These
included maternal age at delivery, parity (1, 2, ≥ 3 children),
socioeconomic position (grouped into four categories: 1) unskilled / semiskilled manual; 2) skilled manual / nonmanual; 3) managerial / technical; and 4) professional), maternal education (< O level: indicating no qualification; O level: indicating completion of school examinations at age 16; and > O level: indicating completion of college or university education at or after age 18), maternal smoking during first trimester in pregnancy (yes / no), housing tenure (mortgaged, subsidised renting, private renting), income (measured in quintiles), and maternal depressive symptoms measured using the Edinburgh Postnatal Depression Scale [40] at 32 weeks gestation