Table 4.

Results of studies describing the association of maternal smoking and homocysteine levels

First author (year)	Definition of smokinga	Measured in	Timeb of measurement	Statistical analysis	Measure of association	Results	SD/SE	95% CI/IQR	P value	Adjustmentsc
Adaikalakoteswari (2015)	Any active smoking	Maternal serum	At birth	Student's t test	Difference in means	sm: 6.33 μmol/L		5.90–7.45d	ns	−
						nsm: 6.15 μmol/L		5.61–8.08
		Umbilical cord blood				sm: 6.21 μmol/L nsm: 5.42 μmol/L		5.80–7.68d	ns	−
								5.06–6.58
Ambroszkiewicz (2007)	nm	Maternal serum	At birth	Student's t test	Difference in means	sm: 5.95 μmol/L	2.50e		<0.05	−
						nsm: 4.60 μmol/L	0.9
		Umbilical cord blood				sm: 6.43 μmol/L	2.21e		<0.001
						nsm: 4.70 μmol/L	0.89
Bakker (2011)	nm	Maternal plasma	Median: 14.4	Linear regression	Regression coefficient	β = 0.05f		0.03–0.06d	<0.01	+++
Bergen (2012)	Any active smoking	Maternal serum	13.2 (11.4–16.2), median (90% range)	Linear regression	Regression coefficient	0.35		0.28–0.42d	<0.001	−
Coker (2013)	≥3 cigarettes/day for >3 years	Maternal serum	At birth	Mann–Whitney U and Wilcoxon paired tests	Difference in means	sm: 6.7 μmol/L nsm: 5.9 μmol/L	2.5g 2.5		0.237	−
		Umbilical cord blood				sm: 8.2 μmol/L	2.5g		0.006	−
						nsm: 6.4 μmol/L	2.0
Furness (2013)	nm	Maternal plasma	18–20	t test	Difference in means	sm: 6.0 μmol/L nsm: 4.4 μmol/L		5.0–6.9d 4.1–4.6	<0.001	−
Gadowsky (1995)	≥1 cigarette/day	Maternal plasma	35.9 ± 0.2	Pearson correlation	Correlation coefficient	nm			ns	−
Hay (2010)	Any active smoking	Umbilical cord blood	At birth	Linear regression analysis	Correlation coefficient	nm			ns	+++
Knudtson (2003)	Any active smoking	Maternal serum	24–32	Pearson correlation	Correlation coefficient	r = −0.08			0.57	−
McDonald (2002)	Any active smoking	Maternal serum	1st and early 2nd trimesters	Unpaired t test	Difference in means	sm: 5.4 μmol/L	1.3g		0.613	−
						nsm: 5.2 μmol/L	1.8
Ozerol (2004)	≥2 cigarettes/day	Maternal serum	16–22	Mann–Whitney U test	Difference in means	sm: 13.1 μmol/L	1.1e		<0.001	−
						nsm: 6.9 μmol/L	0.7
Pagan (2001)	Thiocyanate blood levels in highest quartile	Maternal serum	18	Student's t test	Difference in means	sm: 5.2 μmol/L	2.4g		ns	−
						nsm: 5.0 μmol/L	1.6
			30			sm: 5.7 μmol/L	3.4g		ns
						nsm: 4.9 μmol/L	1.6
Van Wersch (2002)	≥20 cigarettes/day	Maternal plasma	0–10	Mann–Whitney U test	Difference in medians	sm: 6.4 μmol/L nsm: 7.2 μmol/L		5.6–11.4h 6.5–7.8	ns	−
			11–20			sm: 6.1 μmol/L		5.4–8.0h	ns
						nsm: 5.9 μmol/L		5.1–6.3
			21–30			sm: 6.4 μmol/L		5.7–7.9h	0.02
						nsm: 5.1 μmol/L		4.1–6.2
			31–40			sm: 7.5 μmol/L		6.5–9.1h	0.04
						nsm: 6.5 μmol/L		4.8–7.6

Note. SE: standard error; SD: standard deviation; CI: confidence interval; IQR: interquartile range; nm: not mentioned; ns: nonsignificant; sm: smoking women; nsm: nonsmoking women.

^aTobacco unless mentioned otherwise.

^bWeeks of gestation.

^cAdjustment level was categorized as follows: −, unadjusted; +, 4 covariates or less; ++, 5 to 8 covariates; +++, 9 or more covariates.

^d95% CI.

^e SE.

^fLog transformed.

^g SD.

^hIQR.