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The menstrual cycle and contraception
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Four hormones control the menstrual cycle. Understanding them explains contraception and fertility treatment.
The cycle
Roughly 28 days.
Days 1 to 4: menstruation, the uterus lining breaks down.
Days 4 to 14: the lining rebuilds.
Around day 14: ovulation, an egg is released.
Days 14 to 28: the lining is maintained.
Days 1 to 4: menstruation, the uterus lining breaks down.
Days 4 to 14: the lining rebuilds.
Around day 14: ovulation, an egg is released.
Days 14 to 28: the lining is maintained.
The hormones
FSH: makes an egg mature in the ovary.
Oestrogen: builds the uterus lining.
LH: triggers ovulation.
Progesterone: maintains the lining.
Oestrogen: builds the uterus lining.
LH: triggers ovulation.
Progesterone: maintains the lining.
Contraception
Hormonal: the pill (oestrogen and progesterone stop FSH and ovulation), implants, injections.
Barrier: condoms, which also protect against sexually transmitted infections.
Assisted reproduction (Higher): clomifene and IVF use hormones to help eggs mature and be released.
Barrier: condoms, which also protect against sexually transmitted infections.
Assisted reproduction (Higher): clomifene and IVF use hormones to help eggs mature and be released.
Why does the combined pill prevent pregnancy?
- Oestrogen and progesterone inhibit FSH.
- So no egg matures and ovulation does not happen.
Answer: It stops eggs maturing and being released.
FSH matures an egg; oestrogen builds the lining; LH triggers ovulation around day 14; progesterone maintains the lining. Hormonal contraception stops ovulation; barriers stop sperm reaching the egg.
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