Study finds clusters of risk factors in pregnancy point to later problems.
A toddler is far more inclined to behave badly if exposed to more than three risk factors during pregnancy, such as the mother being a teenager, unemployed or financially stressed.
The latest report from the long-term Growing Up in New Zealand study found that 44 per cent of 2-year-olds from the high-risk category in late pregnancy scored as "abnormal" in a parental questionnaire that assesses the level of "negative behavioural outcomes".
High risk was defined as having four or more maternal risk factors from a list of 12, medium was one to three, and low risk was none.
The questionnaire asks parents things such as if the child is considerate of others' feelings, often has tantrums and has a good attention span. Only 8 per cent of toddlers from low-risk pregnancies were in the abnormal behaviour category, and 19 per cent from medium-risk pregnancies.