This sheet is about exposure to natalizumab in pregnancy and while breastfeeding. This information should not take the place of medical care and advice from your healthcare provider.
What is natalizumab?
Natalizumab is a type of medication called an integrin receptor antagonist. It has been used to treat multiple sclerosis (MS) or Crohn’s disease in some people when other medications have not worked. Natalizumab is sold under the brand name Tysabri®.
Sometimes when people find out they are pregnant, they think about changing how they take their medication, or stopping their medication altogether. However, it is important to talk with your healthcare providers before making any changes to how you take this medication. Your healthcare providers can talk with you about the benefits of treating your condition and the risks of untreated illness during pregnancy.
I take natalizumab. Can it make it harder for me to get pregnant?
Studies have not been done in humans to see if natalizumab can make it harder to get pregnant.
Does taking natalizumab increase the chance for miscarriage?
Miscarriage can occur in any pregnancy. Based on the studies reviewed, it is not known if natalizumab can increase the chance for miscarriage. Data from 92 pregnancies in people with MS linked natalizumab exposure with an increased chance of miscarriage when compared to patients with MS who were not treated or exposed to a different treatment. Other studies do not suggest an increased chance of miscarriage.
Does taking natalizumab increase the chance of birth defects?
Every pregnancy starts out with a 3-5% chance of having a birth defect. This is called the background risk. Based on the studies reviewed, it is not known if natalizumab increases the chance for birth defects above the background risk. One study looking at exposure to natalizumab in the first trimester found no increased chance for birth defects. Another study reported a slight increase in the chance of birth defects; however, this study found no pattern of birth defects.
Does taking natalizumab in pregnancy increase the chance of other pregnancy-related problems?
Based on the studies reviewed, it is not known if natalizumab can cause other pregnancy-related problems, such as preterm delivery (birth before week 37) or low birth weight (weighing less than 5 pounds, 8 ounces [2500 grams] at birth). Data from 92 pregnancies in people with MS linked natalizumab exposure to smaller length and lower weight among infants. The study did not report an increased chance of preterm delivery.
Some studies have reported blood conditions such as thrombocytopenia (low number of platelets, which help blood clot) and anemia (low amount of red blood cells) in infants exposed to natalizumab in the third trimester of pregnancy. These are side effects that can also happen in adults who take the medication. Babies who were exposed to natalizumab during pregnancy can be monitored for these conditions after delivery.
Does taking natalizumab in pregnancy affect future behavior or learning for the child?
Studies have not been done to see if natalizumab can cause behavior or learning issues for the child.
Breastfeeding while taking natalizumab:
Natalizumab gets into breastmilk in small amounts in some people. Information about use in breastfeeding is limited.
Natalizumab is a large protein molecule and the amount of medication absorbed by the infant is expected to be small. Be sure to talk to your healthcare provider about all of your breastfeeding questions.
If a male takes natalizumab could it affect fertility (ability to get partner pregnant) or increase the chance of birth defects?
Studies have not been done to see if natalizumab could affect fertility or increase the chance of birth defects above the background risk. In general, exposures that fathers or sperm donors have are unlikely to increase the risks to a pregnancy. For more information, please see the MotherToBaby fact sheet Paternal Exposures at https://mothertobaby.org/fact-sheets/paternal-exposures-pregnancy/.
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OTIS/MotherToBaby recognizes that not all people identify as “men” or “women.” When using the term “mother,” we mean the source of the egg and/or uterus and by “father,” we mean the source of the sperm, regardless of the person’s gender identity.
