While soon-to-be parents find it exciting to guess who their little bundle of joy takes after, they also want to know the baby’s “appearance” within the womb. This is why the ultrasound appointment is a thrilling moment. But a scan doesn’t just allow you to trace the outline of your baby’s face and possibly determine their gender. Through fetal biometry, doctors can also give you specific details of your child’s growth and development within the womb. Here’s what you need to know about fetal biometry.

What Is Fetal Biometry?

Initially, fetal biometry may sound like a complicated test for babies. However, it simply points to your baby’s measurements taken during the scheduled ultrasound.

With fetal biometry, the doctors can determine the size of your baby’s head, body, and thigh bone. They likewise use these measurements to assess the gestational age (how far along you are) and detect normal growth or development abnormalities.

Fetal biometry includes:

• Biparietal diameter, which measures across the head
• Head circumference, which measures around the head
• Abdominal circumference, which measures around the abdomen
• Femur length, which measures the length of the thigh bone

During the first trimester, the doctor may also measure the baby’s crown-rump length, which runs from the top of the head to the fetus’ bottom.

What Are the Possible Findings in Fetal Biometry?

The above measurements help the doctors determine the gestational age. They also use these figures to have the estimated fetal weight.

After knowing the estimated fetal weight, the doctors can then plot it against the gestational age. From there, they’ll be able to tell if the baby’s present size is small for gestational age (SGA) or large for gestational age (LGA).

If the biometry comes back with significant findings (SGA, LGA, etc.), the healthcare provider may recommend further testing to identify the best management options, even before the baby is born.

For instance, a baby who’s SGA may be experiencing placental insufficiency. Fetal growth restriction may also occur due to maternal infection or bad habits, such as smoking or drinking alcohol. On the other hand, LGA is common in babies whose mothers have gestational diabetes.

Let’s also not forget that each measurement in fetal biometry stands for something. Case in point: abdominal circumference is the most useful measurement to assess fetal growth. On the other hand, femur length is the best parameter to evaluate certain bone abnormalities, like skeletal dysplasia.³

When Does a Pregnant Woman Need an Ultrasound Scan?

Pregnant moms do not undergo ultrasound each time they have a prenatal appointment.

Most pregnant women only need to have ultrasound twice: once in the first trimester (6 to 8 weeks) and another in the 2nd trimester (18 to 20 weeks)⁴. The doctor may also order a scan in the third trimester (30 weeks) to check for growth, placental placement, fetal position, or anything that may block the cervix⁵.

Additionally, the doctor may decide you need more scans should some issues arise. Fetal biometry, in particular, is necessary if:

• Your abdomen is smaller or larger than expected
• You have conditions, such as hypertension or diabetes
• You had previous pregnancy complications before

What To Expect Before, During, and After an Ultrasound Scan

Before the scan, you might have to drink plenty of water as a full bladder helps with the imaging.

During the procedure, the sonographer will ask you to lift your shirt and apply gel to your abdomen. They will then use a wand-like scanner around your abdomen, and you’ll be able to see the image instantly on the monitor.

After, you’ll be given wipes to remove the gel, and the results, including fetal biometry, will be sent to the doctor for interpretation.

Key Takeaways

Fetal biometry is taken during an ultrasound scan in pregnancy. It determines the baby’s size, which helps doctors assess gestational age and fetal growth and development. The measurements obtained during the scan can also be used to determine abnormalities.

Learn more about Pregnancy here.