A size-greater-than-date discrepancy usually has an obstetric cause, such as incorrect dating (the most common cause), multiple gestation, polyhydramnios, or gestational trophoblastic disease (eg, hydatidiform mole). However, none of the above conditions would produce an irregular uterine contour in early pregnancy . An abnormal uterus is more likely. In this patient with an irregular uterine contour and history of heavy menses, the most likely cause is leiomyomata uteri (uterine fibroids).
Although most fibroids do not adversely affect pregnancy, having large or multiple fibroids can increase the risk of obstetric complications (eg, spontaneous abortion, preterm labor, postpartum hemorrhage) and the rate of cesarean delivery.