Kato Noriko, Matsuda Tomohiro
Department of Education Training Technology and Development, National Institute of Public Health, 2-3-6 Minami, Wako-shi, Saitama, 351-0197, Japan.
BMC Public Health. 2006 Feb 24;6:45. doi: 10.1186/1471-2458-6-45.
As multiple pregnancies show a higher incidence of complications than singletons and carry a higher perinatal risk, the calculation of birth weight - and gestational age (GA)-specific perinatal mortality rates (PMR) for multiple births is necessary in order to estimate the lowest PMR for these groups.
Details of all reported twins (192,987 live births, 5,539 stillbirths and 1,830 early neonatal deaths) in Japan between 1990 and 1999 were analyzed and compared with singletons (10,021,275 live births, 63,972 fetal deaths and 16,862 early neonatal deaths) in the annual report of vital statistics of Japan. The fetal death rate (FDR) and PMR were calculated for each category of birth weight at 500-gram intervals and GA at four-week intervals. The FDR according to birth weight and GA category was calculated as fetal deaths/(fetal deaths + live births) x 1000. The perinatal mortality rate (PMR) according to birth weight and GA category, was calculated as (fetal deaths + early neonatal deaths)/(fetal deaths + live births) x 1000. Within each category, the lowest FDR and PMR were assigned with a relative risk (RR) of 1.0 as a reference and all other rates within each category were compared to this lowest rate.
The overall PMR per 1,000 births for singletons was 6.9, and the lowest PMR was 1.1 for birth weight (3.5-4.0 kg) and GA (40-weeks). For twins, the overall PMR per 1,000 births was 36.8, and the lowest PMR was 3.9 for birth weight (2.5-3.0 kg) and GA (36-39 weeks). At optimal birth weight and GA, the PMR was reduced to 15.9 percent for singletons, and 10.6 percent for twins, compared to the overall PMR. The risk of perinatal mortality was greater in twins than in singletons at the same deviation from the ideal category of each plurality.
PMRs are potentially reduced by attaining the ideal birth weight and GA. More than 90 percent of mortality could be reduced by attaining the optimal GA and birth weight in twins by taking particular care to ensure appropriate pregnancy weight gain, as well as adequate control for obstetric complications.
由于多胎妊娠比单胎妊娠并发症发生率更高，围产期风险也更高，因此有必要计算多胎分娩的出生体重和孕周（GA）特异性围产儿死亡率（PMR），以便估计这些群体的最低PMR。
分析了1990年至1999年日本所有报告的双胞胎（192,987例活产、5,539例死产和1,830例早期新生儿死亡）的详细情况，并与日本生命统计年度报告中的单胎（10,021,275例活产、63,972例胎儿死亡和16,862例早期新生儿死亡）进行比较。按出生体重每500克间隔和孕周每四周间隔计算每个类别的胎儿死亡率（FDR）和PMR。根据出生体重和孕周类别计算的FDR为胎儿死亡数/（胎儿死亡数+活产数）×1000。根据出生体重和孕周类别计算的围产儿死亡率（PMR）为（胎儿死亡数+早期新生儿死亡数）/（胎儿死亡数+活产数）×1000。在每个类别中，将最低的FDR和PMR指定为相对风险（RR）为1.0作为参考，并将每个类别中的所有其他率与该最低率进行比较。
单胎每100例分娩的总体PMR为6.9，出生体重（3.5-4.0千克）和孕周（40周）时的最低PMR为1.1。对于双胞胎，每1000例分娩的总体PMR为36.8，出生体重（2.5-3.0千克）和孕周（36-39周）时的最低PMR为3.9。在最佳出生体重和孕周时，与总体PMR相比，单胎的PMR降低至15.9%，双胞胎的PMR降低至10.6%。在与每个多胎理想类别相同的偏差下，双胞胎的围产儿死亡风险高于单胎。
达到理想的出生体重和孕周可能会降低PMR。通过特别注意确保适当的孕期体重增加以及充分控制产科并发症，双胞胎达到最佳孕周和出生体重可降低超过90%的死亡率。
