The parietal-buttock diameter is the length of the fetus measured from the top of the head to the lowest part of the buttocks. The vertex-hip diameter refers to the distance from the top of the fetus’ head to the buttocks, and is usually measured after 14 weeks of pregnancy for an ultrasound. By measuring the length of the parietal breech diameter, it can assist in estimating the size of the fetus, determining the development of the fetus, and projecting the duration of the pregnancy. Generally, the length of the breech-parietal plus 6.5cm is the actual number of weeks of pregnancy. Common causes of large biparietal diameter include over-nutrition, lack of exercise and gestational diabetes. A breech-parietal diameter that is significantly small indicates that the fetus is underdeveloped. During pregnancy, you should have regular checkups to monitor the development of the fetus, rationalize your diet, and exercise moderately.