Essentially, the human menstrual cycle is a pattern of changes that occur within the ovary and uterus for the purposes of reproduction.
These changes involve a complex interaction of hormones that allow for follicles to mature and eggs to be released (ovulation) before hormones are produced to nourish an embryo should fertilisation have occurred. If fertilisation hasn’t occurred, the uterine lining is shed through menstruation.
What is regular and what is irregular?
If your period occurs monthly and the length is the same every month it is considered a regular menstrual cycle. Typically, the average length of the menstrual cycle is 28 days, but it can range between 25 and 35 days.
If your cycle doesn’t occur at regular intervals and is of varying lengths it is considered irregular. An irregular or non-existent menstrual cycle can be problematic for several reasons if you are trying to fall pregnant. Irregularity can cause a lack of egg production, a lack of readiness of the uterus for implantation, and difficulties with fertilisation due to not being able to confidently pinpoint when ovulation is occurring. While in most cases it is not dangerous, if you experience irregular menstrual cycles, it is important to seek the help of your GP or a fertility specialist to determine what is causing the irregularity. There are several ways to help regulate menstrual cycles and in turn improve your fertility.
Here are some reasons why a regular menstrual cycle is important when trying to conceive:
Pinpointing when ovulation is occurring
With a regular cycle you can accurately calculate when you are ovulating. The days leading up to ovulation (when the egg is released from the ovary) are the most fertile ones in your menstrual cycle giving you the best chance of conceiving. During this fertile time the egg is moving down the fallopian tube, waiting to be fertilised. You should time having intercourse one to three days before ovulation or every two days around it.
To calculate your fertile window, if your period is regular and the length is the same every month, then you can calculate ovulation by counting back 14 days from the end of the cycle. There are now a range of ovulation calculators that can help you predict your ovulation date.
If your cycle is irregular, you will find it difficult to pinpoint when you are ovulating and should seek advice.
The production of eggs
A regular menstrual cycle is determined by a complex interaction of hormones. Luteinising hormone (LH) and follicle-stimulating hormone (FSH) which come from the pituitary gland, cause the growth of an egg in a fluid-filled follicle within the ovary. Although several follicles start to grow each month, only one will become mature enough to ovulate. Ovulation (release of the egg from the ovary) is triggered by a surge of LH at mid-cycle, about two weeks before menstruation starts.
Preparing the uterus for a pregnancy to occur
During the early phase of your menstrual cycle the ovarian follicles start to mature releasing the hormone oestrogen, causing the formation of a new layer of the endometrium (the lining of the uterus). Then after ovulation the follicle that released the egg (corpus luteum) produces the hormone progesterone, which allows the endometrium to be receptive to implantation of the developing embryo and supports an early pregnancy.
Knowing when you could be pregnant
By 14 days after ovulation, the developing embryo produces enough of the pregnancy hormone hCG to miss a period, and for a home pregnancy test to be positive. When your cycle is regular, it is easy to know when you should test.
For more information visit Understanding your Menstrual Cycle.