לע"נ ר' יואל בן ר' פנחס הלוי
I posted this last year:
The Shulchan Aruch rules that pregnant or nursing women must fast, so it seems to be an open and shut case. But halacha is rarely that simple. The Chofetz Chaim in the Biur Halacha [תקנ"ט סעיף ט] quotes a Rebbe Akiva Eiger who says that on a year such as this when Tisha B'av is pushed off a day the halacha is more lenient and when a woman feels weak or otherwise unwell she may eat. Rav Ovadiah Yosef [Yabia Omer 5/40] takes this one step further and allows all pregnant or nursing women to eat [I am not presenting his argument here ע"ש] and Rav Moshe Shternbuch [Tshuvos Vi-hanhagos 2/253] is open to being lenient as well [although Rav Bentzion Abba Shaul ztz"l in his Or Latzion Vol. 3 29/3 and the Yemenite Gadol Rav Yitzchak Ratzabi Shlita in his Olat Yitzchak 1/67 argue] . Things are VERY hot and we must protect our wives. In any event, a pregnant woman should turn on the AC and lie in bed [if she needs to] and stay COOL.
Halacha Li-myse - ask your local authority and don't posken from my blog:-).
What I meant in quoting the Yabia Omer [and R' Shternbuch] is that they allow all pregnant or nursing women to eat on a Tisha B'av nidche [pushed off from Shabbos to Sunday]. That is an expansion of the heter of Rebbe Akiva Eiger who only permits it only if she is feeling unwell. However I received an email from a Rov in Los Angeles who understood from my words that I meant that they allow pregnant women to eat even on a regular Tisha B'av [such as this year] which is incorrect. Since he understood it that way then many others probably did as well and I apologize for my lack of clarity.
That being said there are many poskim in Yerushalayim who are lenient and allow pregnant women to eat if they suffer from the heat [see, for example, Halichos Beisah (Ch. 25 footnote 3) and Encyclopedia Hilchatit Refuit (Vol. 3 page 17)]. See another very lenient opinion in Tal Li-Bracha [Vol 2 Simman 74].
As for Halacha Li-myse? I reiterate, ask your Rov:).