Abstract
Numerous cross-sectional studies have shown a strong relationship between maternal age, birth order, and the risk of delivering a LBW baby (< 2500g). We analyzed all 366,005 white and black deliveries in North Carolina (360,925 live births, and 5,080 fetal deaths) in two cohorts 10 years apart. Over this period the optimum age-birth order combinations (those with minimum risk for LBW) changed. For white mothers, the lowest risk age shifted about 3 years from 26 to 29 years, and optimum birth order remained constant at 2. For black mothers, the optimum age remained constant in the late 20s, but the lowest risk birth order moved from ≥ 5 to 3. When joint effects of age and birth order were considered, the risk pattern of blacks changed the most, becoming more like that of whites. Both blacks and whites had a shift of births out of higher birth orders, especially into birth orders 1 and 2 with maternal age 23 to 34. Because of a better match between shifting birth frequencies and age-birth order-specific risks, the observed trends appear to have had a more beneficial effect on reducing LBW among white births. Since risk effects of age and birth order change over time in populations studied longitudinally, it is unlikely that the observed low-risk age-birth order combinations represent any fixed “biological optimum” for reproductive timing. Such longitudinal changes also make it difficult to quantify precisely the contributions of changing pregnancy timing; to declining LBW rates.
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David, R., Chen, C. & Hunt, C. 525 CHANGING PATTERNS OF MATERNAL AGE AND BIRTH ORDER: EFFECTS ON INCIDENCE OF LOW BIRTH WEIGHT (LBW). Pediatr Res 19, 198 (1985). https://doi.org/10.1203/00006450-198504000-00555
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DOI: https://doi.org/10.1203/00006450-198504000-00555