The pregnancy has just been conceived on the 30th day of pregnancy, the gestational sac is still very small, you may not be able to see the gestational sac or the sac is only about 0.2-0.3cm. Fetal development in early pregnancy is a complex process. When the egg is fertilized and enters the uterine cavity, the fertilized egg begins to bed, and the embryo and appendages will grow rapidly until maturity, and at this stage, different changes will occur during each pregnancy week. When the pregnancy is about 30 days old, the fertilized egg has just completed its implantation and the amniotic cavity is initially formed. At this time, the gestational sac is so small that the signs of pregnancy are not yet visible on ultrasound. The size of the gestational sac in the ultrasound can be used to determine the development of the fetus during pregnancy, and the size of the gestational sac varies from week to week of pregnancy. Generally speaking, you can go for an ultrasound when you are about 6 weeks pregnant, at which time you can see the gestational sac clearly and can determine whether it is an intrauterine pregnancy or an ectopic pregnancy.