The role of maternal age in twin pregnancy outcomes

BACKGROUND: There are limited data on how maternal age is related to twin pregnancy outcomes. OBJECTIVE: The purpose of this study was to assess the relationship between maternal age and risk for preterm birth, fetal death, and neonatal death in the setting of twin pregnancy. STUDY DESIGN: This population-based study of US birth, fetal death, and period-linked birth-infant death files from 2007-2013 evaluated neonatal outcomes for twin pregnancies. Maternal age was categorized as 15-17, 18-24, 25-29, 30-34, 35-39, and >= 40 years of age. Twin live births and fetal death delivered at 20-42 weeks were included. Primary outcomes included preterm birth (<34 weeks and <37 weeks), fetal death, and neonatal death at <28 days of life. Analyses of preterm birth at <34 and < 37 weeks were adjusted for demographic and medical factors, with maternal age modeled with the use of restricted spline transformations. RESULTS: A total of 955,882 twin live births from 2007-2013 were included in the analysis. Preterm birth rates at < 34 and < 37 weeks gestation were highest for women 15-17 years of age, decreased across subsequent maternal age categories, nadired for women 35-39 years old, and then increased slightly for women >= 40 years old. Risk for fetal death generally decreased across maternal age categories. Risk for fetal death was 39.9 per 1000 live births for women 15-17 years old, 24.2 for women 18-24 years old, 17.8 for women 25-29 years old, 16.4 for women 30-34 years old, 17.2 for women 35-39 years old, and 15.8 for women >= 40 years old. Risk for neonatal death at <28 days was highest for neonates born to women 15-17 years old (10.0 per 1,000 live births), decreased to 7.3 for women 18-24 years old and 5.5 for women 25-29 years old and ranged from 4.3-4.6 for all subsequent maternal age categories. In adjusted models, risk for preterm birth at <34-<37 weeks gestation was not elevated for women in their mid-to-late 30s; however, risk was elevated for women <20 years old and increased progressively with age for women in their 40s. CONCLUSION: Although twin pregnancy is associated with increased risk for most adverse perinatal outcomes, this analysis did not find advanced maternal age to be an additional risk factor for fetal death and infant death. Preterm birth risk was relatively low for women in their late 30s. Risks for adverse outcomes were higher among younger women; further research is indicated to improve outcomes for this demographic group. It may be reasonable to counsel women in their 30s that their age is not a major additional risk factor for adverse obstetric outcomes in the setting of twin pregnancy.