Fetal head circumference is three weeks large may be pregnancy week accounting error, over-nutrition, breeding abnormalities and other reasons, to re-account for pregnancy week, control diet, termination of pregnancy and other ways to deal with. 1. Wrong calculation of gestational weeks: the wrong calculation of gestational weeks will lead to the calculation of gestational weeks is too small, and the actual gestational weeks do not match, showing a large fetal head circumference, it is recommended to go through all the ultrasound reports, to carefully calculate the gestational weeks, after the calculation and fetal development is consistent with the need for special treatment. 2. Over-nutrition: eating too much high protein food in the diet process will cause fetal over-nutrition, the overall size of the body of the fetus, the head will also have a large three weeks of performance, usually to control dietary intake, appropriate weight loss, should not overeat. 3. Developmental abnormalities: head size may also be caused by disease, the fetus will have more typical brain tumors, hydrocephalus and other phenomena, through the examination to determine the abnormalities, we should carefully consider whether to continue the pregnancy, there is a need for induced abortion to terminate the pregnancy. After pregnancy, do a good job of pregnancy and obstetric examination, there are abnormalities can be timely detection of the problem and treatment.