Skip to Main Content
New Patients:
0800 564 2270
Blonde woman sitting down using her laptop with a mug

24/10/2023 - 7 min read

What does your menstrual cycle say about your fertility?

Care Team

Many find the menstrual cycle a helpful way to understand your body. If you are beginning to consider your fertility, you might not know where to start; at Care, we are here to support and guide you at every stage of your fertility journey.

What is the menstrual cycle?

The menstrual cycle is a series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that makes pregnancy possible.

The ovarian cycle controls the production and release of eggs and the release of oestrogen and progesterone. These cyclical changes are usually monthly and result in the growth and release of an egg.

During the first or preovulatory phase of the cycle, the womb lining sheds, resulting in a period that usually lasts around 4 to 5 days. At this time, oestrogen levels are low, stimulating the brain to make FSH (Follicle Stimulating Hormone).

FSH stimulates a number of small egg follicles to start growing in the ovary. By the end of the period, usually, one of these follicles has been selected naturally to carry on growing and become the dominant follicle that starts to produce oestrogen. The production of FSH hormone is reduced, as it is not required again until the next period. The dominant follicle will release an egg that month, and the other follicles die off. A new batch of follicles will begin growing at the start of the next menstrual cycle.

The growing follicle releases an increasing amount of oestrogen hormone, which thickens the womb lining in preparation for possible embryo implantation.

By around day 12 of a monthly (28 day) cycle, the dominant follicle has grown, and its oestrogen level has risen sufficiently to trigger a rise in another hormone called LH or Luteinising hormone. LH can be detected in urine in simple ovulation prediction kits.

The LH surge in the middle of the cycle matures the egg inside the follicle so that it can be fertilised, followed by the release of the egg about 36 to 40 hours after the surge.

LH also starts the production of progesterone hormone from the cells inside the egg follicle. Progesterone causes essential changes in the quality of the womb lining, making it receptive to an embryo. It also has a relaxing effect on the uterus muscles.

If an egg is fertilised and starts to implant in the womb, signals from implantation encourage the follicle to continue to produce oestrogen and progesterone to help establish a pregnancy. If no such signal is detected, the hormones produced by the follicle reduce, and a period arrives.

When the hormones are low, the next cycle of follicle growth, egg release and womb lining preparation begins.

What can the menstrual cycle tell us about fertility?

Cycle length and regularity

The average length of a menstrual cycle is 28 days, but anything between 26 and 32 is considered ‘normal’. If your cycle is shorter or longer than this or is irregular, the implications may depend on your age and personal circumstances.

Additionally, if you have short cycles and but you still ovulate around day 14, you may have a “ short luteal phase” which means that you may need extra progesterone to prolong the post ovulation phase, giving extra time for an embryo to implant properly.

Irregular cycles

If you have very long or irregular cycles in your early teens or twenties, you may have Poly Cystic Ovarian Syndrome (PCOS). PCOS is very common but can make conceiving difficult if you aren’t releasing an egg regularly. PCOS can usually be treated very simply with tablets; you will need an ultrasound scan to see if you have polycystic ovaries.

There are other less common reasons for having irregular cycles when you are young, including an underactive thyroid gland or a raised prolactin level. These both give changes in hormone levels which can be detected by blood tests and managed by your GP or gynaecologist.

If you have an irregular, shorter or longer cycle in your late thirties or forties, it may be a thyroid problem or high prolactin. It also may indicate that your egg numbers (ovarian reserve) are changing; this can be checked by ultrasound scan and blood tests by your GP or gynaecologist.

Long gaps in between periods

If you do not have polycystic ovaries, long gaps could mean the onset of changes associated with menopause, and a hormone test will help to detect this.

Extreme weight loss in younger women can sometimes stop periods, this tends to return once the ovaries have started cycling again.

Light or heavy periods

It can be challenging to describe what a regular menstrual flow is, but if you feel that you have very heavy periods, we recommend that you are checked for fibroids, thyroid gland problems, and hormone irregularities which can cause the lining to be very thick.

If you have spotting or bleeding in between periods, you may have a polyp inside the womb; this can be diagnosed via a scan.

If you have very light periods, this may be due to age and declining hormonal activity in older women.

Painful periods

A little bit of cramping on the first day or two of your period is common, but you should be able to control the pain using simple over the counter medication. Anything more than this over a long time should be investigated, especially if your periods are very heavy.

Fibroids and a hormonal imbalance are the most common reasons for painful periods, but some have endometriosis. Endometriosis can cause severe pelvic pain, even starting just before your period arrives.  If your GP or gynaecologist thinks you may have endometriosis, you may be referred for a laparoscopy to treat it.

What can your menstrual cycle tell you about your fertility?

We can learn a lot from your menstrual cycle, including all of the things already mentioned above.

As a general rule, a regular cycle, however long or short, usually means that you are ovulating (releasing an egg). You can use home testing kits to confirm that you have an LH surge which helps you to time intercourse efficiently. You can also get a blood test for progesterone level about a week after your presumed ovulation; this will confirm if you are ovulating.

Some women notice a change in the consistency of normal vaginal discharge, which occurs around ovulation. Discharge can become more abundant and watery due to rising oestrogen hormone levels. The mucus discharge is thicker at other times of the month.

If you are under 37, have signs of ovulation, have regular cycles, and have been trying for a baby for some time, the reason is likely something other than your ovulation cycles.

Frequently asked questions

Q: When are people most fertile?

A: An egg should be fertilised within 12 to 24 hours of release, so it is essential to time intercourse around ovulation. Sperm can last in the genital tract for up to 72 hours, so it makes sense to have intercourse from just before ovulation (just after your LH surge if you are testing for this).

There are many apps available and urine testing kits that can help you time sex efficiently to maximise your chances.

Q: How can contraception affect your menstrual cycle?

A: Taking the combined pill will usually give you a false but regular withdrawal bleed in the seven days when you don’t take it. The oestrogen in the pill stops you from ovulating hence its contraceptive action.

When you stop taking the pill, most people will start having a regular ovulatory cycle immediately. However, the return to normality can take a couple of months for some.

The progesterone-only pill can give you very irregular bleeding or very light and infrequent periods. The contraceptive implant can also stop your periods and take some months for the cycle to return to normal once it is removed.

The coil (IUCD) can give you heavy periods if it is a simple copper coil, and cycles should return to normal straight away after it is removed. The Mirena coil, which releases hormones, can make your cycles disappear or become irregular. Again, it may take a month or two for your periods to return to normal after its removal.

Care are on hand to offer expert advice. From fertility tests to advice on ways to increase your fertility, we are here to support you.

With love from Care x