Thank you for reaching out to us.

Generally speaking, a woman with gestational diabetes should not fast, out of concern that it might be dangerous.  When fasting is medically unsafe, it is a mitzva of "choosing life" to eat on Yom Kippur, and it is important to keep that in mind when eating.

Whether shiurim are appropriate for you here depends on the specifics of your case in consultation with your physician and a halachic authority. Here are the general guidelines as presented on our page on pregnancy and fasting:

The shiur for drinking is half of one mouthful (measured before the fast by filling the mouth and cheeks with liquid, emptying it into a measuring cup, and halving that). When eating is necessary, a woman may eat up to 30cc at a time. Ideally, these quantities should be consumed at intervals of at least nine minutes; however, opinions vary and some authorities permit intervals as short as four minutes.

We encourage you to discuss with your physician whether this would be relevant for you.

Besha'ah tovah! We wish you a healthy and safe pregnancy and childbirth.

Please let us know if we can be of further assistance. Ketivah v'chatimah tovah!