Pearl index

Pearl index


  • Pearl index indicates the effectiveness of a contraceptive or is an index of contraception failure.
  • Pearl index is called so as it was developed by Raymond Pearl.
  • It is used for studying the effectiveness of a contraceptive 
  • The number of pregnancies includes all pregnancies whether this has terminated as live births, still births or abortions or has not yet terminated.


  • In applying the above formula  :
  1. The total accidental pregnancies shown in the numerator must include every known conception, whatever its outcome.
  2. The factor 1200 is the number of months in 100 years.
  3. The total months of exposure in the denominator is obtained by deducing from the period under review of 10 months for a full term pregnancy and 4 months for an abortion

Three kinds of information are needed to calculate a Pearl Index for a particular study:

  • The total number months or cycles of exposure by women in the study.
  • The number of pregnancies.
  • The reason for leaving the study (pregnancy or other reason).


  • Pearl index is Failure rate/100 women years
  • The most fertile couples will get pregnant in the beginning of the study and will no longer be counted in the denominator. 
  • Couples remaining later in the study, are, on average, of lower fertility.
  • With most birth control methods the effectiveness increases with experience. 
  • The longer a couple is in the study, the better it gets at using the method. So the longer the study length, the lower the Pearl Index will be. Hence comparisons of Pearl Indexes from studies of different lengths cannot be accurate
Exam Question
  • Calculation of pearl index is No. of pregnancies X 1200/( Number of women X number of months)
  • Pearl Index is a measure of Potency of contraceptives
  • Pearl index is Failure rate/100 women years
  • Total accidental pregnancy is important in calculaton of pearl index 
Don’t Forget to Solve all the previous Year Question asked on Pearl index

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