749 - Does maternal body mass index impact umbilical arterial cord pH in term twin pregnancies?

Obesity in pregnancy is associated with adverse perinatal outcomes. Umbilical arterial cord pH < 7.1 is considered a threshold for adverse neurological outcomes in neonates and there is an increased risk of fetal acidosis in term singletons born to pregnant people with obesity. However, the impact of maternal obesity on fetal acidosis in term twin pregnancies is not described.

Objective: To evaluate the impact of pre-pregnancy maternal body mass index (BMI) on umbilical arterial cord pH and to describe the incidence of neonatal hypoxic-ischemic encephalopathy and seizures.

Design/Methods: This is a retrospective study of all pregnant people with twin pregnancies and their neonates between January 2014 and December 2019. Maternal BMI was categorized as follows: underweight (< 18.5), normal weight (18.5-24.9), overweight (25-29.9), BMI class I (30-34.9), BMI class II (35-39.9), and BMI class III (≥ 40). Fetal acidosis was defined as pH < 7.1 in either twin. Maternal and neonatal outcomes, stratified by maternal BMI class, were compared using analysis of variance, Kruskal Wallis test or Fisher’s exact test as appropriate. A generalized estimating equation was used to determine the association between maternal BMI and fetal acidosis while accounting for correlation between a twin pair. Results are presented as number (%), median and inter-quartile range (IQR), and odds ratio (OR) and 95% confidence interval (CI). A p-value < 0.05 is considered statistically significant.

Results: Of the 357 eligible pregnant people, 333 pregnancies resulted in live births of both twins. After applying the exclusion criteria, 275 women and their twins were included. The number (%) of twin pregnancies in each category was as follows: underweight 10 (4%), normal weight 155 (56%), overweight 66 (24%), BMI class I 22 (8%), BMI class II 9 (3%), and BMI class III 13 (5%). Fetal acidosis was present in 14 (5%) and 21 (7.6%) of twin A and B neonates respectively. The median (IQR) umbilical arterial cord pH values were similar between both twins (p-value = 0.5). The umbilical arterial cord pH of neonates born to BMI class II women was statistically significantly lower compared to neonates born to normal weight women (OR 4.9, 95% CI 1.21,19.97; p-value = 0.03). No difference in pH was noted for overweight and BMI class I and III women. No neonates were diagnosed with hypoxic-ischemic encephalopathy or seizures during the study period.

Conclusion(s): Pre-pregnancy maternal BMI was not associated with low umbilical arterial cord pH values in twin term pregnancies.