Sperm are tiny cells responsible for creating life. Males produce millions of sperm per day, but it takes just one to fertilize an egg to cause pregnancy.
When ejaculated, sperm will swim up the cervix and through the uterus and fallopian tubes to reach an egg. If the timing is right, the fertilised egg can start a new life (Fig. 1)
Ejaculation
During sexual intercourse and ejaculation, millions of sperm are released into the female reproductive tract. Most of them are dead (sperm don’t live long) and the few that are still alive will be judged by their ability to move up through the cervix and uterus to the egg and fertilize it. This ability to move, known as motility, and the shape of a typical sperm (known as morphology) determine fertility.
After a man’s semen is discharged from his epididymis, it must make its way through a tube called the vas deferens and into the fallopian tubes. It must then swim through a thick fluid that lines the cervix, uterus and fallopian tubes. This fluid is called cervical mucus and contains a protein that acts as an attractant for sperm.
Sperm have a tadpole shape, with a bulbous “head” and a narrow tail. They are too small to see with the naked eye and measure only about 0.05 mm in length. The chromosomes carried on a sperm determine genetic characteristics and sex.
In order to reach and fertilize an egg, sperm must be able to swim effortlessly through the female cervix, uterus and Fallopian tubes. This artful movement is known as motility. Pregnancy is possible with less than 40% of sperm in an ejaculate moving, but it takes a high percentage to be considered fertilized.
Intercourse
Men release up to 100 million sperm each time they ejaculate. However, only one sperm will make it to the egg to fertilize it and create a baby. And that’s because the sperm must survive a long and tough journey from the testicles to the woman’s uterus and Fallopian tubes.
The sperm must also swim smoothly to overcome obstacles like the cervix, uterus and Fallopian tubes in order to reach the egg. In addition, a healthy sperm has an oval head and a long tail which help it to compete against other sperm and to swim through the female reproductive tract.
While a man’s semen volume naturally decreases with age, the number of sperm that reaches the egg is still enough to allow for pregnancy in most cases. Low sperm count and motility problems are common obstacles to fertility, but they’re not impossible to resolve.
Regular unprotected sex is the best way to increase chances of conceiving. In fact, more than 8 out of 10 couples who have sex on a daily basis are able to get pregnant within a year. However, it’s important to remember that pregnancy is a team effort, meaning both the mother’s egg and the father’s sperm must be healthy to succeed. To improve the odds of a successful conception, women should eat a balanced diet and avoid taking certain medications (like anti-androgens, calcium channel blockers and tricyclic antidepressants), using non-fertility-friendly lubricants during sex, smoking and exposure to toxic chemicals at work and home.
Fertilization
Sperm can survive on a dry surface for about an hour but when they enter the female reproductive tract they can live for up to 72 hours. During this time, they need to find and fertilize an egg. However, only one out of every hundred sperm ever makes it to the egg.
Sperm must first swim through a woman’s vagina, fallopian tube and uterus in order to reach the egg. As they do so, the fast-swimming sperm are battling against a series of natural barriers.
The first hurdle is the cervix, which is a tight and narrow canal. Once sperm pass through this barrier, they begin to head toward the egg in the fallopian tube.
A man should release about 15 million sperm per milliliter of semen, which is around two teaspoons of fluid. Anything less than this amount may signal a low sperm count, which can make it harder to get pregnant.
Once sperm locate an egg, they must break through the tough outer shell of the egg (called the zona pellucida) in order to fertilize it. This is a difficult task because only one out of about 300,000 sperm will be able to penetrate the outer layer of the egg and score a direct hit. If the sperm does not make it through this barrier, the egg will be re-absorbed by the body and that month’s window of opportunity for conception closes.
Ovulation
The chances of getting pregnant increase when a woman has sex during the days leading up to ovulation. Ovulation is when the ovary releases an egg that can be fertilised. This usually happens 12 to 16 days before a woman’s period starts. During this time sperm have a higher chance of reaching the egg and getting it fertilised. It’s important for a couple to be together during this window of fertility to maximise their chances of pregnancy.
While it is the sperm’s ability to fertilize an egg that matters, there are many things that can affect the success of this process. These factors include sperm count, motility and morphology. Getting an accurate reading of these characteristics is crucial to ensuring that a man’s semen is in good condition.
While there are many tips that can help a man to produce healthier, more viable sperm, one of the most critical is to avoid smoking and other recreational drugs. Men should also make sure that they are consuming enough of certain nutrients, including folic acid, zinc and vitamin C. Lastly, men should exercise regularly and maintain a healthy weight. Doing so will help them produce more sperm and improve the health of their semen.
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