At about three months (13-14 weeks), the top of the uterus is usually just above the mother's pubic bone (where her pubic hair begins). At about five months (20-22 weeks), the top of the uterus is usually right at the mother's bellybutton (umbilicus or navel).
Gestational age may be overestimated by up to six weeks by assuming that the fundus reaches the umbilicus or that fetal heart tones appear at 20 weeks. However, carefully derived obstetric estimates potentially may be more reliable than pediatric estimates.
