Increased maternal insulin resistance promotes placental growth and decreases placental efficiency in pregnancies with obesity and gestational diabetes mellitus

Aim Homeostasis model assessment for insulin resistance (HOMA-IR) was measured during pregnancy to analyze placental weight and efficiency in relation to maternal insulin resistance. Methods A retrospective study of 510 pregnant women (130 with gestational diabetes mellitus [GDM], 380 with normal glucose tolerance) was conducted. We reviewed the patients’ demographic data (age, parity, pre-pregnancy body mass index [BMI]) and perinatal outcomes (birth weight, placental weight, BMI at delivery, maternal weight gain, HOMA-IR). The birth weight to placental weight (B/P) ratio was calculated for placental efficiency. The subjects were categorized by BMI at delivery, and maternal, neonatal and placental characteristics were compared between the groups to investigate the determinants of placental weight and B/P ratios. Results Obesity was significantly associated with heavier placental weight and lower B/P ratios. The presence of GDM did not affect placental weight, whereas the B/P ratios in women with GDM were significantly lower than in women with normal glucose tolerance. HOMA-IR was positively correlated with placental weight (ρ = 0.217, P < 0.001) and negatively with B/P ratio (ρ = −0.181, P < 0.001). Conclusions Increased maternal insulin resistance promoted placental growth and inhibited placental efficiency. Maternal insulin resistance may be one of the pathophysiological conditions responsible for altered placental size and function in pregnancies with obesity and GDM.