The saying that “a large biparietal diameter is usually a son” is not scientific and is incorrect. A pregnancy test indicates that the fetus has a large biparietal diameter, which is generally considered to be a result of the fetus absorbing more nutrients in the mother’s body, leading to the fetus being larger, which does not have a significant relationship with the sex of the fetus. Therefore, it is not correct to say that a large biparietal diameter indicates that the fetus is a boy. At the same time, large biparietal diameter may also indicate fetal malformations. Pregnant women are advised to participate in regular obstetric checkups to rule out congenital malformations in the fetus. The sex of the fetus cannot be determined simply by the biparietal diameter and other data, it is recommended that pregnant women pay attention to ensure nutrition during pregnancy, and at the same time adhere to moderate exercise, in order to facilitate the successful delivery of a healthy baby.