Published October 18, 2007 by
Okay – we aren’t overly stupid adults… we do know how conception occurs, we know the birth is followed by mommy gifts, but some of the finer points of getting pregnant might just surprise you.
Human conception is a miraculous and complex event. It is perhaps more surprising that pregnancy occurs so often than that it fails sometimes. A human egg is released every month from a woman's ovary under the influence of a complex cycle of hormones. The hormones are released by the pituitary gland and the hypothalamus, located in the brain. The egg is swept into the fallopian tubes by delicate projections (called the fimbria) at the end of the tubes, where it is normally fertilized by the man's sperm. The fertilized egg then moves down the tube and, helped along by the tiny hair-like cilia that line the tube, enters the uterus, or womb. The embryo must implant into the lining of the uterus (the endometrium). There it starts to produce hormones that will stimulate its growth. The site in the ovary, called the corpus luteum, from which the egg was released, must produce enough of the hormone progesterone to sustain the pregnancy for the first three months. After that the placenta takes over that job.
The woman's uterus must be structurally sound and capable of expanding to contain the growing fetus. The cervix, the opening of the uterus, must be strong enough to hold in the baby until it is ready to be born.
It is estimated that it takes a fertile couple having regular sexual intercourse an average of six months to conceive. At any point, something can go wrong and pregnancy will not result:
Roughly one-third of infertility is caused by a problem in the woman, one-third by a problem in the man. Of the last one-third of cases, infertility is caused by a combination of problems in both partners or, in about 20% of these cases, is unexplained (American Society for Reproductive Medicine, "Frequently Asked Questions about Infertility," I996). The statistics for unexplained infertility have tended to fall with better diagnosis and an improved understanding of what causes infertility, but it is still more common than many doctors like to admit.
The most common cause of female infertility is failure to ovulate, and this condition is the easiest to treat. A course of fertility drugs can be given to see if these will activate the ovaries. There are several fertility drugs, and while the doctor may know which is the best to try, often he simply has to go through each in turn, trying different doses, to see what is or is not successful. This can make the woman feel like a human guinea pig. Tests into other areas of infertility can be long, complicated and invasive. Male infertility is the hardest to treat.