Relationships between cigarette smoking during pregnancy, gestational age, maternal weight gain, and infant birthweight.
OBJECTIVE
To estimate the effect of smoking on infant birthweight independent of gestational age and maternal weight gain during pregnancy.


METHODS
Stepwise regression was used to identify sets of maternal and infant characteristics not modified by prenatal smoking that were predictors of infant birthweight, gestational age, and net maternal weight gain. These were then included in regression analyses to assess the effects of smoking, as measured by cigarette consumption, exhaled carbon monoxide, or urinary cotinine on gestational age, net maternal weight gain, and infant birthweight.


RESULTS
After adjustment for nonmodifiable factors, smoking accounted for 1.5-3.1% of the variance in gestational age at delivery. It accounted for 5.3-7.7% of the variance in net maternal weight gain after adjustment for nonmodifiable factors and gestational age. After adjustment for gestational age and net maternal weight gain, and the nonmodifiable factors, smoking accounted for 2.7-5.2% of the variance in infant birthweight.


CONCLUSIONS
Most of the gain in infant birthweight on quitting smoking is due to the independent effect of smoking on fetal growth restriction, with much smaller gains related to increased maternal weight gain and a slightly longer gestational age.
Secker-Walker
Roger H
RH
Office of Health Promotion Research (RHS-W), University of Vermont, Burlington, VT, USA. rseckerw@zoo.uvm.edu
Vacek
Pamela M
PM
D000328:Adult; D001724:Birth Weight; D001944:Breath Tests; D002248:Carbon Monoxide / Q000378:metabolism; D003367:Cotinine / Q000652:urine; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D011247:Pregnancy / Q000502:physiology*; D011297:Prenatal Exposure Delayed Effects; D012044:Regression Analysis; D012907:Smoking / Q000503:physiopathology* / Q000652:urine; D015430:Weight Gain
D002248:Carbon Monoxide; D003367:Cotinine