'Pearl-index' for accidental pregnancies failure per:

(100 - women - year of exposure): Ref: (439-Park 20th)"PEARL - INDEX" defined as the number of "failure per 100 women years of exposure (HWY)"Failure rate per HWY =Total accidental pregnanciesTotal months of exposurex l200* The total accidental pregnancies shows in the Numerator must include every known conception.* The factor 1200 is the number of months in 100 years* The total month of exposure in the Denominator is obtaining by deducing from the period under review of 10 months for a full term pregnancy and 4 months for an abortion* The pearl index is usually based on a specific exposure (usually one year)