TABLE 3

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

	Univariable			Multivariable^# (1–5)			Univariable sensitivity analyses			Multivariable sensitivity analyses (1–6)
	Subjects n	β (95% CI)	p-value	Subjects n	β (95% CI)	p-value	Subjects n	β (95% CI)	p-value	Subjects n	β (95% CI)	p-value
Tobacco exposure			0.085			0.113			0.110			0.550
Never	1772	Ref.		1772	Ref.		1694	Ref.		1694	Ref.
Snus only	143	91.3 (10.1–172.5)		143	78.1 (4.7–151.5)		137	88.8 (5.6–172.0)		137	36.3 (−37.4–110.0)
Smoke/dual	97	−6.5 (−103.9–90.9)		97	11.0 (−76.6–98.6)		90	−5.0 (−106.4–96.4)		90	−20.1 (−109.1–68.9)
Tobacco exposure			0.120			0.032			0.180			0.250
Never	1772	Ref.		1772	Ref.		1694	Ref.		1694	Ref.
Snus only up to 18 weeks	132	102.0 (17.7–186.3)		132	100.0 (23.9–176.1)		127	96.8 (10.6–183.0)		127	53.8 (−22.6–130.1)
Snus only up to 34 weeks	11	−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/dual	97	−6.5 (−103.9–90.9)		97	10.9 (−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).