What is the significance of biparietal diameter examination at 40 weeks

The general pregnancy period for our female friends is about ten months, so we need to pay special attention to protection at every stage. During every pregnancy, we need to have regular physical examinations. So what is the significance of doing a parietal diameter check when we are 40 weeks pregnant? Many people may not know this, so let’s take a look at it below.

Biparietal diameter concept

Also known as BPD, biparietal diameter of the fetal head. It refers to the length of the widest part between the left and right sides of the fetal head, also known as the "greater transverse diameter of the head." Doctors often use it to observe the child's development and determine whether there is cephalopelvic disproportion and a smooth delivery.

It should reach 9.3 cm or more at full term. According to general rules, after 5 months of pregnancy, the BPD is basically consistent with the month of pregnancy, that is, at 28 weeks of pregnancy (7 months) the BPD is about 7.0 cm, at 32 weeks of pregnancy (8 months) it is about 8.0 cm, and so on. After 8 months of pregnancy, an average weekly growth of about 0.2 cm is normal. When the due date cannot be determined by CRL in the early stage, BPD is often used to predict it; after the middle stage, this data is often also needed to be measured when estimating the fetal weight.

Biparietal diameter fetal periodic table

12 weeks of pregnancy: The fetus grows to 4.58 cm, the external genitalia begin to develop, any deformities will be revealed, and the skull calcification becomes more complete. The skull halo is clear, the biparietal diameter can be measured, obvious deformities can be diagnosed, and the internal organs tend to become more complete afterwards.

Using the biparietal diameter to judge the child's developmental size is a reference data. During the delivery process, the maximum diameter of the fetus's head passing through the birth canal is the biparietal diameter, and the minimum diameter of the birth canal for the fetus to pass through is the transverse diameter of the pelvic outlet. Therefore, if the biparietal diameter is larger than the transverse diameter of the pelvic outlet, whether the child can be delivered naturally becomes a problem. The final choice depends on the pregnant woman's pelvis and the size of the baby at full term.

In addition to height, you also need to look at the pelvis. I am 165cm tall and have a relatively large pelvis. At 38 weeks, my biparietal diameter was 95, and I gave birth to a 8-pound boy. It is said that heavier boys are easier to give birth naturally, while girls are not as strong as boys, so it is more difficult to give birth naturally. It is better to listen to the doctor's advice. Good luck!

The above points can well explain the significance of the 40-week biparietal diameter examination. So we must go to the hospital for examination on time. Only in this way can we have a safe pregnancy. The 40-week biparietal diameter examination is also indispensable. Be sure to do the examination according to the doctor's regulations.