3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> Fertilization Of The Egg

Fertilization Of The Egg

When your partner's sperm meets your egg and the two fuse together at the moment of fertilization, a miraculous event occurs: the beginning of a brand-new life. From this point onwards, the fertilized egg assumes a life of its own, growing and developing at an amazing rate until, some 9 months later, a fully formed, unique, complex human being emerges into the world.

The journey of the egg

Once the egg has been released from one of your ovaries (ovulation), it is drawn into the Fallopian tube. Slight contractions of the tube help to move the egg towards the uterus, helped by tiny hairs, called cilia, which wave and shift the egg along.The egg can survive in the Fallopian tube for 24 hours and, if it is not fertilized, it will be reabsorbed by your body.

As the egg is released, your body begins to prepare for the possibility that it may be fertilized: the lining of your uterus, the endometrium, becomes thick and spongy, ready for a fertilized egg to implant. If fertilization does not take place, the endometrium will come away and you will start to bleed as another menstrual cycle begins.

The Journey of the Sperm

The journey of the sperm

After ejaculation, the sperm swim very quickly from the vagina into the cervix (the neck of the uterus), through the uterus and into the Fallopian tube towards the waiting egg. The egg releases chemicals that tell the sperm where it is and attracts them towards it. The sperm race to penetrate the egg, but only one sperm will succeed: once penetrated, the egg releases chemicals that'seal'it so that no other sperm can break through. Once the sperm has broken through the surface of the egg, its tail breaks off.

After fertilization

Once the egg and the sperm have fused, they become a new type of cell, called a zygote. The sperm and egg each contained 23 chromosomes, so the zygote contains 46 chromosomes. The zygote then travels slowly along the Fallopian tube, dividing into identical cells as it goes - first two, then four, then eight, and so on. By about day 4 it is a solid ball of cells and is called a morula. When it reaches the uterus it is a hollow ball of 50-100 cells and is called a blastocyst. It takes around 6 days for the blastocyst to reach the uterus and implant. Once implanted, it continues to grow and develop until it becomes an embryo.

When an egg fails to implant
In some cases an egg can be successfully fertilized by a sperm but fails to implant in the uterus. This is usually because of an abnormality in the fertilized egg that means it cannot survive. If this happens, you usually will not even know that your egg was fertilized. You will just have a slightly later period than usual, possibly with heavier bleeding.