Adriëtte Oostvogels

78 Chapter 3 Methods Study population This study is part of the ABCD cohort (Amsterdam Born Children and their Development), a large community based birth cohort. 18 Approval of the study was obtained from the Central Committee on Research Involving Human Subjects in the Netherlands, the medical ethics review committees of the Academic Medical Center, Amsterdam, the VU University Medical Center Amsterdam and the Registration Committee of the Municipality of Amsterdam. All women provided written informed consent. Parents or caretakers provided written informed consent for the health check of the 5–6 year old children in the questionnaire that was sent around two weeks after the child’s fifth birthday. This questionnaire was only sent to mothers who initially gave permission for follow-up. This informed consent procedure was approved by the committees of the Academic Medical Center, Amsterdam, the VU University Medical Center Amsterdam and the Registration Committee of the Municipality of Amsterdam. Between January 2003 and March 2004 all pregnant women living in Amsterdam were invited to participate in the ABCD study at the first visit to their obstetric care provider. Women filled out a questionnaire containing questions on sociodemographic characteristics, medical history, lifestyle and dietary habits (16 weeks of gestation; IQR 12–20 weeks). All women who agreed to complete the questionnaire (n = 8266) were asked to attend the ABCD biomarker study. For this latter study, an extra blood sample (10 ml EDTA and 9 ml serum) was taken during the first prenatal visit (13 weeks of gestation; IQR, 12–14 weeks)(n = 4389). Birth outcomes (gestational age at birth, sex, birth weight and congenital abnormalities) were obtained through Youth Health Care (YHC). After the child’s 5th birthday, a questionnaire was sent to the parents who gave permission for follow-up (n = 3501). After that a health check was done at the primary school of the child (age 5.7 years ±0.5 SD; n = 1956). Women who gave birth to twins, delivered preterm (<37 weeks of gestation), with diabetes or used lipid-altering medication (e.g. thyroid hormones, steroids, sleep medication, insulin use and antiepileptic drugs) were excluded (n = 229)(Figure 1). Children with congenital malformations were also excluded. Finally, 1727 mother- child pairs were included (Figure 1).