Is a 99mm biparietal diameter considered a large head?

　　A biparietal diameter (BPD) of 99 mm is generally not considered macrocephaly. The detailed analysis is as follows:

　　In prenatal fetal ultrasound examinations, the biparietal diameter is an important indicator used to assess the size of the fetal head. Normally, the BPD is proportional to gestational age—the fetal head gradually increases in size as pregnancy progresses. The biparietal diameter measures the distance between two points on the outer edges of the fetal skull bones, typically along the parietal bones. BPD measurements are usually evaluated in conjunction with gestational age. The normal range for BPD varies depending on gestational week. At 40 weeks of gestation, a normal BPD typically ranges from 90 mm to 100 mm. Measurements within this range are considered normal. If the BPD measured by ultrasound exceeds the normal range, doctors may conduct further evaluations of the fetus, taking into account other factors, to determine whether macrocephaly is present. In addition to the BPD value, physicians also consider other factors such as fetal weight, measurements of other body parts, gestational age, and maternal individual characteristics. Sometimes, even if the fetal head appears relatively large, if development in other areas is normal, it may simply reflect individual variation and does not necessarily indicate an abnormality.

　　If a pregnant woman is concerned that her fetus's head size exceeds the normal range, she should promptly consult her doctor for further evaluation and examination.