Thursday, February 24, 2011

How to calculate safe days for sex to avoid pregnancy

Natural birth control methods are as effective as artificial methods, if used properly. Each menstrual period is associated with a pre-menstrual infertility window and post-menstrual infertility window.
The menstrual cycle, is commonly divided into three phases: the follicular phase (pre-ovulatory phase), ovulation, and the luteal phase (post-ovulatory phase). The length of each phase varies from woman to woman and cycle to cycle, though the average menstrual cycle is 28 days. Menstrual cycles are counted from the first day of menstrual bleeding.
The follicular phase (or proliferative phase) is the phase of the menstrual cycle; before ovulation, during which follicles in the ovary mature. It ends with ovulation. The main hormone controlling this stage is estradiol.
Ovulation is the process in a female’s menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum. The time immediately surrounding ovulation is referred to as the ovulatory phase. A woman gets pregnant around the days when ovulation occurs.
The luteal phase (or secretory phase) is the latter phase of the menstrual cycle. It begins with the formation of the corpus luteum and ends in either pregnancy or degradation of the corpus luteum. The corpus luteum is a temporary endocrine structure, involved in production of estrogen and progestogen, which is needed to maintain the endometrium, the inner membrane of the uterus.
The infertility period depends on the life span of sperm and on the life span of the egg. The average time of ovulation is the 14th day of an average length (28 day) menstrual cycle. Ovulation time vary for each individual, and can occur from 12th to 19th day of the cycle. Sperm can live up to 3 to 5 days in a woman's reproductive tract, so it is possible to become pregnant if unprotected sex occurs 5 days before ovulation. The life span of the typical egg is relatively short, only around 24 hours. If fertilization does not occur within that time frame, the egg will die.
Safe Period Calculator

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