Abstract
BackgroundRecent studies have shown that older mothers who deliver at preterm gestation have lower neonatal mortality rates compared with younger mothers who deliver at preterm gestation. We examined the effect of maternal age on gestational age-specific perinatal mortality.MethodsWe compared fetal, neonatal and perinatal mortality rates among singleton births in the United States, 2003–2005, to mothers aged ≥35 versus 20–29 years. The analysis was stratified by gestational age and perinatal mortality rates were contrasted by maternal age at earlier (22–33 weeks) and later gestation (≥34 weeks). Gestational age-specific perinatal mortality rates were calculated using the traditional perinatal formulation (deaths among births at any gestation divided by total births at that gestation) and also the fetuses-at-risk model (deaths among births at any gestation divided by fetuses-at-risk of death at that gestation).Logistic regression was used to estimate adjusted odds ratios (AOR) for perinatal death.ResultsUnder the traditional approach, fetal death rates at 22–33 weeks were non-significantly lower among older mothers (AOR 0.97, 95% confidence interval [CI] 0.91-1.03), while rates were significantly higher among older mothers at ≥34 weeks (AOR 1.66, 95% CI 1.56-1.76). Neonatal death rates were significantly lower among older compared with younger mothers at 22–33 weeks (AOR=0.93, 95% CI 0.88-0.98) but higher at ≥34 weeks (AOR 1.26, 95% CI 1.21-1.31). Under the fetuses-at-risk model, both rates were higher among older vs younger mothers at early gestation (AOR for fetal and neonatal mortality 1.35, 95% CI 1.27-1.43 and 1.31, 95% CI 1.24-1.38, respectively) and late gestation (AOR for fetal and neonatal mortality 1.66, 95% CI 1.56-1.76) and 1.21, 95% CI 1.14-1.29, respectively).ConclusionsAlthough the traditional prognostic perspective on the risk of perinatal death among older versus younger mothers varies by gestational age at birth, the causal fetuses-at-risk model reveals a consistently elevated risk of perinatal death at all gestational ages among older mothers.
Highlights
Recent studies have shown that older mothers who deliver at preterm gestation have lower neonatal mortality rates compared with younger mothers who deliver at preterm gestation
Recent studies have suggested a favourable effect of advanced maternal age on neonatal death and serious neonatal morbidity among infants born at early gestation or low birth weight [11,12]
Our study showed that under the traditional perinatal model, fetal mortality rates at early gestation (22–33 weeks) were non-significantly lower among older vs younger mothers, while neonatal mortality and perinatal mortality rates at early gestation were significantly lower among older women
Summary
Recent studies have shown that older mothers who deliver at preterm gestation have lower neonatal mortality rates compared with younger mothers who deliver at preterm gestation. In Canada, the mean maternal age at childbirth increased substantially in four decades from 23.7 years in 1969 to 29.4 years in 2009 [1,2]. The proportion of live births to women age 35 years or older in Canada doubled from 9.2% in 1991 to 18.3% in 2009 [1,2]. While the trend towards delayed childbearing continues, the effect of maternal age on birth outcomes remains a subject of some controversy. Recent studies have suggested a favourable effect of advanced maternal age on neonatal death and serious neonatal morbidity among infants born at early gestation or low birth weight [11,12]
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