The role of obesity and gestational diabetes on placental efficiency and fetal oxygenation

INTRODUCTION Maternal pregestational obesity is a significant risk factor for adverse pregnancy outcomes, such as gestational diabetes. Both these conditions can have an impact on placental development and affect maternal-fetal exchanges, compromising fetal metabolic status. The aim of the study is to investigate the influence of pre-pregnancy BMI on placental biometry and efficiency and to evaluate the role of gestational diabetes on fetal oxygenation in overweight and obese pregnant women. METHODS We enrolled 208 normal-weight (NW), 57 overweight (OW) and 69 obese (OB) women at the time of elective caesarean section. 10 OW pregnancies (18%) and 24 OB pregnancies (35%) were complicated by gestational diabetes (GDM). Maternal, fetal and placental data were collected. Respiratory gases, acid-base balance and lactate concentrations were measured in umbilical venous and arterial blood samples. RESULTS Gestational weight gain was significantly lower in OB women (NW = 12.99 ± 4.48 kg; OB = 8.03 ± 6.16 kg, p < 0.001) and within standard recommendations (IOM: 5-9 kg). OW mothers had a weight gain during pregnancy not significantly different from NW (OW = 12.11 ± 4.80), but they exceeded standard limits (IOM: 7-11.5 kg). We didn’t find significant differences about gestational age, fetal weight and fetal biometry. Placental weights were significantly higher in OB pregnancies (NW = 457.67 ± 92.88 g; OB = 487.60 ± 92.81 g, p < 0.05), despite similar diameters and areas, and placental thickness was significantly higher in OB women, both with and without GDM (NW = 1.66 ± 0.32 cm; OB NON GDM = 1.94 ± 0.53 cm, p < 0.01; OB GDM = 2.00 ± 0.49 cm, p < 0.01). Significantly lower F/P weight ratios were found in GDM pregnancies, both OW and OB (NW = 7.42 ± 1.35; OW GDM = 6.39 ± 1.24, p < 0.05; OB GDM = 6.45 ± 1.42, p < 0.05). Fetuses from OB mothers were significantly more hypoxic and acidemic compared to NW fetuses (pO2 UA: NW = 16.93 ± 8.63 mmHg; OB = 14.94 ± 7.83 mmHg, p < 0.05; lactate concentration UA: NW = 1.69 ± 0.49 mmol/L; OB = 1.99 ± 0.70 mmol/L, p < 0.05). Studying the effect of GDM, also fetuses from OW GDM women showed significantly lower values of pO2 in umbilical artery (14.08 ± 3.18 mmHg, p < 0.05), and fetuses from OB GDM pregnancies the lowest pO2 values (12.91 ± 7.00 mmHg, p < 0.05). CONCLUSIONS Our data show that women with an early nutritional and behavioral counseling, such as OB and GDM mothers, have a better metabolic control and an optimal growth environment for the fetus. We also found that placentas from OB and GDM pregnancies are heavier and thicker, suggesting that an unbalanced pregestational nutritional status can decrease the placental efficiency in maternal-fetal exchanges. Finally, fetuses from OB women are hypoxic and acidemic, while fetuses from GDM mothers are hypoxic, reflecting that an altered pre-pregnancy BMI can affect fetal oxygenation, and GDM can further compromise placental efficiency.