General Obstetrics and Gynecology Obstetrics
Placenta previa in singleton and twin births in the United States, 1989 through 1998: A comparison of risk factor profiles and associated conditions

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Abstract

Objective: The purpose of this study was to compare risk factor profiles for placenta previa between singleton and twin live births. Study Design: This cohort study was based on United States natality data files (1989 through 1998) and comprised 37,956,020 singleton births and 961,578 twin births. Women who were diagnosed with placenta previa were included only if they were delivered by cesarean delivery. Risk factors for placenta previa that were examined included sociodemographic (age, gravidity, education, marital status, and race), behavioral (prenatal care, smoking, and alcohol use), previous preterm birth, and medical and obstetric factors. Effect modification between maternal age and gravidity and the dose-response relationship with number of cigarettes smoked/day on placenta previa risk were also evaluated. Results: The rate of placenta previa was 40% higher among twin births (3.9 per 1,000 live births, n = 3,793 births) than among singleton births (2.8 per 1,000 live births, n = 104,754 births). Comparison of risk factors for placenta previa between the singleton and twin births revealed fairly similar risk factor profiles. Compared with primigravid women <20 years old, the risk for placenta previa increased by advancing age and by increasing number of pregnancies among both singleton and twin births. The number of cigarettes smoked per day also showed a dose-response trend for placenta previa risk in the two groups. Conclusion: The increased rate of placenta previa among twin births underscores the need to monitor carefully such pregnancies with heightened suspicion and awareness for the development of this condition. (Am J Obstet Gynecol 2003;188:275-81.)

Section snippets

Cohort composition

Data for this large, population-based retrospective cohort study were derived from the US natality data files from 1989 to 1998. These data are assembled by the National Center for Health Statistics (NCHS) of the Centers for Disease Control and Prevention, under a cooperative agreement with all the 50 states and the District of Columbia. These natality data files, produced annually, include statistical data from birth that are provided to the NCHS by the individual states, under the Vital

Results

Placenta previa was recorded in 2.8 (n = 104,754) and 3.9 (n = 3,793) per 1,000 singleton and twin live births, respectively (Table I).

. Rates and unadjusted relative risks of placenta previa in relation to maternal characteristics in singleton and twin births: United States, 1989 through 1998

Maternal characteristicSingleton birthsTwin births
Number of birthsPlacenta previa* RateUnadjusted RR 95% CINumber of birthsPlacenta previa* RateUnadjusted RR 95% CI
Total37,956,0202.8961,5783.9
Maternal age

Comment

Despite small differences in the magnitude and strength of the association of risk factors for placenta previa between the singleton and twin cohorts, risk factor profiles appear fairly similar. Nonetheless, placenta previa occurs 40% more frequently among twin pregnancies than singleton pregnancies without any obvious patterns. Obvious strengths of this study include the large, population-based nature of the data, perhaps the largest series on placenta previa ever reported to date. In

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