How you conceive

Couple looking at a positive pregnancy test


Inside the woman's body: how an egg is hatched

For women, the possibility of pregnancy begins in the ovaries. These are the two small, oval organs attached to either side of your uterus (womb). The ovaries are packed with eggs, which are made before you are even born. Every baby girl is born with 1 to 2 million eggs in her ovaries (Rosenblatt 2007). Many eggs begin dying off almost immediately and the rest steadily decrease in number as you get older. You'll probably release about 400 eggs during your fertile years (Rosenblatt 2007), between your first period and the menopause. In countries such as the UK, the average age of menopause is about 52 (CKS 2008).

During each menstrual cycle, sometime after your period, one to three eggs start to reach maturity in one of your ovaries. The ripest egg is then released, a process known as ovulation. The egg is quickly sucked up by the tulip-shaped opening of the nearest fallopian tube. There are two fallopian tubes, each about 10cm in length, which lead from the ovaries to the uterus.

Ovulation is usually about 12 to 14 days before your next period (Fehring et al 2006). The exact time of ovulation depends on the length of your cycle. Several different hormones work together to control the length of your cycle, when your eggs ripen and the timing of ovulation. You can read more about these hormones in our article on the menstrual cycle.

The average egg lives for up to 24 hours after release (NCCWCH 2013:64). It needs to be fertilised within this time by a sperm for a baby to be conceived. If your egg meets up with a healthy sperm on its way to the uterus, the process of creating a new life begins. If not, the egg ends its journey at the uterus and disintegrates.

If you have not conceived, the ovary stops making oestrogen and progesterone. These are the two hormones that would help maintain a pregnancy. When the levels of these hormones drop, the thickened lining of your uterus is shed during your period. The remains of the unfertilised egg are shed at the same time.

Inside the man's body: how sperm are made

Women's bodies mature a single egg each month. Men's bodies, however, are almost constantly at work, producing millions of microscopic sperm. The sole purpose of each sperm is to swim towards and penetrate an egg.

From start to finish it takes two to three months to create a new sperm cell (NCCWCH 2013: 82, Rebar 2008). The average sperm lives only a few weeks in a man's body, and at least 40 million are set free with each ejaculation. It means that men have to make sperm on a regular basis throughout their adult lives (Rebar 2008).

The same hormones that control ovulation in women stimulate the release of testosterone in men. Testosterone is the hormone responsible for producing sperm. Sperm production starts in the testicles, the two glands contained in the scrotal sac beneath the penis. The testicles hang outside the body because they are sensitive to temperature. To produce healthy sperm efficiently they have to stay at a balmy 34 degrees C. This is about four degrees cooler than normal body temperature (Rebar 2008). Once the sperm is created, it's stored in each testicle in the epididymis, a 6-metre long coiled tube. Just before ejaculation the sperm is scooped up and mixed with semen (Lui 2007).

Despite the millions of sperm that are produced and released in each ejaculation, only one can fertilise each egg. The gender of your baby depends on which type of sperm burrows into the egg first. Sperm with a Y chromosome will make a boy baby, and sperm with an X chromosome will make a girl. There are plenty of myths about how to conceive a boy or girl. Some are backed by a bit of scientific evidence, but on the whole, a child's sex is determined randomly.

What happens while you're having sex

In addition to all the fun, your bodies are building up tension that you hope will end in orgasm. Having an orgasm also has an important biological function. In men, orgasm propels sperm-rich semen into the vagina and up towards the cervix at roughly 10 miles per hour. The force of ejaculation gives the sperm a good head start on their way to the egg. A woman doesn't need to orgasm for conception to happen. Gentle uterine contractions can help the sperm along, but these happen without you having an orgasm (Levin 2002).

Many couples wonder if a particular sex position is best for conceiving. No one knows for sure. The most important thing about sex is that you're both having a good time and you're doing it often enough. For you to conceive, live sperm needs to be in your reproductive tract during ovulation.

Not all women ovulate during the middle of their cycle or at the same time in their cycle every month (Fehring et al 2006). To improve your chances of conception, aim to have sex every other day or so throughout your cycle (NCCWCH 2013:69).

While you relax, the sperm's job is just beginning

At this point you can't do much except cross your fingers and hope that you conceive. While you and your partner enjoy a relaxing post-sex cuddle, a lot is going on inside your body. Those millions of sperm have begun their quest to find your egg, and it's not an easy journey. The first obstacle may be your cervical mucus, which can seem like an impenetrable net on your non-fertile days. When you're most fertile, however, it miraculously loosens up so the strongest swimmers can get through.

The sperm that survive still have a long road ahead. In all they need to travel about 18cm from the cervix through the uterus to the fallopian tubes. When you consider that they travel at a rate of roughly 2.5cm every 15 minutes, that's quite a trip. The fastest swimmers may find the egg in as little as 45 minutes. It can take the slowest up to 12 hours. If the sperm don't find an egg in the fallopian tubes at the time of intercourse, they can survive inside you for up to seven days (NCCWCH 2013:64). This means that if you ovulate within this time window you could still conceive.

The mortality rate for sperm is very high and only a few dozen ever make it to the egg. The rest get trapped, lost (perhaps heading up the wrong fallopian tube) or die along the way. For the lucky few that get near the egg, the race isn't over. Each one has to work frantically to penetrate the egg's outer shell and get inside before the others. The egg needs to be fertilised within 24 hours of its release. When the hardiest sperm of the bunch makes it through, the egg changes instantaneously to prevent any others getting in. It's like a protective shield that clamps down over the egg at the exact moment the first sperm is safely inside.

Now a new life is born ...



It will be a couple of weeks until you miss a period and suspect that you're going to have a baby. Once you have missed your period or noticed one of the other signs of pregnancy, a home pregnancy test will confirm it. If you've got a little one on the way, congratulations, and welcome to the start of another incredible journey.

Talk to others who are hoping to get pregnant by joining our Actively trying group.

Think you're newly pregnant? Go to our four weeks pregnant page to find out more.

Last reviewed: April 2013


CKS. 2008. Menopause. Clinical Knowledge Summaries, Clinical topic. [Accessed October 2010]


Levin RJ. 2002. The physiology of sexual arousal in the human female: a recreational and procreational synthesis. Arch Sex Behav 31(5):405-11

Lui PD. 2007. Biology of the male reproductive system. The Merck Manuals [Accessed October 2010]


Rebar RW. 2008. Sperm disorders. The Merck Manuals [Accessed October 2010]

Rosenblatt PL. 2007. Biology of the female reproductive system. The Merck Manuals [Accessed October 2010]

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Very informative
Hello my names is Deborah, am from italy i want to share my happiness with everybody and letting them know the secret of my happiness, the secret of my happiness is through doctor marcus the great herbal doctor, who help to stop my miscarriage and made me a mother after been passing through pains....., but mr marcus put an end to this situation, now am a mother and am living happily with my husband and my new baby which i love so much, am using this medium to thank mr marcus for the great work he did for me with his herbs, Thanks be unto him for helping me, my sisters out there i wan you to thank mr marcus for the great work he did for me and my husband, ....if you need his help also you can contact him through his email via; .after which he will send you his fertility herbs
I made a very bad choice to have sex 2 weeks after my last period(i was definitely ovulating) we used a condom but I'm almost 100% certain some spermicides got in me... Now having cramps but they don't feel like period cramps and I'm 5 days late, should I take a test??
hi mame is viki,am 31yrs old frm Malaysia.i have been married since 2013 june,almost gona be trying to conceive since we are married.unsucessful iui in once, i got discharge problem n my hubby got vry low sperm counting... pls advice

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