Abstract: The Jewish calendar has six fast days, which have different levels of stringency. On Yom Kippur and the Ninth of Av it is assumed that healthy pregnant women will undergo a 24 hour fast (no eating or drinking). In most cases, neither the mother nor the fetus will experience any negative consequences. However, the physician should convey any specific medical concerns to the woman and her halachic advisor so appropriate arrangements can be made. On the other fasts (which last only from dawn to nightfall), pregnant women are not required to fast, although, according to some opinions, they may do so. If the physician feels a woman should not fast on the minor fast days, this should be indicated.
Discussion: The Jewish calendar includes six fast days, which have different levels of stringency.
- The strictest fast, and the only one required by biblical law, is Yom Kippur, the Day of Atonement for sins. On Yom Kippur both eating and drinking are absolutely prohibited for a little more than 24 hours, from sunset on one day until after nightfall the next day. Bathing, applying oil to the skin, sexual relations and leather footwear are also forbidden.
- Next in stringency is the Ninth of Av (Tisha B'Av), the fast that commemorates the destruction of the First and Second Temples in Jerusalem. This rabbinically-ordained fast is parallel to Yom Kippur in that eating and drinking are prohibited for a little over 24 hours and bathing, etc., is proscribed.
- Three additional “minor” fasts (the 10th of Tevet, the 17th of Tammuz, and Tzom Gedaliah) mark other events connected with the destruction of the Temples. The Fast of Esther falls on the day before Purim and commemorates the fighting between the Jews and their enemies. These fasts are less rigorous: eating and drinking are prohibited but only from before dawn until nightfall, and bathing, etc., is permissible.
Healthy pregnant women are obligated to fast on Yom Kippur and the Ninth of Av. On the other, minor, fast days they are exempt. There is debate among halachic authorities as to whether or not they may voluntarily choose to fast on those days. Women with pregnancy complications or other health or medical problems should not fast on the minor fast days.
A woman's vascular system is greater when she is pregnant than when she is not. Thus, there is a greater chance that she will develop symptoms of dehydration, such as headache, fatigue, etc. A woman can reduce her chances of developing such symptoms if she is careful to drink extra fluids before the fast, spends the fast day in a cool environment, and minimizes exertion. According to Jewish law, it is more important for the woman to fast than for either she or her husband to attend synagogue. If symptoms are severe, an individual question should be asked of a rabbi, as health concerns take precedence in Jewish law.
In deciding health concerns, a physician should be honest in realizing the dearth of evidence based medicine on the effects of a one day fast on pregnancy. To date, there have been only two studies on this phenomenon. The first study, showed an increase in deliveries after Yom Kippur, although almost all the women delivered at term  . A more recent study, however, did not reproduce these finding . A few studies conducted during Ramadan showed possible growth reduction  but other studies did not find this effect . It is important to realize that there is a large difference between a one day fast and repeated fasting for a month. In cases of actual danger to health, of course, there is room for leniency even on Yom Kippur and the Ninth of Av. In such cases, an individual question should be asked of a rabbi. The medical information should include the basis for concern.
On Yom Kippur, it is easier within Jewish law to permit eating small amounts frequently (about an ounce of solids and a cheekful of liquids) than to permit eating ad lib. Therefore, it is important to let the halachic professional know if there is a need for larger volumes or if smaller volumes are sufficient.
On the Ninth of Av, a woman who is not fasting may eat and drink normal quantities. A women will also be counseled that if she feels faint during the fast, she should start to eat and drink accordingly.
Once a woman is in labor, she no longer has the halachic status of a pregnant woman. She becomes a yoledet (a woman who gives birth) and is considered an ill person who is at risk. A woman in labor is certainly halachically permitted to eat and drink, even on Yom Kippur.
A woman maintains the status of yoledet for the first week after childbirth. If she gives birth within three days before Yom Kippur she is not allowed to fast. If she gives birth 4-7 days before, she can fast only if she feels well enough and her health care provider does not object. The exact calculation of these time periods is a matter of halachic debate (whether 24-hour days, or nightfall to nightfall). Therefore, in borderline situations, a specific halachic question should be asked. When the birth precedes Tisha B’Av, there is room for even more leniency.
Implications for Care: Health care providers should be aware of the presence of fast days in the Jewish calendar. The epidemiologic evidence suggests that healthy pregnant women can fast without negative consequences. For these women, the physician should give anticipatory guidance how to best manage the fast (e.g., drink extra fluids the two days in advance and minimize exertion during the fast).
When the physician is concerned about the effects of fasting on either the mother or fetus, this information should be conveyed in advance of the fast to allow the woman to ask her rabbi whether she may eat. The information should include any specific health concerns related to the particular woman.
 Kaplan M, Eidelman AI, Aboulafia Y. Fasting and the precipitation of labor. The Yom Kippur effect. JAMA. 1983;250:1317-8.
 Wiser A. Maymon E, Mazor M, Shhomn-Vardi I, Silberstein T, Wiznitzer A, Katz M. Effect of the Yom Kippur fast on parturition [Heb]. Harefuah 1997;132: 745-48, 824.
 Lurie S, Baider C, Boaz M, Sulema V, Golan A, Sadan O. Fasting does not precipitate onset of labour.J Obstet Gynaecol. 2010;30:35-7.
 van Ewijk RJG, Painter RC and Roseboom TJ. Associations of Prenatal Exposure to Ramadan with Small Stature and Thinness in Adulthood: Results From a Large Indonesian Population–Based Study. Am. J. Epidemiol. 2013;177:729-736.
 Petherick ES, Tuffnell D ,Wright J.Experiences and outcomes of maternal Ramadan fasting during pregnancy: results from a sub-cohort of the Born in Bradford birth cohort study.BMC Pregnancy and Childbirth 2014, 14:335.
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