A prospective study of maternal smoking and spontaneous abortion.
BACKGROUND
Cigarette smoking has been considered a risk factor for spontaneous abortion, but conclusions from many studies may be impaired by methodological problems. Studies are required that use data on smoking habits collected before knowledge about outcome of pregnancy and in which adjustment is made for potential confounders.


METHODS
All Danish-speaking pregnant women booking for delivery at the Department of Obstetrics and Gynecology, Aarhus University Hospital, from September 1989 to August 1996 were invited to participate in the study (n=24,608 pregnancies, including 321 spontaneous abortions and 100 induced abortions). Information about smoking habits before pregnancy and during the first trimester was obtained from self-administered questionnaires before the knowledge about pregnancy outcome. Information about spontaneous and induced abortions was obtained from the Danish National Patient Registry. We used Cox regression analyses with delayed entry (left truncation) for analyses, and hazard ratios to express the association between smoking and spontaneous abortion. Multivariate analyses were performed using a model including alcohol and coffee intake during pregnancy, maternal age, marital status, occupation, education, prepregnancy body mass index, and parity.


RESULTS
Overall, 104 (1.3%) of those contributing time at risk in the first trimester experienced a spontaneous abortion in the first trimester, and 217 (0.9%) of those contributing time at risk in the second trimester experienced a second-trimester abortion. We found no association between smoking and first- and second-trimester abortions. Adjustment for alcohol, coffee, maternal age, marital status, occupation, education, prepregnancy body mass index and parity did not change the result substantially.


CONCLUSIONS
Our study did not support findings from previous studies of an association between smoking and spontaneous abortion.
Wisborg
Kirsten
K
Perinatal Epidemiological Research Unit, Aarhus University Hospital, University of Aarhus, Denmark. kiwi@perinatal.dk
Kesmodel
Ulrik
U
Henriksen
Tine Brink
TB
Hedegaard
Morten
M
Secher
Niels Jørgen
NJ
D000022:Abortion, Spontaneous / Q000453:epidemiology* / Q000209:etiology*; D000293:Adolescent; D000328:Adult; D000428:Alcohol Drinking / Q000009:adverse effects; D003069:Coffee / Q000009:adverse effects; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011262:Pregnancy Trimester, Second; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*; D011795:Surveys and Questionnaires
D003069:Coffee