Read the passage and answer the following question :

Over population carries number of family problems. Strategies like birth control methods help to control population explosion. Natural methods of birth control do not involve medications or devices to prevent pregnancy but rather rely on behavioural practices and/or making observations about menstrual cycle. Natural methods work on the principle of avoiding chances of ovum and sperms meeting.

Which fact is not the basis of periodic absence method of birth control? ( Question 3)

Alteration in uterine endometrium.

The correct answer is option (4) -Alteration in uterine endometrium.

Periodic abstinence is a natural method in which the couples avoid or abstain from coitus from day 10 to 17 of the menstrual cycle when ovulation could be expected. Periodic abstinence is a method in which couples avoid coitus during the fertile period of the woman's menstrual cycle to prevent pregnancy. However, it is not considered 100% effective, as there is still a risk of unintended pregnancy. The effectiveness of periodic abstinence depends on various factors, including the regularity of the menstrual cycle and the accuracy of identifying the fertile period. It is not considered a foolproof method of birth control. This method may reduce the chances of pregnancy by about 80 % .However , a great care is needed in its use.

Ovulation occurson about the 14th day (may be 13th to 16th day) of menstruation. Ovum remains alive for above 1−2 days and sperm survives for about 3 days.