What is ovulation?
Ovulation is when one or more eggs are released from one of your ovaries. This happens towards the end of you're fertile window between your periods.
Each month, between 15 and 20 eggs mature inside your ovaries. The ripest egg is released and swept into one of your fallopian tubes. Your fallopian tubes connect your ovaries to your uterus (womb).
Your ovaries do not necessarily take it in turns to release an egg. It happens quite randomly.
To become pregnant naturally, one of your eggs and your partner's sperm have to meet in your fallopian tube. Your egg survives no more than 24 hours after you've ovulated. So the meeting of egg and sperm has to occur within this time.
However, sperm can survive for up to seven days. They'll happily live in your vagina, uterus or fallopian tubes for this length of time.
This means that you don't have to time intercourse to the exact moment you ovulate to get pregnant. You actually have a fertile window of about six days.
This window includes the five days before and the day of ovulation itself. So, if you have intercourse at some time during your fertile window, your freshly ovulated egg could meet live, healthy sperm and be fertilised.
How can I tell when I'm most fertile?
The simplest way to work out your most fertile time is to note down the length of your menstrual cycle. Then look out for signs of hormonal and physical changes in your body.
You'll start to notice signs that you're fertile about five days before you ovulate. Ovulation ideally occurs between 12 and 14 days before your period starts. This is an average, so it could be a few of days earlier or later if you have a regular cycle.
For example, say you have a regular 28-day menstrual cycle. Count the first day of your period as day one. Your fertile window is likely to be around days 12 to 17.
However, a lot of women have an irregular cycle. If your cycle is irregular, ovulation may occur a week earlier or later from one month to the next.
Working out your fertile window using your cycle dates alone is an inexact science. This is why learning to spot your body's fertile signs can help. These include:
Changes in cervical mucus
Cervical mucus is the discharge that you see in your knickers or on toilet tissue when you go for a wee.
Changes in your cervical mucus can signal when you are fertile. After your period has finished, your cervical mucus gradually increases in amount and changes in texture.
This change reflects the rising levels of the hormone oestrogen in your body. It also shows you are close to ovulating.
You are most fertile when your mucus becomes clear, slippery and stretchy. It's a bit like raw egg white. This fertile mucus speeds the sperm on its way up through your uterus. It nourishes and protects the sperm as it travels towards your fallopian tubes to meet your egg.
An ache in your belly
About a fifth of women can actually feel something happening in their ovaries around ovulation. This can range from mild achiness to twinges of pain. Some women feel ovulation as one-sided backache or a tender area. The condition, called mittelschmerz, may last anywhere from a few minutes to a few days.
If you notice these sensations at roughly the same time each month, check your cervical mucus. Ovulatory pain can be a useful guide to when you're fertile.
You may notice a peak in sexual desire at this time.
Some women use ovulation predictor kits to pinpoint their most fertile time. Most of these kits test for the peak of luteinising hormone, or LH, which is the actual trigger for egg release. You could use these to find out when you are most fertile during your cycle
This is a method where you take your basal temperature and record it on a chart to help pinpoint your exact ovulation day. When done correctly this is very accurate.