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.