The Interplay between Maternal Smoking and Genes in Offspring Birth Weight

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Table 1

Descriptive Statistics of the Main Analysis Sample (ALSPAC)

	Mean	SD	Min.	Max.	N
Outcome Variable
Birth weight (grams)	3,406.24	556.60	703	5,600	7,598
Main Explanatory Variables
Smoking regularly	0.22	0.42	0	1	7,417
Smoking regularly (adjusted)	0.31	0.46	0	1	2,777
Number of cigarettes smoked per day	2.02	5.09	0	51	7,598
Number of cigarettes smoked per day (adjusted)	4.96	6.64	0	51	3,784
Cotinine (ng/mL)	743.76	1,923.57	0	24,674	2,844
Birth weight PGS (child)	0.00	1.00	–3	3	5,006
Instrumental Variable
rs1051730	0.67	0.67	0	2	7,598
Control Variables
Mother’s birth weight (grams)	3,269.01	601.43	909	6,108	4,541
Mother’s age (years)	28.47	4.66	15	44	7,598
Mother’s marital status (married = 1)	0.78	0.41	0	1	7,540
Mother’s education (categories)	3.65	1.61	0	6	5,484
Mother’s social class (categories)	2.85	1.07	1	6	6,141
Grandmother’s education (categories)	2.45	1.29	1	5	4,267

Notes: SD, standard deviation; Min., minimum; Max., maximum; PGS, polygenic score.

Table 2

Results of the OLS Regressions Explaining the Child’s Birth Weight in ALSPAC

	(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)
#Cigarettes smoked per day	–14.8**	–12.7**	–13.4**	–13.7**
#Cigarettes smoked per day	(1.3)	(1.3)	(1.7)	(1.7)
#Cigarettes smoked per day (adjusted)					–12.0**	–8.3**	–9.4**	–9.5**
#Cigarettes smoked per day (adjusted)					(1.3)	(1.5)	(1.8)	(1.8)
Birth weight PGS (child)			108.2**	104.6**			118.5**	112.8**
Birth weight PGS (child)			(7.0)	(7.4)			(10.0)	(12.0)
#Cig. smoked per day × Birth weight PGS				2.2
#Cig. smoked per day × Birth weight PGS				(1.5)
#Cig. smoked per day (adj.) × Birth weight PGS								1.3
#Cig. smoked per day (adj.) × Birth weight PGS								(1.6)
Control variables	No	Yes	Yes	Yes	No	Yes	Yes	Yes
R-squared	0.019	0.059	0.101	0.101	0.021	0.069	0.128	0.128
N	7,598	7,598	5,006	5,006	3,784	3,784	2,408	2,408

Notes: Coefficients are displayed with robust standard errors in parentheses; Columns 1–4 use the self-reported measure for smoking, and Columns 5–8 use the self-reported measure for smoking corrected using cotinine levels. PGS, polygenic score. All regressions correct for genetic relatedness among the mothers using the first four principal components of the genetic relationship matrix. +p < 0.1, *p < 0.05, **p < 0.01.

Table 3

Results of the OLS (First Stage) Regressions Explaining Smoking in ALSPAC

	#Cigarettes Smoked per Day		#Cigarettes Smoked per Day (Adjusted)
	(1)	(2)	(3)	(4)
rs1051730	0.5**	0.4**	0.6**	0.6**
rs1051730	(0.1)	(0.1)	(0.2)	(0.1)
Control variables	No	Yes	No	Yes
R-squared	0.004	0.132	0.005	0.202
Effective F-statistic	25.3	27.2	15.6	15.1
N	7,598	7,598	3,784	3,784

Notes: Coefficients are displayed with robust standard errors in parentheses. Column 1–2 use the self-reported smoking measure, and Column 3–4 the self-reported smoking measure corrected using cotinine levels. All regressions correct for genetic relatedness among the mothers using the first four principal components of the genetic relationship matrix. +p < 0.1, *p < 0.05, **p < 0.01.

Table 4

Results of the OLS (Reduced Form) Regressions Explaining Birth Weight in ALSPAC

Notes: Coefficients are displayed with robust standard errors in parentheses. All regressions correct for genetic relatedness among the mothers using the first four principal components of the genetic relationship matrix. +p < 0.1, *p < 0.05, **p < 0.01.

Table 5

Results of the OLS (Reduced Form) Regressions Explaining the Control Variables in ALSPAC

	Mother’s Birth Weight	Mother’s Age	Mother’s Marital Status	Mother’s Education	Mother’s Social Class	Grandmother’s Education
rs1051730	–19.5	–0.0	–0.0	–0.1	0.0*	0.1
rs1051730	(13.3)	(0.0)	(0.0)	(0.0)	(0.0)	(0.1)
R-squared	0.001	0.001	0.001	0.001	0.001	0.000
N	4,541	7,540	4,267	5,484	6,141	7,598

Notes: Coefficients are displayed with robust standard errors in parentheses. All regressions correct for genetic relatedness among the mothers using the first four principal components of the genetic relationship matrix. +p < 0.1, *p < 0.05, **p < 0.01.

Table 6

Results of the 2SLS Regression Explaining Birth Weight in ALSPAC

	(1)	(2)	(3)	(4)
#Cigarettes smoked per day	−36.7+	−37.9+
#Cigarettes smoked per day	(21.1)	(21.7)
#Cigarettes smoked per day (adjusted)			−36.5+	−38.5
#Cigarettes smoked per day (adjusted)			(21.4)	(23.9)
Control variables	No	Yes	No	Yes
Effective F-statistic	25.3	27.2	15.6	15.1
N	7,598	7,598	3,784	3,784

Notes: Coefficients are displayed with robust standard errors in parentheses. All regressions correct for genetic relatedness among the mothers using the first four principal components of the genetic relationship matrix. +p < 0.1, *p < 0.05, **p < 0.01.

Table 7

Results of the OLS (Reduced Form) Regression Explaining Birth Weight in ALSPAC

Notes: Coefficients are displayed with robust standard errors in parentheses. PGS, polygenic score. All regressions correct for genetic relatedness among the mothers using the first four principal components of the genetic relationship matrix. +p < 0.1, *p < 0.05, **p < 0.01.

Table 8

Results of the OLS (Reduced Forms) Regressions Explaining Birth Weight in UK Biobank

	Full Sample	Smoking Mothers	Nonsmoking Mothers	Full Sample
	(1)	(2)	(3)	(4)
rs1051730	−5.7**	−17.3**	−1.3	−5.9**
rs1051730	(2.0)	(4.0)	(2.4)	(2.0)
(–1) Birth weight PGS (child)				−83.0**
(–1) Birth weight PGS (child)				(1.8)
rs1051730 × (–1) Birth weight PGS (child)				1.0
rs1051730 × (–1) Birth weight PGS (child)				(2.0)
R-squared	0.001	0.001	0.001	0.016
N	256,702	67,915	160,530	256,702

Notes: Coefficients are displayed with robust standard errors in parentheses. PGS, polygenic score. All regressions correct for genetic relatedness using the first twenty principal components of the genetic relationship matrix. +p < 0.1, *p < 0.05, **p < 0.01.