Safety of medications prescribed before and during early pregnancy in a cohort of 81 975 mothers from the UK General Practice Research Database

Purpose To demonstrate a linkage methodology for mother and baby automated medical records, and describe frequency, type, and pregnancy risk level of medications prescribed during pregnancy in a GPRD cohort, 1991-1999. Methods We linked records using a two-stage algorithm and selected pairs with >= 7 months prenatal records and >= 2 records in baby's first year of life. Periods of interest were: 90 days prior to a woman's earliest identified pregnancy record (Period I), and this record plus 70 days (Period II, approximate early pregnancy). Medications were classified using the British National Formulary and US Food and Drug Administration Pregnancy Risk Categories. Results We achieved over 80% record linkage and defined a cohort of 81975. Sixty-five percent of mothers had >= 1 prescription during both periods combined. Most frequent medications in Period I were anti-bacterial, contraceptive, topical steroid, and bronchodilator. In Period II, they were folic acid, anti-bacterial, antacid, and gynecological anti-infective. In Period I, 4% were FDA category A (considered safest), 34% B, and 49% C and D combined. By Period II, prescription of category A medications increased (folic acid, iron) while other categories declined. Category X medications, with potential teratogenic risk that outweighs maternal benefit, were prescribed to 5714 (7%) women in Period I, and 501 (0.6%) women in Period II (46% progesterone). Conclusions One in every 164 women received a category X prescription in early pregnancy. The visit when pregnancy is first medically recognized represents an opportunity to review prescribed medications in light of contraindication and/or fetal risk. Copyright (c) 2006 John Wiley & Sons, Ltd.