👩‍🍼 Always consider all women of childbearing age pregnant until proven otherwise before prescribing. Even common medications can cross the placenta and harm the fetus. Always check the 💊 BNF and weigh risk vs benefit carefully.

📖 About

Most drugs cross the placenta; some have no effect, while others are teratogenic or toxic.
👶 First trimester (weeks 1–12): Highest risk for congenital malformations (organogenesis).
🤰 Second & third trimesters: Drugs may cause growth restriction, functional defects, or direct fetal toxicity.
There is no drug that is 100% "safe" in pregnancy.
⚠️ General principle: Use the lowest effective dose for the shortest duration.
🚫 Avoid all unnecessary medications, especially in the first trimester.

✅ Drugs considered relatively safe

💉 Penicillins & Cephalosporins (safe antibiotics)
💉 Heparin (anticoagulation – does not cross placenta; Warfarin is unsafe)
💊 Ranitidine (historically used; though now largely replaced by famotidine/PPIs if needed)
💊 Paracetamol (analgesia of choice)
💊 Codeine (short-term, with caution)

🚫 Drugs to avoid (BNF check essential)

❌ Antibiotics: Tetracyclines, Streptomycin, Quinolones
❌ Cardiovascular: Warfarin, Thiazides, ACEi/ARBs
❌ Neurological/Psychiatric: Lithium, Valproate, Phenytoin, Barbiturates
❌ Others: NSAIDs (esp. 3rd trimester), Retinoids, Cytotoxic drugs, Thalidomide
❌ Lifestyle: Alcohol, recreational drugs

⚠️ Unsafe Drugs and Potential Effects

💊 Name	⚠️ Effect / Advice
Lithium	Ebstein’s anomaly, other congenital cardiac defects
Warfarin	“Warfarin embryopathy” – nasal hypoplasia, stippled epiphyses, skeletal abnormalities. Heparin is preferred.
Sodium Valproate	Neural tube defects, cognitive impairment – neurology review essential
Retinoids (e.g. Isotretinoin)	Highly teratogenic – neural tube defects, miscarriage
Carbimazole (antithyroid)	Fetal goitre, scalp defects, may obstruct labour
Gentamicin	Ototoxicity → congenital deafness
Alcohol	Fetal alcohol syndrome, growth restriction, stillbirth
ACEi / ARBs	Renal agenesis, oligohydramnios, growth restriction
Live-virus vaccines	Contraindicated in pregnancy
Thalidomide	Phocomelia (limb deformities)
Diethylstilbestrol (DES)	↑ risk of clear-cell vaginal/cervical cancer in teenage offspring
Phenytoin	“Fetal hydantoin syndrome” – cleft lip/palate, growth restriction
Methotrexate	Abortifacient, severe birth defects
Chloramphenicol	“Grey baby syndrome” – cardiovascular collapse
Isoniazid	Peripheral neuropathy, seizures (give pyridoxine if essential)
Radioactive Iodine	Fetal hypothyroidism, cretinism

💡 Teaching Pearls

📌 Always balance maternal benefit vs fetal risk – e.g., uncontrolled maternal epilepsy or hypertension may be more harmful than the medication itself.
📌 Pre-pregnancy counselling is key in women of childbearing age with chronic disease (neurology, rheumatology, psychiatry, cardiology).
📌 Use folic acid supplementation in women taking anticonvulsants to reduce neural tube defects.
📌 Record drug exposure in the notes & inform antenatal services for fetal monitoring.

The content on this website is provided for educational and informational purposes only to support exam preparation (e.g., MLA, MRCP, USMLE) and learning. This is NOT medical advice, diagnosis, treatment, or professional guidance. It does not replace consultation with a qualified healthcare professional, official guidelines (e.g., NICE, GMC, BNF), or supervised clinical practice. Always verify information with current, authoritative sources. Makindo and its contributors accept no liability for any reliance on this content, including errors, omissions, or any resulting harm, loss, or consequences. By using this site, you agree to these terms.

Prescribing in Pregnancy

📖 About

✅ Drugs considered relatively safe

🚫 Drugs to avoid (BNF check essential)

⚠️ Unsafe Drugs and Potential Effects

💡 Teaching Pearls

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