The effect of obesity on pregnancy outcomes among Australian Indigenous and non-Indigenous women.

OBJECTIVE To assess whether the effect of pre-pregnancy overweight or obesity on maternal complications and perinatal outcomes is modified by Indigenous status. DESIGN, PARTICIPANTS AND SETTING Population-based study using de-identified aggregate data on pregnancies resulting in singleton births from Indigenous (n = 13 582) and non-Indigenous (n = 241 270) women from the Queensland Perinatal Data Collection, 1 July 2007 to 31 December 2011. MAIN OUTCOME MEASURES Prevalence of maternal (gestational diabetes mellitus [GDM], hypertensive disorders of pregnancy [HDP]) and delivery (preterm birth, birthweight, Apgar score) outcomes by Indigenous status and their association with pre-pregnancy body mass index. RESULTS In 57% of Indigenous pregnancies and 49% of non-Indigenous pregnancies, the mother was overweight, obese or severely obese. Prevalences of GDM, preterm birth and low birthweight were higher in Indigenous than non-Indigenous pregnancies. Overall rates of HDP were similar for Indigenous (5.1%) and non-Indigenous pregnancies (4.9%); however, rates were higher in normal-weight Indigenous pregnancies (4.0%) than in normal-weight non-Indigenous pregnancies (3.0%). We found that overweight or obesity was associated with higher prevalence of GDM, HDP, high birthweight and low Apgar score. However, the associations with HDP, preterm birth and low birthweight were modified by Indigenous status (P for interaction, < 0.001 for all). Overweight or obesity accounted for significantly fewer cases of HDP in Indigenous versus non-Indigenous pregnancies (population attributable fraction, 30% v 41%). CONCLUSIONS Maternal overweight or obesity is more common among Indigenous pregnancies, and Indigenous status may modify its association with pregnancy outcomes. Further research needs to explore the issue of increased insulin resistance and higher rates of HDP among normal-weight Indigenous women.