After the third trimester, i.e. 12 weeks of gestation, the uterus begins to grow out of the pelvic cavity and the base of the uterus can be palpated from the pubic symphysis during an obstetric examination. Ultrasound and NT measurement are required at 12 weeks of gestation. Oral folic acid is required before 12 weeks of gestation to prevent neural tube abnormalities in the fetus, and the fetal heart can be auscultated with Doppler in the abdomen after the uterus has grown out of the pelvic cavity in the middle of pregnancy. Although the bottom of the uterus has grown out of the pelvic cavity at 12 weeks of gestation, most pregnant women do not have a significant abdominal bulge and do not show pregnancy, and at about four months of gestation, the bottom of the uterus will reach between the navel and the pubic symphysis, and most pregnant women will show pregnancy and can feel fetal movement.