Preconception insulin resistance and neonatal birth weight in women with obesity: role of bile acids

Research question: Does maternal preconception insulin resistance affect neonatal birth weight among women with obesity? Is insulin resistance associated with circulating bile acids? Do bile acids influence the association between maternal preconception insulin resistance and neonatal birth weight?Design: An exploratory post-hoc analysis of the LIFEstyle randomized controlled trial comparing lifestyle intervention with conventional infertility treatment in women with a BMI of ≥29 kg/m2. Fasting blood samples were collected at randomization and after 3 and 6 months in 469 women. Insulin resistance was quantified using the homeostasis model assessment of insulin resistance (HOMA-IR). Bile acid sub-species were determined by liquid chromatography with tandem mass spectrometry. Singletons were included (n = 238). Birth weight Z-scores were adjusted for age, offspring gender and parity. Multilevel analysis and linear regressions were used.Results: A total of 913 pairs of simultaneous preconception HOMA-IR (median [Q25; Q75]: 2.96 [2.07; 4.16]) and total bile acid measurements (1.79 [1.10; 2.94]) µmol/l were taken. Preconception HOMA-IR was positively associated with total bile acids (adjusted B 0.15; 95% CI 0.09 to 0.22; P < 0.001) and all bile acid sub-species. At the last measurement before pregnancy, HOMA-IR (2.71 [1.91; 3.74]) was positively related to birth weight Z-score (mean ± SD 0.4 ± 1.1; adjusted B 0.08; 95% CI 0.01 to 0.14; P = 0.03). None of the preconception bile acids measured were associated with birth weight.Conclusion: Maternal preconception insulin resistance is an important determinant of neonatal birth weight in women with obesity, whereas preconception bile acids are not.