Gynecology & Obstetrics
Open Access

Abstract

Infant Mortality of Zygotic Twins and Influencing Factors in Japan, 1995 2008

Yoko Imaizumi

We aimed to determine the infant mortality rates (IMRs) for monozygotic (MZ) and dizygotic (DZ) twins along with risk factors associated with these IMRs. Study design: IMRs of zygotic twins were estimated using vital statistics from Japan between 1995 and 2008.  Results: In 1995, IMRs were 21.7 for MZ twins and 15.6 for DZ twins per 1000 deliveries, and they significantly decreased to 9.8 and 5.8, respectively, in 2008. During the study period, IMRs were the lowest at maternal ages (MAs) of 35–39 years for MZ (14.4) twins and 30–34 years for DZ twins (8.2). The highest IMRs were for MZ (23.6) and DZ (24.9) twins at MAs of <20 years. At MAs of 20–24 and 35–39 years, IMRs were significantly higher for MZ than DZ twins. IMRs were also the lowest at gestational ages (GAs) of 37 weeks for MZ (3.0) twins and 39 weeks for DZ twins (1.9). At GAs of <29 weeks and 33–34 weeks, IMRs were significantly higher for MZ than DZ twins. Conclusion: IMR was significantly higher for MZ than DZ twins, although these rates significantly decreased each year. For both MZ and DZ twins, mortality risk factors were MAs of <20 years and GAs of up to 35 weeks.