by Hilary Dervin Flower, MA

Are you ready to try to conceive your second child, but still enjoying a breastfeeding relationship with your firstborn? Or perhaps you are breastfeeding your child over a kicking baby belly? If so you are not alone -- far from it. In a study of 179 mothers who had breastfed for at least six months, 61% had also breastfed during a subsequent pregnancy.1 Of these, 38% went on to nurse both newborn and toddler postpartum, an arrangement known as "tandem nursing."

Moreover, continued breastfeeding can be helpful to your toddler's adjustment to a new baby. Besides, what better way to rest your tired pregnant body while caring for an active baby or toddler?

In contemplating the healthiness of an overlap you will want to consider how breastfeeding is fitting in with your needs for rest, adequate pregnancy weight gain, and your overall sense of well-being. You will do well to take into account that breastfeeding can be painful or agitating for many mothers for some or all of pregnancy, leading some mothers to push for weaning. The milk tends to dwindle by mid-pregnancy; some children self-wean in response, while others don't seem to care.

Another concern you may have is the fact that breastfeeding causes contractions. Could breastfeeding trigger preterm labor or miscarriage? I have dug deep in the scientific literature and interviewed over 200 mothers, seeking hard facts to help mothers make the most informed and balanced assessment they can of this important safety question. Indeed, this question was my top priority as I researched my new bookAdventures in Tandem Nursing: Breastfeeding during Pregnancy and Beyond, published in July 2003 by La Leche League International. Here's what I learned.

Breastfeeding and Contractions

Nipple stimulation releases the hormone oxytocin into the bloodstream. Oxytocin is important for breastfeeding because it is the chemical messenger that tells breast tissue to contract and eject milk (the "milk ejection reflex"). Oxytocin also tells the uterine tissue to contract. All women experience uterine contractions during breastfeeding, although they are usually too mild to be noticed. Nipple stimulation can be used to ripen the cervix when a woman is at term, and can also augment labor after it is underway. Postpartum breastfeeding efficiently shrinks the uterus back to pre-pregnancy size.

Given these associations, it seems a short jump to guess that breastfeeding might trigger labor before its time. This question deserves medical study, and it is important to bear in mind that at this time there have been no controlled studies. At the same time, preliminary data do suggest that breastfeeding and healthy term births are quite compatible. Sherrill Moscona's 1993 survey of 57 California mothers who breastfed during pregnancy concluded that breastfeeding resulted in no apparent adverse consequences to the mothers' pregnancies.2 There are also countless anecdotal reports of mothers who have breastfed throughout pregnancy and given birth to healthy term babies. Of course, some pregnancies are not destined to proceed as we hope, whether the mother is breastfeeding or not, and so breastfeeding mothers have suffered their share of preterm labor and miscarriage as well.

Most mothers notice no contractions during breastfeeding, even during pregnancy (93% in the Moscona survey).3 Interestingly, even those who experience intense "nursing contractions" often find that the contractions cease soon after ending the breastfeeding session.4 Like Braxton-Hicks contractions, nursing contractions commonly occur without disrupting the pregnancy. How might that work? The scientific literature has a lot to tell us about that.

A Primer on the Signs of Preterm Labor
Remember to contact your caregiver immediately if you experience any of these possible warning signs:

• Four or more uterine contractions in an hour -- entire uterus is tight, hard, "balled up" to the touch; may or may not feel painful
• Low backache
• Pelvic pressure
• Cramping (like menstrual cramps)
• Increased vaginal discharge, which may include mucus, blood, or water

If these signs occur (or any contractions concern you) during a breastfeeding session, end the session. It is important to remember that breastfeeding can cause contractions, and, like Braxton-Hicks, these contractions do not automatically mean you are going into labor.

If you have stopped nursing -- or weren't nursing at that particular time -- and you are still having or think you are having more than two or three contractions an hour, you should:

1) Begin timing how often one occurs and how long each lasts.
2) Empty your bladder.
3) Drink a large glass of water (dehydration can sometimes lead to contractions).
4) Lie on your left side, or recline with feet elevated, consciously relaxing. 
5) And again, if after this you find you are having four or more contractions in an hour, you should call your prenatal care provider immediately.

The Well-Protected Uterus

The specter of breastfeeding-induced preterm labor appears to spring in large part from an incomplete understanding of the interactions between nipple stimulation, oxytocin, and pregnancy.

The first little-known fact is that during pregnancy less oxytocin is released in response to nipple stimulation than when a woman is not pregnant.5

But the key to understanding breastfeeding during pregnancy is the uterus itself. Contrary to popular belief, the uterus is not at the beck and call of oxytocin during the 38 weeks of the "preterm" period. Even a high dose of synthetic oxytocin (Pitocin) is unlikely to trigger labor until a woman is at term.6

Instead, the uterus must actively prepare in order for labor to commence. You could say that there are two separate states of being for the uterus: the quiescent baby-holder and the active baby-birther. These states make all the difference in how the uterus responds to oxytocin, and so, one can surmise, to breastfeeding. While the baby is growing, the uterus is geared to have a muffled response to oxytocin; at term, the body's preparations for labor transform the uterus in ways that make it respond intensely to oxytocin.

Many discussions of breastfeeding during pregnancy mention "oxytocin receptor sites," the uterine cells that detect the presence of oxytocin and cause a contraction. These cells are sparse up until 38 weeks, increasing gradually after that time, and increasing 300-fold after labor has begun.7 The relative scarcity of oxytocin receptor sites is one of the main lines of defense for keeping the uterus quiescent throughout the entire preterm period -- but it is not the only one.

A closer look at the molecular biology of the pregnant uterus reveals yet more lines of defense. In order for oxytocin receptor sites to respond strongly to oxytocin they need the help of special agents called "gap junction proteins." The absence of these proteins renders the uterus "down-regulated," relatively insensitive to oxytocin even when the oxytocin receptor site density is high. And natural oxytocin-blockers, most notably progesterone, stand between oxytocin and its receptor site throughout pregnancy. 8, 9, 10

With the oxytocin receptor sites (1) sparse, (2) down-regulated, and (3) blocked by progesterone and other anti-oxytocin agents, oxytocin alone cannot trigger labor. The uterus is in baby-holding mode, well protected from untimely labor. 4

A Balanced Approach

Only direct research can definitively tell us whether breastfeeding can elevate the risk of preterm labor or miscarriage in any woman. But as you can see, the available research gives us valid reasons to doubt that breastfeeding could trigger labor before the body has already begun to prepare for it. With increasing first-hand experience among health professionals, many well-respected sources are asserting that breastfeeding is safe in healthy pregnancies, including Ina May Gaskin, LM,4 the American Academy of Family Physicians,11 and Ruth Lawrence, MD, in Breastfeeding: A Guide for the Medical Profession.12

Complicated pregnancies always call for more complicated decisions, but weaning can still be avoided in many cases. I have corresponded with many mothers who breastfed through high risk pregnancies, even threatened preterm labor, and have given birth to healthy term babies.4 Sometimes reduced nursing or weaning seems to be for the best; no two mothers' choices are the same.

You may wish to work with your medical care provider to draw up a plan for moving forward with your eyes open. As in any pregnancy, you should be on the look out for signs of preterm labor. Any mother who is experiencing contractions that concern her should end the breastfeeding session and see if the contractions stop as well. Some medical caregivers judge that it is helpful to observe the effects of breastfeeding on uterine contractility, fetal heart rate, or the state of the cervix.

In closing, I would like to share a bit of my own story. When I became pregnant with my second child, I worried that breastfeeding might interfere with my healthy pregnancy. My midwives Anne Hirsch, LM, and CharLynn Daughtry, LM, CPM, were accustomed to supporting breastfeeding mothers. They provided me with the support I needed to hold onto my breastfeeding relationship with my two-year-old Nora Jade. What a difference it made. After I gave birth to Miles at home, my daughter rushed in to meet her brother, and she immediately wanted to nurse with him. "That 'na-na' is for brother," she said. As they nursed and gazed at each other wide-eyed across my chest, I wrapped an arm around each of them, marveling at my body's powers to provide.

When deciding about the health of breastfeeding during pregnancy, each mother must sort through her options, her feelings, and what her own body is telling her. Trust yourself to make the best choice for your family.

Hilary Flower lives in Florida with her partner Ben, daughter Nora Jade (5) and son Miles (2). She is the author of Adventures in Tandem Nursing: Breastfeeding During Pregnancy and Beyond, published in July 2003 by La Leche League International. She tandem nursed for 18 months while writing the book. Adventures in Tandem Nursing is approved for API libraries.

References Cited

1 From an unpublished study by Kathleen Kendall-Tackett, Ph.D., IBCLC, Sugarman, M., M.D., 2003; data published in Flower, Hilary. Adventures in Tandem Nursing: Breastfeeding During Pregnancy and Beyond. La Leche League International, Schaumburg, Illinois, 2003. p. 16.
2 Bøhler, E. Bergström, S. Subsequent Pregnancy affects morbidity of previous child. J Biosoc Sci 1995 27:431-442.
3 Moscone(sic), SR., Moore, M.J, Breastfeeding during pregnancy. J Hum Lact 1993; 9(2):83-88.
4 Flower, Hilary. Adventures in Tandem Nursing: Breastfeeding During Pregnancy and Beyond. La Leche League International, Schaumburg, Illinois, 2003. p. 225-30, 235.
5 Amico, J., and Finley, B., Breast stimulation in cycling women, pregnant women and a woman with induced lactation: pattern of release of oxytocin, prolactin and luteinizing hormone. Clinical Endocrinology, 1986 25:97-106.
6 Kimura T, Takemura, M., Nomura, S., et al. Expression of oxytocin receptor in human pregnant myometrium. Endocrinology 137:780-785. 1996.
7 Fuchs AR, Fuchs F, Husslein P, Soloff MS. Oxytocin receptors in the human uterus during pregnancy and parturition. Am J Obstet Gynecol 1984 Nov 15;150(6):734-41.
8 Chwalisz, K, Fahrenholz, F, Hackenberg, M., Garfield, R., Elger, W. The progesterone antagonist onapristone increases the effectiveness of oxytocin to produce delivery without changing the myometrial oxytocin receptor concentrations. Am J Obstet Gynecol 1991; 165: 1760-70.
9 Grazzini E, Guillon G, Mouillac B, Zingg HH. Inhibition of oxytocin receptor function by direct binding of progesterone. Nature. 1998 Apr 2;392(6675):509-12.
10 Zingg HH, Grazzini E, Breton C, Larcher A, Rozen F, Russo C, Guillon G, Mouillac B. Genomic and non-genomic mechanisms of oxytocin receptor regulation. Adv Exp Med Biol 1998;449:287-95.
11 AAFP Policy Statement on Breastfeeding can found at http://www.aafp.org/x6633.xml; the selected quote is from the sub-heading "Nursing Beyond Infancy."
12 Ruth Lawrence, M.D. in Breastfeeding: A Guide for the Medical Profession, 5th edition. Mosby. St. Louis. 1999. p. 671.