Breastfeeding and Fertility
by Katherine A. Dettwyler, Ph.D.
Department of Anthropology,
Texas A & M University
2004 Update: Peter Ellison has published two books on this topic. They are
On Fertile Ground, by Peter T. Ellison, May 2003, Harvard University Press. Available from www.amazon.com (click HERE)
Reproductive Ecology and Human Evolution (Evolutionary Foundations of Human Behavior), edited by Peter T. Ellison, December 2001, Aldine de Gruyter Publishers, New York. Available from www.amazon.com (click HERE)
----------------------------------------------------------------------------------------------------------My original post from 1995:
There is a chapter in Breastfeeding:
Biocultural Perspectives on "Breastfeeding, Fertility and Maternal
Conditon," by Peter Ellison. He is an anthropologist and head of the anthropology
department at Harvard University. This chapter takes a historical look at the research
that has been done on understanding the links between breastfeeding and fertility, from
the earliest days up to 1993, when he finished his chapter (it takes forever to get
a manuscript through all the stages in to print).
Here's my brief synopsis of his thorough chapter. Suckling
by the baby causes the mother's pituitary to release prolactin. It used to be thought that
prolactin directly affected ovulation/fertility, but new research suggests that there is
another hormone intermediate between prolactin and the ovaries. So that high levels of
prolactin lead to either high or low levels of this other factor, which then affects
fertility. Fertility is not an "either/or" sort of phenomenon. Post-partum, a
woman does not ovulation for a while, even if she isn't breastfeeding. If she is
breastfeeding frequently enough to keep her prolactin levels above her individual critical
threshhold for fertility (and women vary in this threshhold) then her fertility is
The greatest level of suppression is not ovulating, but as
your prolactin levels go up, your fertility will gradually return. First you will ovulate,
but not have the proper hormone levels for fertilization; then you will ovulate and
fertilization may occur, but you still may not have the proper hormone levels for
implantation; finally, you may ovulate, be fertilized, and implant, but not have the
proper hormone levels for continuing the pregnancy, so you have a very early miscarriage,
probably along the lines of minutes or hours after implantation, so you wouldn't know you
had been pregnant. It is also possible to ovulate without having the right hormonal levels
in the right combinations for the uterus to have been preparing for implantation, so yes,
it is possible to ovulate without menstruating. For all of these stages, there seems to be
incredible individual variation between women. Some women get pregnant again the first
time they ovulate, with no intervening menstrual periods. I knew a woman in Indiana years
ago who had three children in six years with no menstrual periods! Her doctor couldn't
figure out when to predict her due date :)
Also, would you believe there is no research out there yet,
none at all, on whether it is possible for the trajectory of gradually returning fertility
to be reversed as a result of increased nursing? I specifically asked Peter Ellison to
include this research in his chapter, and he assures me there isn't any, though as he puts
it "Logically, it makes sense." That is, if the baby nurses more frequently
again,, after the mother's periods have returned, it would raise the mother's circulating
levels of prolactin, presumably high enough to affect fertility again.
I am sure that this works, both from personal experience and
from anecdotal reports from other nursing moms. To give a specific example, with my third
child Alexander, I worked mainly from home the first year of his life, and spent many
hours at my computer writing with me logged on and him latched on! The summer of 1992,
when he was a year old, I was at home for the summer (not teaching classes) and he nursed
a lot. When he was 13 months old, and fall semester was starting, I put him in day care 6
hours a day, so I could have more time at the office, and my periods promptly returned the
next month. I had a period in October, and one in November, then we finished for the
semester in mid-December and I was at home with him all day for 5 weeks (what a job :)). I
didn't have a period in December or January, then resumed again for good in February.
Sigh. I wish someone would develop a pill that mimicked the actions of lactation
amenorrhea so I didn't have to have periods for the next who knows how many years. And I
don't have PMS or menstrual cramps or anything, so I know I shouldn't complain. Back to
the subject at hand -- my understanding is that a woman is born with thousands of eggs,
and that menopause has nothing to do with using up all your eggs.
I would imagine that there could be some connection between
continued breastfeeding and failure to sustain a pregnancy, especially in a woman who
released large amounts of prolactin in response to nursing, or whose ovaries were
especially susceptible to whatever level of prolactin (or other hormone) she did produce.
You should consult a reproductive endocrinologist to see if this is the case. I don't
think the oxytocin levels that cause uterine contractions could be leading to miscarriages
that long after the birth of the first child, but the prolactin levels might be
interfering with implantation or continuation of the pregnancy.
You can find much of Peter Ellison's information in his
already published works. If you have access to a university library, look him up on the
computer and see what they have by him. I hope this helps.
Prepared by Sue Ann
Kendall, August 3, 1995.
Last updated March 11, 2004 , by kad. Contents copyright 1999-2004 Sue Ann Kendall and Kathy Dettwyler. Thanks to Prairienet, the Free-Net of east-central Illinois , for hosting this site from 1999 through 2004.
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