During pregnancy, expectant mothers need to go to the hospital for different prenatal examinations, including B-ultrasound examination to measure fetal length, biparietal diameter, femur length, abdominal circumference and other data to understand the individual development of the fetus. Recently, a expectant mother asked if the biparietal diameter of the fetus will decrease after entering the pelvic cavity? Next, let me explain to expectant mothers.
The biparietal diameter, also known as the fetal head biparietal diameter or head transverse diameter, refers to the length of the widest part between the left and right sides of the fetal head. A biparietal diameter value greater than 8.5 centimeters measured under ultrasound indicates fetal maturity. The biparietal diameter is not only a basis for judging fetal development, but also for determining whether there is a mismatch between the head and pelvis, which is the basis for expectant mothers to choose the delivery method.
Fetus entering the pelvic cavity refers to the position of the fetus in the late stage of pregnancy, with its head facing downwards and hips facing upwards, and its whole body curled up. The fetal head will enter the pelvic cavity through the maternal pelvic entrance, fixing its position. Entering the pelvic cavity indicates that the fetus is ready for a smooth birth, and it often occurs between 37 and 38 weeks of pregnancy.
After the fetus enters the pelvic cavity, it generally does not affect the biparietal diameter, and the biparietal diameter of the fetus continues to grow and develop. At 39 weeks of pregnancy, the average biparietal diameter of the fetus should be between 9.21 centimeters plus or minus 0.59 centimeters. At 40 weeks of pregnancy, the average biparietal diameter of the fetus should be between 9.28 centimeters plus or minus 0.50 centimeters.
