The association between maternal insulin resistance in mid-pregnancy and neonatal birthweight in uncomplicated pregnancies.

There have been few studies performed to address the association between the degree of physiological increase in maternal insulin resistance during pregnancy and neonatal birthweight in non-diabetic pregnancy. We attempted to determine whether maternal insulin resistance, as measured by homeostasis model assessment-insulin resistance (HOMA-IR), in mid-pregnancy is associated with neonatal birthweight in normal pregnancies. In this retrospective observational study, we measured HOMA-IR in singleton healthy pregnant women who underwent a 75 g oral glucose tolerance test (OGTT) in mid-pregnancy because of a positive diabetes screen. Using multivariate analyses to adjust for maternal parity, pre-gestational obesity, gestational weight gain, plasma glucose levels, and gestational age at delivery, we tested the association between HOMA-IR and birthweight in their offspring. We also tested the association HOMA-IR and a risk of large-for-gestational-age (LGA) infants. In 655 Japanese women, HOMA-IR was positively associated with birthweight after adjusting for these confounders (p<0.05). A higher HOMA-IR was significantly associated with an increased incidence of LGA infants with an adjusted odds ratio of 1.53 (95% confidence interval, 1.10-2.15) per 1 unit of HOMA-IR. The degree of maternal insulin resistance in mid-pregnancy was associated with birthweight and the risk of giving birth to an LGA infant in normal pregnancies, independent of maternal obesity and glucose levels.