Bibian van der Voorn

39 INTERPRETATION OF GC LEVELS IN NEONATAL HAIR that it is an indication of GC concentrations during fetal life, while at the OPV only the centimeter of hair closest to the scalp was analyzed, with the assumption that it gives an indication of GC concentrations during the first weeks of life 20,21 . Maternal hair was also collected on the first day postpartum and at the OPV. Only the centimeter closest to the scalp of maternal hair was analyzed. As, in adults, hair grows approximately 1 cm every month 17,20,21 , the hair measurement postpartum is indicative for the GC levels during the last month of pregnancy. GC levels (cortisol and cortisone) were measured in hair as previously described 20 . In short, in the presence of deuterium-labeled GCs as internal standard, cortisol was extracted using LC-grade methanol at 25°C for 18h. These extracts were subsequently centrifuged and cleaned using solid phase extraction. GC concentrations were quantified by LC-MS/MS (Waters XEVO-TQ-S system, Waters Corporation, Milford, MA, USA). GC concentrations were reported as pg per mg hair, and 1.25mg was required for a reliable measurement. STATISTICS Analyses were performed with regard to: 1. Concentrations of GCs in neonatal hair directly postpartum and at the OPV. GC levels were expressed as median (range). Subsequently, GC levels were log- transformed and paired t-tests were performed. 2. The relation between maternal and neonatal (log-transformed) hair GC levels postpartum and at the OPV, was assessed using Pearson correlation coefficients and linear regression. 3. Factors associated with neonatal hair GCs directly postpartum were assessed using linear regression. Additional analyses were performed to assess the effect of the factors associated with GC levels directly postpartum on the course of GC levels (expressed as delta cortisol and cortisone) and on the GC levels at the OPV, corrected for age at the time of sampling. The following factors, based on literature 15-18 , were taken into consideration: a. Perinatal: gestational age, birth weight (in kg and SD-score), sex, mode of delivery, perinatal infection, respiratory distress (meconium-containing amniotic fluid, respiratory insufficiency, respiratory support, PPHN [persistent pulmonary hypertension of the neonate]). b. Maternal: age, ethnicity, maternal smoking, parity (primi- vs. multipara), hypertensive disorders (pregnancy-induced hypertension, pre-existent hypertension, pre-eclampsia/HELLP syndrome).