Bibian van der Voorn

46 CHAPTER 3 was relatively high (67%). Finally, there was a discrepancy between mother and child in the time frame that the hair measurements represented. In mothers, only the last centimeter of hair was analyzed. As adult hair grows with approximately 1cm per month 20,21 , these analyses are representative of only the last month of pregnancy. Neonatal hair was analyzed in its entirety, and is therefore representative of the intrauterine period during which cortisol can be incorporated in hair. Correlations between GCs in maternal and neonatal hair should therefore be interpreted in this context. In conclusion, our findings suggest that infant hair GCs reflect the third trimester increase in cortisol, which might be caused by the positive feedback loop, a placenta- driven phenomenon, represented by a positive associationwith GA. Between birth and 1.5 months postpartum, cortisol concentrations decrease sharply. At this time point, GC levels appear to reflect both the intra- and extrauterine period, since neonatal levels are significantly higher than maternal GC levels. Perinatal complications and maternal HPA axis activity had minor influences on infant hair GCs.