Methods
In MoBa, 78,117 mothers of 91,378 children completed a series of
questionnaires in the 17th and 30thweek of gestation of each unique pregnancy (Figure 1). The
questionnaires asked the mothers to report their anxiety level, in
addition to providing information regarding their age, education,
marital status, smoking and drinking habits, and their relationship with
their partner. The MoBa cohort12 was also linked to
the Medical Birth Registry of Norway (MBRN), which contains detailed
medical information about new-born children (gender, birthweight, and
gestational age) as well as their mothers (parity and birth
complications).
Among these full data sets, there were 12,480 pairs of siblings. The
mean age difference between siblings was 2.77 years. The numbers of
pairs dropped slightly after excluding half-siblings who had the same
mother but different fathers (Figure 1). We used version eight of the
quality-assured data files.