Usually after the appearance of the gestational sac, more estrogen and chorionic gonadotropin are secreted due to the yolk sac, and also due to the ovaries themselves. Usually, under the influence of estrogen and progesterone, the uterus slowly enlarges to meet the space requirements for the gestational sac to settle in the uterus and for the growing fetus later on. In general chorionic gonadotropin, or HCG hormone as it is commonly known, is a hormone that can be tested for pregnancy with an early pregnancy test. The mammary glands are also affected by progesterone and estrogen, and the lobules of the mammary glands continue to grow progressively, as well as for all organs of the body.