, 31 (61%) were without menses by 9 months postpartum. He found that the return of menstruation occurred most frequently in the 9- to 12-month period following childbirth. Many of the mothers in this study were associated with La Leche League, which encourages total breastfeeding in the early months of life, and this probably accounts for the longer duration of amenorrhea in Dr. Prem's study.35

In our survey we found that those women who totally breastfed for at least 5 months averaged 11.6 months without menses and that the return of menstruation occurred most frequently in the 9- to 12-month period following childbirth. Of those mothers who followed the natural mother program [ecological breastfeeding program] the average duration of amenorrhea was 14.6 months and the greatest frequency of menses return occurred in the 13- to 16-month period following childbirth.36

Infertile Periods
Inés de Allende of Argentina made a thorough review of the research that had been done to determine whether or not a woman could have a menstrual period without

32. J. E. Tyson, H. G. Friesen, and M. S. Anderson, "Human Lactational and Ovarian Response to Endogenous Prolactin Release," Science, September 1972, 897, 899.

33. E. Salber, M. Feinleib, and B. Macmahon, "The Duration of Postpartum Amenorrhea," American Journal of Epidemiology 82 (1966), 349-351.

34. Op. cit., 825.

35. Op. cit.

36. S. Kippley and J. Kippley, "Report on Breastfeeding and Amenorrhea," Marriage and Family Newsletter, March 1972. Later published in a revised form as "The Relation between Breastfeeding and Amenorrhea: Report of a Survey" in the Journal of the Nurses Association of the American College of Obstetricians and Gynecologists 1 (November-December 1972), 18. having ovulated beforehand. From his investigation he found that these infertile periods were first suggested in the 1920s by Corner as a result of his studies on the monkey. Corner's belief was soon proven to be fact in the 1930s by three different research projects; all three projects carried out their diagnostic procedures on the human female.

In 1956 de Allende reported from his own work and that of others that 1) infertile periods occur occasionally even in the healthy, non-pregnant, non-nursing mother during the full sexual activity period, 2) that rarely does a woman have only fertile periods, and 3) that there are more infertile periods in proportion to fertile periods at the beginning and at the end of a woman's reproductive life.37

In 1938 Dr. Paul Lass and his associates from the Department of Obstetrics and Gynecology and Biochemistry of the College of Physicians and Surgeons at Columbia University, New York City, carried out a study on 47 menstruating mothers in which regular monthly periods were observed for a nine-month period following childbirth. These women who were not nursing their babies completely (weaning occurred during the time of the study) and who were having regular menstrual cycles had 55% of those periods recorded as infertile. One mother, on the other hand, who nursed every four hours had all infertile periods (8 in number) before weaning was completed. After cessation of breastfeeding, her menstrual cycles were fertile. The first menstrual periods in this study were experienced 30 to 100 days after childbirth.38 The duration of amenorrhea among these mothers was equivalent in length to the expected norm of non-nursing mothers following childbirth.

In 1950 Dr. Isadore Udesky from Northwestern University Medical School and Michael Reese Hospital studied one group of 36 mothers who had their first periods while nursing. He found that 14 percent of these women gave evidence of ovulation either preceding or "from twenty days on" after the first period; over 28% of the periods after the third period occurred with ovulation during lactation.

On the other hand, in the same study there were also 200 endometrial biopsies taken on another group of 85 normal nursing mothers who had no return of menses. Of these biopsies, 98.5% were infertile in character and 1.5% (three mothers) were fertile in character. In each of the 3 cases menstruation followed. Udesky also referred to a 1937 study by Rock and Bartlett that answered the question of whether a woman can become pregnant during lactation amenorrhea by saying that it was possible in "about 3.5% of cases where the first ovulation is followed immediately by conception."

Dr. Udesky's paper was presented at the Chicago gynecological Society in 1949. After his presentation several doctors had these points to offer during the discussion period that followed:39

1. Dr. George W. Bartelmez, who has himself done studies on the human uterus during menstruation, pointed out that there is a possible error that one will diagnose too many fertile periods during lactation that are actually infertile, since Dr. Udesky's work and Dr. Hartman's work show us that the change from the atypical or infertile to the typical or fertile state is a very gradual

37. Inés de Allende, "Anovulatory Cycles in Women," American Journal of Anatomy 98 (1956), 303.

38. P. Lass, J. Smelser, and R. Kurzrok, "Studies Relating to Time of Human Ovulation: III During Lactation," Endocrinology 23 (1938), 39-43.

39. Op. cit., 844-5, 849. change. (This point of diagnosing too many ovulations, I might add here, was also determined to be true by de Allende when using the basal temperature method. He found that about a third of the cycles (49 out of 155 periods) that were recorded as fertile according to the basal temperature method were infertile according to the vaginal smear tests.)

2. Dr. M. Edward Davis said that Dr. Scheitema and he carried out a study in 1942 to determine ovarian activity after delivery among non-nursing mothers. His endometrial biopsies revealed that ovulation rarely occurred before the first menstrual period, that ovulation occurred in about 50% of the second periods, and that ovulation was associated with nearly all of the third periods. The two doctors concluded that this gradual pattern from the fertile to the infertile or from the infertile to the fertile condition in the adult female was witnessed at the beginning of the menstrual cycles in early life, at the end of the menstrual cycles in later life, and also at the return of the menstrual cycles following childbirth.

Dr. Udesky closed the discussion period by saying that ovulation is more likely to occur during the weaning process and that this is why doctors know of mothers who have conceived while nursing their babies.40

Dr. Albert Sharman carried out a study on 85 menstruating mothers from a period of 5 days to 9 months following childbirth. Of these 85, 68 were non-nursing mothers and 14 were nursing mothers throughout the duration of the study. The number of nursing mothers was small, since most mothers stopped nursing before menstruation returned. First biopsies showed that 11 (79%) of the 14 nursing mothers were in an infertile condition and 3 (21%) [at 13, 19, and 28 weeks] were in a fertile condition. On the other hand, about 71% of the non-nursing mothers were shown to be in a fertile condition. Dr. Sharman concluded that breastfeeding does tend to retard the return of ovulation.41

Natural Spacing
During the 1950s Dr. Otto Schaefer noted that with traditional nursing among the Eskimos the next baby arrived about three years later. He concluded that the traditionally small-size Eskimo family was due to prolonged nursing more than high infant mortality. In fact, in another study done by his Canadian Medical Service between 1962 and 1965, it was found that infant mortality was always higher among bottle-fed infants. In addition, the bottle-fed children had more gastrointestinal diseases, respiratory and middle-ear diseases, and more anemia.

Dr. Schaefer observed that the rapid introduction of bottles from the trading posts changed feeding habits and fertility patterns drastically. The birthrate jumped 50%, from less than 40 births per 1000 in the mid-1950s to 64 per 1000 ten years later. The closer the Eskimo families lived to the trading posts, the more frequently their babies arrived. He mentioned that in the last twenty years the Eskimos have had a population explosion as great or greater than that experienced by any other developing nation. This explosion is "due less to the reduction in infant mortality than to the jump in birthrate"; the increased birthrate is attributed to bottle-feeding and a shortened lactation period. This

40. Op. cit., 851.

41. Sharman, "Ovulation after Pregnancy," 380, 385.

factor, he claimed, is overlooked when studying the population problem in other countries.42

In 1960 and 1971 Dr. J. A. Hildes and Dr. Schaefer conducted studies on the Igloolik Eskimos. One outstanding observation dealt with the difference in the fertility rates among the older women as opposed to the younger women. Women aged 30 to 50 years who had traditionally breastfed for 2 to 3 years conceived 20 to 30 months after childbirth, whereas the younger mothers under 30 years of age who bottle-fed conceived 2 to 4 months after childbirth. These doctors noted that other researchers attribute the population explosion in other countries to a reduced mortality rate. However, the Iglooliks have a population problem in spite of their high infant death rate. The doctors found that it is the rapid urbanization of these Eskimos during the past 20 years that is responsible for the increase in births, urbanization that brought rapid communication, and thus a rapid introduction of the baby bottle, to these people. Thus they lost the natural population control that prolonged breastfeeding had previously given them.43

This review and most of the material written on breastfeeding and amenorrhea or the rate of conception fail to describe clearly the type of breastfeeding or mothering involved. In spite of this fact, it becomes fairly obvious that breastfeeding plays an important role in postpartum infertility and can influence the birthrate of an individual family as well as a nation.

42. Otto Schaefer, "When the Eskimo Comes to Town," Nutrition Today, November-December 1971, 15-16.
43. J. A. Hildes and O. Schaefer, "Health of Igloolik Eskimos and Changes with Urbanization" (Paper presented at the Circumpolar Health Symposium, Oulu, Finland, June 1971).

Published in Breastfeeding and Natural Child Spacing, 2nd edition, Harper & Row, 1974 and Penguin Books, 1975.