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Is it safe? · Pregnancy Smart

Is Azathioprine (Imuran) Safe During Pregnancy?

Assigned clinical reviewerMatt Stahl· PharmDDraft · pending clinical reviewUpdated

What does the evidence say about azathioprine during pregnancy?

  1. MotherToBaby summarizes more than 1,500 azathioprine or 6-mercaptopurine pregnancy exposures without a demonstrated increase in birth differences or miscarriage, while noting that underlying illness complicates prematurity and low-birth-weight findings. 1
  2. In the prospective PIANO cohort of singleton IBD pregnancies, 242 thiopurine exposures were not associated with more congenital malformations, miscarriage, preterm birth, low birth weight, or infant infection than the 379 unexposed IBD pregnancies after adjustment for key clinical factors. 2
  3. The current British Society for Rheumatology guideline considers azathioprine compatible throughout pregnancy and with breastmilk exposure, based largely on observational evidence. The dose still requires specialist selection and monitoring. 3
  4. In a prospective cohort of 106 newborns, including 19 with in-utero thiopurine exposure, median newborn hemoglobin did not differ among exposed IBD, unexposed IBD, and control groups; only one exposed infant had mild anemia. 4
  5. The current U.S. label describes rare newborn immune and blood-count abnormalities, dose-dependent maternal cytopenias, and a need for regular blood counts. It also warns about intrahepatic cholestasis of pregnancy and directs clinicians to discontinue azathioprine if that condition develops. 5

Is azathioprine safe in each trimester?

  • First trimester. Do not stop azathioprine after a positive pregnancy test without contacting the prescriber. More than 1,500 reported exposures have not shown a consistent birth-difference pattern, and a disease flare or transplant rejection can carry its own risks.
  • Second trimester. Azathioprine monitoring continues through pregnancy because maternal blood counts and liver results can change. Contact the prenatal and prescribing teams promptly for new itching or jaundice. The current label warns about intrahepatic cholestasis of pregnancy and directs clinician-led discontinuation if it develops.
  • Third trimester. The obstetric, prescribing, and newborn teams should know about late-pregnancy azathioprine exposure. Most available IBD cohort data do not show more newborn anemia or cytopenia, but rare reports and the product label support individualized newborn blood-count planning when clinically indicated.

Frequently asked questions

Can you stay on azathioprine while pregnant?

Azathioprine can remain part of a pregnancy plan when disease control or transplant protection requires it. Current specialist guidance supports compatible use, but continuation, dose, blood work, and any medication changes should be coordinated with the prescriber and obstetric clinician.

Should azathioprine be stopped after a positive pregnancy test?

Azathioprine should not be stopped abruptly without urgent contact with the prescribing specialist. MotherToBaby emphasizes discussing changes first because uncontrolled autoimmune disease or transplant rejection may pose substantial maternal and pregnancy risks.

Does azathioprine raise the chance of major birth differences?

Available human data do not show a clear rise in major birth differences with azathioprine. In the prospective PIANO IBD cohort, thiopurine exposure was not associated with more congenital malformations than disease-matched unexposed pregnancies, but observational data cannot exclude uncommon outcomes.

Why are preterm birth and low birth weight reported with azathioprine?

Some azathioprine cohorts report earlier delivery and lower birth weight, but the medication is often used for inflammatory disease or after transplant. Those conditions and other medicines can influence the same outcomes, so observational associations do not establish azathioprine as the cause.

Can azathioprine cause low blood counts in a newborn?

Rare newborn blood or immune abnormalities have been reported after azathioprine exposure, but a recent IBD cohort found no group difference in newborn hemoglobin and only one mildly anemic exposed infant. Newborn testing is individualized rather than automatically required for every exposure.

What monitoring is used for azathioprine during pregnancy?

Azathioprine monitoring commonly includes complete blood counts and liver tests, with frequency set by the prescribing specialist. TPMT or NUDT15 status, dose changes, interacting medicines, infection, itching, jaundice, or falling blood counts can alter the plan.

Is azathioprine used in pregnant transplant recipients?

Azathioprine has long been used in some transplant pregnancies when continued immunosuppression is necessary. Transplant pregnancy remains high risk because graft function, hypertension, kidney disease, rejection risk, and the full medication regimen matter beyond azathioprine alone.

Why does the azathioprine label sound stricter than current specialist guidance?

The azathioprine label preserves strong warnings from animal findings and rare human reports. Current specialist guidance also weighs larger observational pregnancy datasets and the harm of uncontrolled disease, so it may support continued use after an individualized risk-benefit discussion.

Can you breastfeed while taking azathioprine?

The British Society for Rheumatology considers azathioprine compatible with breastfeeding based on low infant exposure and available follow-up. The infant's age, prematurity, maternal dose, other medicines, and any infection or blood-count concern should be reviewed with the clinical team.

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References

  1. Azathioprine | 6-mercaptopurine

    MotherToBaby via NCBI Bookshelf · https://www.ncbi.nlm.nih.gov/books/NBK582591/

  5. AZATHIOPRINE tablet

    DailyMed · https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=040d010a-b1b2-4db7-905d-8aa7f1bab0cd

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.