Can Breastfeeding During Pregnancy Cause Miscarriages?

Toddler breastfeeding
Getty Images/(c) Jaime Monfort

Everyone's heard the advice that "breast is best" for feeding new babies, but what happens when you get pregnant with a new baby while you're still nursing your older one? Is nursing during pregnancy safe?

Breastfeeding and Miscarriage

Although there are numerous conflicting opinions on the issue of breastfeeding during pregnancy, no research has ever found an increased risk of miscarriage in women who continue breastfeeding an older child during pregnancy.

In the past, doctors used to advise women to stop nursing when they became pregnant again. The concerns were that breastfeeding could deprive the developing baby of nutrients, or that it could stimulate uterine contractions (because breastfeeding causes increased oxytocin levels, which also can cause uterine contractions).

But there is no conclusive evidence that this occurs. Babies born to mothers who breastfed during pregnancy appear to be perfectly healthy. The consensus is that it's up to the moms to decide whether to keep nursing during a new pregnancy. In a few high-risk conditions, such as placenta previa, doctors may advise increased caution. But for most, nursing during pregnancy is probably safe.

Causes of Miscarriage

About three of every four miscarriages occur during the first trimester of pregnancy. These miscarriages are usually attributable to a problem with the fetus. Miscarriages that happen during the second trimester are often attributable to a health problem that the mother is experiencing. Breastfeeding is unrelated to either of these.

In women aged 30 years or fewer, about one of 10 pregnancies end in miscarriage. This estimate doubles among women aged 35 to 39, to two of 10 pregnancies resulting in miscarriage.

What Doesn't Cause Miscarriage?

Breastfeeding during pregnancy is an unlikely reason for the miscarriage. Expectant parents may also worry about sex, lifting or exercise, stress or depression, or experiencing a sudden shock or fright. None of these has been shown to cause pregnancy loss.

First-Trimester Miscarriage

About two of three first-trimester miscarriages are due to chromosomal abnormalities in the fetus. Often, when there are chromosomal abnormalities, the fetus doesn't have the needed information to develop properly and miscarriage results.

Just because a mother experiences miscarriage due to chromosomal abnormalities once does not necessarily mean that the problem will happen again. Furthermore, a miscarriage attributable to chromosomal abnormalities doesn't mean that either the mother's or father's chromosomes are faulty.

Aside from chromosomal abnormalities, other conditions and lifestyle factors may increase the risk of miscarriage during the first trimester. These include problems with the placenta, smoking, drug or alcohol use, and obesity.

Second-Trimester Miscarriage

During the second trimester, miscarriage is often attributable to underlying health conditions that the mother is experiencing, such as:

In addition to chronic health conditions and infection, other risk factors for second-trimester miscarriage include weakened cervix, fibroids, irregularly shaped uterus, and polycystic ovarian syndrome (PCOS).

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