Introduction: During gestation diminished maternal insulin sensitivity (IS) increases the availability of fuels allowing fetal growth. Very severe obesity (Class III obesity (OB), BMI≥40 kg/m2) is associated with reduced IS but it is 28 how nutrient availability differs and how this impacts on birth weight versus normal pregnancies (CON).
Methods: 213 OB (median (interquartile range) 43.2(41.146.3) kg/m2) and 87 CON (BMI 22.6(21.223.5) kg/m2) pregnant Caucasians with normal glucose tolerance at booking, were recruited. Maternal anthropometrics, blood pressure, fasting plasma glucose, non-esterified fatty acid (NEFA) and insulin concentrations were recorded at 16, 28 and 36 weeks (wk). Five women (4 OB, 1 CON) had premature (<37 weeks) deliveries and were excluded from analyses.
Results: Weight gain (WG) was greater in CON vs OB (10.4(7.613.0) kg vs 5.2(2.48.3) kg; P<0.0001; 1636 wk). Glucose, NEFA and insulin were higher in OB vs CON at all time points (P<0.0001). IS (HOMA%S) was lower in OB vs CON (P<0.0001), decreasing with gestation (OB ANOVA P=0.026; CON ANOVA P<0.0001). Glucose peaked at 28 wk: OB (16wk 4.5(4.24.7) mmol/l; 28 wk 4.6(4.34.9) mmol/l; 36 wk 4.5(4.14.8) mmol/l; ANOVA P=0.05) and CON (16wk 4.2(4.14.4) mmol/l; 28 wk 4.2(4.04.5) mmol/l; 36 wk 4.1(3.94.3) mmol/l; ANOVA P=0.0003). NEFA troughed at 28 wk: OB (16 wk 0.49(0.410.60) mmol/l; 28wk 0.44(0.370.55) mmol/l; 36 wk 0.50(0.390.61) mmol/l; ANOVA P=0.005) and CON (16 wk 0.31(0.250.40) mmol/l; 28wk 0.29(0.220.36) mmol/l; 36 wk 0.33(0.270.46) mmol/l; ANOVA P=0.03). Birth weights after adjusting for gestational age, gender, parity, smoking and social class were greater in OB 3610(3280-3980) g vs CON 3600(3260-3860) g (P=0.03). In multivariate regression analyses, 36 wk glucose was associated with birth weight in OB (P=0.03) whereas 28 wk NEFA, BMI and WG were associated with birth weight in CON only (all P<0.05).
Conclusion: Class III obese women are more insulin resistant during pregnancy than controls, with greater glucose and NEFA concentrations. After adjustments birth weights were greater in this obese cohort. Glucose is associated with birth weight in the OB and NEFA in the CON which may indicate altered fetal preference for metabolites during these pregnancies.
Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.