Background: For many regularly used drugs, evidence for safe use in pregnancy has not been established. Despite this, international studies have identified high levels of drug prescribing among pregnant women.
Objective: To investigate the patterns of prescribing of drugs to women who gave birth in Tayside, Scotland, in 2007.
Methods: Scottish maternity records were linked to dispensed prescribing data for all women who gave birth in Tayside in 2007. Drugs prescribed were coded according to the US FDA classification for risks of drugs in pregnancy. Patterns of prescribing were investigated during the 3 trimesters of pregnancy and the 3 months prior to conception.
Results: Prescribing in pregnancy was common, with 21 093 prescriptions dispensed to 3356 (85.2%) of the 3937 women. The most frequently prescribed drugs were antacids, antibacterials, oral iron, folic acid preparations and analgesics. Category A drugs (positive evidence of safety in pregnancy) and Category B drugs (some evidence of safety in pregnancy) accounted for 19.6% and 26.9% of all prescriptions dispensed, respectively.
Prescribing of Category X drugs (evidence of risk to the fetus; use contraindicated in women who are or may become pregnant) during pregnancy was rare, with 112 prescriptions dispensed to 68 women (1.7%). Most of these were oral contraceptives or sex hormones. Prescribing of Category X drugs fell markedly during the first trimester and remained very low thereafter. Category D drugs (evidence of risk to the fetus but benefits of therapy may outweigh the potential risk)  were dispensed to 166 women (4.2%) during pregnancy. The most commonly prescribed Category D drugs were anxiolytics, nicotine replacement therapy and antiepileptic drugs. The frequency of prescribing of Category D drugs reduced in the third trimester. Prescribing of Category C drugs (insufficient evidence to know whether they are harmful) was common. Thirty percent of women received a total of 3641 Category C prescriptions, which accounted for 17.3% of all prescriptions issued during pregnancy. Prescribing of Category C drugs showed only a very modest decline during pregnancy. No FDA code was available for 4035 prescriptions issued (87 different items), the majority of which were for antacids and preparations for indigestion. More than 40% of women received such medications.
Conclusions: Prescribing of drugs during pregnancy was very common, but the levels of prescribing of drugs that are known to be harmful were low. Much of the prescribing was for drugs related to the pregnancy. While this study provides some evidence that primary-care prescribers in Tayside are prescribing potentially harmful drugs appropriately and with caution during pregnancy, safety data during pregnancy are unavailable for many drugs that are commonly prescribed.