Impact of short maternal height on preterm birth: A retrospective cohort study

To assess the impact of short maternal height on preterm birth by different body mass index (BMI) classes and type of preterm birth.

This retrospective cohort study evaluated women with singleton pregnancies delivering from January 2012 to December 2019 in the Eastern Zone of Newfoundland and Labrador, Canada. Maternal height was divided into three groups: <25% (short), 25%-75% (average), and >75% (tall). Univariate and multivariate regression analyses were performed to determine whether short height independently predicted preterm birth before 37 weeks, stratified by BMI class. Subgroup analyses were performed for spontaneous and indicated preterm birth.

Of 16 023 pregnancies assessed, 1245 (7.8%) were associated with preterm birth. Among all BMI categories combined, short height independently predicted preterm birth (odds ratio [OR], 1.37 [95% confidence interval (CI), 1.18-1.61], P < 0.001). In stratified analyses, short height independently predicted preterm birth among individuals with normal BMI (OR, 1.52 [95% CI, 1.16-2.00], P = 0.002), overweight BMI (OR, 1.52 [95% CI, 1.03-2.08], P = 0.010), and obese BMI (OR, 1.32 [95% CI, 1.002-1.72], P = 0.048). In subgroup analyses, short height independently predicted spontaneous preterm birth among those with a normal BMI (OR, 1.59 [95% CI, 1.15-2.17], P = 0.005) but not those in higher BMI categories. Short height independently predicted indicated preterm birth among those overweight or obese (OR, 1.60 [95% CI, 1.18-2.16], P = 0.002) but not in those with a normal BMI.

The association between short maternal height and preterm birth before 37 weeks of gestation varies by type of preterm birth (spontaneous or indicated) and BMI class. Among women with a normal BMI, short maternal height is associated with spontaneous preterm birth. Among women who are overweight or obese, short maternal height is associated with an increased risk of indicated preterm birth.