Question

The Pearl Index, used to express contraceptive failure rate, is defined as:

• A. Number of accidental pregnancies per woman year
• B. Number of accidental pregnancies per 100 woman-years of exposure
• C. Number of pregnancies over number of losses per 100 woman-years
• D. Number of accidental pregnancies per 1000 women per year

Hint:

Denominator is 100 woman-years of exposure, and lower is better.

Answer 1

The Correct Option is B

Step 1: Purpose of the Pearl Index. The Pearl Index is the standard measure of the effectiveness (failure rate) of a contraceptive method.

Step 2: Definition and formula. It is the number of accidental pregnancies per 100 woman-years of exposure (HWY):
\[ \text{Pearl Index} = \frac{\text{Total accidental pregnancies} \times 1200}{\text{Total months of exposure}} \]
The factor 1200 converts to 100 woman-years (100 women x 12 months). A lower Pearl Index means a more effective method.

Step 3: Why the others are wrong. "Per woman year" omits the standard denominator of 100 woman-years. The option dividing pregnancies by losses is not the definition. "Per 1000 women" uses the wrong denominator.

Key fact: Pearl Index = accidental pregnancies per 100 woman-years of exposure; lower value = better contraceptive.