Low birthweight at term and the timing of fetal exposure to maternal smoking

Am J Public Health. 1994 Jul;84(7):1127-31. doi: 10.2105/ajph.84.7.1127.


Objectives: This study was undertaken to evaluate the risk of small-for-gestational-age birth for women who stop smoking or begin to smoke during pregnancy.

Methods: Women with term singleton pregnancies from a hospital-based cohort of 11,177 were classified as (1) nonsmokers; (2) smoked throughout pregnancy; (3) smoked during first trimester only; (4) smoked during first and second trimesters only; and (5) smoked during second and third trimesters or during third trimester only. Risk of small-for-gestational-age birth according to smoking category was estimated and adjusted for confounding factors by logistic regression.

Results: Women who stopped smoking by the third trimester were not at increased risk of small-for-gestational-age birth compared with nonsmokers. Women who began smoking during the second or third trimester had an elevated risk of small-for-gestational-age birth (odds ratio [OR] = 1.83; 95% confidence interval [CI] = 1.25, 2.67) similar to that for women who smoked throughout pregnancy (OR = 2.20; 95% CI = 1.90, 2.54). Risk of small-for-gestational-age birth increased with the number of cigarettes smoked during the third trimester.

Conclusions: It is during the third trimester that smoking retards fetal growth, presenting a compelling opportunity for smoking cessation interventions. Programs must emphasize the importance of not resuming smoking late in pregnancy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Birth Weight / drug effects*
  • Cohort Studies
  • Female
  • Fetal Growth Retardation / chemically induced*
  • Fetus / drug effects
  • Humans
  • Infant, Newborn
  • Infant, Small for Gestational Age*
  • Linear Models
  • Logistic Models
  • Pregnancy
  • Risk Factors
  • Smoking / adverse effects*
  • Smoking Cessation*
  • Time Factors