Data Collection
Data about maternal lifestyle factors, maternal diseases and drug intake during pregnancy was obtained via three sources:
1. Prospective, medically recorded data. Mothers were requested to send the prenatal maternity logbook and every medical record concerning their diseases during the study pregnancy. Prenatal care was mandatory for pregnant women, thus nearly 100% of them attended prenatal care, on average 7 times between the 6thgestational week and delivery. The task of obstetricians in prenatal care was to record all maternal diseases and medicinal products used by women during the study pregnancy in the logbook.
2. Retrospective, maternal self-reported information. A structured questionnaire and a printed informed consent were also mailed to the mothers of cases and controls. It comprised questions regarding maternal diseases and related drug treatments, pregnancy supplements. Mothers were asked to read the enclosed list as a memory aid before they filled-in the questionnaire and signed the informed consent.
3. Supplementary data collection . After 1996 regional nurses made home visits to all cases and controls. They helped mothers collect their medical records and fill in the questionnaire. The collection procedure was impugned by one mother in 2002 alluding to concerns of data privacy. The activity of the HCCSCA was stopped when the legal procedure started in 2003 and the HCCSCA could continue its work again only in 2005.
The following data are available for each case and control pregnancy: CA(s), gender, maternal age, paternal age, birth year/month/date, birth weight, gestational age, area of mother’s living, birth order, mother’s and father’s qualification, employment status and type of employment, mother’s marital status, outcome of previous pregnancies, maternal diseases during pregnancy (according to pregnancy months), drug intake during pregnancy (according to pregnancy months), mother’s smoking habits and alcohol consumption patterns.
Evaluation of cases with viral infections
The presence of congenital anomalies may affect pregnancy outcome, therefore cases with birth defects were excluded from the present study. Thus, viral infections during the 57,231 control pregnancies were analysed. Data were eligible for evaluation in the case of the following diseases: influenza, hepatitis B, varicella-zoster, herpes simplex, enterovirus, respiratory syncytial virus and unspecified viral infections.
Since the first trimester is critical for the development of several pregnancy complications the effects of the above-mentioned infections occurring during the first 3 months were analysed separately.