Adriëtte Oostvogels

36 Chapter 2 Methods The ABCD study This study was embedded in the prospective Amsterdam Born Children and their Development (ABCD) study (http://www.abcd-study.nl ). Details on the study design are described elsewhere. 21 This study was conducted according to the guidelines of the Declaration of Helsinki and all procedures were approved by the Central Committee on Research Involving Human Subjects, the Medical Research Ethics Committees of the participating hospitals, and the Registration Committee of the municipality of Amsterdam. Study population Between January 2003 and March 2004 all pregnant women living in Amsterdam were invited to participate in the ABCD study at their first antenatal screening (median: 13 (IQR: 12-14) weeks of gestation). All women were asked to participate in the ABCD biomarker study and to fill out a pregnancy questionnaire, which contained an informed consent to grant permission for perusal of their medical files. Of all 12373 pregnant women approached, 8266 returned the pregnancy questionnaire (response rate 67%) at an average of 16 weeks gestation [inter quartile range (IQR) 14-18 weeks] and 4389 women also participated in the biomarker study (53%). For this study, non-fasting blood sampling (10-ml EDTA and 9-ml serum) took place during routine blood collection for screening purposes [median: 13 (IQR: 12-14) weeks of gestation] of which 4269 had reliable and available measurements of one of the lipids used in the present study. A total of 7043 women (85%) gave permission to collect data from their medical files and, of these, the medical files of 6741 women (96%) could be traced. Excluded from the study were women carrying twins or who had no data on the gestational age at blood sampling, women with diabetes (both pre-existent and pregnancy-induced), with pre-existing hypertension, and those using lipid-altering medication (e.g. antiepileptic drugs, antidepressant, steroids, thyroid hormones, or sleep medication). Also excluded were women with <3 BP measurements, or with first BP measurement after 20 weeks of gestation. The final sample included 3100 women (Figure 1).