Data sources, instruments and scales
Baseline data was obtained from two key data sources namely a participant maternal baseline survey and hospital perinatal data related to the birth of the child. The maternal baseline questionnaire was self-administered, and consisted of 48 multi-item questions taking approximately 30 minutes to complete. Items included maternal, family and household characteristics, socio-economic factors, Kessler 6 (K6) psychological distress scale, [10, 11] short form of the Family Environment Scale (FES), [12, 13] neighbourhood and community connectedness (NCC),  maternal smoking and drinking behaviour, health supplement usage, and recreational substances used during pregnancy. Perinatal data was extracted from the medical records following maternal discharge from hospital. Data items included previous pregnancies, maternal conditions, obstetric care and complications, delivery information, and baby information such as gender, plurality, gestational age, birth weight and any complications. Information collected on the biological father has been specified as ‘paternal’ whereas information collected on the current partner (which was not necessarily the biological father) has been specified as ‘partner’ information.
Variable calculation and classifications include: Using Australian National birth weights for full-term singletons, birth weight was classified as low (<2500 g), normal (2500-4000 g) and high (>4000 g) . BMI was calculated from weight in kilograms and height in meters (Weight/Height2). Pre-pregnancy maternal BMI measures were determined by self-report and paternal BMI measures by proxy-report from the maternal participant. BMI was classified as underweight (<18.5), normal weight (18.5-24.9), overweight (25.0-29.9) and obese (>30) . Maternal and paternal ages were calculated in years at the time of the birth of their child.
Women and their partners were classified as employed if they reported working full-time, part-time, were self-employed or on paid maternity/paternity leave at the time of enrolment. Gross annual household income was reported in $10,000 increments and standardised in AUD$2010 values using published Consumer Price Index [17, 18]. Standardised median household income is reported along with the income share in each quintile as an indicator of income distribution for the five recruitment years.
The K6 is intended to yield a global measure of “psychological distress” based on questions about the level of anxiety and depressive symptoms in the most recent 4-week period. The K6 has been widely used and has demonstrated excellent internal consistency, reliability and the ability to discriminate between community mental health cases and non-cases [10, 19]. The six-items form a 24-point scale and the following cut-offs were used: No or low distress (0–7), moderate distress (8–12), and high distress (13–24) [11, 20].
The NCC is a five item measure of perception of satisfaction with the local community . NCC scores were classified as good (5–8), average (9–14) and poor (15–25) based on ±1 SD mean. Data was not available from the 2006 pilot cohort for the K6 and NCC.
For the purpose of this paper, self-reported alcohol consumption, recreational drug use, and multivitamin supplement use during pregnancy were dichotomised. Alcohol consumption was defined as any consumption of alcohol during pregnancy regardless of period, frequency, or quantity. Drug use for recreational or non-medical purposes, was asked using questions modified for pregnancy from the Australian National Drug Strategy Household Survey 2004 . This included a range of drugs including steroids, barbiturates, cannabis, heroin, methamphetamines/amphetamines, cocaine, ecstasy, ketamine, solvents, and kava. A ‘prefer not to answer’ option was also provided. Multivitamin supplement use included any general multivitamin or pregnancy specific supplement taken during pregnancy.