Fetal Biometry

Medically Reviewed by Traci C. Johnson, MD on June 09, 2023
2 min read

Most pregnant women get a routine fetal biometry.

Fetal biometry measures your baby's size. During an ultrasound, your doctor measures the baby's head, body, and thigh bone. It helps show your baby's development.

Fetal biometry is a measurement taken during a standard ultrasound. During the ultrasound, a technician puts a gel on your belly, and then gently moves the ultrasound wand on your stomach to see images of your baby.

Your doctor will use the fetal biometry to estimate your baby's age, size, weight, and growth. You may get a report after your scan with the measurements. The report may include:

  • BPD (biparietal diameter), the diameter of your baby's head
  • HC (head circumference), the length going around your baby's head
  • CRL (crown-rump length), the length from the top of the head to your baby's bottom, measurement taken in the first trimester
  • AC (abdominal circumference), the length going around your baby's belly
  • FL (femur length), the length of a bone in your baby's leg

If your baby's results are unusual, your doctor will suggest further testing. Small size may be a sign of intrauterine growth restriction (IUGR.) Large size may be a sign that the mother has a health problem, such as gestational diabetes.

Your doctor will estimate the size of your baby during standard ultrasounds. Most women get one to three ultrasounds when they're pregnant. If you're at high risk, or if you're having twins, you may need ultrasounds more often.