Janelle McAlpine MMRes BA (Human Bioscience) BMid
Registered Midwife
Your menstrual cycle lasts from the first day of your period up to, but not including, the first day of your next period. The length of a woman’s menstrual cycle can vary. Anything from 24 to 35 days is common, although it could be longer or shorter than this. On average, it lasts 28 days. Knowing your cycle is an essential when it comes to family planning. If you are planning a baby then time your sexual activity for when you are most fertile. Conversely, if you really dont want a baby then avoiding sexual intercourse at this time is a good idea.
Phase 1: The Follicular Phase
The first full day of bleeding is considered day 1 of your cycle. Hormone levels (progesterone and estrogen) drop at the end of the previous cycle. The pituitary gland detects this and responds by increasing the production of follicle stimulating hormone (FSH) causing number of follicles (tiny sacs of fluid containing eggs) to develop within the ovaries in the days leading up to your period. The developing follicles cause FSH production to progressively drop, until there is only enough to support the continuing development of one follicle. This follicle (the ‘dominant follicle’) secretes increasing estrogen which in turn increases the thickness of the lining of the uterus in preparation for pregnancy. It also causes the cervical mucus to become thinner so sperm can pass through it more freely. This will continue for a few days before ovulation.
Phase 2: Ovulation (release of the egg)
The increasing level of estrogen causes the pituitary gland to release a spurt of luteinizing hormone (LH). This hormone triggers ovulation, by causing the dominant follicle to mature and release the egg. The egg is only able to survive about 24 hours before it must be fertilised, however sperm can survive there for 2 to 3 days, awaiting arrival of the egg.
Phase 3: After ovulation
The follicle that the egg was released from now begins to make and release progesterone. Progesterone is the hormone responsible for maintaining pregnancy. If conception takes place the baby will start to make another hormone – human chorionic gonadotrophin (hCG) – the hormone measured in pregnancy tests. This hormone enables the continued production of estrogen and progesterone to keep the pregnancy going. If there is no fertilisation the hormone production drops off and triggers the next period.
