Hydroxyure in pregnancy
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PMID: 40381805
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Hydroxyurea in Pregnancy
Overview
Hydroxyurea (HU) is an antimetabolite/ribonucleotide reductase inhibitor used in sickle cell disease (SCD), chronic myeloid leukemia (CML), essential thrombocythemia (ET), polycythemia vera (PV), and psoriasis. Its use in pregnancy is a nuanced topic that has evolved in recent years.
FDA Pregnancy Classification
Hydroxyurea is classified as FDA Category D (older classification) - meaning there is positive evidence of human fetal risk. It is listed as a known teratogen based on animal studies and limited human data, and has historically been contraindicated in pregnancy and lactation.
- Fitzpatrick's Dermatology, 9e - Absolute contraindications include active pregnancy/lactation.
- Dermatology 2-Volume Set 5e - Described as a "known teratogen; not to be used during pregnancy or lactation."
Mechanism of Concern
HU inhibits DNA synthesis by blocking ribonucleotide reductase. This affects rapidly dividing cells, which includes fetal tissue - raising concern for:
- Congenital malformations
- Intrauterine growth restriction
- Fetal hematologic suppression (myelosuppression)
- Teratogenicity (especially first trimester)
Indications Where the Question Arises
1. Sickle Cell Disease (Most Common Scenario)
HU is the cornerstone therapy for SCD, reducing vaso-occlusive crises by increasing fetal hemoglobin (HbF). Pregnant women with SCD face difficult choices:
- Traditional guidance: Discontinue HU at least 3 months before conception
- Harrison's 22e (2025): Addresses HU in the context of SCD pregnancy management
- The underlying disease (SCD) itself carries significant pregnancy risks: preterm birth, maternal death, preeclampsia, vaso-occlusive crises
2. Myeloproliferative Neoplasms (ET, PV)
- Goldman-Cecil Medicine: "Hydroxyurea should be avoided, including during the breast-feeding period." Interferon is the preferred cytoreductive agent in pregnancy for ET/PV when treatment is required, as it is generally considered safe.
Updated Evidence (2025 Systematic Review)
A major 2025 systematic review by Al Sulaimani et al. in J Obstet Gynaecol Can reviewed 7,227 pregnancies (567 HU-exposed):
| Finding | Detail |
|---|---|
| Studies included | 15 studies, published 1993-2023 |
| HU-exposed pregnancies | 567 (7.8%) |
| Primary diagnosis | SCD (n=502), CML (n=26), ET (n=24) |
| Teratogenic effects | None observed |
| Hematologic fetal effects | None observed |
| Conclusion | "Pregnancy risks associated with HU are lower than anticipated. Use may be justified given significant risks of untreated SCD." |
⚠️ Important caveat: Quality of evidence is low (observational data). Traditional guidance to discontinue HU ≥3 months before conception is still widely recommended pending more robust evidence.
Practical Clinical Guidance
| Situation | Recommendation |
|---|---|
| Planning pregnancy (SCD) | Discontinue HU ≥3 months before conception; counsel about risks |
| Inadvertent exposure in 1st trimester | Discontinue immediately; refer to high-risk obstetrics; discuss risks |
| SCD in pregnancy (uncontrolled) | Consider risk-benefit - new evidence suggests HU may be used when maternal risk without treatment is very high |
| ET/PV in pregnancy | Prefer interferon-alpha over HU for cytoreduction |
| Breastfeeding | Contraindicated - HU is excreted in breast milk |
| Male partners on HU | Use adequate contraception - HU can impair sperm motility and spermatogenesis |
Key Adverse Effects Profile (General)
- Myelosuppression (most common) - anemia, leukopenia, thrombocytopenia
- Megaloblastosis (occurs in all patients on HU)
- Dermatomyositis-like eruption
- Transient hepatitis / elevated liver enzymes
- Sporadic renal toxicity
- Fever / flu-like illness (rare)
- Increased risk of nonmelanoma skin cancer (long-term use)
Fitzpatrick's Dermatology recommends discontinuing HU if Hb drops by >3 g/dL, WBC <4,000/mm³, or platelets <100,000/mm³.
Pre-Pregnancy Counseling Checklist
Per Fitzpatrick's:
- Pregnancy test in all women of childbearing age before initiating HU
- Counsel on teratogenic risk and need for contraception
- Males should also use contraception
- Discuss the 3-month washout before attempting conception
Summary
Hydroxyurea is traditionally contraindicated in pregnancy (Category D, known teratogen in animals). However, the most recent 2025 systematic review (PMID: 40381805) of 567 HU-exposed pregnancies found no teratogenic or fetal hematologic effects, suggesting risks may be lower than historically assumed. The clinical decision must balance:
- Disease severity (especially SCD, where untreated disease carries serious maternal/fetal risk)
- Gestational timing of exposure
- Availability of safer alternatives (interferon-alpha for myeloproliferative neoplasms)
For SCD in pregnancy, a multidisciplinary team including hematology and high-risk obstetrics should guide management. For myeloproliferative neoplasms, interferon-alpha remains the preferred cytoreductive agent during pregnancy.
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