Estimated serum folate insufficiency threshold by BMI, waist circumference, and elevated HbA1c strata Estimated serum folate concentrations corresponding to the RBC folate concentration of 748 nmol/L, by BMI [n =176 (<18.5 kg/m2), 440 (18.5 to <25.0 kg/m2), 213 (25.0 to <30.0 kg/m2), and 88 (≥30.0 kg/m2)], waist circumference [n = 123 (>88.9 cm) and 794 (≤88.9 cm)], and elevated HbA1c strata [(n = 732 (<5.7%), 196 (≥5.7 to <6.5%), and 49 (≥6.5%)]. The dashed lines correspond to the estimated median. Abbreviations: HbA1c, glycated hemoglobin; NTD: neural tube defect.