BACKGROUND: Research suggests exposure to secondhand tobacco smoke (STS) during pregnancy is associated with reduced birthweight and possibly gestational duration. Less is known about various sources of STS exposure throughout different time periods in pregnancy. The current study aimed to assess associations between self-reported sources of STS exposure and birth outcomes.
METHODS: Questionnaires were completed by 8,024 women following delivery from 2000-2003 in San Diego County, California. STS exposure data obtained from the questionnaire related to number of closest friends/family that smoke, presence of household smokers, baby’s father smoking, and time spent with smokers in 4 places during 4 time periods (3 months before pregnancy and each trimester). Birth record outcomes included preterm (< 37 weeks) low birthweight (< 2500 grams) (Y2), term low birthweight (Y3), preterm non-low birthweight (Y4), term non-low birthweight (Y5; comparison group), and mean birthweight in Y5 births. Multivariable logistic regression was employed to assess each STS exposure variable for Y2, Y3, and Y4 versus Y5 births while controlling for maternal race/ethnicity/birthplace, age, education, parity, prenatal care payment source, infant sex, and questionnaire version. Multivariable linear regression was used to compare exposure variables and birthweight in Y5 births controlling for confounders. Analyses were repeated stratifying by infant sex.
RESULTS: Several STS exposure variables were positively related to Y2 and Y3 versus Y5 births in unadjusted analyses; after controlling for confounders, any household smokers before pregnancy was associated with 1.6 times higher odds of Y2 births. No exposure variables were associated with Y4 births. Increased birthweight was observed for several STS exposure variables in Y5 births. In females, the number of closest friends/family that smoke and any household smokers before pregnancy were associated with 1.1-2.2 times higher odds of Y2 births after controlling for confounders; no associations for Y3 births were found. In males, no significant relations of exposure variables on Y2 births were seen; odds of Y3 births were 3.1-4.6 times higher for time spent with people smoking at home in the 1st trimester, and in automobiles in the 2nd and 3rdtrimester.
CONCLUSIONS: Indicators of STS exposure at various time points in pregnancy, largely in the home environment, were related to slow weight gain in males and slow weight gain with early birth in females. Characterizing risks associated with various indicators and sources of STS exposure during pregnancy can help direct intervention efforts aimed at reducing adverse birth outcomes and subsequent chronic health problems.