ESTIMATED GAINS IN BIRTH-WEIGHT ASSOCIATED WITH REDUCTIONS IN SMOKINGDURING PREGNANCY

OBJECTIVE: To compare the estimated effect on birth weight of reductio ns in maternal cigarette consumption and urinary cotinine during pregn ancy. STUDY DESIGN: An observational study of 641 women with complete data on cigarette consumption, urinary cotinine and infant birth weigh t. Correlation and regression analyses were used to examine relationsh ips between birth weight, cigarette consumption and urinary cotinine a t first and last prenatal visits. RESULTS: Correlations of cigarette c onsumption and urinary cotinine with infant birth weight were -.23 and -.30 (first visit) and -.26 and -.31 (last visit); all P values were <.001. The regression equation relating urinary cotinine concentration s at first and last visits to infant birth weight explained a signific antly larger proportion of the variability in birth weight than the eq uation relating cigarette consumption at these visits to infant birth weight, 11% vs. 7%, P=.04. Among continuing smokers, both equations pr edicted gains in birth weight in association with reductions in cigare tte consumption, but quitting smoking before the first visit was assoc iated with the most weight gain. As compared to the average infant bir th weight of a woman who smoked 20 cigarettes per day throughout pregn ancy, the estimated gain in birth weight would be 105 g if she cut dow n by 10 cigarettes per day after the first visit, 210 g if she quit af ter this visit and 310 g if she quit before the first visit. CONCLUSIO N: For women still smoking at their first prenatal visit, infant birth weight is already compromised, but subsequent reductions in cigarette consumption are associated with gains in birth weight. For women who cannot quit smoking, these reductions need to be substantial if increa ses in birth weight of > 100 g are to be achieved.