@misc{indiciaec133125127e7,
  title = {Ovulation method of contraception.},
  author = {J J Billings},
  year = {1981},
  doi = {10.5694/j.1326-5377.1981.tb135299.x},
  url = {https://pubmed.ncbi.nlm.nih.gov/7207299/},
  note = {Source identifier: 7207299}
}