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OP14.02: Estimation of fetal weight at term: comparison of the INTERGROWTH and Hadlock formulas

Objectives: Conventional weight-based criteria for neonatal growth restriction (GR) do not account for the growth potential of an individual fetus, nor do they effectively separate constitutionally small fetuses from ones that are malnourished. Individualised growth assessment (IGA) uses 2nd trimester (TM) growth velocity of anatomical size parameters as an estimate of growth potential in an individual fetus to evaluate third TM fetal growth and neonatal growth outcome. We hypothesized that differences in maternal body composition and/or energetics can be detected when individual fetuses are categorised by the presence or absence of GR. Methods: Serial 2D fetal biometry (BPD, HC, AC, FDL) and neonatal measurements were obtained in 20 women with dichorionic-diamniotic (DCDA) pregnancies. Based on IGA, 10 women had at least one GR infant and were compared to 10 others with no neonatal GR. Changes in maternal body composition (fat free mass and fat mass) were estimated from total body water (TBW) using deuterium dilution, body volume by air displacement plethysmography, and total body potassium/protein by whole body counting. Energetic changes in resting energy expenditure by respiration calorimetry, total energy expenditure by doubly labelled water, and physical activity level were measured. Comparisons between groups were made at each TM adjusted for GA at delivery and prepregnancy BMI. Results: Lower accretion of maternal fat-free mass in the first TM as well as lower accretion of body protein in the second TM were associated with infant GR (p=0.01, p=0.02, respectively). No association was seen with gestational weight gain, fat mass, TBW, resting energy expenditure, total energy expenditure, and physical activity. Conclusions: Suboptimal gestational weight gain (Institute of Medicine) has been linked to low birth weight in DCDA pregnancies. Lower accretion of maternal fat free mass and total body protein may represent the major components of gestational weight gain with neonatal GR in DCDA twins.