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Normal Conception

Normal Conception | Birmingham Fertility CenreNormal Conception begins with a series of complex, coordinated sequence of events within the ovary regulated and modified by chemical substances called hormones.

Each month, about 20-30 eggs begin to grow independent of any hormones, within the ovary in little fluid filled structures called follicles. By the time the woman is around the second day of her menstrual cycle these measure about 5- 10 mm in diameter. At this stage, there is a rise in hormone called Follicle Stimulating Hormone (FSH). This hormone selects one of these follicles, leading to a rapid increase in growth of that follicle with its contained egg, while the other follicles and eggs self destruct.

The leading or ‘dominant’ follicle grows to a size of approximately 20 mm or more by day 14 of the cycle with rise in the production of the hormone oestrogen. At this stage a second hormone called Luteinizing Hormone (LH) is released in a ‘surge’ which leads to final maturation of the egg and its release from the follicle with its surrounding cells. It is picked up by the fallopian tube and remains there awaiting fertilisation.

If intercourse takes place around this time, the motile sperms will swim up the cervix (neck of the womb), up the uterine cavity, along the tube, to reach the egg in the outer third of the tube. If all the conditions are suitable, the sperm will then fertilise the egg. The fertilised egg then develops into an embryo and takes three days to journey down the tube to enter the uterine cavity. It will then develop further in the uterine cavity for another two days, before it begins to implant or bury into the lining of the womb which has been prepared by the rising oestrogen levels. When implantation is successful, the embryo will continue to develop into an ongoing pregnancy.

All of these steps need to occur at exactly the right time in a synchronous manner; hence it is not surprising that pregnancy does not happen with each ovulation.