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Title: The Impact of Maternal Birth Month on Reproductive Performance: Controlling for Socio-Demographic Confounders
Citation Type: Journal Article
Publication Year: 2010
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Abstract: Based on a 1900 census sample of 34,166 post-reproductive females(R45 years), the birth month effect was put to the test, for both lifetime fertilityas well as child survival, controlling for maternal birth cohort (18261835,18361845, 18461855), Duncans SEI, urbanity, nativity, literacy and maritalduration. Testing for potential cohort effects did not indicate a temporal trendin fertility by maternal birth month (seasonal Mann-Kendall test, p=0.578),while a minute increase in offspring survival was detected (p<0.001, Sensestimator of slope=0.02, 95% CI=0.02 to 0.03). Further analyses of the maternalbirth month effect on child survival were therefore seized. For lifetime fertility,ANOVA results indicated that maternal birth month was a major predictor fortotal offspring count (F11, 33606=1809.0, p<0.001), accounting for 37.2% of thetotal variability. In addition to main effects, a statistically significant interactioneffect was observed (F538, 33606=2.2, p<0.001), with a corresponding effect size of2=0.40. Planned contrasts revealed that birth-month-specific differences infertility achieved statistical significance (F11, 31798=1712.9, p<0.001), while posthocmultiple comparisons for literacy and nativity displayed an inverse relationshipwith fertility, which meets demographic expectations. Controlling forall factors of interest, models of cohort-specific offspring counts (independentANOVAs for 18261835: F157, 3467=26.3, p<0.001; 18361845: F182, 10299=75.5,p<0.001; 18461855: F199, 19859=137.9, p<0.001) indicated that women born inthe first half of the year (particularly, January, February, April and May)achieved above-average parity, while those born in the latter half (namely,July, October, November and December) displayed markedly lower fertilityaverages. These monthly disparities are in line with previous observations andappear to be linked to seasonal optimal ripening of the oocyte or seasonalpreovulatory over-ripeness ovopathy (Jongbloet, 1992).
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Authors: Kemkes, Ariane
Periodical (Full): Journal of Biosocial Science
Issue: 2
Volume: 42
Pages: 177-194
Data Collections: IPUMS USA
Topics: Fertility and Mortality
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