In brief — the direct answer
When you receive your ultrasound report, it often looks like an alphabet soup of abbreviations and numbers. While your doctor will always explain the findings to you, many parents like to read the report themselves. This guide breaks down the standard medical jargon into simple English, so you can understand exactly how we measure your baby's growth and health.
The Big Four: Fetal Biometry
During a growth scan, we measure four specific bones and body parts to estimate the baby's size. These are called fetal biometrics:
- BPD (Biparietal Diameter): The distance across the baby's head, from one side to the other.
- HC (Head Circumference): The measurement all the way around the baby's head.
- AC (Abdominal Circumference): The measurement around the baby's belly. This is the most important measurement for checking if the baby is getting enough nutrition from the placenta.
- FL (Femur Length): The length of the thigh bone, which is the longest bone in the body.
Estimated Fetal Weight (EFW) & Percentiles
The ultrasound machine takes the BPD, HC, AC, and FL measurements and puts them into a mathematical formula to calculate the Estimated Fetal Weight (EFW).
You will also see a 'Percentile' (or Centile) next to the weight. Think of 100 babies lined up from smallest to largest. If your baby is in the 50th percentile, they are right in the middle. If they are in the 25th percentile, they are larger than 24 babies and smaller than 75 babies. Anything between the 10th and 90th percentile is completely normal.
Amniotic Fluid and Placenta
The report will also comment on the environment around the baby:
- AFI (Amniotic Fluid Index) or DVP (Deepest Vertical Pocket): These are two different ways of measuring the volume of fluid around the baby. Normal fluid means the baby's kidneys and swallowing are working well.
- Placenta Position: Indicates where the placenta is attached (e.g., Anterior, Posterior, Fundal). If it says 'Low-lying', it means the placenta is close to the cervix.
Doppler Ultrasound Jargon
If you have a high-risk pregnancy, the report may include 'Doppler' measurements, which assess blood flow:
- Umbilical Artery (UA) Doppler: Checks the blood flow from the placenta to the baby through the umbilical cord.
- Middle Cerebral Artery (MCA) Doppler: Checks the blood flow in the baby's brain. Used to check for fetal anemia or oxygen supply.
- PI (Pulsatility Index): A numerical value representing the resistance in the blood vessel.
What Does 'Normal' Mean?
It is incredibly important to remember that ultrasound is an estimation, not an exact scale. The Estimated Fetal Weight can be off by up to 10-15%. Furthermore, babies, just like adults, come in all shapes and sizes. A baby in the 15th percentile is just naturally smaller, while a baby in the 85th percentile is naturally larger. Neither is 'better' or 'worse'.
When Measurements Cause Concern
If a baby drops below the 10th percentile, it is called Small for Gestational Age (SGA) or Fetal Growth Restriction (FGR). If a baby is above the 90th percentile, it is called Large for Gestational Age (LGA) or Macrosomia. In these cases, your MFM specialist will arrange closer monitoring, more frequent scans, and possibly Doppler studies to ensure the baby is thriving safely in the womb.
Questions to ask your doctor
