566: Optimal timing of delivery in women age 40 and over

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The number of women of advanced maternal age is increasing. In order to determine optimal delivery timing, the risk of stillbirth and infant death in women aged 40 and over was calculated for each gestational age at term. This is a population-based retrospective cohort study using US birth certificate data. Singleton live births and stillbirths of women aged ≥ 40 who delivered at term between January 2007 and December 2013 were included. Women with pre-gestational diabetes, hypertension or fetal anomalies were excluded. Maternal age was stratified into two groups: women aged 40-44 and women aged ≥ 45. At each gestational age the prospective stillbirth risk, the infant mortality risk, and the composite fetal-infant mortality risk of each additional week of expectant management were calculated (Figure 1). We considered the optimal gestational age of delivery to be when the infant mortality was less than the composite risk of expectant management for one additional week. There were 23,589,521 births included in the analysis; 23,519,868 live births, 22,234 stillbirths, and 47,419 infant deaths. In women ≥ 40 years, the composite risk of expectant management until 40 weeks exceeded the risk of infant death at 39 weeks (63.2 composite risk vs 15.6 infant deaths per 10,000, p< 0.001). When the data was stratified by maternal age, the risk beyond 39 weeks was greater in women ≥ 45years (113.4 composite risk vs 14.7 infant deaths per 10,000, p< 0.001) as well as in women age 40-44 (60.4 composite risk vs 15.6 infant deaths per 10,000, p< 0.001). For women aged ≥45, the number of women was small, and our data suggests a trend toward increasing risk of mortality with expectant management beyond 38 weeks, although this was not statistically significant (29.8 composite risk vs 18.8 infant deaths per 10,000, p=0.130). Delivery at 39 weeks minimizes stillbirth and infant mortality risk for women age over 40, and in particular in women aged over 45. This study suggests a trend favoring delivery at 38 weeks in women aged over 45 in order to minimize risk of fetal and infant death.View Large Image Figure ViewerDownload Hi-res image Download (PPT)