Hi there and congratulations!
I am also recently pregnant (first one) and experienced the same thing around 11 weeks (I am now in the middle of my 13th week). I had read on this old blog that this is to be expected in general terms. But when it happened, I was also reading a new book called Pregnancy and Type 1 Diabetes by Ginger Vieira and Jennifer Smith where they go into a little more detail about why that happens and also how to manage it when it does. I do recommend the book and if you get it, the relevant pages are 63-67.
In short, there are two main reasons for this: the development of the placenta around this time, which takes over the progesterone-producing action previously conducted by the ovaries. They don’t explain why exactly that different source of progesterone impacts the insulin sensitivity, but my own guess is that the hormone gets directly to the fetus from the placenta, without circulating as much in the mother’s blood (maybe). The second factor is that the immune system apparently “backs off” a little bit from its normal level of activity in order not to treat the fetus as a “foreign body” and so if the mother has some residual beta cells (I happen to know I do since I was part of a study that looked at that right after diagnosis + tried a medication that seemed to additionally help preserve some of the beta cell action), they are able to produce some small levels of insulin. Pretty insane, ha? All in all, this can be expected to last until about weeks 15-16 when insulin needs start to gradually increase again.
As far as management, in my case, I have been lowering my basal rates a little bit at a time (0.005 each time, but I am fairly insulin sensitive to begin with) a few times now over the past 2 weeks. I have also started planning for a little fresh-fruit snack at the times that I seem to start going low (I am also on a CGM which helps catch the trend quickly), esp. in the middle of the afternoon.
I do all my own adjustments anyway (I mean, prior to pregnancy) and am very comfortable doing that. If you are not used to it, however, I would try to contact the doctor’s office now, even before it’s time for your appointment. Mine specifically advised me to call anytime I want assistance with adjustments and they’ll review my BG results over the phone and discuss what can be changed. I am pretty sure your doctor’s office won’t refuse to do the same (and in fact it might be common procedure but they just forgot to mention it – make sure you ask how best to get your results to them in case they need them faxed or something else).
Best of luck and feel free to update us here on the thread how you’re dealing with things!