2 Temsirolimus Sigma (Nilsen et al., 2009). During the complete recruitment period, the consent percentage was somewhat reduced to a total of 38.5%. The present cohort includes about 108,000 children, 90,000 mothers, and 71,500 fathers in total. This study is based on version 6 of the quality-assured data released for research in spring 2011, using data from primiparous married or cohabiting women who completed questionnaires at weeks 17 and 30 of gestation, yielding a total of 45,369 participants. Of these, 10,890 women participated twice in the MoBa study and completed questionnaires also at weeks 17 and 30 of gestation during their second pregnancy. In addition, this study used data from the Medical Birth Registry of Norway, which contains information about all births in Norway (Irgens, 2000).

The study was approved by the Regional Committee for Medical Research Ethics in Southeastern Norway. Measures Maternal smoking was assessed by self-report items at gestation weeks 17 and 30, in addition to face-to-face interviews when the women were hospitalized to give birth, as reported to the Medical Birth Registry of Norway. At gestation week 17, the women were asked to report if they had ever smoked and, if so, if they smoked three months prior to the pregnancy and if they were currently smoking. At gestation week 30, the women were asked to indicate their current smoking status in addition to retrospectively report their smoking status at gestation week 17. At both assessment points, smoking was assessed as a categorical variable coded no, occasionally and daily.

If the woman reported occasional smoking at either source, both at present or at retrospectively, she was coded as an occasional smoker for the respective pregnancy, over-riding possible prior reports of nonsmoking. Similarly, women reporting daily smoking at either source were coded as daily smokers, over-riding possible prior reports of nonsmoking or occasional smoking. Psychological distress was assessed using a five-item short version of the Hopkins Symptom Checklist (SCL-5), administered at weeks 17 and 30 of gestation (Strand, Dalgard, Tambs, & Rognerud, 2003). The scale measures symptoms of anxiety and depression and typical items are Feeling fearful and Worrying too much about things, all measured on the four-point scale not bothered, a little bothered, quite bothered and very bothered.

The SCL-5 showed adequate internal consistency at both assessment points in both pregnancies (�� �� 0.78). To obtain a robust measurement of psychological distress Batimastat during pregnancy, a pooled mean score of the SCL-5 at weeks 17 and 30 from each of the pregnancies was computed and showed adequate temporal stability in both the first (r = 0.58) and second pregnancies (r = 0.59). Information regarding age, marital status, parity, and year of birth was retrieved from the Medical Birth Registry of Norway.