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. This sheet talks about whether exposure to mepolizumab may increase the risk for birth defects over that background risk. This information should not take the place of medical care and advice from your health care provider.

What is mepolizumab?

Mepolizumab is a prescription medication used with other medicines to treat a severe type of asthma called eosinophilic asthma. Eosinophils are a type of blood cell. In eosinophilic asthma, the amount of these cells increases in the body. Mepolizumab is thought to reduce the amount of eosinophils which might help reduce the number of future asthma attacks. Mepolizumab is not effective in stopping immediate symptoms when you are having an asthma attack.

Mepolizumab is given in a health care 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 break down medicines at different rates. On average, it takes about 4 months for mepolizumab to leave your body. Talk to your health care provider before you stop taking any medication. It is important to consider the benefits of controlling asthma symptoms and preventing asthma attacks 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?

We don’t know. No studies have been done to see if mepolizumab increases the chance for miscarriage.

Can taking mepolizumab while pregnant cause birth defects?

It is not known if mepolizumab can cause birth defects. Animal studies done by the manufacturer have not shown an increase in the risk 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 health care 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