PurposeNational dispensing data for subsidised prescription medicines have recently been approved for linkage to the population-based health datasets in Western Australia (WA), creating the capacity to study how these medicines are used and their impact on pregnancy outcomes.MethodsPregnancy events were identified in the Hospital Morbidity Data System from 2002 to 2005 (N = 164 278 admissions; N = 98 265 women) and linked to the midwives' notification system (MNS), the registry of births and deaths, the Western Australian birth defects registry and the pharmaceutical benefit scheme. Dispensing records were extracted for each pregnancy event (N = 1 276 084 dispenses).ResultsThere were 106 074 births, 1527 ectopic pregnancies and 25 180 terminations of pregnancy. Dispensed medicines were linked to 28.0% of the pregnancy events. Multiple birth pregnancies were 50% more likely to be dispensed a medicine in the first trimester. As parity increased, so did the likelihood of a medicine being dispensed in pregnancy. Women who were dispensed a medicine were twice as likely to smoke during pregnancy and were 14% more likely to have a registered birth defect. During the first trimester, medicines from category D or X of the risk of drug use in pregnancy were dispensed to 2.1% of all pregnancy events. The WHO ATC ‘Psychoanaleptics’ category was dispensed to 3.8% of all pregnancy events.ConclusionLinkage of dispensing data to pregnancy events is feasible and this approach to post-marketing surveillance will add to the resources available in Australia to investigate pregnancy outcomes in relation to the safe use of prescribed medicines in pregnancy. Copyright © 2009 John Wiley & Sons, Ltd.