User Input: The tool requires users to estimate three characteristics of the proposed study:

• The total number of women expected to be enrolled.
• The duration of the time during which participants should avoid pregnancy (in months). This should include any pre-intervention assessment/wash-out, time during which participants are receiving trial-related interventions, and any post-exposure time during which pregnancy is to be avoided based on preclinical or other data.
• The expected age distribution of female participants. Because age is the single biggest predictor of pregnancy risk, and because pregnancy probabilities change dramatically after age 35, the tool asks for estimates in 5-year age increments from age 18 through 54, then for the remaining percentage over age 55.

Based on the number of women at risk for pregnancy, their age distribution, and the study duration, the model estimates the number of expected test results for different thresholds of hCG detectability. Note that some numbers may be less than 1.0 for relatively small studies with few women at risk.

Detected pregnancies: Women with pregnancies and hCG levels above the threshold of a given hCG test.

Undetected pregnancies, hCG below threshold: Women with pregnancies and hCG levels below the threshold of a given hCG test.

Undetected pregnancies, test performed prior to implantation: Women who will become pregnant in a given month but whose randomly timed pregnancy test is performed in the 3 weeks prior to implantation.

False positive/indeterminate: Non-pregnant women (typically perimenopausal women) with very low levels of pituitary hCG.