When a woman is nearly 4 months pregnant, which is approximately around 16 weeks of pregnancy, she has entered the second trimester. Most of the fetus is located within the abdominal cavity. Under normal circumstances, a woman should start to show, meaning that her abdomen will bulge to some extent. However, some women may not show obviously. Possible reasons include the following:1. Some women have thicker abdominal walls, which can conceal the uterus and result in less obvious showing.2. Some women may be carrying only one fetus during pregnancy, and usually, one fetus doesn't make the belly show very obviously at this stage.3. There may be some pathological conditions. For example, oligohydramnios, fetal malformation, or stillbirth can all cause the uterus to be smaller in size, leading to less obvious showing.There's no need to be overly worried about this situation. Generally, it is recommended to have regular prenatal check - ups. As long as the B - ultrasound shows that the fetus is developing normally, it's okay even if the woman doesn't show obviously.