Stillbirth Rates and Risk Factors for Stillbirths among Zygotic Twins in Japan, 1995-2008

Abstract

We aimed to determine the Stillbirth Rates (SRs) for monozygotic (MZ) and dizygotic (DZ) twins, with the risk factors for stillbirth. SRs were estimated using Japanese vital statistics from 1995 to 2008. The SRs of zygotic twins significantly decreased during the period. The SR was the lowest at maternal age (MA) of 30-34 years for MZ (66) and DZ twins (18) and significantly higher at MA <20 years than the other MA groups for both zygosities. The SR was the lowest at Gestational Age (GA) of 37 weeks for MZ (5.7) and DZ twins (1.8). The SR was significantly higher for MZ than for DZ twins at each GA group except for those born at GA 39 and GA ≥ 40 weeks. The SR significantly decreased from 1995-1998 to 2004-2008 except GA ≥ 40 for both zygotic twins and 32-35 weeks for DZ twins. Incidences of preterm delivery increased from 1995 (43% for MZ and 38% for DZ twins) to 2008 (62% and 55%, respectively). The SRs were significantly higher in like-sexed twins than in unlike-sexed twins in every birth weight (BW) group. The SR was similar between BW 2000–2499 g and ≥ 2500 g in each twin group. The SR increased progressively when the percentage of BW discordance exceeds 10% for MZ twins and exceeds 20% for DZ twins. The SR due to twin–twin transfusion syndrome was 14% among spontaneous stillbirths in MZ twins. In conclusion, declining SR attributed to medical care during twin pregnancies less than 40 weeks for MZ and DZ twins. Excess BW discordance of 10% for MZ twins lead to higher SRs compared with those in DZ twins. The increased premature rate in twins might bring severe problems such as cardiovascular risk in their future life.