This occurs about 6-7 days after fertilization. This is an extremely complex process requiring not only the hormones estrogen and progesterone but also many other substances that allow interaction of the expanded, hatched blastocyst with the endometrial lining of the uterus.
After implantation, the part of the embryo that will become the future placenta starts to produce a hormone called human chorionic gonadotropin (hCG), which can be detected in the mom’s blood by sensitive laboratory hCG tests as early as 12 days after fertilization.
If the embryo continues to grow and develop normally, then a gestational sac will form around 5 weeks of gestation, followed by the appearance of a fetus with a heart beat. This is the point at which a clinical pregnancy has been established, and can best be viewed by transvaginal ultrasound after 7 weeks of gestation. [Gestational age is roughly calculated from the time of ovulation plus 2 weeks]. Once a patient has achieved a clinical pregnancy, she will typically be referred to her obstetrician for further management and delivery.
