We invited all pregnant women booking for delivery at the Department of Obstetrics and Gynaecology, Aarhus University Hospital, from September 1989 to August 1996 to participate in the study. Nearly all women in the area comply with the antenatal care programme. The women completed two questionnaires before the first visit for routine antenatal care at about 16 weeks of gestation.
We used information from the first questionnaire to obtain data on medical and obstetric history, maternal age, smoking habits before pregnancy and during the first trimester, and alcohol intake during pregnancy. From the second questionnaire we obtained information on intake of coffee, tea, drinking chocolate, and cola and marital status, education, and employment status. We asked about current intake of coffee, tea, drinking chocolate, and cola, and women could indicate any whole number of daily cups of coffee, tea, and drinking chocolate, or bottles of cola. Information about delivery was obtained from birth registration forms filled in by the attending midwife immediately after delivery. Before data entry, all birth registration forms were manually checked and compared with the medical records by a research midwife.
Information about stillbirths was obtained from the data that we collected at our department and from the Danish medical birth register12,13
through record linkage using the mother's personal identification number. Information about deaths during the first year of life was obtained from the registry of causes of death,14
administered by the Danish National Board of Health, and from the civil registration system. Deaths of four children who died according to data from the civil registration system were not registered in the registry of causes of death. The children's medical records confirmed these deaths. We defined stillbirth as delivery of a dead fetus at or after 28 completed weeks of gestation and infant death as death of a liveborn infant before the age of 1 year.
The study population was restricted to singleton pregnancies among Danish speaking women who filled in the first questionnaire and who delivered after 28 completed weeks of gestation (n=25
395). The study population was further restricted to those with valid information about coffee intake during pregnancy (n=18
We analysed coffee intake as number of cups and in ordered categories (0, 1-3, 4-7, and
8 cups/day). One cup of coffee corresponds to about 100 mg of caffeine.15
The intake of decaffeinated coffee in Denmark was negligible during the study period. We also obtained information on consumption of tea, drinking chocolate, and cola, but only a few women were exposed to high doses of caffeine from tea and hardly any from drinking chocolate or cola. Therefore we could not fully explore the effects of consumption of caffeine from sources other than coffee.
We have presented associations between intake of coffee and stillbirth and infant death as odds ratios with 95% confidence intervals. Table shows other variables accounted for in the analyses. Missing values were included as a separate category when we adjusted for the covariates in multivariate logistic regression analyses. To take into account the time of death after delivery we evaluated the association between coffee intake and infant death in a Cox regression analysis. However, as the conclusions were similar to those from logistic regression analyses, they are not presented. We evaluated effect modification by variables in table by stratified analyses and tested linear association between different levels of coffee intake by χ2 test for trend. To take into account the fact that 3922 women contributed more than one pregnancy to the study we used logistic regression with robust standard errors to adjust for possible correlation within women (Stata; StataCorp, College Station, TX).
Table 1 Maternal coffee consumption during pregnancy and other sociodemographic and lifestyle factors and rate of stillbirth and infant death, Aarhus, Denmark, 1989-96
The study was approved by the regional ethics committee, the Danish National Board of Health, and the Danish Data Protection Agency.