Menstruation is a spontaneous cyclic (monthly) physiological shedding of internal lining of uterine cavity (endometrium) due to invisible interplay of female hormones. In simple terms, it is a regular monthly bleeding which a woman experiences. The first menstruation occurs usually at the age of 12 – 15 years. It is also called as 'menarche'. For the past couple of decades, the age of menarche is gradually declining with improvement of nutritious and environmental conditions.

Once, the menstruation starts, it continues cyclically at an interval of 22 - 35 days with a mean of 28 days.

Physiologically, it stops during pregnancy and lactation.

Ultimately, it ceases between the ages of 45 - 50 years when menopause sets in.

The duration of menstruation (menses) is about 4 - 5 days and the amount of blood loss is estimated to be 20 – 80 ml with an average of 50ml.

The menstrual discharge consists of mainly a dark altered blood, mucus, vaginal epithelial cell fragments of endometrium, prostaglandin, enzymes and bacteria.

Usually, at the midcycle, a mature egg is released (ovulation). If it gets fertilised, the menses ceases. Thus the absence of menstruation suggests that pregnancy has occurred.


Ovulation is a process by which a mature egg (mature Graffian follicle after secondary oocyte is released) is released from the surface of ovary to be available for fertilisation viz. conception.

Usually only one mature egg is released in each ovarian cycle. In relation to the menstrual period, the event occurs 14 days prior to the expected date of menses. However, menstruation can occur without ovulation. Fertility is very high during mid cycle, for the same reason.

Ovulation remains suspended during pregnancy and lactation.

Following ovulation, the mature egg (ovum) is picked up into the fallopian tube and undergoes further maturation, if fertilization has occurred or degeneration if it does not get fertilized.

Following ovulation, the ruptured follicle undergoes a change called corpus luteum formation, which secretes hormone progesterone.

Menstruation is unrelated to ovulation and no ovulation during menstrual cycle is quite common during young age (adolescence), following childbirth and in women approaching menopause.


Fertilisation is a process of meeting (after mating) of the sperm with a mature egg. It begins with sperm egg collision and ends with a formation of life called zygote (single mononucleated cell mass). The ovum immediately following ovulation is picked up by the fimbrial end of the fallopian tube and is rapidly transported to the ampullary part of the tube.

Out of hundreds of millions of sperms deposited in the vagina after intercourse, only thousand specialised sperms enter the uterine tube while only 300 – 500 reach the egg.

Out of this elite community, only one lucky member is allowed to get into the mature egg.

The sperm either contains (22 X) or (22 Y) pattern of chromosomes while the egg contains 22 X only.

The sex of the child is determined by the pattern of the sex chromosome supplied by the sperm.

If the sperm contains (22 X) a girl child (46 XX) is formed, if it contains (22 Y) a boy child (46 XY) is formed.

Fertile period

The fertile period is period around ovulation, during which if relations are kept, the chances of pregnancy are high. In order to improve the chances of pregnancy, it is important to understand how to calculate the fertile period.