(ORLANDO, Dec. 6, 2025) Taking the sickle cell drug hydroxyurea during or shortly before pregnancy does not appear to cause specific issues in newborns, according to the first prospective study of pregnancies involving hydroxyurea exposure.
Since there may yet be undocumented effects, the authors still recommend discontinuing the drug before pregnancy, if possible. However, the findings offer reassurance that hydroxyurea exposure may not cause harm when unplanned pregnancies occur or when the drug is the only or best option for managing sickle cell complications during pregnancy. Blood transfusions can offer an alternative treatment for some, but they are not available in all countries and not safe for all patients.
"Overall, the rate of live births was better than that seen in previous studies, and we had no maternal mortality, even though these patients were highly symptomatic," said lead study author Anoosha Habibi, MD, associate professor in the sickle cell referral center of Hôpitaux Universitaires Henri Mondor in Créteil, France. "Based on these findings, we call for a pragmatic approach. We have to decide case by case and evaluate the risk from transfusion and stopping hydroxyurea."
Hydroxyurea is an oral medication that helps blood cells maintain a healthy shape, aiding in the prevention of sickle cell complications like painful vaso-occlusive crises and tissue damage. Since the drug has never been tested in pregnant women, its effects during pregnancy are unknown, and as a precaution, women are advised to stop taking the drug three to six months before they plan to conceive.
"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."
Drawing from a collection of prospective cohort studies involving 77 medical centers in Europe, the study included data from 245 pregnancies that occurred in 183 women taking hydroxyurea between 2009 to 2025. Most of the women had been taking hydroxyurea for many years before conceiving. In 84% of cases, the women were taking hydroxyurea when they became pregnant, suggesting that many of the pregnancies may have been unplanned.
Researchers analyzed outcomes from a subset of 178 pregnancies after excluding pregnancies that were voluntarily aborted, ongoing at the time of analysis, and those in which hydroxyurea was discontinued before conception. Of these 178 pregnancies, three-quarters resulted in live births. No maternal deaths and no hydroxyurea-related newborn malformations were reported.
The rate of miscarriage (17%) was similar to that seen in the general population, and the rate of premature birth (17%) was similar to that seen in previous studies of people living with sickle cell disease. Two pregnancies were discontinued in the hydroxyurea-exposed group for maternal medical reasons, and two fetal deaths occurred, one a late-term miscarriage before 21 weeks and one a stillbirth at 34 weeks, with neither death deemed to be related to hydroxyurea exposure.
Overall, the results provide no evidence of specific harms related to hydroxyurea exposure during pregnancy. This suggests that continuing hydroxyurea during pregnancy could be a reasonable choice when transfusion is not an option and a woman is at high risk of complications of untreated sickle cell disease, according to researchers.
While the data were collected prospectively, the researchers pointed out that the cohort study was not designed to monitor pregnancies, so the data regarding pregnancy outcomes are limited and the data on the percentage of transfusions performed may not be exhaustive. Dr. Habibi said that more studies are needed to confirm the research findings and assess long-term outcomes in children who were exposed to hydroxyurea in the womb.
The study was requested by the European Medicines Agency and funded by AddMedica.
Anoosha Habibi, MD, of Hôpitaux Universitaires Henri Mondor, will present this study on Sunday, December 7, 2025, at 2:25 p.m. Eastern time during the plenary scientific session in West Hall D2 of the Orange County Convention Center.
