During sexual intercourse as many as 300 million sperm will be ejaculated, but just a tiny percentage - around two hundred at the most - will make it as far as the fallopian tube. The vast majority do not even manage to get through the cervix into the womb.
Once they are inside the female body, sperm can survive for up to a week, although most will not live longer than a couple of days. An egg is more likely to be fertilized if there are fresh sperm ready to meet it in the fallopian tube when it is released.
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| Fallopian Tube Infertility |
In order to be able to fertilize an egg, the sperm goes through a process called capacitation. The outer coating of each sperm's head is stripped off, and at the same time the tail stops beating gently and begins to make wide, whiplash beats. This will help the sperm to make its way through the thick outer layer that surrounds the egg. Only the strongest will be able to do this. Once a sperm has successfully got past the outer layers, it binds itself to the egg. Enzymes immediately act on the shell to prevent any other sperm breaking through.
The luteal phase
When an egg has been released, the follicle surrounding it collapses. Soon it is filled with small cells that proliferate to occupy the space. These cells have a yellow pigment and the mass of cells is called the corpus luteum, or yellow body. The corpus luteum produces progesterone, which helps to build up a thick, healthy womb lining ready for implantation,
Meanwhile, the egg travels down the fallopian tube towards the womb, a journey that takes about a week, If the egg has met a sperm in the tube and been fertilized, it then embeds itself into the womb lining and begins to develop.
If the egg is not fertilized, it will disintegrate within 24 hours. The corpus luteum will carry on producing progesterone for a couple of days, but it then disintegrates. The drop in progesterone causes the lining of the womb to begin to break up, and it is shed as the period begins and we are back to day one of the cycle again.
When am I most likely to conceive?
We tend to have it in our heads that we are most likely to get pregnant around day 14 of our cycle, but in fact, that's not particularly useful unless you have a regular 28-day cycle. Ovulation occurs roughly 14 days before your period arrives, no matter how long your cycle is, and it is the first half of the cycle, when the egg is growing and maturing, that causes most of the variation in menstrual cycle length. This means that if your cycle is 35 days long, you will ovulate somewhere around day 21; whereas a woman with a 25.day cycle will ovulate around day 11. It may sound confusing, but you just work two weeks back from your period to work out when you have ovulated. If you have a regular cycle, you can use this to tell when you are likely to be ovulating in future months.
It is obviously far more difficult to pinpoint ovulation if your periods are not always regular. In general, if you are having sex every two or three days, you are likely to be hitting your most fertile time, and this will maximize your chances of conception.
Fertility specialists estimate that women are usually fertile for between six and eight days of their cycle, up to and including the day of ovulation. You are most likely to get pregnant if you have intercourse a couple of days before you ovulate, as this will give sperm time to be ready and waiting in the fallopian tubes for an egg. To find out more, you can check out Fallopian Tube Infertility.
