Hilgers was also able to identify and treat other complications that can contribute to increased risk of miscarriage, such as endometriosis and polycystic ovarian syndrome (PCOS).
His second main area of research was in establishing what constitute normal levels of progesterone throughout pregnancy, Kenney continued.
"He looked at thousands of pregnant women who carried out very, very healthy normal pregnancies, and he looked at their progesterone levels in each week of pregnancy, all the way through the third trimester, to establish a normal range of progesterone levels in pregnancy."
Hilgers then compared these to pregnancies that were not normal – for example, those that ended in miscarriage or experienced premature labor, placental complications, or fetal distress. He found that pregnancies experiencing poorer outcomes often had lower than normal progesterone levels.
"And so in practice, what we do here at Pope Paul VI Institute is to treat those pregnancies that have lower than normal progesterone in pregnancy, and we reduce the risk of poor outcomes," Kenney said.
Dr. Kathleen Raviele, an OB-GYN and former president of the Catholic Medical Association, said that if a woman has undergone a miscarriage – particularly very early in pregnancy – she recommends that her progesterone levels be tested following ovulation during a normal cycle. If numbers are low, she recommends supplementing progesterone.
"That seems to be the most effective at preventing subsequent miscarriages if progesterone deficiency is the problem," she told CNA.
Kenney and Raviele both stressed that there can be many reasons for miscarriage, and progesterone does not solve all problems. Somewhere between 10-25% of pregnancies result in a miscarriage, according to the National Institutes of Health.
"Fifty percent of miscarriages happen because the baby has a chromosomal problem," Raviele said. "There are also structural problems with a woman's uterus that can cause miscarriages, infection in the mother, other problems such as diabetes and thyroid disease."
However, for those patients who do experience low progesterone, offering a simple solution that allows them to carry a healthy pregnancy can be "so healing" for them, she said.
She recalled one woman who came to her after having six consecutive miscarriages. Raviele tested her and found that the woman had a progesterone deficiency. The woman was given supplemental progesterone and had two healthy babies.
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"It's such an easy thing to do, if that's what the problem is," Raviele said.
While hundreds of doctors have been trained in Hilgers' methods, the FDA has never approved the use of progesterone in pregnancy for the prevention of miscarriage. As a result, it is not part of the standard of care followed by most doctors in the majority of pregnancies.
And even if a doctor does decide to test for progesterone in pregnancy, the reference range that is generally used by laboratories is much broader than that established by Hilgers, Kenney said.
"So what we see as suboptimal progesterone is not always what a traditional lab will. We have a lower threshold for treatment because our research has proven that there is a tighter window that progesterone levels should be in pregnancy."
Raviele said that in her experience, "treatment with progesterone in early pregnancy is very often regional. There are different parts of the country where it's used frequently, like in the Southeast, and then there are other parts of the country where they don't have any confidence that progesterone is making a difference."
But some concerns that are attributed to the use of progesterone are actually the result of the form used and the timing of administering it, she said.