We recently contacted WOOMB to confirm what we should be quoting when asked about effectiveness studies for the Billings Ovulation Method®.
They sent an interesting document that starts off discussing the need to include the range of published studies that meet the requirements for medical evidence in relation to the design of the study. So, in other words, don’t just look at one study when quoting success rates.
The current standard way of reporting effectiveness rates of contraceptive methods is the Pearl Index. It gives effectiveness rates based on the number of pregnancies expected if 100 women used a given method for a year.
Studies on natural family planning and/or contraception will also refer to both user and method effectiveness. When method effectiveness is cited, it refers to perfect use, meaning users follow a particular method’s instructions exactly.
WOOMB states that the most accurate way of quoting contraceptive success rates is in “initiates.” The document explains, “That is, the first-time use including any learning period. The reason for quoting figures for initiates is that the effectiveness rates will improve the longer a group has been using a method because those who are likely to become pregnant may already have become pregnant and be lost to the study if the initial period is not included.”
The following three international studies of the Billings Ovulation Method® produced method effectiveness rates in initiates:
The World Health Organization (1978-1981)
The Indian Medical Research Council (1996)
The Jiangsu Health Institute in China (1997)
“The studies recruited women who had not previously used the Billings Ovulation Method® and recorded the pregnancy rates for those who became pregnant either during the teaching phase or after.”
Based on those studies, we can cite the Billings Ovulation Method® with a method-related pregnancy rate of 0-2.2 pregnancies per hundred women years in initiates.
All three studies had impressive numbers of women included in their study, living in many parts of the world.
▪ The World Health Organization’s multi-center study took place from 1997 – 1981. The locations included Auckland, Dublin, San Miguel, Bangalore, and Manila. There were 869 women in the study, equaling 10,215 cycles of use. There were 2.2 method-related pregnancies per hundred women years in initiates. (2.8 when the initial phase excluded)
Published: Fertility and Sterility 1981 Vol. 36, p. 152ff, 1981 Vol. 36, p. 591ff.
▪ Indian Council of Medical Research Task Force on NFP (1995) had the states of Uttar Pradesh, Bihar, Rajasthan, Karnataka, and Pondicherry. They had 2,059 women with 32,957 women months of use. The study concluded there were 0.86 method-related pregnancies per hundred women years in initiates.
Published: Contraception 1996, Vol. 53 pp. 69-74.
▪ Jiangsu Family Health Institute, China (1997) Dr. QIAN Shao Zhen. This study had 1,235 women with 14,280 women months of use. No method-related pregnancies in initiates. (5 user-related pregnancies)
Published: Chinese Medical Journal 1998.
Good to note: Evidence-based method-related Pearl Index for Billings Ovulation Method® is 0-2.2 per hundred women years in initiates.
BOMA-USA provides education and training for The Billings Ovulation Method® which is a natural method of fertility management that teaches you to recognize the body's natural signs of fertility.