During ejaculation, sperm are released into the female reproductive tract, usually from an erect penis. While sperm make up only a small part of semen, around 1–5% of its volume, they immediately begin their journey through:
- The vagina
- The cervix
- The uterine cavity
- The Fallopian tubes, where they hope to encounter an egg.
The first minutes, in the vagina
Semen lands at the top of the vagina, close to the cervix. It first thickens into a gel, then turns liquid again within about 15 to 30 minutes. The vagina is naturally acidic, which is hostile to sperm, but semen buffers that acidity for a short time. The sperm that do not leave the vagina quickly do not survive there for long.
The cervix: gatekeeper and reservoir
For most of your cycle, the mucus in your cervix is thick and acts as a barrier. Around ovulation it becomes clear, thin and stretchy, like raw egg white. Sperm can then swim through it, and the most mobile ones get through first.
The cervix also stores sperm in its folds and releases them gradually over the following hours and days. This is why sex a few days before ovulation can still lead to pregnancy.
Through the uterus and into the tubes
Sperm swim, but they are also helped along by gentle contractions of the uterus. Your immune cells clear many of them on the way. Those that remain then have to pass the narrow junction between the uterus and one of the tubes, which lets only a few through. Some reach the tubes within minutes, others hours later.
Do all sperm reach the egg?
No. Most sperm do not reach the Fallopian tubes and are naturally eliminated within the female reproductive tract. Along their journey, the surviving sperm undergo final maturation, a process known as capacitation, which allows them to gain their full fertilizing potential.
Only a small number of sperm will make it to the egg, and usually, only one successfully fertilizes it. Out of tens of millions in one ejaculation, only a few hundred reach the tubes. Once one sperm gets through the egg’s outer layer, the egg changes to block all the others.
How long do sperm live inside you?
In fertile cervical mucus, sperm can survive up to five days. The egg, by contrast, lives only about 12 to 24 hours after ovulation. Your fertile window is therefore the five days before ovulation plus the day of ovulation, and your chances are highest with sex in the two or three days before you ovulate.
What happens to the sperm that don’t make it?
Some flow out of the vagina, which is normal and doesn’t lower your chances. The rest are broken down and cleared by your body within a few days. This is harmless and goes unnoticed.
Can you help sperm along?
Not really. Lying down or raising your legs after sex has not been shown to help, though a few minutes lying down does no harm. Whether a female orgasm helps sperm transport is unclear; the evidence is weak. Some common lubricants can slow sperm down, so if you need one, choose a fertility-friendly lubricant. Sex every two to three days through your cycle keeps fresh sperm waiting without having to time it perfectly.
When to see a doctor
- No pregnancy after 12 months of regular sex without contraception, or after 6 months if you are 35 or older.
- Very irregular or absent periods, which can signal an ovulation problem.
- Pain during sex, or unusual discharge with itching or a bad smell.
