The fertile period begins 3-4 days before ovulation (which corresponds to the lifespan of sperm in the genital tract) and continues in the next 24 hours (corresponding to the lifetime of the oocyte). The time when fertilization is possible, therefore, is only 5 days on a cycle that has 28.
Conversely, the infertile period begins on the 2nd day after ovulation and extends to the following rules. By cons, ovulation does not necessarily come 14 days after the onset of menstruation, because menstrual cycles are not always regular and constant.
At each sexual intercourse, at the time of ejaculation of semen of the man, about 300 million sperm are released into the woman's vagina. Using their flagella, sperm move at a speed of a half-millimeter per minute.
Their migration to the uterus of the woman is also facilitated by two phenomena related to ovulation. Initially, the cervical mucus, a sticky liquid a little at the origin of white discharge in women and whose production is at its worst at the time of ovulation, promotes sperm motility. Also, during the female orgasm, the cervix tenses and these contractions help the sperm to reach the destination.
Once in the uterus, the sperm move into crypts that are sort of small caves in the cervix. All times, groups composed of thousands of sperm out to attack to win the egg. They can survive for 3 to 5 days in the female genital tract.
However, only a hundred sperm manage to get near the egg. In this journey, they have also acquired their fertilising through secretions from the uterus and the fallopian tube.
Among the hundred sperm joins with the region near the egg, only a dozen are faufileront through the cells and peri-oocyte zona pellucida that protect the egg.
Foeutus of sex is determined through the 23rd chromosome called sexual. In women, this chromosome can only be of type X, while that of man can be either X or Y. When both sex chromosomes are gathered Type X (XX), the fetus is a girl and when the combination is in the form XY, it's a boy.
Thirty to fifty hours after fertilization, the first cell of the baby will be divided.
Between the 72th hour and day 4 post-fertilization, the egg will reach the uterus through contractions and movement of cilia of the fallopian tubes to help him through those few inches.
Arrived in the uterus between the fourth and fifth days, the egg floats freely in the uterine cavity until it reaches the stage of development required and the uterine lining is ready to welcome him.