Predicting the Risk of Macrosomia at Mid-Pregnancy Among Non-Diabetics: A Retrospective Cohort Study

Objective To identify factors known in mid-pregnancy to be associated with risk of macrosomia (≥4000 g) among non-diabetic women and to develop a risk score to allow early identification of women at high risk. Methods Data were obtained from a population-based perinatal database and a hospital laboratory database in Nova Scotia, Canada. The study included singleton live births born to non-diabetic women between 1998 and 2005. Logistic regression was used to identify risk factors significantly associated with macrosomia. Risk scoring systems were developed for nulliparous and parous women separately and validated using the C-statistic. Results Of the 23 857 mother-infant pairs included in the study, 16.7% of the infants were macrosomic. In nulliparous women, seven risk factors were identified, of which pre-pregnancy weight ≥90 kg with an OR of 4.8 (95% CI: 3.9 to 6.0) contributed a greater number of points to the risk score. The resulting risk score corresponded to a range of estimated risk of 0.2% to 47.0% and had a C-statistic of 0.70. In parous women, the most points were assigned to women with a previous large birth (OR: 3.7; 95% CI: 3.2–4.0) and a pre-pregnancy weight ≥90 kg (OR: 3.8; 95% CI: 3.1–4.7). The resulting risk score corresponded to a range of estimated risk of 0.4% to 88.0% and had a C-statistic of 0.75. Conclusions Macrosomia risk can be estimated by a simple calculation based on a woman's risk factor profile at mid-pregnancy.