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Objective: To estimate rates of fetal death, perinatal mortality, and infant mortality as well as the prevalence, concordance rates, and birth weight discordance attributed to twin-twin transfusion syndrome (TTTS).
Study design: These rates were estimated using Japanese Vital Statistics from 1995 to 2008. The total number of one or both members of a twin pair with TTTS was 1102.
Results: During 1999 and 2000, fetal death and perinatal and infant mortality rates related to TTTS decreased (48 per 10,000 births, 44 per 10,000 live births and fetal deaths after 22 weeks of gestation, and 16 per 10,000 live births, respectively) compared with those during 2007 and 2008 (31, 21 and 7, respectively). The fetal death rate was higher in male than in female fetuses. Furthermore, fetal death and infant mortality rates were the highest during gestational weeks 22–25; these rates decreased with gestational age and reached their lowest values at ≥38 weeks. Frequency of birth weight discordance ≥15% was 82% among all subjects. The concordance rate was 44% (484/1102 pairs of twins), whereas the overall prevalence was 1.1 per 100 monozygotic twin pairs from 1995 through 2008.
Conclusion: Fetal death and infant mortality rates decreased with maternal age. The declining rates of fetal death and perinatal and infant mortality related to TTTS may be related to recent improvements in medical treatments for TTTS in Japan.