The Menstrual Cycle – Simple step by step guide to understanding your periods
Whether you are trying to conceive or trying not to conceive, this simplified step by step account of what happens during your menstrual cycle gives you everything you need to know.
Ovulation and Conception
Every month, the reproductive organs in a healthy woman prepare for pregnancy.
A complex interaction between the pituitary gland in the brain, the ovaries and the uterus work to create the perfect environment for ovulation (the release of an egg) to occur, for the sperm and egg to meet and for the fertilised egg to implant itself in the uterus.
We have already covered what are the fertility hormones in this article here
Now we will understand under the influence of these hormones what is the sequence of physiological changes happening in the ovaries and uterus during the menstrual cycle:
Ovarian cycle: The period of follicular growth in the ovaries leading to ovulation
Uterine Cycle: The period of shedding of old endometrium and growth and thickening of new endometrium in preparation for possible implantation
A step-by-step guide to ovulation
- Every month the Hypothalamus, which is in your brain, releases a hormone called GnRH. This hormones tells the pituitary gland which is also in your brain to release gonadotropins FSH and LH
- FSH hormone tells the ovaries to produce a number of fluid-filled cysts called follicles. As the follicles grow they secrete the hormone oestrogen. Oestrogen works to thicken the wall of your uterus in preparation for pregnancy.
- On day seven of your cycle, the follicles stop growing except for one. This follicle continues to grow and to nourish a maturing egg (oocyte) within.
- On day 12 the maturing follicle releases a burst of oestrogen into the blood stream. The oestrogen travels through your blood. When the oestrogen reaches the pituitary gland in your brain, the pituitary gland responds by releasing the luteinising hormone. This hormone gives the follicle a sudden growth spurt.
- Right before ovulation, the egg inside the follicle detaches itself. The follicle starts to release chemicals that encourage the nearby fallopian tube to move closer and surround the follicle.
- The follicle swells until it bursts open, ejecting the egg and fluid into the abdominal cavity.
- Small finger like protrusions at the end of the fallopian tube, called fimbriae, sweep across the burst follicle and pick up the egg.
- The egg is transported to the entrance of the fallopian tube. Once inside the walls of the fallopian tube, muscle contractions push the egg gently towards the uterus.
- The egg will either meet sperm on its journey through the fallopian tube and fertilisation will happen, or it will arrive in the uterus unfertilised and be absorbed back into the body.
- The lifespan of an egg is 12-24 hours.44
A step-by-step guide to conception
- After ovulation the egg is viable for 12 to 24 hours inside the womb. The window of fertilization only last for one day during which time It must be fertilised if pregnancy is to be achieved.
- We talked about a burst of estrogen just before ovulation that causes LH surge and Ovulation to occur. This Burst of estrogen also has another important physiological effect that aids conception. It induces the cervix to make a protein-rich clear mucous that covers the top of the vagina.
- This makes the vagina acidic (which prevents thrush and other infections). This is also a suitable environment for sperm survival.
- If the sperm is deposited in the vagina around the time of ovulation, the sperm rapidly travel up and into the cervix, where they can survive in the mucus for up to five days before an egg is released.
- When the egg is released at ovulation, it is covered in sticky cells, which help the fallopian tube to catch it.
- The egg and the sperm meet in the fallopian tube, although many sperms attach to the egg only one of them can penetrate the outer membrane of the egg and fertilize it.
- After fertilisation, the egg and sperm merge and divide to form an embryo. Chemicals released post fertilization stop the other sperm from entering the fertilized egg.
- Over the next four or five days the fertilised egg continues to divide and to travel towards the uterus. So the embryo traverses the fallopian tube for 5 days after fertilization before it reaches the uterus.
- The hormone progesterone, which is secreted into your blood stream by the burst follicle (now called the corpus luteum) prepares the uterus for the egg to implant.
- As the pregnancy grows and implants itself into the mother’s uterine lining and blood vessels, it is sending an increasingly strong signal to the ovary to prolong and increase its production of progesterone, which the pregnancy needs to survive.
Optimising Conception - Getting pregnant
You are more likely to get pregnant if you:
- Are younger. Fertility is highest in women aged between 18 and 32, after which a woman’s fertility declines at a rate of 5–8 per cent per year. By the age of 40, a woman has a 50 per cent chance of being infertile.
- Have sex more often. Women who have sex every night conceive four times as quickly as those who have sex once a week.
- Have regular ovulation cycles. While 28 days is the average, the fertile cycle length in it can vary between 21 to 35 days in women. The duration of cycle will vary from woman to woman but it is important to track your ovulation and make sure that the cycles are regular. If you missed periods for more than 3 months or have an irregularities it is best to see a gynaecologist.
- Women who have been pregnant before get pregnant again more easily.
With regular, unprotected sexual intercourse 80 per cent of women become pregnant within a year. Even so, fertility varies from person to person and up to 15 per cent of couples experience some difficulties.
There are many reasons for infertility that can be related to the male or female partner. If you have been trying unsuccessfully to get pregnant for a year or more, you may wish to consider a fertility specialist.
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