A reference range of fetal abdominal circumference growth velocity between 20 and 36 weeks' gestation.

OBJECTIVE: To create a single equation and reference range for abdominal circumference growth velocity (ACGV) between 20 and 36 weeks in singleton pregnancies.

METHOD: Observational study of pregnant women having routine scans for abdominal circumference (AC) at 20 and 36 weeks' gestation. Exclusion criteria were multiple pregnancy, abnormal karyotype, major fetal abnormalities, and absent data on first-trimester dating. Scan image quality and AC measurement reliability were assessed according to INTERGROWTH-21st criteria. Regression models for the AC mean and standard deviation were fitted separately at 20 and 36 weeks, and z scores were calculated. Abdominal circumference growth velocity was defined as the z score difference between 20 and 36 weeks divided by the interval in days and multiplied by 100.

RESULTS: The study population included 3334 fetuses. The equation for ACGV is (((AC36  - 53.090 - 1.081*GA36 )/(0.057638*GA36  + 0.622741)) - ((AC20  + 68.349 - 1.571*GA20 )/(0.06265*GA20  - 2.55361)))*100/(GA36  - GA20 ), where AC is expressed in millimeters and GA is gestational age in days. The 3rd, 5th, 10th, 50th, 90th, 95th, and 97th centiles are -1.8997, -1.6785, -1.3091, -0.0069, 1.3255, 1.7279, 1.9973, respectively.

CONCLUSION: We have defined ACGV between 20 and 36 weeks, and we have established its reference range. Further studies are needed to evaluate the clinical significance of growth patterns in the tail ends of this distribution.