Table 1.
Summary of the 32 studies included in this review that studied the association between exposure to smoking during pregnancy levels of folate, vitamin B12, and homocysteine
| First author (year) | Study setting | Outcome measuresa | Study design | Total N | Mean age (year) | Quality score |
|---|---|---|---|---|---|---|
| Adaikalakoteswari (2015) | United Kingdom | Folate, homocysteine, vitamin B12 | Cross‐sectional | 91 | 32.7 | 3 |
| Ambroszkiewicz (2007) | Poland | Folate, homocysteine | Cross‐sectional | 57 |
Median: s: 26 ns: 32 |
4 |
| Baker (2009) | United Kingdom | Folate, cobalamin | Prospective cohort | 306 | Range: 14–18 | 6 |
| Bakker (2011) | The Netherlands | Homocysteine | Prospective cohort | 6,294 | 29.9 | 8 |
| Bergen (2012) | The Netherlands | Folate, homocysteine, vitamin B12 | Prospective cohort | 5,805 | 29.8 | 6 |
| Bodnar (2010) | United States | Folate | Prospective cohort | 313 |
<20: 12% 22–29: 73% ≥30: 15% |
4 |
| Coker (2011) | Turkey | Folate, homocysteine | Prospective cohort | 58 |
s: 26.1 ns: 27.1 |
5 |
| Dayaldasani (2014) | Spain | Vitamin B12 | Prospective cohort | 204 | 30 | 5 |
| Frery (1992) | France | Vitamin B12 | Cross‐sectional | 188 | 29.2 | 4 |
| D. Furness (2013) | Australia | Folate, homocysteine, vitamin B12 | Prospective cohort | 137 | 33 | 4 |
| D. L. Furness (2012) | Australia | Folate | Retrospective case–control | 400 | 24.8 | 3 |
| Gadowsky (1995) | Canada | Folate, homocysteine, vitamin B12 | Cross‐sectional | 58 | 17.0 | 3 |
| Hay (2010) | Norway | Folate, homocysteine, cobalamin | Retrospective cohort | 340 | 29.9 | 6 |
| Jauniaux (2007) | United Kingdom | Folate | Cross‐sectional | 125 | nm | 4 |
| Knight (1994) | United States | Folate, vitamin B12 | Prospective cohort | 87 | Range: 16–35 | 5 |
| Knudtson (2004) | United States | Homocysteine | Case–control | 198 |
Cases: 25 Controls: 24 |
4 |
| Larroque (1992) | France | Folate | Prospective cohort | 245 |
≤22: 25% 23–29: 43% ≥30: 32% |
4 |
| Matsuzaki (2008) | Japan | Folate | Cross‐sectional | 537 | 30.5 | 4 |
| McDonald (2002) | Canada | Folate, homocysteine, vitamin B12 | Cross‐sectional | 80 |
s: 24.0 ns: 26.2 |
4 |
| Mito (2007) | Japan | Folate | Cross‐sectional | 70 | 29.9 | 4 |
| Nilsen (2010) | Norway | Folate | Prospective cohort | 2,934 | 29.8 | 8 |
| Ozerol (2004) | Turkey | Folate, homocysteine, vitamin B12 | Cross‐sectional | 33 | nm | 3 |
| Pagan (2001) | United States | Folate, homocysteine, vitamin B12 | Prospective cohort | 196 | 25.5 | 5 |
| Prasodjo (2014) | Canada/United States | Folate | Prospective cohort | 362 |
18–25: 23% 25–35: 60% ≥35: 17% |
7 |
| Relton (2005) | United Kingdom | Folate, vitamin B12 | Prospective cohort | 998 | 27.8 | 5 |
| Sram (2005) | Czech Republic | Folate | Case–control | 766 | nm | 5 |
| Stark (2005) | United States | 5‐MTHFA | Prospective cohort | 116 | 24.5 | 6 |
| Stark (2007) | United States | 5‐MTHFA | Prospective cohort | 58 | 24.8 | 6 |
| Van Uitert (2014) | The Netherlands | Folate | Prospective cohort | 77 | 32.7 | 4 |
| Van Wersch (2002) | The Netherlands | Folate, homocysteine, vitamin B12 | Cross‐sectional | 138 | nm | 3 |
| Vandevijvere (2012) | Belgium | Folate | Cross‐sectional | 1,285 | 28.5 ≤ 19: 1% | 6 |
| Yila (2016) | Japan | Folate | Prospective cohort | 15,266 |
<20: 1% 20–24: 12% 25–29: 31% 30–34: 37% ≥35: 19% |
9 |
Note. 5‐MTHFA: 5‐methyltetrahydrofolic acid; nm: not mentioned; ns: nonsmokers; s: smokers.
a
Nomenclature as in original paper.