For those who practice them, the Jewish laws of nidda — laws regulating sexual relations with regard to menstruation — have been a boon to the Jewish community, protecting the family and promoting procreation.

As Rabbi Shmuely Boteach puts it in Kosher Sex, his popular guide to rabbinic sexual laws, “the fertility benefits of this practice are obvious and undeniable,” referring to the 12- to 14-day separation of husband and wife during and after the onset of menstruation.

But the very opposite may be true, according to Evyatar Marienberg, a visiting scholar who addressed a small audience at Princeton University in early December.

Marienberg, a yeshiva-trained Judaic scholar from France, explained the dilemma of women who ovulate before the period of separation ends and as a result cannot conceive.

“For many hundreds of years, countless Jewish women with a short cycle who observe the nidda laws had a very small chance to become pregnant,” he said, in a talk sponsored by the Program in Judaic Studies. “It is very possible that for many of them, this meant the difference between having offspring or not having one, between being a mother or considering oneself a barren woman.”

Marienberg presented his scholarly paper — “Jewish Menstrual Laws and Jewish Fertility-A Historical Reconsideration” — in a small conference room at Princeton’s Scheide Caldwell House, home of the university’s Program in Jewish Studies.

A graduate of Yeshivat ha-Kibbutz ha-Dati, the Institut Catholique de Paris, and the Ecole des Hautes Etudes en Sciences Sociales, Marienberg is currently the Carey Postdoctoral Fellow at the Erasmus Institute of the University of Notre Dame, where he is writing the first book in Hebrew to explore the contemporary Catholic Church. His first book, Niddah, was published in Paris in 2003.

“I’m dealing with issues of sexuality,” Marienberg said in an interview before his presentation. “A big part is the study of menstruation in many Jewish contexts, in different sources. It opens a window onto Jewish culture.”

In his study of both rabbinic and medical sources, he said, it becomes clear that regulations regarding sexual relations can cause a woman to lose her chances to conceive if ovulation occurs during the prohibited time.

“According to Leviticus, relations are prohibited for seven days since the appearance of new bleeding,” Marienberg told the gathering. “But in the talmudic period, that period became extended for [another] seven days, beginning after the end of blood flow, after a woman made sure she was not bleeding.”

When you factor in the addition of those seven “clean” days to the prohibited time, he said, that leaves perhaps as few as nine to 13 days per month when sexual relations are permitted. “A short window of fertility of about 24 hours occurs during this time frame,” he said.

However, he said, “the reality is that although many women have more or less stable 28-to-29-day cycles, many women do not.” A woman may have a cycle of 22 days or 35 days or anything in between, or a cycle that is not totally fixed, he said.

“For women with long cycles or short cycles of less than 25 days, there is a good chance that when ovulation occurs, they will still be considered impure,” Marienberg said. “If they are planning on having children, this is bad news.”

In some contemporary Orthodox communities, this problem is recognized, and women with short cycles are given hormones to extend their cycles, according to Marienberg. “In a certain mindset,” he said, “if you can’t modify Halacha [Jewish law], modify the woman. How many women today need this type of hormonal assistance? What happened in the past?”

The debate over what one Orthodox women’s group calls “halachic infertility” was taken up recently in the pages of HaTsofe, an Israeli daily newspaper serving the Orthodox Zionist community. In November, a physician cowrote an article arguing, like Marienberg, that extended nidda restrictions can lead to infertility. In subsequent weeks, the newspaper printed responses by various Orthodox rabbis and physicians, most of whom defended hormone treatments and suggested that rabbis are best equipped to deal with the issue on a case-by-case basis.

Nevertheless, Marienberg insisted that the problem is widespread, saying some of his sources suggest that the combination of a short cycle and the observance of the laws of nidda can cause difficulty in conceiving among perhaps 20 percent of women, Marienberg added.

“In that way, Halacha made perfectly healthy women to be seen as sterile,” he said. “I can hope that Orthodox women who have to deal with this issue consult with specialists and get help.”