For many medicines, safety information regarding use in pregnant women is lacking but their use during pregnancy has increased considerably in recent decades. A substantial proportion of pregnant women overseas, in particular women of lower socioeconomic status, take prescribed drugs during pregnancy. Selective serotonin reuptake inhibitor (SSRI) antidepressants, widely used in New Zealand, have been associated with several adverse fetal outcomes. Selective serotonin noradrenaline reuptake inhibitors (SNRIs) may be less risky in pregnancy but evidence is limited. This study has three aims. First, the overall patterns of dispensing for pregnant women in New Zealand will be described, with specific consideration of several medicines known to cause fetal harm. Second, the patterns of SSRI/SNRI use during pregnancy and adverse fetal and maternal outcomes will be investigated. Third, the effectiveness of undertaking studies of drug safety in pregnancy by linking the National Maternity Collection with other national datasets will be assessed.