Smulian John C, Ananth Cande V, Kinzler Wendy L, Kontopoulos Eftichia, Vintzileos Anthony M
Department of Obstetrics, Gynecology and Reproductive Sciences, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School/Robert Wood Johnson University Hospital, New Brunswick, New Jersey 08901-1977, USA.
Obstet Gynecol. 2004 Aug;104(2):278-85. doi: 10.1097/01.AOG.0000134524.58795.bd.
Time is an important variable in understanding the recent increase in twin deliveries in the United States. Therefore, this study was designed to estimate the influences of maternal age, period (year) of delivery, and maternal-birth-year cohort on trends in rates of twin deliveries.
United States natality data were used to assess trends in twin pregnancies resulting in live births. This age-period-cohort analysis included 7, 5-year maternal-age groups (15-19 through 45-49 years), 6 twin delivery periods (1975, 1980, 1985, 1990, 1995, and 2000), and 12, 5-year maternal birth cohorts (1926-1930 through 1981-1985). The independent effects of maternal age, twin delivery period, and maternal birth cohort on twin delivery rates for blacks and whites were modeled using Poisson regression techniques.
Our study assessed 95,042 blacks and 401,989 whites with twin deliveries. Twin deliveries increased by 46% for blacks and 62% for whites from 1975 to 2000, with the largest increase occurring in the year 2000. For blacks, maternal age had the strongest impact on the increasing twin delivery rates, followed by period of delivery. For whites, the greatest effect was due to period of delivery, followed by maternal birth year cohort and, lastly, maternal age.
Our data confirm the importance of nature's biologic contribution of maternal aging to twin delivery rates, but suggest that recent changes in the environment surrounding pregnancy (nurture) also influence twin delivery rates. The relative contributions of biologic versus environmental influences appear to differ among blacks and whites.
时间是理解美国近期双胎分娩增加情况的一个重要变量。因此，本研究旨在评估产妇年龄、分娩时期（年份）和产妇出生年份队列对双胎分娩率趋势的影响。
使用美国出生数据来评估导致活产的双胎妊娠趋势。这种年龄-时期-队列分析包括7个5岁产妇年龄组（15 - 19岁至45 - 49岁）、6个双胎分娩时期（1975年、1980年、1985年、1990年、1995年和2000年）以及12个5岁产妇出生队列（1926 - 1930年至1981 - 1985年）。使用泊松回归技术对黑人与白人的产妇年龄、双胎分娩时期和产妇出生队列对双胎分娩率的独立影响进行建模。
我们的研究评估了95,042名有双胎分娩的黑人以及401,989名有双胎分娩的白人。从1975年到2000年，黑人的双胎分娩增加了46%，白人增加了62%，最大增幅出现在2000年。对于黑人，产妇年龄对双胎分娩率上升的影响最大，其次是分娩时期。对于白人，最大的影响归因于分娩时期，其次是产妇出生年份队列，最后是产妇年龄。
我们的数据证实了产妇年龄增长对双胎分娩率的生物学贡献的重要性，但表明近期孕期周围环境的变化（后天因素）也会影响双胎分娩率。生物学与环境影响的相对贡献在黑人和白人中似乎有所不同。
