Perinatal mortality in the normal siblings of anomalous triplets

To estimate the risk of survival of unaffected cofetuses of anomalous triplets.

Retrospective cohort study of triplets delivered in the United States from 1995 through 1998. Four triplet clusters were identified: cluster A (all members anomaly-free); cluster B (1 anomalous member); cluster C (2 anomalous members), and cluster D (all 3 members anomalous). We compared the risk for stillbirth and infant mortality among nonanomalous fetuses in clusters A, B, and C after adjusting for intracluster correlations.

A total of 7,560 triplet clusters (98.9%) were analyzed after excluding cluster D (1.1%). The total stillbirth rate was 20.9 (cluster A), 61.0 (cluster B), and 81.1 (cluster C) per 1,000 (P for trend < .001), and infant mortality rate was 56.4 (cluster A), 108.8 (cluster B), and 196.1 (cluster C) per 1,000 (P for trend < .001). Using cluster A as the referent category, the risk for stillbirth among anomaly-free clustermates climbed with increase in the number of siblings with anomalies in a dose-response pattern (adjusted odds ratio, 95% confidence interval 1.5, 0.7-3.1, for cluster B; and 5.2, 1.4-18.8, for cluster C; P for trend = .03). For infant mortality, the only rise in risk was in cluster C (3.3, 1.6-6.7), whereas cluster B showed comparable risk with the referent category (0.8, 0.5-1.4; P for trend > .05).

The presence of anomalous fetuses compromises the survival of normal cotriplets. These findings could prove useful for counseling affected parents and highlight the need for follow-up of normal coinfants of anomalous fetuses.