The embryo has been laid at 4 weeks of pregnancy. Embryo implantation is the process in which the embryo combines with the wall of the uterus, and the sperm and the egg are able to meet and form a fertilized egg after men and women have intercourse, and it may implant in about 6~8 days, and the fact that a pregnancy has been detected at 4 weeks of gestation indicates that the fertilized egg is in the state of implantation. At 4 weeks of pregnancy, the fertilized egg has been deposited and can be seen by ultrasound without echoes in the uterus. Go to the hospital for an ultrasound in 2-3 weeks to see if the yolk sac can be seen in the uterine cavity, to determine if it is a normal intrauterine pregnancy and to rule out ectopic pregnancy. You can also test the blood HCG level and doubling during pregnancy to determine if the embryo is developing normally. A good maternity test during pregnancy will allow any abnormalities to be detected and dealt with in a timely manner.