When you are about 40 days pregnant, you can go to the hospital for an ultrasound. It is generally recommended to have a black and white ultrasound of the abdomen, but not a vaginal ultrasound or an abdominal ultrasound. Because the fertilized egg has just been laid in the early stage of pregnancy, the ultrasound may cause some radiation which may affect the health of the fetus, so a black and white abdominal ultrasound is recommended. Also, if each period is delayed, you can start counting from the first day of your last period and go to the hospital for ultrasound monitoring when you are 45 days pregnant, because the delay in menstruation may also cause the fertilized egg to lay late. If there is an early menstruation, ultrasound monitoring can be performed at about 38 days of pregnancy. Because of early menstruation, fertilization of the egg may occur earlier. If you have abdominal pain or bleeding during pregnancy, there is no time limit and you can go to the hospital for ultrasound monitoring at any time.