The association between maternal smoking and hyperemesis gravidarum: a meta-analysis.
BACKGROUND
The majority of studies have not found hyperemesis to be a protective and some others have not. To date, no meta-analysis has quantitatively assessed the association between smoking and risk of hyperemesis gravidarum. To help close that research gap, we performed meta-analysis of the association between smoking and risk of hyperemesis gravidarum.


METHODS
A literature search was carried out in PubMed, Web of Science, and Scopus from the earliest possible year to January 2016. The heterogeneity across studies was explored by Q-test and I2statistic. The possibility of publication bias was assessed using Begg's and Egger's tests. The results were reported using odds ratio (OR) estimate with its 95% confidence intervals (CI) using a random-effects model.


RESULTS
The literature search yielded 607 publications until January 2016 with 1 400 000 participants. Based on the random-effects model, compared to nonsmoker people, the estimated OR of hyperemesis gravidarum was 0.40 (95% CI: 0.24, 0.56).


CONCLUSIONS
We showed based on reports in epidemiological studies that smoking before and during pregnancy is not a risk factor for hyperemesis gravidarum but also can reduce the risk of it.
a Department of Midwifery , Toyserkan Branch, Islamic Azad University , Toyserkan , Iran and.
Ensiyeh
E
Jenabi
b Department of Midwfery, Nursing and Midwifery Faculty , Tehran University of Medical Sciences , Tehran , Iran.
Bita
B
Fereidooni
D016009:Chi-Square Distribution; D016021:Epidemiologic Studies; D005260:Female; D006801:Humans; D006939:Hyperemesis Gravidarum / Q000209:etiology* / Q000517:prevention & control; D015233:Models, Statistical; D016017:Odds Ratio; D011247:Pregnancy; D012306:Risk; D012907:Smoking / Q000009:adverse effects*
Hyperemesis gravidarum; meta-analysis; pregnancy; smoking