If you want to read a full list of reasons for infertility, you would need to clear your whole day. You would have a lot of reading to do.

There are many causes why a couple or a person is infertile. There are hormonal imbalances, physical disorders or sometimes it can brought about by different factors like age, vices and individual lifestyles.

But before we get into the most common causes of it, let's first define infertility. It is said to be the inability to get pregnant after at least one year of repeated, frequent attempts. So if you and your partner have been trying for 12 months to have a baby, without any luck, medically speaking, you are infertile.

But let me introduce you to another concept that isn't really known to many: subfertilty.

Subfertility is when there is no physical disorder on either the woman or man's side wherein conception is still a distinct possibility. The problem lies more in the timing of the pregnancy than in the lack of it. The event just isn't happening as quickly as you would like.

Another reason why you may be infertile is because of the fact that the reproductive system is very complex. In fact, if one considers everything involved in getting pregnant, you're in awe that anyone of us was born at all.

A possible pregnancy starts anew every month when the pituitary gland in a woman's brain signals her ovaries to prepare an egg for ovulation. This releases the follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Once the pituitary gland secretes these, thus stimulating the ovaries, a woman is fertile.

Once the hormones have prepared the ovaries, the woman's egg travels through her fallopian tube in anticipation of being fertilized. The window of opportunity here is usually 24 hours.

While the female is fertile, it's necessary for the sperm to unite with the egg in the fallopian tube. The sperm, by the way, is capable of fertilization for up to 72 hours following its release. Obviously, the sperm need to be in the tube at the same time the egg is there.

But that's not all! Not only does there need to be a significant amount of sperm present to ensure conception, but the sperm needs to be just the right shape. And it needs to move in the proper way. Those are the requirements on the man's part.

For the woman, she needs to have a healthy vagina and uterus in order for the sperm to travel to the egg!

It's only when all these criteria are met that the egg is fertilized. You would think that's the end of the story, but no, the process isn't quite complete, yet. This fertilized egg now must move into the uterus. Here it attaches itself to the uterine lining. And that's when the nine months of growth begin. Finally!

As you can see, there are many factors that are needed for a successful conception. It is complicated and the slightest mistake will ruin the whole process.