Background and aims: Research on both animals and humans is providing more and more evidence that prenatal factors can have long-term effects on development. Most human studies have examined the effects of prenatal stress on birth outcome (i.e. shorter pregnancies, smaller infants). The few studies that have looked at the infants' later development have found prenatal stress to be related to more difficult temperament, behavioral/emotional problems and poorer motor/cognitive development. In this paper, we have examined links between late pregnancy cortisol levels and infant behavior during the first 5 months of life.
Study design and subjects: Seventeen mothers and their healthy, full-term infants participated in this prospective, longitudinal study. The mothers' cortisol was determined in late pregnancy. The infants' behavior was videotaped during a series of bath sessions at the home: at 1, 3, 5, 7, 18 and 20 weeks of age. The mothers filled in temperament questionnaires (ICQ) in postnatal weeks 7 and 18.
Results and conclusions: The infants were divided into two groups based on their mothers' late pregnancy cortisol values: high and low prenatal cortisol groups. A trend was found for the high cortisol infants to be delivered earlier than the low cortisol group. Furthermore, the behavioral observations showed the higher prenatal cortisol group to display more crying, fussing and negative facial expressions. Supporting these findings, maternal reports on temperament also showed these infants to have more difficult behavior: they had higher scores on emotion and activity. The differences between the infants were strongest at the youngest ages (weeks 1-7).