What is BPD in Pregnancy? Meaning, Full Form & Normal Range

If you have been confirmed with the pregnancy, it is common to have ultrasound procedures during prenatal visits. Every ultrasound performed in pregnancy has its own specific purposes, from confirming the conception to determining the fetal abnormalities. These scans are performed at different stages to gather crucial insights. For example, the anomaly scan, which is done between 18 and 22 weeks of pregnancy, monitors the growth of fetal anatomy.

Similarly, BPD is one such measurement taken during prenatal ultrasound, commonly included as part of an anatomy scan. Using these measurements, healthcare providers estimate the baby’s weight, gestational age, and its growth and development.

This blog can explain to you what BPD in pregnancy is, why, when and how it is performed, along with what the BPD ultrasound results mean.

What is BPD in Pregnancy?

The biparietal diameter (BPD) measurement is the distance between the two parietal bones of the fetus’s head. The BPD is a crucial measurement in fetal biometry, which is done through an ultrasound scan. It helps the healthcare providers, along with other measurements, to estimate the gestational age, the baby’s weight, monitor its growth, and identify potential abnormalities.

The BPD full form in pregnancy is biparietal diameter, as it involves measuring the two parietal bones. BPD (biparietal diameter) may generally be measured during the second trimester of pregnancy. This is because the baby’s head only grows rapidly at this time, making the skull bones sufficiently calcified for more accurate results.

This BPD measurement may, however, tend to change throughout the pregnancy as the baby grows. The normal BPD measurement at 13 weeks of pregnancy can be around 21-28 mm, while 86-102 mm at 40 weeks of pregnancy. When BPD is measured after the second trimester, the results may reduce the accuracy of dating.

Like BPD, other key measurements in fetal biometry may include head circumference (HC), abdominal circumference (AC), and femur length (FL). All these measurements are essential to determine the complete growth and development of the fetus.

The BPD, HC, AC, FL normal range in weeks may include:

Why are BPD Measurements Important in Pregnancy?

The BPD meaning in pregnancy serves several important purposes, which may include:

Gestational age

By comparing the assessed BPD measurement with the standard growth chart, healthcare providers can determine the gestational age and expected delivery date (EDD). Other measurements, such as head circumference (HC) and femur length (FL), are often used to improve the accuracy.

Fetal weight

The BPD, along with other fetal biometric measurements, helps to estimate the baby’s weight. Fetal weight is basically estimated using certain formulas that combine biparietal diameter (BPD) and other measurements like femur length (FL) and abdominal circumference (AC). The formulas may range from simple to the more complex ones. The common formulas to estimate fetal weight may include:

Simple formulas: Weight (grams) = [BPD (mm) – 60] x 100

• For example, if BPD in 28 weeks of gestation is 72 mm, then the weight would be 72 – 60 x 100 = 1200 grams or 1.2 kg.

Another simple formula is: Weight (grams) = 88.69 x BPD (mm) – 5062

• For example, if BPD in 28 weeks of gestation is 72 mm, then the weight would be 88.69 x 72 – 5062 = 1323.68 grams or 1.3 kgs.

The baby’s weight can be approximately 1.2 to 1.3 kg when the BPD is 72 mm during the 28 weeks of pregnancy.

Growth monitoring

Monitoring the BPD measurements regularly can also help the healthcare providers ensure the baby is growing at a normal, expected rate according to their gestational age.

Identifying issues

The BPD measurements beyond or above the normal range may potentially indicate an abnormality in fetal growth. This may demand further assessments to identify potential issues, such as slow growth (growth restriction) or medical conditions like gestational diabetes.

When is Biparietal Diameter (BPD) Measured?

Biparietal diameter, or BPD in ultrasound is typically measured during the prenatal visits, most approximately around 13 to 20 weeks of gestation. However, the following are the frequent timings when a pregnant woman gets BPD measured.

11-14 weeks

Around 11 and 14 weeks of gestation, the BPD measurements are taken to confirm the due date.

18–22 weeks

BPD in pregnancy 20 weeks is taken to assess fetal growth as part of the anatomy scan.

28-32 weeks

Around this time, the BPD measurements are taken to monitor the fetal growth and development as part of the growth scan.

After 36 weeks

While BPD measurements are accurate when done before the second trimester, they can still be done after 36 weeks if there are growth concerns.

How is BPD measured?

The biparietal diameter (BPD) is a simple prenatal routine ultrasound examination. The procedure is generally done to measure the width of the developing baby’s head to ensure that it correlates with the standard growth chart.

Here’s the step-by-step process of how BPD is measured.

Preparation

Prenatal ultrasound scans are primarily done using a transabdominal approach. The procedure starts by applying a clear gel to the abdomen of the pregnant woman. A handheld transducer is used to move over the gel to capture clear images of the fetus.

Imaging

The transducer uses inaudible high-frequency sound waves to create the images of the fetus on the monitor. The sonographer or the healthcare provider looks for a specific position of the baby’s skull to capture the biparietal diameter (BPD) measurement.

Measurement

Once the correct position is obtained, the digital measuring tool (medically termed a calliper) is placed on the image of the baby’s skull, which is displayed on the monitor. The BPD measurements are achieved by placing the calliper on one edge of the parietal bone to another opposite edge of the parietal bone. The results are typically measured in millimetres (mm).

Perform other measurements

The healthcare provider may also measure other essential fetal biometrics, such as abdominal circumference (AC) and head circumference (HC), to determine the accurate growth and development of the fetus.

What do the BPD Results Mean?

The BPD results are widely correlated with the standard growth chart to determine the baby’s development.

Normal BPD

When the BPD measurements are within the expected range for its gestational age, it indicates that the baby is growing normally.

Outside the Range

The BPD measurements beyond or above the normal range may potentially indicate an abnormality in fetal growth. This may demand further assessments to identify potential issues, such as slow growth (growth restriction) or medical conditions like gestational diabetes.

However, the BPD normal range by trimesters may include:

First trimester

• 13 weeks: 21 – 28 mm

Second trimester

• 14 weeks: 24 – 30 mm
• 20 weeks: 40 – 58 mm

Third trimester

• 28 weeks: 65 – 81 mm
• 40 weeks: 86 – 102 mm

Biparietal Diameter Chart by Percentile

The following BPD chart by percentile shows the expected measurement of fetal head circumference at different gestational ages. While the 50th percentile is the average measurement, anywhere between the 10th and 90th percentile is generally considered normal.

However, it is essential to understand that there can be slight variations in the baby’s BPD measurements according to the gender.

Biparietal Diameter (mm) Chart by Percentile

Summary

The biparietal diameter (BPD) is one of the crucial measurements in fetal biometry that assesses the width of the baby’s head. This is done as a part of a prenatal scan to estimate the gestational age, monitor fetal growth, and identify potential abnormalities. Healthcare providers often use a combination of other fetal biometrics, like femur length (FC), to achieve the complete picture of fetal health.

Although a slight variation from the standard growth chart is generally normal, a significant deviation may require further assessments.

Any concerns about the baby's BPD should be discussed with the healthcare provider, who can recommend additional tests if necessary.

Above all, talk to your healthcare provider for any guidance.

If you still have any concerns, having a consultation with experts at Aval Clinics is recommended. They can guide you.

Contact us today for expert advice and personalized care:

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