Normal head circumference, small biparietal diameter

After the baby is born, mom and dad are his only ones, and we need to observe the baby strictly. Because the baby's every move may indicate its development status. If we cannot protect the baby carefully, it may cause him not to develop normally. Many people are new parents for the first time, so they need to enrich their knowledge through learning. So, what are the reasons why a baby’s head circumference is normal but the biparietal diameter is smaller?

1. What is the standard of biparietal diameter?

The standard for biparietal diameter of a 12-week fetus: The fetus grows to 4.58 cm, the external genitalia begin to develop, any deformities can be revealed, and the calcification of the skull 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.

The standard of biparietal diameter of 13-week fetus: the average value of biparietal diameter is 2.52±0.25

The standard of biparietal diameter of 14-week fetus: the average value of biparietal diameter is 2.83±0.57

The standard of biparietal diameter of 15-week fetus: the average value of biparietal diameter is 3.23±0.51

The standard of biparietal diameter of 16-week fetus: the average value of biparietal diameter is 3.62±0.58

The standard of biparietal diameter of 17-week fetus: the average value of biparietal diameter is 3.97±0.44

The standard of biparietal diameter of 18-week fetus: the average value of biparietal diameter is 4.25±0.53

The standard of biparietal diameter of 19-week fetus: the average value of biparietal diameter is 4.52±0.53

The standard of biparietal diameter of 20-week fetus: the average value of biparietal diameter is 4.88±0.58

The standard of biparietal diameter of 21-week fetus: the average value of biparietal diameter is 5.22±0.42

The standard of biparietal diameter of 22-week fetus: the average value of biparietal diameter is 5.45±0.57

The standard of biparietal diameter of 23-week fetus: the average value of biparietal diameter is 5.80±0.44

The standard of biparietal diameter of 24-week fetus: the average value of biparietal diameter is 6.05±0.50

The standard of biparietal diameter of 25-week fetus: the average value of biparietal diameter is 6.39±0.70

The standard of biparietal diameter of 26-week fetus: the average value of biparietal diameter is 6.68±0.61

The standard of biparietal diameter of 27-week fetus: the average value of biparietal diameter is 6.98±0.57

The standard of biparietal diameter of 28-week fetus: the average value of biparietal diameter is 7.24±0.65

The standard of biparietal diameter of 29-week fetus: the average value of biparietal diameter is 7.50±0.65

The standard of biparietal diameter of 30-week fetus: the average value of biparietal diameter is 7.83±0.62

The standard of biparietal diameter of 31-week fetus: the average value of biparietal diameter is 8.06±0.60 ...

2. Other methods of judging gender by biparietal diameter

In fact, using the biparietal diameter to determine whether the fetus is male or female is not scientific and has no basis.

At present, the practical and relatively reliable methods that obstetricians and gynecologists can use to determine the sex of the fetus are:

1. Ultrasound scan: Ultrasound is a type of sound wave. Reports so far have shown that it has no adverse effects on the fetus, so it is very commonly used in the obstetrics and gynecology community. When using ultrasound to diagnose the sex of a fetus, the accuracy for a boy can reach over 95%, while the reliability for a girl is only about 85%.

2. Amniocentesis: Amniocentesis is mainly used to diagnose whether the fetus has chromosomal or neural tube defects, and is usually performed between 16 and 20 weeks of pregnancy. Since the chromosomes of the fetus can be known, the sex of the fetus can also be known. The accuracy is 99%, but there is a 1% chance of miscarriage. Therefore, doctors do not recommend performing amniocentesis just to find out the sex of the fetus.

3. Chorionic villus sampling: also known as chorionic villus sampling, is usually performed at 8 to 10 weeks of pregnancy. The main purpose is the same as amniocentesis, which is to diagnose whether the chromosomes of the fetus are normal, but some people also use it to diagnose the gender of the fetus, with an accuracy rate of up to 98%.