Under normal circumstances, the enlarged uterus is still located in the pelvic cavity during the second trimester of pregnancy and does not visibly appear to have an enlarged abdomen. Possible reasons for a very large belly in the second trimester include: 1) reduced activity and excessive calorie intake during pregnancy, leading to excessive fat deposition in the lower abdomen; 2) possible twin pregnancy with significant uterine enlargement; 3) pregnancy combined with larger ovarian cysts, fibroids, and other gynecological disorders, resulting in a significantly enlarged abdomen; and 4) abnormal pregnancies such as hyperemesis gravidarum, which results in excessive uterine enlargement. When this phenomenon occurs, pregnant women should go to the public hospital as soon as possible, ultrasound examination to further clarify the specific causes for targeted treatment.