The latest time for the gestational sac to become implanted is no more than seven days.
The egg and sperm combine to complete fertilization, which usually occurs in the abdomen of the fallopian tube. The fertilized egg is then propelled into the uterine cavity and undergoes orderly division with the help of peristalsis and tubal epithelial cilia. On day 4 of fertilization, early blastomeres enter the uterine cavity, and on days 4 to 5 of fertilization, late blastomeres form. Thus, after normal fertilization, the gestational sac will be implanted on the 4th day and no later than 7 days.
Human chorionic gonadotropin (HCG) increases in the blood the day after implantation, so you can indirectly tell if the fertilized egg has implanted by the level of HCG in the blood. To be on the safe side, a human chorionic gonadotropin sample can be collected on the tenth day of fertilization. If the HCG increases, it means that the implantation was successful. If the HCG does not increase, consider the implantation a failure.
Fertilized eggs can also be checked with a pregnancy test, usually 10 to 14 days after intercourse.
It is recommended to take oral folic acid for 3 months before pregnancy and 3 months after pregnancy under the guidance of doctor’s advice to prevent fetal malformation.