To compare the correlation of various fetal ultrasound parameters to foot length, crown-rump length, and gestational age by date to determine the best estimate at 10–14 completed weeks’ gestation and to provide ratios of fetal parameters for assessment of fetal abnormalities in the first trimester. 35 routine obstetric scans were performed at 10–14 completed weeks’ gestation for fetal parameters and ratios. The fetal crown-rump length (CRL), biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL) showed a linear correlation with the estimated gestational age by date (GA), crown-rump length (CRL), and foot length (FT) (p < 0.001), with the least correlation observed with GA and highest with FT. A combination of BPD, HC, AC, and FL correlated best with FT and then CRL and GA (R2 = 0.881, 0.795, and 0.685, respectively, p < 0.001). With the addition of CRL, R2 was 0.859. The ratio of FL/AC and FL/FT to FT, CRL, GA, BPD, and HC increases in an inverse relationship at 10–14 completed weeks’ gestation. The combination of BPD, HC, AC, and FL provides a better estimation of gestational age than (and hence may replace) CRL or GA at 10–14 weeks’ gestation.
Part of the book: Complications of Pregnancy