A team of Catholic Medical Association physicians and students are working on a comprehensive literature review of the medical effects of contraception, set to be available later this year.

With about 10.6 million women of reproductive age in the U.S. currently using the pill, according to the Centers for Disease Control, these physicians want to spread the word about the dangers of hormonal contraception on women's health, particularly those that are not well known.

Dr. Bill Williams, who is an immunologist, medical researcher and professor at the University of Pennsylvania, talked with Catholic News Service about the latest research regarding contraception and the increased risk of breast cancer.

Published in December 2017 in the New England Journal of Medicine, this study followed 1.8 million Danish women for over a decade and found that even newer versions of hormonal contraceptives with lower doses of hormones had an elevated risk.

"This was an important study because we are at the fourth generation of the pill and they keep changing the amount of steroids that are in there," Williams said. "People thought with the lower amounts (of hormones) there would be a lower risk, but this study disproved that. This is the newest study, but there is much more (evidence) out there."

The researchers for the Danish study found that women on contraception overall experienced a 20 percent increase in the relative risk for developing breast cancer, with the relative risk increasing to 38 percent for women who stayed on contraception for 10 or more years.

Estrogen-progestogen oral contraceptives (combined) are considered by the World Health Organization to be a Group 1 carcinogen, in the same category as asbestos. The explanation is physiological, Williams said.

"Contraception causes a woman's risk of breast cancer to go up because it stimulates the mammary gland cells to grow and divide, increasing the chance that there will be a mistake made in the growth and division of cells," he explained. "If those mistakes are in the wrong place, that can lead to cancer."

Williams added that the risk is especially high before a woman's first pregnancy, because the immature mammary gland cells divide more than mammary gland cells that have matured through childbirth and nursing.

Another lesser known risk of hormonal contraception Williams has found in the research is autoimmune disease development. With his training in rheumatology, Williams said it was this connection that particularly caught his attention.

"The pill predisposes to the development of several autoimmune diseases, which has been best proven for Crohn's disease, systemic lupus erythematosus, multiple sclerosis, ulcerative colitis and interstitial cystitis," he told CNS.

Most of the studies done have looked at ever use vs. never use, but there are also studies looking at duration of use, he said. "It does increase the risk the longer you are on these drugs," Williams added.

Other risks the CMA research team has found include more commonly known side effects such as weight gain, irritability and reduced sex drive, as well as more severe risks such as heart attacks, strokes, DVT (deep vein thrombosis, or blood clots) and pulmonary embolisms (blood clots that travel to the lungs and can cause death).

Dr. Kathleen Raviele said that the vaginal ring and patch particularly increase a woman's risk of blood clots and pulmonary embolisms.

An OB-GYN based in Atlanta and member of the association's research team, Raviele discussed why this information has not been made widely known to patients by many doctors. The research is there, but often scattered, she said.

"These studies are not reported in the literature of people prescribing these pills or in OB-GYN journals," -- Raviele explained. "Most are in breast cancer or international journals, not ones that OB-GYNs would be reading." The CMA physicians hope that their cumulative literature review will help raise awareness about these dangers in the medical and wider community.

The CMA doctors also want to raise awareness about an alternate approach to managing fertility, called natural family planning. NFP methods are based on monitoring or "charting" a woman's daily physical signs that indicate when the fertile or infertile times in her menstrual cycle are, and using that knowledge to avoid or achieve pregnancy.

When used correctly, NFP is up to 99 percent effective at avoiding pregnancy. NFP involves no barriers, internal devices such as IUDs, or surgical procedures like sterilization that would be contraceptive, and therefore is the only method of family planning that is completely consistent with Catholic teaching.

The Catechism of the Catholic Church states that "these methods respect the bodies of the spouses, encourage tenderness between them, and favor the education of an authentic freedom."

A woman or couple can check with their diocese to learn where NFP classes are offered in their area. A listing of classes by state can be found at www.usccb.org/NFP.

Learning NFP can help a woman detect abnormalities as well, said Raviele. Charting with NFP can help a woman notice signs of health issues such as causes of infertility, hormonal conditions, like polycystic ovary syndrome, and endometriosis.

"With her chart, you can see if she has a normal post ovulatory phase, hormonal or structural problems like fibroids, polyps, or problems with the uterus," Raviele explained. "It is a tremendous help to tell if a woman's (reproductive) health is normal."

Madeline Watkins is staff assistant with the Natural Family Planning Program of the Secretariat of Laity, Marriage, Family Life and Youth at the U.S. Conference of Catholic Bishops.