Written by:

Dr Matt Prior


Dr Matt Prior is a specialist in Reproductive Medicine and Surgery in the North of England. His areas of interest include assisted reproduction, recurrent miscarriage and patient engagement. Matt is a member of the Royal College of Obstetricians and Gynaecologists (RCOG) and is a former member of the RCOG Council.

Understanding ovulation

In this article:

  • What is ovulation?
  • Menstruation basics
  • When do you ovulate? – The signs of ovulation
  • The difference between ovulation and fertile days.
  • Ovulation sticks
  • When am I most fertile?
  • How do Ovulation Calculators work?
  • How can I increase my chances of getting pregnant?
  • Main points:

Understanding ovulation

What is ovulation?

Quite simply, ovulation is the release of an egg from the ovary. Girls are born with all of the eggs they will ever have. Many die away in childhood before periods even start. Each month, several eggs begin to mature in fluid filled follicles which grow in size. However, normally only one, but sometimes two, make it as far as being released to allow the possibility of conception.

Menstruation basics

A normal menstrual cycle lasts between 21 and 35 days, although most women tend to have a period once a month. The menstrual cycle is under the control of four hormones. Follicle stimulating hormone (FSH) and luteinizing hormone (LH) are produced by the pituitary gland in the brain. FSH and LH act on small follicles which contain immature eggs, making them grow. As the follicles grow, they start to produce the hormone oestrogen. Oestrogen feeds back to the pituitary to stop FSH and LH so that only one follicle becomes dominant. Oestrogen continues to rise and thickens the lining of the womb to get it ready to accept a pregnancy. When oestrogen rises above a certain level, the pituitary produces a sudden surge of LH – this triggers the ovary to release the egg. The now empty follicle is called a corpus luteum, and produces the hormone progesterone. This maintains the lining of the womb, so if the egg is fertilised and implants, a pregnancy will be supported. If fertilisation does not occur, eventually progesterone falls, resulting in a period.

When do you ovulate? – The signs of ovulation

Some women may be able to identify when they ovulate by monitoring signs such as change of body temperature, change in cervical mucus, or experiencing lower abdominal pain. Body temperature remains the same through most of the cycle but dips just before ovulation and then sharply rises. Around ovulation, oestrogen is the dominant hormone, which makes cervical mucus stretchy and clear to help sperm swim towards the egg. Some women may feel mild lower abdominal pain due to ovulation and follicular fluid causing irritation in the pelvis.

The difference between ovulation and fertile days.

Signs of ovulation are not that accurate, so correctly identifying when ovulation occurs is difficult. In fact many women can’t tell. This is why the rhythm method of contraception, where a woman tracks her cycle, is notoriously ineffective. Furthermore, even when trying to conceive, knowing when you ovulate is not that important. On average sperm live for 48 hours, but this can be as long as a week, so providing couples have regular intercourse around the fertile period, there is a good chance sperm will be around when the egg is released.

Ovulation sticks

These strips test for luteinising hormone (LH) in the urine attempting to identify the LH surge just before ovulation. Some couples use them to identify their fertile window. However, I advise caution, as they aren’t always that accurate. Firstly, the quality of some of these sticks is questionable, especially if bought over the internet. Secondly, studies have shown that rising levels of urinary LH can be delayed compared with blood LH. So if couples wait until the stick goes positive to indicate ovulation, it may actually be too late, and they would have missed ovulation. Thirdly, studies have shown trying to identify ovulation, either through signs or ovulation sticks, can result in stress and added pressure on the couple, taking the fun out of trying to conceive.

When am I most fertile?

Women usually ovulate about two weeks before their period starts. So, with a 28 day cycle, ovulation occurs around day 14. With a 34 day cycle, ovulation is around day 20.

Unless fertilised, an egg only lives for around 12 – 24 hours after it has been released. Nonetheless, sperm can survive for longer, so women are fertile for the few days before and after when ovulation is predicted to happen.

How do Ovulation Calculators work?

Ovulation calculators, sometimes called period calculators, use simple maths to predict when ovulation will occur based on the usual cycle length. For example, a woman with a regular 28 cycle will usually ovulate on day 14. A woman with a 34 day cycle will usually ovulate on day 20.

How can I increase my chances of getting pregnant?

Most women don’t follow the textbooks and can ovulate a couple of days before or after ovulation is predicted. So the advice is regular intercourse every two to three days around the fertile window. They should also follow general advice on staying healthy.

Main points:

  • Ovulation is when an egg is released from an ovary
  • Each month, one egg (or sometimes two) is released to allow for the possibility of conception.
  • A menstrual cycle normally lasts between 21 and 35 days and is controlled by four hormones: follicle stimulating hormone and luteinizing hormone (which are produced by the pituitary gland), oestrogen, and progesterone.
  • The signs of ovulation include changes in body temperature and cervical mucus as well as lower abdominal pain, but correctly identifying the signs of ovulation can be difficult.
  • As sperm can live for 48 hours, or even up to a week, in the female body, pinpointing ovulation isn’t necessarily that important for a couple trying to conceive. This means that a woman is fertile for a few days before and after ovulation.
  • Strip tests for luteinising hormone may help predict ovulation, but these are not always accurate and aren’t recommended.
  • Ovulation occurs two weeks before a woman’s period starts.
  • Because women can ovulate a couple of days before or after ovulation is predicted to start, the best advice is to have regular intercourse around the fertile window.