Breastfeeding During Pregnancy and Risk of Miscarriage

CQ #165 - October 7, 2019

by Anne Eglash MD, IBCLC, FABM

#LactFact

Exclusive breastfeeding during pregnancy may increase the risk of miscarriage.

Breastfeeding During Pregnancy and the Risk of Miscarriage
Perspectives on Sexual and Reproductive Health 2019, 51(3)

What is the risk of miscarriage when breastfeeding during pregnancy?

Until recently there has been very little data on the risk of breastfeeding during pregnancy. Some have hypothesized that the uterus down-regulates its oxytocin receptors during pregnancy, so that the uterus is not as likely to contract during oxytocin release due to sexual activity, nipple stimulation, or breastfeeding.

Clinical Question of the Week #54 addressed a systematic review that did not have any evidence indicating an increased risk of miscarriage due to breastfeeding during pregnancy.

The article for this week is based on data collected on 10,661 pregnancies in the U.S. from the National Survey of Family Growth, covering various years between 2002-2015. The authors focused on women with singleton births who breastfed, who had no barriers to breastfeeding during a subsequent pregnancy. They evaluated answers to questions regarding breastfeeding during a subsequent pregnancy, the interpregnancy interval, whether the mothers exclusively breastfed during pregnancy or also offered complementary foods to the nursing child. Demographics such as age, education, race/ethnicity, pregnancy intention, and history of miscarriages were evaluated as well.

The authors described the frequency of breastfeeding during pregnancy as 6% of the total time at risk (person-months).

What do you suspect were findings in this survey data regarding breastfeeding during pregnancy? Choose 1 or more:

Most mothers were already giving complementary foods when they were nursing during pregnancy.
Mothers who breastfed during pregnancy, and were also giving complementary feedings to their children did not have a higher risk of miscarriage compared to pregnant women who were not breastfeeding.
Mothers who breastfed exclusively during pregnancy had a significantly higher risk of miscarriage vs mothers who breastfed during pregnancy but also gave complementary foods to their children.
Breastfeeding during pregnancy was more common for mothers who became pregnant earlier than planned, vs those who viewed the pregnancy as occurring at the right time.
Breastfeeding during pregnancy was found to be highest among teenage mothers.
Breastfeeding-during-pregnancy rates were highest among the shortest interpregnancy interval, less than 12 months.

Click here to view the answer to this question.

Correct Answers: All are true

Breastfeeding During Pregnancy and the Risk of Miscarriage
Perspectives on Sexual and Reproductive Health 2019, 51(3)
Molitoris, J

Abstract

Context

Breast-feeding rates and durations have been increasing among U.S. women in recent decades. As a result, women may be more likely to practice breast-feeding during pregnancy (BDP), which has been hypothesized to increase the risk of miscarriage, yet there has been little research into the issue.

Methods

Data on 10,661 pregnancies from several waves of the National Survey of Family Growth, covering the years 2002–2015, were used to calculate unadjusted miscarriage rates according to BDP status. Multivariate Cox pro¬portional hazards models were employed to investigate the association between BDP and the risk of miscarriage.

Results

BDP was practiced for 6% of the total time at risk of miscarriage. The miscarriage rate was higher when mothers exclusively breast-fed during pregnancy (35%) than when they practiced either complementary BDP (i.e., the child also consumed other food) or did not breast-feed (14% and 15%, respectively). After adjustment for maternal and pregnancy characteristics, the risk of miscarriage was greater when mothers exclusively breast-fed than when mothers did not breast-feed (hazard ratio, 3.9), but no increased risk was found with complementary BDP. The miscarriage risk during exclusive BDP was similar to that for women who conceived when they were 40 or older (3.2).

Conclusions

Exclusive BDP is associated with an elevated risk of miscarriage, but it remains unclear whether and how the practice is associated with health outcomes for the mother and breast-fed child. Research is needed to further explore these outcomes to inform recommendations regarding BDP.

IABLE Comment by Anne Eglash MD, IBCLC, FABM

I believe that this is the first set of U.S. data on the frequency of breastfeeding during pregnancy, and the first study to show a link between exclusive breastfeeding during pregnancy and miscarriage. The biggest limitation of this study is that is based on recall of breastfeeding and pregnancy details.

The study controlled for other risk factors for miscarriage such as maternal age, education, history of miscarriages, but they did not control for socioeconomic level. Interestingly, the risk of miscarriage was much higher for exclusively breastfeeding than for breastfeeding with complementary feeding. The authors surmise that this may represent a nutritional problem for mothers who are exclusively breastfeeding. The systematic review on breastfeeding during pregnancy that was addressed in Clinical Question of the Week #54 also raised evidence that the newborn may be at risk for low birth weight and mothers at risk for nutritional compromise, with most of that data coming from non- U.S. countries. The authors of this week’s article suggest that we need more prospective data, e.g. following a large cohort of mothers over time so that we can be more exact about their breastfeeding behaviors and identification of miscarriages. In the meantime, it would be reasonable to encourage and provide longitudinal nutritional management for all pregnant mothers who are breastfeeding.

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Comments (7)

Naomi

October 7, 2019 at 8:39 PM

I’m curious what the risk of miscarriage is when pregnancies are close together. As in, does it appear that BDP while exclusively breastfeeding (generally within the first six months postpartum) increases miscarriage frequency because the pregnancies were close together (rather than further spaced when complementary foods may have been introduced)?

Heidi

October 9, 2019 at 5:50 PM

I was wondering this same thing. That the increased risk may not be breastfeeding-related but risk associated with close interval pregnancies.

SD

October 8, 2019 at 9:15 AM

What about sex/orgasm? Do those not produce higher levels of oxytocin?

Anna G

October 8, 2019 at 1:01 PM

Seems like it could be confounded by interpregnancy interval. Patients who are EBF in early pregnancy likely have younger infants and thus less time between pregnancies. A number of adverse pregnancy outcomes are associated with short IPI. IPI data in turn is probably confounded by the socioeconomic factors associated with unplanned, short interval pregnancies. Nutritional deficiency or stress may also contribute to the adverse outcomes.

Irena Zakarija-Grkovic

October 9, 2019 at 2:27 AM

We need to keep in mind that only a minority of women will conceive during the period of EBF, i.e. during the first six months after giving birth; therefore, for the majority of women who conceive when their infant/toddler is well into the complementary feeding phase, breastfeeding poses no risk at all to the unborn baby, and confers numerous benefits to the mother and child.

Susie

February 8, 2024 at 9:08 PM

I breastfeed my son, who I’m currently trying to break. I don’t nurse during the day, but at least 3-5 times a night. I’m also 7 weeks pregnant. Am I increasing my risk of having a miscarriage? I’ve had one in the past

IABLE

February 11, 2024 at 12:10 PM

Hi, thanks for reading this blog. We cannot give any medical advice to individuals. I suggest talking to your physician about your circumstances. I encourage you to share this research with your physician.