Researchers from Norway compared pregnancy outcomes in 31,683 women who changed partner between their first two births and 456,458 women with the same partner for both births.
After taking into account the mother's age and education, interval between births, and decade of birth, the risk of having a preterm, low birthweight baby with an increased risk of infant death was higher for women who changed partner between their first two births compared with those who had the same partner for both births.
One theory implies that women who change partner have a higher prevalence of risk taking behaviour, such as heavier smoking and alcohol consumption and poorer nutrition, which may affect pregnancy outcomes, suggest the authors.