When to have sex, and ten more fascinating facts about conception

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Image: Getty Images
Image: Getty Images

When you’re trying for a baby it can seem like the simplest thing in the world… or the hardest. And old wives tales and movie-fueled ideas are rife when talking fertility.   

Here, Julia Boltt looks at the medical facts that may change your approach to conceiving. 

1. The odds are…

Although everyone knows a story of someone who fell pregnant "by accident", the odds are actually not nearly as high as you’d think. At 20 years old, it takes on average four months to conceive, by the time you’re 30, it will take up to eight months and after 35, it can take on average up to 18 months to conceive.

So a woman aged 20 has a 25% chance of conceiving every month, whereas a woman aged 40 has less than a 5% chance of conceiving monthly. 

2. Weight matters

If you’re seriously underweight, you won’t be able to conceive – a minimum of 22% body fat is required for ovulation. On the other hand, being overweight or obese can also hamper your chances of ovulating. 


What has your fertility journey been like so far? Share your story or comments with us, and we could publish your letter. Anonymous contributions are welcome.


3. There’s not just one day    

Sperm can live in the woman’s reproductive tract for up to three days after sex, so waiting until the day you ovulate to have sex isn’t always the best strategy.

According to scientists, having sex one to two days before you ovulate gives you the best chance of conceiving.

4. Timing is everything

If you’re not sure when you’re ovulating, try using an ovulation calculator.

They’re easily available at your local pharmacy, and "knowing when you ovulate and the timing of your fertile windows, can increase your chances of conception or diagnose ovulatory problems early," recommends gynaecologist and fertility expert Dr Gerhard Hanekom.  

5. Birth control can affect your chances   

The pill does not have any delay in the return of fertility.

However, other contraceptive methods like the injectable progestogen (Petogen, Nur-Isterate) may cause a delay in return of fertility of six to nine months, says Dr Jana Rossouw, a specialist in gynaecology and obstetrics at Tygerberg Hospital in Cape Town. 

Also see: What is the ‘right’ age to have a child?

6. Egg life

Did you know that the egg only lives for about 12 to 24 hours after it’s released from the ovary? Once the egg cell has matured and is released from the ovary, it goes into the fallopian tube, where it lives for 12 to 24 hours.

If it isn’t fertilised, it moves through the uterus and disintegrates. Your hormone levels go back to normal, your body sheds the thick lining of your uterus and your period will start.   

7. Super sperm

After ejaculation, sperm is found within the cervix within 90 seconds and sperm that is motile (moves actively) should reach the fallopian tube within five minutes.

There’s no reason to lie with your legs in the air after sex because position doesn’t matter. 

8. Pink or blue

At the very moment of conception, the baby’s sex is determined, along with its genetic profile. Although there are plenty of old wives’ tales about how you can influence the gender of your baby, none of them are true – you have a 50% chance either way.

It’s actually the sperm that determine the sex of your baby. The egg a woman ovulates carries an X chromosome, while sperm carry either an X or a Y chromosome. If the sperm with an X chromosome fertilises the egg (XX), the embryo will develop into a girl, while an XY embryo, fertilised by sperm with a Y chromosome, will develop into a boy. 

Also see: WATCH: Could stressing about getting pregnant be the reason you’re not getting pregnant?

9. Seal the deal

Once your egg is fertilised, it seals itself off to exclude any other sperm. The fertilised egg stays in the fallopian tubes for about three days before moving to the uterus, where it will attach to the lining of the uterus (this is called implantation).

Some women notice some spotting for one to two days around the time of implantation. 

10. Nice to meet you

Once the sperm enters the egg and fertilisation takes place, the genes or chromosomes from both of you combine to create a cell. Within 24 hours of fertilisation, it starts dividing fast into many cells, becoming a blastocyst.

Within three weeks, the cells start to grow as clumps, and the baby’s first nerve cells have already formed. 

11. Double the fun

Older women are more likely to release two eggs at a time (called hyperovulation), so twins are more likely for moms conceiving after the age of 35.

Having identical twins is not genetic – it’s a random event that happens by chance, but having fraternal twins (two fertilised eggs in one pregnancy) can run in families. 

This article was originally published in Your Pregnancy Magazine's February/March 2018 issue. 

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