Preconception 101

Lesson 1: Hormones 101

Post-Ovulatory Hormones - Progesterone and hCG

Once the pre-ovulatory hormones estrogen, FSH, LH and GnRH have made ovulation happen, the second half of the menstrual cycle occurs. This time period is known as the luteal phase. The luteal phase normally lasts about fourteen days. A normal luteal phase can range from ten days to about 16 days. When the hormones that rule the luteal phase are dysfunctional, then the luteal phase can be too long or deficient. The most important hormone in the post-ovulatory phase is progesterone.

Progesterone

Progesterone is produced by the corpus luteum, the cyst that was formed when the egg burst forth from the ovary, after ovulation has occurred. Progesterone is the one hormone that regulates the entire endocrine system. This hormone is responsible for maintaining the luteal phase length. If there is a deficiency in progesterone, the luteal phase will be under ten days. If there is too much progesterone, the luteal phase will go past seventeen days without a positive pregnancy test, though the latter is rare. Progesterone is also known as the warm hormone, progesterone is the reason the basal body temperature climbs and maintains its height during the luteal phase. It helps to build and maintain the uterine lining for the fertilized egg and helps to keep the lining should pregnancy occur. Progesterone is also responsible for the drying up of the cervical fluid and for the change in cervical position during the second half of the reproductive cycle.

Though progesterone is produced in the ovaries, primarily by the corpus luteum, the cyst left from the egg, small amounts of progesterone is made in the adrenal glands in both males and females. When pregnancy occurs the placenta takes over the production of progesterone when the corpus luteum dies a couple of months into the pregnancy and it produces large amounts of progesterone. Progesterone derives its name because of pregnancy. It literally means “pro-Gest” or pro-gestation, one that sustains life (pregnancy.)

Human Chorionic Gonadotropin (hCG)

hCG is produced if a pregnancy occurs, so the existence of this hormone will only come into play if conception happens. If pregnancy is desired, then hCG plays a very important role in the post-ovulatory hormones. hCG is produced when the fertilized egg implants into the uterine wall, at about five to twelve days past ovulation. As the placenta is being formed, small amounts of hCG is emitted. The placenta is responsible for the production of hCG. The production of hCG helps to maintain the corpus luteum thus keeping up the hormones estrogen and progesterone until the placenta takes over.

Levels of hCG will start small, increasing by doubling every other day. It’s hCG that a urine home pregnancy test detects to give a positive reading. When a pregnancy test is taken too soon, the result could be a false negative. hCG will begin production anywhere from about five to twelve or later days past ovulation. Because it doubles every two days for about ten weeks, if you don’t see a positive pregnancy test right away, you can always wait a couple of days and then will probably see one.

See the Mayo clinic Complete Book of Pregnancy and Baby's First Year to take a look at what happens in early pregnancy with the hormones.

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