Fasting on Yom Kippur while pregnant may trigger early birth, according to a new Israeli study — providing the first clear evidence against doing so.
In the retrospective cohort study of 725 deliveries in Israel on Yom Kippur over 23 years, Jewish women were twice as likely as others to have their babies early, the study found. Premature babies are at elevated risk for various health problems and for death.
Jews are religiously obligated to fast on Yom Kippur, which falls this year on Friday night and Saturday, considered the holiest day on the Jewish calendar. Pregnant women are included in this, but if a doctor gives them a pass, they can eat and drink a bit.
Still, many pregnant Jewish women at least partially refrain from eating or drinking during the 25 hour period, according to their religious beliefs.
Although doctors often advise their patients not to fast while pregnant, the recommendation is not supported by clear evidence or by official medical guidelines. The large cross-sectional study, published in The Journal of Maternal-Fetal & Neonatal Medicine this month, adds empirical weight to recommending leniency on the matter.
“We found that during the Day of Atonement, Jews had twice as many preterm deliveries. And I’m not talking about one year, I’m speaking about the whole study period,” said Prof. Eyal Sheiner, an obstetrician and gynecologist at Ben-Gurion University of the Negev and at Soroka Medical Center in Beersheba, who led the study. “This is the first evidence based study to support our recommendation (to pregnant women) not to fast on Yom Kippur.”
Sheiner’s post-doctoral students Dr. Natalie Shalit and Dr. Roy Shalit co-authored the study.
Soroka Medical Center is the largest hospital in southern Israel. About half of the patients who give birth at the hospital are Jewish, and about half are Bedouin. Sheiner noticed a boost in deliveries every year on Yom Kippur in the obstetrics and gynecology department he heads.
To investigate why, he matched data on deliveries at the hospital from 1988 to 2012 with the Jewish calendar. Of the mothers, 388 were Jewish and 357 were Bedouin. Forty-seven, or 6.3 percent, of the births were premature, or earlier than 37 weeks after conception. Data analysis revealed that the Jewish mothers were twice as likely as their Bedouin counterparts to give birth early on Yom Kippur.
The difference remained significant after controlling for other factors that could explain early birth — the mother’s age, previous early delivery, and problems with fetal development. Significantly — looking at the day exactly a week before Yom Kippur each year, Sheiner found no significant difference in early births between the two groups of mothers.
Several previous studies showed an increase in labor and in deliveries on Yom Kippur and on the following day, but none of them specifically addressed early birth. Sheiner said that since many pregnant Jewish women do not fast completely or at all on Yom Kippur, the risk of a 25 hour fast may be even greater than is reflected in the study.
Babies born prematurely are at increased risk of complications at birth, and the risks rise according to how early a baby is born. Seventy-five to 80 percent of babies who die at birth are born early. They are also more likely to develop cerebral palsy, impaired cognitive skills, sensory, dental, behavioral and psychological problems, and chronic health issues later in life.
“The best incubator for the first 37 weeks is the uterus,” said Sheiner.
The relationship between early delivery and fasting is not well understood. The leading theory is that fasting increases the thickness of the blood, which promotes the secretion of a hormone shown to induce contractions of the uterus.
Sheiner said dehydration and stress are both risk factors for early delivery. The first thing he says doctors at his hospital do when a woman comes in with preterm contractions is to hydrate her. He said he will continue advising women to take a break from the Yom Kippur fast when they are pregnant, especially now that he’s armed with the numbers to support his recommendation.