Biparietal diameter at 18 weeks of pregnancy

Biparietal diameter is actually a more professional term, which refers to the reference data of the fetal head and pelvis. When a pregnant woman is 18 weeks pregnant, the biparietal diameter of the baby is generally around 4 cm. This is just a reference value. After the prenatal check-up, the pregnant woman can listen to the doctor's advice and learn more about whether the child's development is normal. This will also help her to better adjust her future habits.

18-week fetal biparietal diameter standard

At 18 weeks of pregnancy, the normal range of the fetal biparietal diameter is: 3.72-4.78CM. The normal range of femur length is: 2.25-3.17CM. But everyone's eating habits are different. Therefore, there can be certain differences.

The biparietal diameter of the fetal head, also known as BPD, is a reference data. Doctors often use it to observe the child's development and determine whether there is cephalopelvic disproportion and a smooth delivery. 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.

When the baby is full-term, the BPD should reach 9.3 cm or more. 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, the average weekly growth of about 0.2 cm is normal. The standard biparietal diameter of the fetus at 36 weeks is 8.81 ± 0.57.

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.

The biparietal diameter of the fetus is usually measured by ultrasound. As the fetus grows older, the skull continues to grow. When measuring the biparietal diameter, it should be measured from the inner edge of the skull on one side to the outer edge of the skull on the opposite side. This value is more accurate. If the examination is conducted in different hospitals, by different doctors, and on different machines, the value will be biased.

Is it reliable to predict gender by using biparietal diameter of femur?

At full term, the biparietal diameter of the fetus should reach 9.3 cm or more. 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.

Experts remind: It is not scientific to use the biparietal diameter to determine whether the fetus is male or female. However, the biparietal diameter is used to calculate the fetal weight. The formula is: fetal weight = biparietal diameter * 900-5200 (g)

Femoral length (FL) is an indicator commonly used by doctors to observe fetal development when performing pregnancy examinations on pregnant women using B-ultrasound (or color ultrasound).

The femur and humerus are both typical long tubular bones in the human body, and can be divided into two ends. The femur is the largest long bone in the human body and refers to the thigh bone; the humerus is located in the upper arm and is also called the upper arm bone. So as the names suggest, femur length refers to the length of the thigh bone, and humerus length refers to the length of the upper arm bone.

Femur length and humerus length are both fetal biological indicators for predicting fetal weight. However, fetal humerus length is better than femur length in predicting fetal weight.

Experts remind: Using the length of the femur to determine whether the fetus is male or female is unscientific and has no basis.