Changes in the gestational age distribution among U.S. singleton births: impact on rates of late preterm birth, 1992 to 2002.

There is mounting evidence that infants born late preterm (34-36 weeks) are at greater risk for morbidity than term infants. This article examines the changing epidemiology of gestational length among singleton births in the United States, from 1992 to 2002. Analyzing gestational age by mode of delivery, the distribution of spontaneous births shifted to the left, with 39 weeks becoming the most common length of gestation in 2002, compared with 40 weeks in 1992 (P < 0.001). Deliveries at > or =40 weeks gestation markedly decreased, accompanied by an increase in those at 34 to 39 weeks (P < 0.001). Singleton births with PROM or medical interventions had similar trends. Changes in the distribution of all singleton births differed by race/ethnicity, with non-Hispanic white infants having the largest increase in late preterm births. These observations, in addition to emerging evidence of increased morbidity, suggest the need for investigation of optimal obstetric and neonatal management of these late preterm infants.

Research agenda for preterm birth: recommendations from the March of Dimes.

Preterm birth (PTB) is a common, serious, and costly health problem affecting nearly 1 in 8 births in the United States. Burdens from PTB are especially severe for the very preterm infant (<32 weeks' gestation), comprising 2% of all US births. Successful prevention needs to include newly focused and adequately funded research, incorporating new technologies and recognition that genetic, environmental, social, and behavioral factors interact in complex pathogeneses and multiple pathways leading to PTB. The March of Dimes Scientific Advisory Committee created this prioritized research agenda, which is aimed at garnering serious attention and expanding resources to make major inroads into the prevention of PTB, targeting six major, overlapping categories: epidemiology, genetics, disparities, inflammation, biologic stress, and clinical trials. Analogous to other common, complex disorders, progress in prevention will require incorporating multipronged risk reduction strategies that are based on sound scientific discovery, as well as on effective translation into clinical care.

Estimated effect of 17 alpha-hydroxyprogesterone caproate on preterm birth in the United States.

OBJECTIVE: A multicenter, randomized placebo-controlled trial among women with singleton pregnancies and a history of spontaneous preterm birth found that weekly injections of 17 alpha-hydroxyprogesterone caproate (17P), initiated between 16 and 20 weeks of gestation, reduced preterm birth by 33%. The current study estimated both preterm birth recurrence and the potential reduction in the national preterm birth rate. METHODS: Using 2002 national birth certificate data, augmented by vital statistics from 2 states, we estimated the number of singleton births delivered to women eligible for 17P through both a history of spontaneous preterm birth and prenatal care onset within the first 4 months of pregnancy. The number and rate of recurrent spontaneous preterm births were estimated. To predict effect, the reported 33% reduction in spontaneous preterm birth attributed to 17P therapy was applied to these estimates. RESULTS: In 2002, approximately 30,000 recurrent preterm births occurred to women eligible for 17P, having had a recurrent preterm birth rate of 22.5%. If 17P therapy were delivered to these women, nearly 10,000 spontaneous preterm births would have been prevented, thereby reducing the overall United States preterm birth rate by approximately 2%, from 12.1% to 11.8% (P < .001), with higher reductions in targeted groups of eligible pregnant women. CONCLUSION: Use of 17P could reduce preterm birth among eligible women, but would likely have a modest effect on the national preterm birth rate. Additional research is urgently needed to identify other populations who might benefit from 17P, evaluate new methods for early detection of women at risk, and develop additional prevention strategies. LEVEL OF EVIDENCE: III.

Mode of conception, placental morphology and perinatal outcome of twin gestations.

OBJECTIVE: To compare the perinatal outcome and placental morphology of twins conceived by assisted reproductive technologies (ART) or natural conception (NC). METHODS: The present retrospective study included 88 twin pairs. Methods of ART included in vitro fertilization, intrauterine insemination, embryo transfer and induced ovulation. Placental morphology was described by chorionicity, amnionicity, placental weight, umbilical cord insertion and the number of cord vessels. Perinatal outcomes included maternal age, gestational age, birth weight (BW), BW discordance and mode of delivery. RESULTS: The mothers of ART twins were 4 years older than NC mothers. ART twins delivered 2.2 weeks earlier than NC twins. The BW of ART twins A and B were less than NC twins A and B. There was no difference in the proportion of discordant twins in either group. Dichorionic diamniotic (DD) placentas accounted for the majority of placentas in both groups. There were no monochorionic-monoamniotic placentas in ART pairs, but there were 2.9% in NC pairs. Mode of conception had no effect on placental weight in DD or monochorionic-diamniotic twins in either group except for larger DD fused placentas in the ART group. CONCLUSION: ART twin pairs were delivered at an earlier gestational age at lower birth weights to older mothers predominantly by cesarean section. This perinatal outcome was not reflected by placental morphology.

The changing epidemiology of multiple births in the United States.

OBJECTIVE: To describe changes in the epidemiology of multiple births in the United States from 1980 to 1999 by race, maternal age, and region; and to examine the impact of these changes on birth weight-specific infant mortality rates for singleton and multiple births. METHODS: Retrospective univariate and multivariable analyses were conducted using vital statistics data from the National Center for Health Statistics. RESULTS: Between 1980 and 1999, the overall multiple birth ratio increased 59% (from 19.3 to 30.7 multiple births per 1000 live births, P <.001), with rates among whites increasing more rapidly than among blacks. Women of advanced maternal age, especially those aged 30-34, 35-39, and 40-44 experienced the greatest increases (62%, 81%, and 110%, respectively). Although all regions of the United States experienced increases in multiple birth ratios between 1991 and 1999, the Northeast had the highest twin (33.9 per 1000 live births) and higher order birth ratios (280.5 per 100,000 live births), even after adjusting for maternal age and race. Between 1989 and 1999, multiple births experienced greater declines in infant mortality than singletons in all birth weight categories. Consequently, very low birth weight and moderately low birth weight infant mortality rates among multiples were lower than among singletons. CONCLUSION: It is important to understand the changing epidemiology of multiple births, especially for women at highest risk (advanced maternal age, white race, Northeast residents). The attribution of infertility management requires further study. The differential birth weight-specific infant mortality for singletons and multiples demonstrates the importance of stratifying by plurality when assessing perinatal outcomes.