In trials method related pregnancy rates have ranged between 0% to 2.9%. In a recent trial in China 992 couples using the Billings Method were compared to 662 couples using the IUD. The method-related pregnancy rate amongst Billings users was zero and the total pregnancy rate was 0.5%. In studies up to the 1980's teaching related pregnancies ranged between 0% to 6%. Total pregnancy rates vary between 1 and 25%. Reasons for a higher total pregnancy rate include misunderstanding the method, risk taking, ambivalence toward pregnancy, and deciding to become pregnant.

Fertility A woman ovulates at only one time during her cycle, and an ovum can survive for only 12-24 hours. Cervical mucus enabling healthy sperm cells to navigate the genital tract is necessary for fertility Spermatozoa have an average life of only 3 days in the presence of fertile mucus, with survival of longer than 5 days being rare. Menstruation will occur about 2 weeks after ovulation.

How the method works
In the days leading up to ovulation the cervix responds to oestrogen by producing mucus capable of sustaining sperm survival. This mucus leaves the vagina as the woman is in an upright position. The mucus is observed through the sensation at the vulva and by looking at any discharge. Daily charting of these observations will reveal either an unchanging pattern indicating infertility or a changing pattern of sensation and discharge indicating fertility. Both of these patterns follow the hormonal patterns which control sperm survival and conception.

Billings Method teachers help women recognize and understand their signs of fertility. This can help in the early diagnosis and treatment of gynaecological disorders, and can contribute to a woman's reproductive health.