A new study has found that taking hydroxyurea, a drug used to manage sickle cell disease, during or shortly before pregnancy does not appear to cause specific issues in newborns. This research is the first prospective study of pregnancies involving exposure to hydroxyurea.
Despite these findings, the authors advise that women should discontinue hydroxyurea before pregnancy if possible because there may still be undocumented effects. The results provide reassurance for situations where unplanned pregnancies occur or when hydroxyurea is the only viable option for managing sickle cell complications during pregnancy. Alternatives such as blood transfusions are not always available or safe for all patients, especially in certain regions.
Hydroxyurea helps maintain healthy-shaped blood cells and prevents complications like painful vaso-occlusive crises and tissue damage in people with sickle cell disease. Because its effects during pregnancy were previously unknown, women have been advised to stop taking it three to six months before conception.
"Women are usually advised to stop hydroxyurea several months before pregnancy, but this is extremely difficult because these patients are often highly symptomatic and no one knows exactly when pregnancy will occur," said Dr. Habibi. "So, many women remain without treatment for months, during which some develop severe vaso-occlusive crises and complications."
"In higher-resourced settings, we can manage treatment interruption and provide safe transfusions for most patients, but in many regions in Africa, India, and the Caribbean, the safety of transfusion is limited, or the access is simply unavailable," said Dr. Habibi. "In those contexts, asking women to stop hydroxyurea may actually put them in danger of vaso-occlusive crises, and both maternal and fetal outcomes can worsen."
The study included data from 245 pregnancies among 183 women who took hydroxyurea between 2009 and 2025 at 77 medical centers across Europe. Most participants had used the drug for years prior to conceiving; in 84% of cases they were on hydroxyurea at conception—suggesting many pregnancies were unplanned.
Researchers analyzed outcomes from a subset of 178 pregnancies after excluding those that ended voluntarily or were ongoing at analysis time as well as cases where medication was stopped before conception. Of these cases, about three-quarters resulted in live births with no reported maternal deaths or newborn malformations linked to hydroxyurea use.
The miscarriage rate (17%) was comparable to rates seen generally among pregnant individuals; premature birth rates (17%) matched earlier studies on sickle cell disease patients. Two pregnancies ended due to maternal health concerns unrelated to the drug; two fetal deaths occurred—one late-term miscarriage prior to 21 weeks gestation and one stillbirth at 34 weeks—but neither was attributed by researchers to hydroxyurea exposure.
Researchers concluded there is no evidence linking hydroxyurea exposure during pregnancy with specific harms. They suggest that continuing the medication could be reasonable if transfusion options are unavailable and risk from untreated sickle cell disease remains high.
The authors noted limitations: their cohort study was not designed specifically for monitoring pregnancies so outcome data may be incomplete—especially regarding frequency of transfusions performed—and called for further research into long-term child health following prenatal exposure.
This research was requested by the European Medicines Agency and funded by AddMedica.
Dr. Anoosha Habibi from Hôpitaux Universitaires Henri Mondor will present these findings on December 7, 2025 at the Orange County Convention Center.
