My wife and I have been married 3 years and unfortunately still do not have any children. We are currently undergoing our first (and hopefully only!) IVF cycle and just had the embryo transfer last week. We will not know the results of this transfer before Yom Kippur. We spoke with our doctor (who is frum) about fasting and he said "I am not a rabbi, but I can tell you from a medical perspective that fasting definitely hinders the chance of successful implantation. When your body feels malnourished, it is less likely to accept the transfer."
Can you please provide some halachic guidance about our situation.
Thank you, Gmar Chatima Tova
Since the transfer was last week, implantation will have already (be"H) taken place by Yom Kippur. We follow the opinions that the rules of pikuach nefesh apply also to a fetus before forty days.
As your doctor said, there is some potential concern for the success of the implantation, and hence a potential concern of pikuach nefesh. Thus, your wife should take the necessary steps not to possibly endanger the developing fetus.
Therefore, she should drink sweet liquids b'shiurim (about 40 cc waiting 10 minutes) and reduce exertion, by staying in an airconditioned environment and minimizing walking back and forth from shul and standing during davening. [If she experiences difficulty fasting, in general, it would be best to stay home and rest on a couch or in bed.]
Check with your doctor, but a liter and a half should suffice if she is in an airconditioned environment. There is usually no need to begin drinking until morning, unless she feels particularly thirsty.
Gmar Chasima Tova,
Rabbi Meir Orlian