Drug Side Effects in Pregnancy

Drug side effects in pregnancy

Medicines in pregnancy require balancing maternal benefit against fetal and neonatal risk.

Physiological changes in pregnancy alter drug handling, and vulnerability varies by stage: organogenesis in the first trimester confers the greatest risk for structural teratogenesis; the second and third trimesters are important for growth, functional maturation and fetal haemodynamics (for example, ductus arteriosus closure).

In emergency practice you must act quickly but follow clear principles: check authoritative guidance, involve specialists where needed, document counselling, and report suspected adverse drug effects via the MHRA Yellow Card scheme.

Key principles

• Use drugs in pregnancy only when clinically necessary and discuss maternal indications, likely fetal risks and alternatives with the patient.
• Check the product SmPC and national guidance (GOV.UK/MHRA, NICE) before prescribing or advising on exposures.
• Consider timing of exposure: first trimester risks relate mainly to structural teratogenesis; later trimesters are more important for growth restriction, functional maturation and fetal haemodynamic effects.
• Prefer agents with established safety profiles, use the lowest effective dose for the shortest necessary duration, and avoid starting known teratogens.
• Seek specialist input (obstetrics/maternal medicine, paediatrics/neonatology, clinical pharmacology or teratology services) for exposures to known teratogens or when management is complex.
• Report suspected drug reactions in pregnancy, including effects in the baby, via the MHRA Yellow Card scheme.
• Document counselling, decisions, reporting and follow‑up...