Here the egg is shown surrounded by sperm. Although only one sperm will fertilize the egg, several hundred are thought to be necessary to break down its defensive layers and enable fertilization to take place.
You are likely to have ovulated and your unfertilized egg now begins its journey. Once it has been released by the ovary, the egg is swept up by one of your fallopian tubes and, moving in the direction of the uterus, comes to rest in the widest portion of the tube, awaiting fertilization.
It is no exaggeration to say that for each sperm released the chance of even reaching the site of fertilization is in the order of one in a million. Around 300 sperm reach the tube but only one will fertilize the egg. Once the sperm has penetrated, it triggers a reaction that makes the surface impenetrable. Each sperm and egg contain 23 chromosomes, half of the total genetic material required. The egg will always contain an X chromosome but the sperm will carry either an X or Y chromosome and therefore determines the sex of the embryo. The sperm and egg chromosomes combine forming the "zygote" and fertilization is complete.
The hormones responsible for the production of sperm are released every 60 to 90 minutes. So a man is constantly producing sperm cells.
In theory, this means that a male is always fertile, but it takes sperm a 72-day period to fully develop. So leading an unhealthy lifestyle during that time will impinge on the quality. For this reason, if you're trying to conceive, your partner should embark on a healthy lifestyle for three months to produce good sperm.
If you want to become a dad, there are many reasons why you should ensure you're in good shape, not least to support your partner as she prepares for pregnancy. However, while a couch potato lifestyle isn't desirable for men who want to conceive, it seems that pulling out all the stops at the gym might not be the best course of action either.
Researchers asked a group of fit young men to exercise intensively four times a week for two weeks. Afterward, their semen was tested and found to contain fewer sperm and lower levels of the hormones essential for conception. These hormonal changes were temporary and returned to near normal within a few days of the men resuming previous levels of activity.
The concern is that recovery might not be so fast among older men, or in those who have poor sperm counts and/or low hormone levels. So stay in shape but don't overdo it.
Excerpted from Pregnancy Day by Day.
Copyright ©2009 Dorling Kindersley Limited.
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