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Once each month, or every twenty eight days on the average, the uterus in the female body prepares itself to host a pregnancy. The cycle begins with the building up of the uterine lining with soft tissue and a rich blood supply. Sometimes after this, often about mid-cyle, the ripened ovum will burst form the ovary. This is when ovulation occurs. The ovum is gently swept into the tubes leading to the uterus, then if sperm cells are present in the reproductive tract, even without intercourse the egg will encounter the sperm. It can then become fertilized and embed itself in the prepared uterine lining and then a pregnancy begins.
In every ovary there are more than 50,000 potential ova a birth, but only 400 or 500 reach maturity. The others will degenerate or die at some other time in the sexual cycle. At puberty, usually between ll and l4 years, the first ovum will ripen and be released by the rupture of the Giraafian follicle and be discharged into the Fallopian tube. When an ovum matures every 28 days, it is discharged. In some cases there can be two or more ova discharged at the same time, and this accounts for most forms of multiple births. The process of ovulation will continue until menopause, and the female sex cycle will last from 30 to 35 years.
The passage of the ovum down the fallopian tube takes about three days. If unfertilized, the ovum reaches the uterus, where it degenerates or passes to the outside. The cavity left when the Graafian follicle ruptures to release the egg becomes filled with a body of connective tissue and reddish-yellow cells known as the corpus luteum. This persists for a couple of weeks, if no pregnancy occurs but in case of pregnancy, it may last for the greater part of the period of gestation. One of the functions of the hormone progestion, produced by the corpus luteum, is to prepare the walls of the uterus for the reception of the fertilized ovum.
A controversial topic is whether or not the female, during her monthly cycle, has definite periods of fertility during which conception is likely to occur or when it is likely not to occur. There is a contention that the germinating ability of the sperm and ova are such that they can only live a few days unfertilized and that they must reach the Fallopian tube within a day or so after the ovum has left the ovary. It seems there is some evidence that germ cells live for several days, but they have not discovered how long they have fertilizing power. It is known though that the period of ovulation is variable and may occur either early or late in the cycle.
Records have been made of the temperature of many women and show that the temperature drops from 24 to 36 hours before the onset of menses and reaches a low level during the first day or two after the beginning of the period. The low level of temperature will continue during the entire period and up to the time of ovulation. There will be a sharp drop in temperature occurring just before ovulation and then a prompt rise until 24 to 48 hours before menstruation in the following period, when the temperature will drop again.
Conception is most likely in the five-day period preceding ovulation. Pregnancy will occur when there is coitus during the period of temperature rise preceding ovulation and, though less likely, immediately after the temperature reaches its plateau.
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