Objective To compare the prescription of drugs in women over a period from 2 years before until 3 months after pregnancy, regarding the type of drugs used and the fetal risk. Design A cohort study based on pharmacy records of women giving birth to a child between 1994 and 2003. Setting The study was performed with data from the InterAction database, containing prescription-drug-dispensing data from community pharmacies. Population The study population included 5412 women for whom complete pharmacy records were available. Methods Drugs were classified into three categories: (1) drugs for chronic conditions, (2) drugs for occasional use and (3) drugs for pregnancy-related symptoms and also classified according to the Australian classification system. Main outcome measures The prescription rate was calculated as the number of women per 100 women who received one or more prescriptions for a given drug within a specified time period. Results About 79.1% of the women received at least one prescription during pregnancy. The prescription rate for most drugs for chronic diseases and for occasional use decreased during pregnancy, whereas, as expected, the prescription rate for pregnancy-related drugs increased. During the first trimester of pregnancy, 1.7% of all drugs prescribed for chronic conditions and 2.3% of the occasional drugs were classified as harmful. Conclusions The increase in prescription rate during pregnancy is caused by an increase in prescription rate of drugs for pregnancy-related symptoms. The prescription of harmful drugs is more commonly associated with drugs for occasional use rather than with drugs for chronic conditions. Therefore, a more cautious prescribing of drugs to healthy women in the fertile age is necessary.