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The fourth (luteal) phase: (Day 15-27)

Catherine McDiarmid-Watt | Monday, September 17, 2007 | 0 comments

Around 20 eggs develop and the most mature egg gets released. While the eggs are developing, the sacs produce estrogen. And just before the most mature egg gets released, progesterone is also secreted in addition to estrogen.

Estrogen and progesterone have their respective functions. Estrogen increases the flow of blood to the uterus and helps thicken its lining. Progesterone helps produce substances that will nourish a Ovum fertilized egg implanted in the lining.

The sacs (follicles) produce estrogen and progesterone due to the stimulation of LH and FSH. And once estrogen and progesterone reach a certain level, the production of LH and FSH stops. This stops the development of the other eggs, after the most mature egg has released.

If fertilization takes place:

The ruptured sac, after the egg has broken through (Corpus luteum), continues producing progesterone, aimed at nourishing the growth of the embryo. Progesterone blocks the release of further eggs till pregnancy is terminated.

Estrogen, while regulating progesterone, begins one of the major processes of fetal maturation. Without estrogen, the lungs, liver and other organs and tissues cannot mature.

If fertilization does not take place:

Estrogen and progesterone levels drop. Without these hormones, the lining of the uterus breaks up and is released through the vagina, to mark the onset of the menstrual period.

What happens after the uterine lining is shed?

A new cycle menstrual begins.


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About Catherine: I am mom to three grown sons, two grandchildren and two rescue dogs. After years of raising my boys as a single mom, I remarried a wonderful man who had never had a child of his own. Unexpectedly, I found myself pregnant at 49!
Sadly we lost that precious baby at 8 weeks, and decided to try again. Five more losses, turned down for donor egg, foster care and adoption due to my age and losses - we have accepted that there will be no more babies in our house.

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