Information on how conception (getting pregnant) happens, how to find your most fertile time and confirming you're pregnant.
To become pregnant (conceive) an egg must be fertilised by a sperm and become implanted in the uterus (womb).
Conception is a process that begins with fertilisation and ends with successful implantation of a fertilised egg in the uterus.
An egg is released from one of your ovaries during each menstrual cycle. This is called ovulation. You can get pregnant only for a few days around the time of ovulation. This is known as the fertile time.
The egg travels down one of your fallopian tubes towards your uterus. The egg lives for up to 24 hours only. Each month, the lining of your uterus thickens to prepare for a possible pregnancy.
Fertilisation and implantation
During sex, when your partner ejaculates (comes), millions of sperm enter the vagina. Many of these will swim up through your cervix (the entrance to your uterus) into the uterus and the fallopian tubes.
Although millions of sperm may be released, only one sperm will enter the egg. This is known as fertilisation. The fertilised egg travels down the fallopian tube over a number of days and eventually reaches the uterus, where it attaches itself to the thick nutritious lining.
Implantation has now taken place and conception is complete. The time from ovulation to implantation is usually around ten days.
For more information see our guide to understanding reproduction.
Getting to know your menstrual cycle
The menstrual cycle is the process during which an egg develops and is released from an ovary, and the lining of the uterus (womb) thickens in preparation for a possible pregnancy.
If you don't become pregnant, the lining of the uterus is shed as your period. These events are caused by hormones – chemical messengers which travel around the body in the blood stream.
How long does the cycle take?
The number of days in the menstrual cycle is calculated from the first day of a period to the day before the start of the next period.
The average length of the menstrual cycle is around 28 days, although many women have longer or shorter cycles and this is normal.
What happens during the menstrual cycle?
The first day of the period is known as day one of the cycle. When you have your period, about 20 eggs start to develop in the ovary.
The hormone estrogen causes the lining of the uterus (endometrium) to start to thicken in preparation for a fertilised egg. It also causes the cervical mucus (noticed as vaginal secretions) to become clearer, wetter and more stretchy, allowing sperm to reach an egg more easily.
Regardless of how long or short your cycle is, ovulation (egg release from an ovary) will usually happen around 10–16 days before the start of your next period. However, the time from the first day of the period to ovulation can vary between women.
Occasionally, more than one egg is released (if this happens it will occur within 24 hours of the first egg being released). If more than one egg is fertilised it can lead to a multiple pregnancy, such as twins.
Ovulation triggers the production of a second hormone, progesterone. This prepares the lining of the uterus even further, ensuring that it is spongy, thick and full of nutrients so that a fertilised egg can implant into it.
After ovulation the cervical mucus goes back to being thick and sticky. If the egg isn't fertilised it will be reabsorbed naturally by the body, the level of hormones falls, and this menstrual cycle comes to an end.
The cycle then begins again. The lining of the uterus breaks down and leaves the body through the vagina as a period, also called menstruation.
Cervical mucus changes
You can learn to identify your fertile time by noting the changes in your cervical mucus. At the beginning and end of your cycle cervical mucus is creamy, sticky and thick. As your body prepares for ovulation, and around ovulation, it becomes wetter, clearer, slippery and stretchy like raw egg white. You may be able to stretch an unbroken thread of it between your thumb and forefinger.
Some women, however, notice only a small amount of milky wetness which lasts for a few days and then dries up after ovulation. Keeping track of your cervical mucus can give you a clear picture of your body’s pattern and should make it easier for you to learn to identify the fertile times of your cycle.
Some women keep track of their basal body temperature (your temperature when you wake after at least three hours sleep). This may let you know if you've ovulated, as your basal temperature rises after ovulation, but as the rise occurs after you've ovulated, it isn't useful in planning a pregnancy.
Using a kit
Ovulation kits are available to buy at pharmacies, and can tell you when ovulation is likely to occur. Using a kit involves testing your urine on specific days in your cycle to detect the luteinising hormone which surges 24–36 hours before ovulation.
Getting to know your body and your menstrual cycle, and monitoring your cervical mucus, is a more effective way to find your fertile time.
The earliest and most reliable sign of pregnancy, if you have a regular menstrual cycle, is a missed period. Sometimes women who are pregnant have a shorter or lighter period than normal.
You can carry out a pregnancy test from the first day of a missed period. Tests carried out earlier than this are not always accurate. If you don’t have regular periods, the earliest time you can do a test is 21 days from the last time you had unprotected sex. For some women the test doesn't show positive until their period is at least a week late.
Pregnancy tests look for the pregnancy hormone human chorionic gonadotrophin (hCG), which is found in the urine of pregnant women. A positive test is almost always correct. But women can sometimes get a negative result if the test is carried out too early or not correctly, even though they may be pregnant.
This website can only give you general information. Our information about planning a pregnancy is based on evidence-guided research from the Royal College of Obstetricians and Gynaecologists and the National Institute for Health and Care Excellence.
Contact your doctor, practice nurse or a contraception clinic if you're worried or unsure about anything.