Table 1 Prediction equations for growth parameters (in mm) as a function of gestational age (in days)

Gestational sac (GS):

GS = -9.66 + 1.40(GA)

R² = 0.9602

Crown-rump length (CRL):

CRL = -9.42 + 1.09(GA) + 0.0281(GA)²

R² = 0.9682

Biparietal diameter (BPD):

BPD = 50.47 - 17.14(GA) + 2.07(GA)² - 0.103(GA)³ + 0.00186(GA)⁴

R² = 0.9733

Abdominal circumference (AC):

AC = -55.75 + 7.52(GA) - 0.166(GA)²

R² = 0.9723

Femur length (FL):

FL = -5.02 + 0.392(GA)

R² = 0.8215

Lens diameter (LD):

LD = 2.205 - 0.518(GA) + 0.0401(GA)² - 0.000856(GA)³

R² = 0.9618

Body weight (BW):

BW = 0.5488 - 0.01714(GA) - 0.01180(GA)² + 0.0008279(GA)³

R² = 0.9906

Placental diameter (PD):

PD = -11.96 + 2.09(GA) - 0.046(GA)² - 0.0005(GA)³

R² = 0.8941

Placental thickness (PT):

PT = 4.10 - 1.14(GA) + 0.115(GA)² - 0.0031(GA)³

R² = 0.7562

Placental weight (PW):

PW = -0.54180 + 0.07887(GA) - 0.002243(GA)²

R² = 0.8237