WOOMB International

Science of Fertility

Efficacy of the Billings Ovulation Method® for Avoiding Pregnancy

The Billings Ovulation Method has undergone intensive study and research and has been the subject of a number of published trials. What is clear from all the studies on the Billings Ovulation Method® is that couples wishing to use the Billings Ovulation Method should be made aware of the importance of gaining accurate information and encouraged to seek the assistance from an experienced accredited teacher of the method to achieve success.

Details of some of the trials:

The first published trial of the Billings Ovulation Method® was in Tonga in 1972
The results revealed:
0.5%  –  method-related pregnancy rate  (pregnancies occurring despite correct use of the method)
1%     –  teaching-related pregnancy rate (pregnancies resulting from incorrect teaching of the method, or misunderstanding of the method by the user).

This trial confirmed the rules of the method as well as the importance of accurate teaching and understanding of the signs and symptoms of fertility.

Published: Lancet 1972, Vol. 300  pp 813-816

1976-78 an independent trial was conducted by the WHO, in five countries (India, the Philippines, New Zealand, Ireland and El Salvador).

 This study had two phases:  
869 couples entered the three-month ‘teaching phase’,
725 couples continued in the 13-cycle ‘effectiveness phase’,
with a total of 10,215 cycles in the entire study.

The teaching phase showed that in the first cycle of charting, 93.1% of women were able to record an identifiable ovulatory mucus pattern denoting fertility, and that by the third cycle of charting, 97.1% of women had an excellent or good interpretation of the method.

The results for the entire study were:
2.2 pregnancies/ hwy    (per 100 woman years)  –  method-related pregnancy rate
22.3 pregnancies/hwy  (per 100 woman years)   –  total pregnancy rate

The total Pearl Index  – 22.3/hwy  comprised:
• Conscious departure from the rules of the method: 15.4/hwy.
• Inaccurate application of instructions: 3.9/hwy.
• Method failure: 2.2/hwy.
• Inadequate teaching: 0.3/hwy.
• Uncertain: 0.5/hwy.

Conscious departure from the rules of the method will always present difficulties in assessing a pregnancy rate for natural fertility regulation, as couples may choose to change their motivation from avoiding pregnancy when they know the woman is fertile. A more realistic way of assessing of whether a natural method is successful is to identify both the method-related pregnancy rate and the teaching-related pregnancy rate.

Published: Fertility and Sterility 1981 Vol. 36, p. 152ff, 1981 Vol. 36, p. 591ff.

Indian Council of Medical Research Task Force on NFP (1995) (States of Uttar Pradesh, Bihar, Rajasthan, Karnataka and Pondicherry).

0.86% / hwy  (per 100 woman years)  –  method-related pregnancy rate   

In this study of 2,059 women with 32,957 women months of use 32.2% were illiterate. The majority were Hindus (87.8%) and 9.6% were Muslims.

Published:  Contraception 1996, Vol. 53 pp. 69-74.

1996-97 Billings Ovulation Method conducted in China 

0.0%   – method related pregnancy rate
0.5%. – teaching-related pregnancy rate

These pregnancy rates reflect current stringent teacher training requirements.

Published:  Chinese Medical Journal 1998.