Effect of maternal origin on the association between maternal height and risk of preterm birth in Belgium: a retrospective observational cohort study.

Objectives: To investigate the effect of maternal origin on the association between maternal height and the risk of preterm birth (PTB).

Design: Retrospective observational cohort study.

Setting: Two of the three Belgian regions, including Brussels-Capital and Walloon regions.

Participants: A total of 245 204 women spontaneously delivered live singletons between 2009 and 2013. Maternal nationality at the time of birth included Belgium, Congo, French, Italy, Morocco, Poland, Romania and Turkey.

Outcomes Measures: The outcome variable was spontaneous PTB, defined as childbirth occurring at less than 37 weeks' gestation.

Results: Average height, demographic characteristics and the spontaneous PTB rate differed according to maternal origin, defined as maternal nationality at birth. The pattern of association between maternal height and the risk of PTB was not uniform by maternal nationality at birth. The low maternal height category was associated with a statistically significant increased risk of spontaneous PTB for Belgian (adjusted OR (aOR) 1.23, 95% CI 1.16 to 1.32), Italian (aOR 1.48, 95% CI 1.12 to 1.96) and Polish (aOR 1.76, 95% CI 1.11 to 2.78), respectively. However, this association was not observed for the women from Congo, France, Morocco, Romania and Turkey.

Conclusions: The association between height and the risk of PTB was modified by maternal nationality, even for mothers from the same region of the world. For example, there was a significant inverse association for the Belgians and Italians but not for French women. Our data suggest that PTB risk assessment should take into account the specific height of maternal origin.