Congratulations on your pregnancy successes in the past! Maintaining tight control of blood glucose levels during pregnancy has been well-known for decades to be of critical importance in having a good outcome for pregnancies in women with diabetes. And, as you found during your prior pregnancies, it's frequently necessary to add insulin therapy to assure tight control.
As your obstetrician mentioned, there have been occasional studies using oral medications, including metformin and sulfonylureas (the two ingredients in the combination pill Glucovance), in pregnant women. But, as you have found out, there's little or no information about Glucovance itself. Indeed, the latest official prescribing information (available at the FDA website) says: " Most experts recommend that insulin be used during pregnancy to maintain blood glucose as close to normal as possible... GLUCOVANCE should not be used during pregnancy unless clearly needed... There are no adequate and well-controlled studies in pregnant women with GLUCOVANCE or its individual components. No animal studies have been conducted with the combined products in GLUCOVANCE."
I would vote for you to plan to use insulin again, and I'd suggest to not use oral diabetes medications during pre-pregnancy planning, nor during pregnancy itself. There are several reasons for my opinion:
1) From your statement in the e-mail, you have previously been comfortable with using insulin and obtained tight control, and you didn't indicate any reason why you won't be able to do so again.
2) It's a lot easier to adjust insulin doses to maintain around-the-clock glucose control, than to adjust doses of oral diabetes medications, as insulin doses can be adjusted meal-by-meal if needed.
3) Side effects of insulin are well-known. The side effects of using an unstudied combination of two pills during the critical early months of pregnancy are probably no worse than use of either pill alone, but why would you want to run the risk?
What should you do at this time?
First, if you have also been seeing a diabetes team, talk to them, and ask them to manage your diabetes. Traditionally, obstetricians handle pregnancies, and diabetes specialists handle glucose management, and your obstetrician should be glad to have other specialists assisting with your care.
Second, make it clear to your OB that you are very comfortable with resuming insulin, having used it before, and that you are aware that using insulin during diabetes pregnancies is the standard of care. You might need to point out that you don't want to risk your upcoming pregnancy by using non-standard medications (even though some studies have been done).
If your OB is unwilling to prescribe insulin and/or is unwilling to coordinate your care with other specialists, you should look elsewhere for
your obstetric care.
Very best wishes for a successful pregnancy and healthy child!