You are 2 weeks and 1 day

Your newly released egg survives only 24 hours, but hopefully it will meet sperm and be fertilized in that time.

265 days until your due date

You've probably ovulated, and your unfertilized egg is starting its journey. After leaving the ovary, it's swept into a fallopian tube and moves toward the uterus, resting in the widest part of the tube to wait for fertilization.

Each sperm's chance of even reaching the egg is about one in a million. Around 300 sperm reach the tube, but only one fertilizes the egg. Once it gets in, it triggers a reaction that makes the egg's surface impossible for other sperm to get through.

Each sperm and egg carries 23 chromosomes, half the genetic material needed. The egg always carries an X chromosome, while the sperm carries either an X or a Y, so the sperm decides the baby's sex. When the sperm and egg chromosomes combine to form a zygote, fertilization is complete.

As a matter of fact

Men are always making sperm

The hormones that drive sperm production are released every 60–90 minutes, so a man is constantly making sperm.

In theory, that means men are always fertile. But sperm take 72 days to fully develop, so an unhealthy lifestyle during that time affects their quality. If you're trying to conceive, your partner should live healthily for three months to produce good sperm.

Focus on

Dads: Fit but not fertile?

Being in good shape is a good idea for a dad-to-be, not least to support his partner. But while being a couch potato isn't ideal, going all out at the gym may not help either.

In one study, fit young men exercised intensively four times a week for two weeks. Afterward, their semen had fewer sperm and lower levels of hormones essential for conception. These changes were temporary and returned to near normal within a few days of going back to their usual activity.

The worry is that recovery may be slower in older men or those with low sperm counts or hormone levels. So stay in shape, but don't overdo it.

Explainer

One sperm wins

A few hundred sperm survive the journey and reach the egg in the fallopian tube, but just one fertilizes it.

This is general information based on NHS guidance, not medical advice, and every pregnancy is different. Talk to your midwife or GP about anything that worries you. If your baby's movements slow down or change, or you have bleeding, severe pain or leaking fluid, call your maternity unit straight away. In an emergency, call 999.