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Updated: May 16, 2026

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Published on: May 5, 2018
Congenital heart defects in a large, unselected cohort of monochorionic twins
K E Pettit1, M Merchant, G A Machin
1Department of Reproductive Medicine, University of California, San Diego Health System, San Diego, CA 92103-8433, USA. kpettit@stanfordalumni.org
Objective:
To determine the prevalence of congenital heart defects (CHDs) in a large, unselected cohort of monochorionic (MC) twins.
Study Design:
We completed a chart review of all MC twin pregnancies in the Kaiser Permanente Northern California population from 1996 to 2003. CHDs were identified by diagnostic codes and confirmed by postnatal echocardiograms. Follow-up was obtained through one year of age.
Result:
A total of 926 liveborn MC twins met inclusion criteria. The prevalence of CHDs was 7.5%, 11.6 times the general population rate (CI 9.2 to 14.5). Septal defects were most common. 20% of infants with heart defects had twin-to-twin transfusion syndrome (TTTS) versus 8% of infants without defects (P<0.01); this association remained significant when controlling for potential confounders.
Conclusion:
The prevalence of CHDs in this large cohort of MC twins was significantly higher than the general population rate, with TTTS an added risk factor.
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