Fetal Growth Calculator

Hadlock Sonographic Biometry & Fetal Growth Standards

In maternal-fetal medicine, Estimated Fetal Weight (EFW) is calculated using regression algorithms developed by Dr. Frank Hadlock:

• Hadlock 4-Parameter Formula (Measurements in cm):

_10(EFW) = 1.3596 + (0.0064 × HC) + (0.0424 × AC) + (0.174 × FL) + (0.00061 × BPD × AC) - (0.00386 × AC × FL)

• Key Biometric Parameters:

• BPD (Biparietal Diameter): Width of the fetal head from temple to temple.

• HC (Head Circumference): Outer perimeter around the fetal skull.

• AC (Abdominal Circumference): Single most sensitive parameter for fetal liver glycogen reserves and soft tissue growth.

• FL (Femur Length): Length of the thigh bone, used to estimate total crown-to-heel length.

• Clinical Growth Categories:

• SGA (Small for Gestational Age): EFW < 10th percentile (requires Doppler umbilical artery assessment).

• AGA (Appropriate for Gestational Age): EFW between 10th and 90th percentile.

• LGA (Large for Gestational Age): EFW > 90th percentile (risk of shoulder dystocia and gestational diabetes).

How to Use This Calculator

Enter your Gestational Age (Weeks) (e.g. 28), Biparietal Diameter (BPD in mm) (e.g. 71), Head Circumference (HC in mm) (e.g. 260), Abdominal Circumference (AC in mm) (e.g. 240), Femur Length (FL in mm) (e.g. 53), and Ultrasound Gestational Benchmark — select from Custom Ultrasound Biometry, 20 Weeks Mid-Pregnancy Anatomy Scan (EFW ~330g), 28 Weeks 3rd Trimester Start (EFW ~1,150g / 2.5 lbs). Results update instantly — no submit button needed. Use metric or imperial units as labeled. For the most accurate result, measure height and weight in the morning without shoes.

The Formula

Fetal length from femur length: Length (cm) = 6.18 + 0.59 * FL(mm)

Worked Example

An ultrasound at 32 weeks showing an AC of 280 mm and FL of 62 mm calculates an EFW of 1,865 grams (4 lbs 1.8 oz) at the 50th percentile, confirming healthy AGA growth trajectory.

Understanding Your Result

Naegele's Rule (LMP + 280 days) gives the estimated due date — only about 5% of babies arrive on their exact due date. The normal delivery window is 37–42 weeks gestation. Babies born 37–38+6 weeks are "early term" and may have higher risk of respiratory and feeding difficulties than babies born 39–40 weeks. Ovulation typically occurs 12–16 days before the next menstrual period, not necessarily on day 14 — cycle length variation shifts this window significantly.