Linear regression analyses: effect of tobacco exposure during pregnancy on birthweight (grams)

UnivariableMultivariable# (1–5)Univariable sensitivity analysesMultivariable sensitivity analyses (1–6)
Subjects nβ (95% CI)p-valueSubjects nβ (95% CI)p-valueSubjects nβ (95% CI)p-valueSubjects nβ (95% CI)p-value
Tobacco exposure0.0850.1130.1100.550
 Snus only14391.3 (10.1–172.5)14378.1 (4.7–151.5)13788.8 (5.6–172.0)13736.3 (−37.4–110.0)
 Smoke/dual97−6.5 (−103.9–90.9)9711.0 (−76.6–98.6)90−5.0 (−106.4–96.4)90−20.1 (−109.1–68.9)
Tobacco exposure0.1200.0320.1800.250
 Snus only up to  18 weeks132102.0 (17.7–186.3)132100.0 (23.9–176.1)12796.8 (10.6–183.0)12753.8 (−22.6–130.1)
 Snus only up to  34 weeks11−36.4 (−318.9–246.1)11−183.1 (−436.5–70.3)10−13.1 (−310.3–284.1)10−180.6 (−440.6–79.5)
 Smoke/dual97−6.5 (−103.9–90.9)9710.9 (−76.7–98.4)90−5.0 (−106.4–96.4)90−20.0 (−108.9–69.0)

The reference group “never” includes all females who did not report use of tobacco or nicotine during pregnancy. The “smoke/dual” group includes dual smokers and snus users during pregnancy, of whom most quit before 6 weeks of pregnancy. The nonsignificant global p-values for snus-only and smoke/dual indicate that no significant associations were observed with birthweight. Covariates used in multivariable analyses: 1=parity, 2=gestational age at birth, 3=fetal sex, 4=pre-pregnancy body mass index, 5=maternal age, 6=gestational weight gain up to 18 weeks of pregnancy. Ref.: reference value. #: the results of the multivariable analyses restricted by the same study population as in the sensitivity analyses without adjusting for gestational weight gain, were similar in both populations (data not shown).