This sheet talks about exposure to mepolizumab in a pregnancy or while breastfeeding. This information should not take the place of medical care and advice from your healthcare provider.

What is mepolizumab?

Mepolizumab is a prescription medication used with other medicines to treat a severe type of asthma called eosinophilic asthma, and to treat eosinophilic granulomatosis with polyangiitis (Churg-Strauss Syndrome). Eosinophils are a type of white blood cell. In eosinophilic diseases, the number of these cells increases in the body. Mepolizumab is thought to reduce the number of eosinophils. Mepolizumab is given in a healthcare provider’s office by an injection (a shot just under the skin) every 4 weeks. It is sold under the brand name Nucala®.

How long does mepolizumab stay in the body? Should I stop taking it before getting pregnant?

Individuals eliminate medication at different rates. On average, it takes about 4 months for mepolizumab to leave your body. Talk to your healthcare provider before you stop taking this medication. It is important to consider the benefits of controlling your disease during pregnancy.

Untreated or poorly controlled asthma increases the risk for complications for both the mother and the baby. For more information about asthma in pregnancy, please see the MotherToBaby fact sheet on Asthma at

Will taking mepolizumab make it harder for me to get pregnant?

We don’t know. No studies have been done to see if mepolizumab would make it harder for a woman to get pregnant.

Does taking mepolizumab increase the chance for a miscarriage?

Any woman can have a miscarriage. No studies have been done to see if mepolizumab increases the chance for miscarriage.

Can taking mepolizumab while pregnant cause birth defects?

In every pregnancy, a woman starts out with a 3-5% chance of having a baby with a birth defect. This is called her background risk. It is not known if mepolizumab can cause birth defects. Animal studies done by the manufacturer have not shown an increase in the chance for birth defects. While this is reassuring, there are no well-controlled human studies looking at exposure to mepolizumab during pregnancy.

Can taking mepolizumab cause other pregnancy complications?

No studies have been done looking to see if exposure to mepolizumab would cause other pregnancy complications.

Can I take mepolizumab while breastfeeding?

Mepolizumab has not been studied for use during breastfeeding. Because it is a very large protein, it is not likely that very much of the medication would be able to pass into breast milk. Also mepolizumab is not thought to be well absorbed in the stomach, so any of the medication that gets into breastmilk would be unlikely to enter the baby’s system. Premature babies (born before 37 weeks of pregnancy) have digestive systems that may not be fully developed. This could allow more of the medication to be absorbed from the breast milk. Be sure to talk to your healthcare provider about any medications you take while breastfeeding.

What if the father of the baby takes mepolizumab?

There are no studies looking at possible risks to a pregnancy when the father takes mepolizumab. In general, exposures that fathers have are unlikely to increase risks to a pregnancy. For more information, please see the MotherToBaby fact sheet on Paternal Exposures and Pregnancy at

MotherToBaby is currently conducting a study looking at mepolizumab and other medications used to treat asthma in pregnancy. If you are interested in taking part in this study, please call 1-877-311-8972 or sign up at

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