Normal values ​​for head circumference and biparietal diameter

Every time I had an ultrasound examination, I would study the examination form for most of the day, eager to know the growth and development of the fetus. As a first-time pregnant mother, I was confused by the baby's growth data in the ultrasound examination report. If I didn't understand something, I could find out immediately by searching on the Internet. As the number of weeks of pregnancy increases, more and more fetal growth indicators can be seen, including head position, biparietal diameter, fetal abdominal circumference, femur length, and weight.

Many mothers do not know the difference and connection between head position and biparietal diameter. In fact, the two are two completely different concepts. The only thing in common is that they are both data related to the size of the fetal head.

What is the fetal head circumference?

Fetal head circumference refers to the maximum length around the fetal head. The largest part of the fetal head from front to back is generally the distance from the bridge of the nose on the forehead to the occipital protuberance on the back of the head. Therefore, the baby's head circumference is the length of the distance from the bridge of the nose on the forehead to the occipital protuberance on the back of the head.

What is the biparietal diameter?

The biparietal diameter of the fetus refers to the length of the widest part between the upper and lower sides of the fetal head, also known as the "greater thick diameter of the head".

Also known as BPD, doctors often use it to observe the baby's development, determine whether there is cephalopelvic disproportion, and complete delivery of pregnant women.

At full term, it should be 9.3 cm or above. According to general regularity, after the fifth month of pregnancy, it is basically consistent with the month of pregnancy. In other words, the BPD is about 7.0 cm at 28 weeks of pregnancy (July), about 8.0 cm at 32 weeks of pregnancy (August), and so on. After the eighth month of pregnancy, an average increase of about 0.2 cm per week is normal. When the delivery date cannot be determined based on CRL (brachial head diameter) in the early stages of pregnancy, BPD is usually used for prediction; in the middle and late stages of pregnancy, this data is often also required to accurately measure when determining the fetal weight.

The correlation between baby's head circumference and biparietal diameter

The fetal biparietal diameter is directly proportional to the baby's head circumference. The larger the biparietal diameter, the larger the baby's head circumference will be.

What should I do if my baby's biparietal diameter is too small?

The biparietal diameter is small. If the gestational age is accurate, it is very likely that the pregnant mother does not get enough nutrition. If there are no significant growth and development abnormalities, there is no need to worry too much. It is recommended to pay attention to the regularity of food, clothing, housing and transportation, pay attention to improving nutrition, eat more high-protein foods, and have regular physical examinations.

What should I do if my baby's biparietal diameter is too large?

The larger biparietal diameter of the fetus indicates that the pregnant mother's nutrition is sufficient, which leads to the slightly larger growth of the baby. This is a more common manifestation nowadays, so there is no need to worry. As long as there is no abnormality in the fetus's head, you can rest assured.