The production of progesterone will normally drop away after about 10 days beyond ovulation.  It is this sudden reduction in the hormone that will prompt the menstruation period to begin due to the reduced oxygen supply from the blood vessels that were previously encouraged to grow by the progesterone hormone.

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The Feminine Cycle

If however, the released egg is fertilized and manages to embed itself into the uterine wall, then the hormone b-HCG is released from the developing placenta, which has the effect of telling the "yellow body" to continue to produce both progesterone and estrogen.  This in turn prevents the start of the menstrual cycle and stops further eggs from being released.

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b-hCG Levels in Pregnancy

The ovaries continue to produce progesterone (and estrogen) during the first 8 to 9 weeks until the placenta begins to reduce the amount of b-HCG secreted, which is a signal to the "yellow body" that it is capable of producing these hormones for itself and requires less help.

Introduction

1. Progesterone production

2. The role of progesterone

3. The role of estrogen (oestrogen)

4. Summary of some other hormones