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The Menstrual Cycle

Understanding Your Monthly Cycle, Ovulation and Fertility

Knowing your menstrual cycle and the signs of ovulation will help you calculate your most fertile days.   This can help you to optimise your chances of falling pregnant.

Hormone levels in the body govern your menstrual cycle.  These levels rise and fall in a monthly pattern until menopause.

Each month, the pituitary gland in the base of the brain produces a hormone called ‘follicle stimulating hormone (FSH).  FSH stimulates a fluid-like sac surrounding the egg to grow into a follicle about 2cm wide.

When the egg is ready, about two weeks before your period, the pituitary gland produces another hormone, the ‘luteinising hormone’ (LH).  This hormone prompts the follicle to release one egg into the fallopian tube.  This process is known as ‘Ovulation’.

At this same time, the ovaries are releasing other hormones (oestrogen and progesterone) that thicken the lining of the uterus and prepare it for pregnancy.

If the egg meets sperm and conception occurs the egg is now referred to as an embryo.  The embryo implants into the lining of the uterus and produces a hormone called ‘human chorionic gonadotrophin (hCG) which tells your body you are pregnant. If conception doesn’t occur, the levels of oestrogen and progesterone decline and the lining of the uterus comes away as your period.

What does ovulation mean, and how do you know if you’re ovulating?

Knowing your monthly cycle will help you determine when you’re ovulating.

To calculate your monthly cycle, you would count from the first day of your period, up to the first day of your next period.

So, the day you get your period is Day 1 of your cycle, and then you would count every day until your period starts again. 

A typical menstrual cycle is 28-days. But this can vary in women.  Some women can have a 27-day cycle, others a 35-day cycle.  It’s perfectly normal for a cycle to be anything between 21 to 35 days.  That’s why it’s essential we treat each patient individually.

What happens During Ovulation?

Women are born with all the eggs they will ever have.  They are stored in the ovaries.  Ovulation occurs each month with the release of an egg from one of the ovaries.  Occasionally, more than one egg is released.

The egg begins to travel slowly down the fallopian tube.  If there is active sperm, the egg may become fertilised.

If the egg is not fertilised, it passes out of the body, or is resorbed.

Fertility Calculator

You are the most fertile 14 days from the end of your monthly cycle.

To calculate when your are most fertile, based on a 28 day cycle:

  • Day 1 of your period is day 1 of the cycle.
  • Day 28 is when your next period starts
  • The day when the egg is released is Day 14
  • The day to have intercourse is Day 14.

If the cycle is 35 days, then the fertile day is always 14 days before the end, so it would be day 19.

If it were a 30-day cycle, then the fertile day would be day 16. 

You can use a fertility calendar to help track your fertile days.

Ovulation Signs

There are a couple of other signs of ovulation you might experience.

Women often recognise that their mucus changes from a thicker discharge with a white or yellow colouring, to a clear, thinner mucus just before ovulation.  This clear, slippery mucus makes it easier for sperm to travel through to the cervix.

A lot of women feel a little bit of tenderness at the time of ovulation. Others can experience a “twinge” in their lower stomach. 

These changes can be a sign that you’re ovulating. 

Infrequent Periods / Infrequent Ovulation

If you are not ovulating regularly, you will have reduced opportunities to conceive, or if your periods are irregular, it may be difficult to calculate your fertile window.

There can be many reasons for infrequent or occasional periods or no periods at all.  Some causes are natural, while others are medical conditions that need to be treated.

When And How Often To Have Sex When Trying To Get Pregnant

Eggs and sperm have about a 24-hour crossover period.  You’re most likely to get pregnant if you have sexual intercourse a few days before, the day of, ovulation, and up until the day after ovulation.

Using the 28-day cycle example, the fertile day is day 14.  To get pregnant, the best times to have sex would be on days 12, 14 and 16.


Read More:

Stopping contraception – how long until things go back to ‘normal’?

Problems getting pregnant?

Ask your GP for a referral to Dr Michael Flynn - print this Referral Request and hand it to your GP.

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