On the other hand, normally such precision is not required. In order to understand what about a day – plus or minus two came the conception suffice it to recall the date of the last Bang before pregnancy menstruation. Why?
The women's menstrual cycle usually lasts about 28 days and consists of two equal phases, lasting for 14 days. During the first phase of each cycle, a woman's body is preparing for pregnancy: under the influence of certain hormones thickens the inner layer of the uterus (where to attach the fertilized egg, if fertilization happens in this cycle), in the ovary formed by the follicle (the cavity in which the egg develops, before you go out and move into the fallopian tube). The release of an egg from the ovary happens in the middle of the cycle, usually on the 14th day from the first day of menstruation. The egg, carrying the movement of large villi, located on the edge of the fallopian tube, tightened it and moves toward the uterus through the small tubular fibers. It is in the pipe usually does the meeting of egg and sperm, fertilization and the subsequent movement is already ovum into the uterus to attach to its bottom, and the development of a full pregnancy.
If fertilization has not occurred, then comes the second phase of the menstrual cycle – is activated by another set of hormones that prepares the body for exfoliation of excess tissue in the uterus. Then, on the 28th day of the cycle is menstruation, which is the rejection of the tissue, necessary for implantation of the ovum.
Thus, the most likely day of conception is the 14th day of the menstrual cycle, plus or minus two days. Therefore, adding two weeks to the first day of the last pregnancy before menstruation, you can quite accurately determine the day of conception.