The effect of pregnancy on aortic root in women with repaired conotruncal anomalies (CTA) has not been clarified. This study examined aortic diameters during and after pregnancy in women with repaired CTA. A retrospective review of consecutive pregnant women with repaired CTA was performed for results of echocardiography from 1 year before pregnancy to 3 years after delivery and compared with findings from healthy pregnant volunteers. Participants comprised 42 subjects and 49 deliveries with repaired CTA (CTA group), and 47 healthy pregnant women (control group). Although no maternal aortic events were encountered, aortic diameters during pregnancy increased by 1.0 ± 2.2 mm (maximum, 7.0 mm) in the CTA group and 0.6 ± 1.3 mm (maximum, 3.4 mm) in the control group (p = 0.13). The CTA subgroup with increase in aortic diameter ≥ 3.5 mm during pregnancy showed no reversion to baseline diameter at follow-up > 6 months after delivery. Significant risk factors for increased aortic diameter and no reversal included pulmonary atresia, history of aortopulmonary shunt, older age at repair, and smaller left ventricular end-diastolic diameter pre-pregnancy. Women with repaired CTA tolerated pregnancy and delivery well. However, the aortic root progressively dilated during pregnancy and 1/4 of them, especially those with longstanding high aortic blood flow before repair, showed an increase of aortic root size of ≥ 3.5 mm during the peripartum period; this dilatation tended not to revert to the pre-pregnancy diameter. Therefore, serial measurement of the aortic root during pregnancy and after delivery is recommended in these women.