Results
In the full cohort (Table 1-A), the mean birthweight of infants of mothers reporting severe anxiety symptoms in the 17thgestational week was 85.3 grams lower than that of infants born to mothers with very light anxiety symptoms or none at all. Similarly, the mean birthweight of infants born to mothers reporting severe anxiety symptoms in the 30th gestational week was 94 grams lower than that of infants not exposed to high levels of maternal anxiety. The mean gestational age between light and severe maternal anxiety differed by two days for those reporting maternal anxiety in the 17th gestational week. Between light and severe anxiety symptoms reported in the 30th gestational week, the mean gestational age decreased by three days.
Among the 25,058 siblings (see Table 1-B), a mean birthweight difference between infants born to mothers reporting light anxiety symptoms and infants born to mothers reporting severe anxiety symptoms was also found. However, for the sibling subsample, only a 53.1-gram difference in mean birthweight was recorded for infants exposed to light anxiety or none at all, as reported in the 17th gestational week. Mean birthweight for infants exposed to severe compared to light or no maternal anxiety, as reported in the 30th gestational week, differed by 148.3 grams. Mean gestational age decreased by two days between infants born to mothers reporting severe symptoms and infants born to mothers reporting light symptoms in the 17th gestational week; however, this difference was five days for those reporting symptoms in the 30thgestational week.
Differences in anxiety levels between the two pregnancies were also examined. Of mothers participating twice, a sample of 1,502 mothers (17%) experienced more anxiety during their first pregnancy than during their second pregnancy, while 2,756 mothers (9%) had the opposite experience. The rest of the mothers (74%) experienced the same anxiety levels during their first and second pregnancies. The mean difference between maternal anxiety during first and second pregnancies was small (meandiff = 0.05).