Bold claim: current evidence suggests hydroxyurea exposure during pregnancy does not cause specific harm to newborns. But the full story remains nuanced, and uncertainties mean careful management is essential. This summary reworks the key findings from a large, multi-center study while preserving the original meaning and details, and adds context to help readers grasp what it means for patients and clinicians.
Hydroxyurea is an oral medicine used to help blood cells retain a healthy shape, reducing painful sickle cell crises and tissue damage. Because its effects in pregnancy have not been formally studied before, pregnancy safety has been treated with caution, and women are typically advised to stop the drug three to six months before attempting conception. Yet for many patients, stopping the medication can provoke severe sickle cell complications, creating a difficult balance between maternal health and fetal safety.
The latest prospective analysis examined pregnancies exposed to hydroxyurea across a broad European network, including 245 pregnancies in 183 women between 2009 and 2025. Most participants had used hydroxyurea for years before conceiving, with 84% continuing the drug at the time pregnancy was established. This pattern indicates that many pregnancies occurred unintentionally or without prior termination of the drug.
From a subset of 178 pregnancies—after excluding voluntary terminations, ongoing pregnancies at analysis time, and those who ceased hydroxyurea before conception—the study found that about 75% resulted in live births. Importantly, there were no maternal deaths and no hydroxyurea-related congenital abnormalities reported.
Key outcomes mirrored expectations from prior sickle cell research: the miscarriage rate stood at 17%, and the rate of premature birth was 17%, both aligning with general population benchmarks or earlier disease-focused studies. There were two pregnancy discontinuations due to maternal health concerns and two fetal losses: one late-term miscarriage (before 21 weeks) and one stillbirth at 34 weeks. In both fetal-loss cases, investigators did not attribute the deaths to hydroxyurea exposure.
Overall, the data did not reveal specific harms linked to in-utero exposure to hydroxyurea. The researchers suggest that continuing hydroxyurea during pregnancy could be a reasonable option in certain scenarios—particularly when transfusion is unavailable or when stopping treatment would significantly worsen sickle cell disease complications—and when maternal or fetal risk from uncontrolled disease is high. This stance supports a pragmatic, individualized approach, weighing transfusion risks and the potential consequences of stopping the drug on a case-by-case basis.
Lead author Anoosha Habibi, MD, associate professor at the sickle cell referral center of Hôpitaux Universitaires Henri Mondor in Créteil, France, notes that decision-making must account for resource disparities. In higher-resource settings, interruptions to treatment can be managed alongside safe transfusion practices. In many parts of Africa, India, and the Caribbean, safe transfusion access may be limited or unavailable, making the option of stopping hydroxyurea potentially dangerous and potentially worsening both maternal and fetal outcomes.
The study draws on a prospective cohort spanning 77 centers in Europe and emphasizes that while the findings are reassuring, they do not establish long-term or rare effects. The authors caution that the study was not originally designed to monitor pregnancy outcomes in depth, so some data—such as precise transfusion rates—may be incomplete. They advocate additional research to confirm results and to track long-term outcomes for children exposed to hydroxyurea in utero.
Context and funding: the European Medicines Agency requested the study, with funding from AddMedica. Dr. Habibi will present these results in person at the plenary scientific session in West Hall D2, Orange County Convention Center, on Sunday, December 7, 2025, at 2:25 p.m. Eastern.
Bottom line: while no specific hydroxyurea-related harms were detected in this large review, uncertainty remains. The findings support a nuanced, individualized treatment plan that weighs the risks of ongoing disease activity against the availability and safety of transfusions, especially in settings with limited healthcare resources. This topic invites ongoing discussion about best practices and patient-centered care in sickle cell management during pregnancy.
