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What is AC in pregnancy?

Published in Fetal Measurements 2 mins read

AC in pregnancy refers to abdominal circumference, which is the measurement of the length around the baby's belly.

Understanding Fetal Measurements

During prenatal ultrasounds, several measurements are taken to monitor the growth and development of the fetus. These measurements include:

  • HC (Head Circumference): The length around the baby's head.
  • AC (Abdominal Circumference): The length around the baby's belly.
  • FL (Femur Length): The length of the thigh bone.
  • CRL (Crown-Rump Length): The length from the top of the head to the bottom of the buttocks. This measurement is most accurate in the first trimester.

Why is AC Important?

The abdominal circumference (AC) is a crucial measurement because:

  • It helps assess the baby's overall size and growth.
  • It's one of the key indicators of the baby's weight.
  • It's used in conjunction with other measurements to estimate gestational age, especially when CRL is less reliable.
  • It provides insights into the baby's nutritional status. A smaller than expected AC may suggest issues with fetal growth.

How is AC Measured?

During an ultrasound, a sonographer measures the abdominal circumference by:

  1. Identifying a specific cross-section of the baby’s abdomen.
  2. Using the ultrasound machine’s software to trace around the perimeter of the abdomen.
  3. Calculating the length of the trace.

Examples of AC Measurement Usage:

  • Growth Monitoring: Regular AC measurements help track if the baby is growing at an appropriate rate.
  • Gestational Age Assessment: If the conception date is uncertain, AC, along with other measurements, can help estimate the pregnancy's duration.
  • Fetal Weight Estimation: The AC is a vital component in formulas that estimate the baby's weight before delivery.

Practical Insights

  • It's important to note that babies grow at slightly different rates, so a single measurement outside of the average doesn't automatically indicate a problem.
  • Multiple measurements over time provide a more accurate picture of the baby's growth trajectory.
  • The sonographer will compare all fetal measurements to standard growth curves.