The Menstrual Cycle

The menstrual cycle is (on average) a 28 day cycle where the female reproductive organs prepare and break down the uterus lining for the possibility of fertilisation as the focus of reproduction. The cycle consists of four main stages which are controlled by hormones;

1. Day 1-5 on average is the bleeding starts, the thick walls of the uterus break down and the lining is lost due to a lack of unfertilised egg in its walls. Interestingly, most of menstruation is mucus and tissue where only a small proportion is blood, despite it being called 'bleeding'
2. After the lining fully breaks down, the uterus will start to build up the lining again for another potential zygote (the name given to the group of cells dividing after the egg is fertilised).The lining is a thick, spongy and rich in blood vessels for a good blood supply. This happens from day 4-14. 
3. After the lining is built up, the uterus essentially 'waits' for an egg. At day 14, the egg is released from the ovaries and travels down the Fallopian tube and again, 'waits' to meet sperm. The uterus 'awaits' the fertilised egg for 10 days (until day 28) by which if it is not received, the lining will start to break down and the cycle will start again.

 (Erol Ahmed)

As mentioned, the menstrual cycle is controlled by hormones called FSH, Oestrogen, progesterone and LH. FSH (follicle stimulating hormone), produced in the pituitary gland, causes the egg to mature in one of the ovaries and also stimulates the ovaries to produce oestrogen. Oestrogen causes the pituitary gland to secrete LH, thickens the lining of the uterus and inhibits the further production of FSH. Due to the release of oestrogen, the pituitary gland later releases LH (luteinising hormone) which causes the ovaries to release the egg at day 14. The hormone progesterone is released from the ovaries to sustain the built up lining and also inhibits the production of LH and FSH so that no more eggs are matured/released. As the lining breaks down, progesterone levels drop and the cycle starts again! Remember that the endocrine system works as the hormones travel in the blood- meaning its not a quick process and these changes happen throughout the cycle of 28 days. Hormonally, let's do a flow diagram (I'm aware of the irony).

1. The pituitary gland releases FSH. FSH causes egg to mature and stimulates oestrogen
2. Oestrogen stimulates LH from pituitary gland, thickens uterus lining and inhibits extra FSH
3. LH causes egg to be released from the ovaries. As the egg is released, progesterone levels increase causing FSH and LH to be inhibited. Progesterone maintains the lining until the lining is lost.
4. Progesterone levels drop again and FSH is released to start the cycle again.

Hormones can be used to reduce and also increase fertility. A woman can take oestrogen to prevent the release of an egg (which seems odd as it would usually cause LH to be released) but if taken every day, the high oestrogen levels will inhibit egg maturation from FSH; after a while egg maturation and production will come to a stop.

 Contraceptive pills often are taken for three quarters of
each month (Simone van der Koelen)

Additionally, a woman can ingest progesterone which causes the uterus lining to become increasingly thick to not allow sperm through (however this can cause menstruation to be significantly heavier). In the early 1950s, the combined oral contraceptive pill was developed and it contained high levels of oestrogen and progesterone to try to prevent pregnancy. Although it was effective, it had many side affects like blood clots. Nowadays, the pill contains lower doses of the oestrogen and progesterone to reduce the harsh side effects. Pros and cons of this pill include;

• The pill is over 99% effective at preventing pregnancy (PRO)
• It reduces the chances of getting some types of cancer  (PRO)
• It isn't 100% effective (CON)
• It can cause side effects like headaches, nausea, irregular menstruation and fluid retention (CON)
• It doesn't protect against STDs unlike other methods of contraception (CON)

There is also a progesterone only pill which can be taken and has less side effects. However, it isn't as effective as taking combined hormones.

Just like reducing the chances of pregnancy, we can also use hormones to increase the chances of pregnancy. Some women have FSH levels that are too low to cause a release of oestrogen or to mature the eggs in the ovaries, these women can be injected with FSH and LH to stimulate and mature the egg. There are pros and cons of this too;

• It can increase the chance of becoming pregnant! (PRO)
• It can lead to over-stimulation of ovaries leading to multiple eggs being released causing multiple pregnancy of twins, triplets etc (CON)
• It doesn't always work so the woman may have to try multiple times- this can cost financially and physically (CON)

(Kelly Sikkema)

We can further use hormones in processes like IVF. Often when a couple can't get pregnant, they may look for other methods of conception. IVF (In-vitro-fertilisation). In case you wanted to know, vitro is Latin for in glass which refers to the fertilisation being done in a lab. IVF involves collecting the eggs from a woman's ovaries and fertilising the eggs using the man's sperm. Before the eggs are collected, the woman is injected with FSH and LH stimulate many eggs to be collected. In the lab, these are fertilised and grown into embryos. The best, healthiest one or two embryos are then inserted into the woman's uterus lining which is maintained by progesterone. Although there is an obvious pro here that a couple can conceive, there are some cons;

• Some women have strong reactions to the hormones like vomiting, abdominal pain and dehydration
• Some reports suggest the hormonal treatment has been linked to an increased chance of cancer (no definite link made yet)
• The insertion of multiple embryos can also lead to multiple births of twins and triplets etc which can further lead to problems like stillbirth, miscarriage etc
• This process also might not work first time and is costly