Objective  To compare the risks of complications during pregnancy in women with repaired and unrepaired atrial septal defects (ASDs) without associated complex cardiac lesions.

Design  A retrospective multicentre study.

Setting  Tertiary centres in the Netherlands and Belgium.

Population  Women with ASD without associated complex cardiac lesions.

Methods  Women were identified using two congenital heart disease registries. One hundred women were identified who had 243 pregnancies, including 49 miscarriages and six terminations of pregnancy. Detailed information on each completed pregnancy (n = 188; unrepaired ASD, n = 133; repaired ASD, n = 55) was obtained using medical records and telephone interviews. In addition, data from the Generation R database (a prospective cohort study; n = 9667) were used to determine the background risk (control group).

Main outcome measures  Adjusted odds ratios (AORs) for cardiac, obstetric and neonatal events controlled for multiple pregnancies per woman using general estimating equation analysis.

Results  Women with an unrepaired ASD had a higher risk of neonatal events (AOR = 2.99, 95% confidence interval [CI] 1.14–7.89, P = 0.027) than women with a repaired ASD. The risk of cardiac and obstetric complications was comparable between women with unrepaired and repaired ASDs. Compared with the general population, women with an unrepaired ASD had higher risks of pre‐eclampsia (AOR = 3.54, 95% CI 1.26–9.98, P = 0.017), small‐for‐gestational‐age births (AOR = 1.95, 95% CI 1.15–3.30, P = 0.013) and fetal mortality (AOR = 5.55, 95% CI 1.77–17.4, P = 0.003). By contrast, no differences were observed when comparing women with a repaired ASD versus controls.

Conclusions  Women with an unrepaired ASD are at increased risk of neonatal events in comparison with women with a repaired ASD. Compared with the general population, women with an unrepaired ASD are at increased risk of pre‐eclampsia, small‐for‐gestational‐age births and fetal mortality.