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Safe period or infertile window is a time in woman’s menstrual cycle with lowest likelihood of pregnancy resulting from sexual intercourse, for a woman having regular 28 days cycle this time begins around 19th day from the first day of last menstrual cycle and lasts till 7th day after the first day of next menstrual cycle, this period also includes menstruation days. The chance of pregnancy in this period is around 0% to 5%. Safe period or infertile window is sometime referred as a natural way of birth control.
Male sperm generally survive inside woman uterus for about 5 days and sometime up to a week, fertilization occurs when male sperm fuses into woman’s egg released from either of her ovary, egg cell however cannot survive more than 2 days without being fertilized and if there is no male sperm present inside the uterus of a woman when the egg is released, no fertilization will occur and hence no pregnancy.
For most women with regular 28 days cycle, Ovulation occurs about midway through the menstrual cycle, for most women usually 14.6 days from the beginning of the last menstrual period (LMP), however ovulation may occur little earlier or could be delayed by couple of days this differs from woman to woman and period to period with an overall 95% prediction interval of 8.2 to 20.5 days.
A variety of methods have been developed to help individual women estimate the relatively fertile and the relatively infertile days in the cycle; these systems are called as fertility awareness. Of fertility awareness methods that solely rely on cycle length alone are called calendar-based methods and method that requires observation of one or more of the three primary fertility signs viz. basal body temperature, cervical mucus, and cervical position are known as symptoms-based methods.