Fetal Biometry - Purpose, Procedure, Results Interpretation, Normal Values and more

Fetal biometry is a crucial component of prenatal care that involves the measurement of the size and growth of a fetus during pregnancy. Through the use of ultrasound, fetal biometry provides valuable insights into the development of the baby and helps healthcare providers assess if the fetus is growing at a healthy rate. These measurements also play a vital role in detecting potential complications and guiding clinical decisions throughout the pregnancy.

What is Fetal Biometry?

Fetal biometry refers to the process of measuring various parts of the fetus using ultrasound during pregnancy to evaluate fetal growth. These measurements include the size of the baby’s head, abdomen, and femur (thigh bone), and are used to estimate the baby’s weight and assess overall development. Fetal biometry helps track how well the baby is growing inside the womb and can identify growth abnormalities that may need further investigation.

Fetal biometry is typically performed during routine prenatal ultrasounds, especially during the second and third trimesters of pregnancy. These measurements can provide a clearer picture of fetal health and development, helping healthcare providers make informed decisions about the next steps in prenatal care.

The Key Measurements in Fetal Biometry

Fetal biometry involves several key measurements, each of which provides important information about the baby’s development. Some of the most common measurements include:

• Crown-Rump Length (CRL): This measurement is usually taken during the first trimester and measures the length of the baby from the top of the head (crown) to the bottom of the bottom (rump). It is used to estimate the gestational age early in the pregnancy.
• Biparietal Diameter (BPD): This measurement is the distance between the two sides of the baby’s head and is taken at the level of the thalamus. It is one of the most commonly used measurements to assess fetal head size and is particularly useful for monitoring the progress of the pregnancy after the first trimester.
• Head Circumference (HC): This is the circumference of the baby’s head. It is measured at the level of the thalamus and can be used to assess brain development and potential concerns with head growth.
• Abdominal Circumference (AC): The measurement of the baby’s abdominal circumference helps assess fetal growth and the function of the placenta. This measurement is particularly important for detecting intrauterine growth restriction (IUGR), a condition in which the baby does not grow properly in the womb.
• Femur Length (FL): The length of the baby’s femur (thigh bone) is measured to assess skeletal development. This measurement helps estimate the overall size of the fetus.

These measurements, along with the fetal weight estimation, are analyzed to provide an overall assessment of the baby’s growth and development in relation to gestational age.

How Fetal Biometry is Performed

Fetal biometry is typically performed through an ultrasound examination. Ultrasound waves are used to create images of the fetus in the womb, which are then analyzed by a healthcare provider to take the necessary measurements. The process is non-invasive and is usually performed on the mother’s abdomen, although in some cases, a transvaginal ultrasound may be necessary.

• Preparation for Ultrasound: Before the procedure, the mother may be asked to drink water or not empty her bladder in order to ensure better imaging. The healthcare provider will apply a gel to the abdomen to help transmit the ultrasound waves and ensure clear images.
• Procedure: During the ultrasound, the technician will use a transducer (a small device) to send and receive sound waves. These waves bounce off the baby and create an image on a screen. The technician will measure the baby’s head, abdomen, and femur to assess growth.
• Duration: The ultrasound typically takes about 20-30 minutes, and the results are often available immediately after the procedure.

Interpretation of Fetal Biometry Results

The results of fetal biometry are used to assess the baby’s growth and development in relation to gestational age. The measurements are typically compared to standardized growth charts to determine whether the fetus is growing as expected. The interpretation of fetal biometry results can provide important insights into the health of both the mother and the baby.

• Normal Growth: If the fetal measurements are within the normal range for gestational age, it is an indication that the baby is growing well and developing at a healthy rate. This suggests that the pregnancy is progressing normally.
• Intrauterine Growth Restriction (IUGR): If the baby’s measurements fall below the expected range for gestational age, it could indicate that the fetus is not growing properly. This condition, known as intrauterine growth restriction (IUGR), may be caused by issues such as placental insufficiency or maternal health conditions like hypertension or diabetes.
• Large for Gestational Age (LGA): On the other hand, if the fetal measurements are larger than expected for the gestational age, it could indicate that the baby is growing too large. This can be associated with conditions such as gestational diabetes, where high blood sugar levels cause the baby to grow excessively.
• Gestational Age Estimation: The fetal biometry measurements, particularly the crown-rump length and biparietal diameter, can help estimate the gestational age of the baby. This is especially important when the exact date of conception is not known.
• Abnormal Head or Abdominal Circumference: If there are abnormalities in the head or abdominal circumference, it can indicate developmental issues, such as hydrocephalus (excess fluid on the brain) or abdominal problems.

Normal Range for Fetal Biometry

The normal range for fetal biometry depends on several factors, including the gestational age of the fetus. Generally, fetal biometry is performed at various points in the pregnancy, and the normal ranges for the measurements are as follows:

• First Trimester: Early in the pregnancy, the crown-rump length (CRL) is the most commonly used measurement to estimate gestational age. At 7 weeks, the CRL is approximately 10-15 mm, and by 12 weeks, it is around 50-60 mm.
• Second Trimester: During the second trimester, the biparietal diameter (BPD) ranges from about 2.5 cm at 14 weeks to 7.5 cm at 20 weeks.
• Third Trimester: In the third trimester, fetal biometry measurements continue to increase, with the head circumference (HC) reaching approximately 30 cm at 32 weeks and the abdominal circumference (AC) measuring around 27 cm at 32 weeks.

The healthcare provider will compare the baby’s measurements to these ranges to determine if growth is proceeding as expected.

Uses of Fetal Biometry

• Assessing Fetal Growth: The primary use of fetal biometry is to monitor the growth and development of the fetus. Regular measurements help ensure that the baby is growing at a healthy rate and allow for early detection of growth abnormalities.
• Screening for Complications: Fetal biometry is used to screen for complications such as intrauterine growth restriction (IUGR) or macrosomia (large for gestational age). These conditions can be associated with maternal health issues or complications during labor and delivery.
• Estimating Gestational Age: Accurate measurements of the fetus help estimate the gestational age, particularly when the exact date of conception is unknown. This is important for monitoring the baby’s development and planning for delivery.
• Planning for Delivery: The measurements can help healthcare providers plan for delivery. For example, if a baby is determined to be large for gestational age, the healthcare provider may plan for a cesarean section to reduce the risk of delivery complications.
• Monitoring High-Risk Pregnancies: Women with high-risk pregnancies due to conditions such as hypertension, diabetes, or a history of preterm birth will often undergo more frequent fetal biometry scans to monitor fetal development and identify potential issues early.

How to Prepare for Fetal Biometry

Preparing for a fetal biometry ultrasound is simple and non-invasive. Here are a few things you may need to consider:

• Hydration: Depending on the type of ultrasound being performed, you may be asked to drink plenty of water before the appointment. This is especially important for a transabdominal ultrasound, as a full bladder can improve image clarity.
• Clothing: Wear loose, comfortable clothing that allows easy access to your abdomen. You will be asked to lie on your back during the procedure while the ultrasound technician applies gel to your abdomen.
• Follow Instructions: Be sure to follow any specific instructions given by your healthcare provider to ensure the most accurate results.
• Timing of the Ultrasound: Fetal biometry is typically performed in the second and third trimesters, but it can also be done earlier in the pregnancy if there are concerns about fetal growth or gestational age.

FAQs About Fetal Biometry

1. What is fetal biometry?

Fetal biometry is the measurement of various parts of the fetus during pregnancy using ultrasound. These measurements include the size of the head, abdomen, and femur, and are used to assess the baby’s growth, development, and health.

2. What measurements are taken during a fetal biometry scan?

During a fetal biometry scan, the technician typically measures the biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL) to evaluate the baby’s growth and development.

3. Why is fetal biometry important?

Fetal biometry is important because it helps healthcare providers track fetal growth, detect potential complications such as intrauterine growth restriction (IUGR), and estimate gestational age, all of which are essential for ensuring a healthy pregnancy and delivery.

4. What does it mean if my baby is measuring small?

If your baby measures smaller than expected, it could indicate intrauterine growth restriction (IUGR), a condition where the baby does not grow properly. This may be caused by issues with the placenta or maternal health conditions. Further monitoring and testing may be required.

5. Can fetal biometry predict when I will give birth?

Fetal biometry can help estimate the gestational age, but it is not used to predict the exact date of delivery. The estimated due date is typically based on early ultrasounds and the baby’s growth pattern.

6. How accurate is fetal biometry?

Fetal biometry is a highly accurate method for assessing fetal growth and development. However, like any medical test, it is not 100% perfect, and the accuracy of measurements can vary depending on factors such as the baby’s position or the quality of the ultrasound equipment.

7. What happens if my baby is measuring large for gestational age?

If your baby is measuring larger than expected, it may indicate macrosomia, which can be associated with conditions like gestational diabetes. This may require additional monitoring and planning for delivery, including potential cesarean delivery if necessary.

8. Is fetal biometry safe?

Yes, fetal biometry is a safe, non-invasive procedure. It is performed using ultrasound technology, which does not pose any harm to the mother or baby. It is a standard part of prenatal care for monitoring fetal health.

9. How often will I need a fetal biometry scan?

The frequency of fetal biometry scans depends on your pregnancy and any associated risks. Healthy pregnancies may only require one or two scans, while women with high-risk pregnancies may need more frequent monitoring.

10. What should I do if I’m concerned about my fetal biometry results?

If you have concerns about your fetal biometry results, discuss them with your healthcare provider. They will explain the results in detail and may recommend additional tests or scans if necessary.

Conclusion

Fetal biometry plays an essential role in monitoring the health and development of your baby during pregnancy. Through non-invasive ultrasound measurements, healthcare providers can assess fetal growth, detect potential complications, and ensure that the pregnancy is progressing normally. Regular fetal biometry scans are a key part of prenatal care, helping to identify any issues early and guide decisions regarding the best course of action for both mother and baby. If you have any concerns about your fetal biometry results, it is important to communicate openly with your healthcare provider to ensure the best outcomes for your pregnancy.