pregnancy rate, (in statistics) the ratio of pregnancies per 100 woman-years, calculated as the product of the number of pregnancies in the women observed multiplied by 12 (months), divided by the product of the number of women observed multiplied by the number of months observed. For example, if 50 women used one contraceptive method for 12 months and 5 of them became pregnant, the pregnancy rate would be 10 per 100 woman-years.
