Travel Insurance that Would Permit Cancellation if Pregnant?

I would like to plan a trip through eastern and southern Africa for next summer (June - August). I am, however, a bit concerned that if between now and then I became pregnant, that most travel insurers do not seem to allow refunds (flights/tours) with pregnancy as the reason. I don't want to put my life on hold because I might become pregnant, but on the other hand I am a bit nervous about the large expenses for arranging flights and tours. I also am concerned that some things I wish to book at specific dates sell out, which is why I'd like to make some arrangements now if I can find a way to have some peace of mind regarding the ability to get some of the upfront expenses refunded if I do become pregnant.

Is there any difference regarding how it is handled with travel insurance if my tour/flights will be to malarial areas and ones requiring yellow fever vaccination, which are both recommended against for pregnant women? If I was just going for a holiday in the U.K. or somewhere that wouldn't require prophylaxis such as I'd need in Africa, then I understand that the companies don't want to always permit cancellation due to pregnancy, but I thought perhaps it is different with situations such as this where women are advised to avoid travel if possible while pregnant due to the medical precautions necessary. I realize that some anti-malarials are considered ok to use while pregnant, but I'd still be a bit uncomfortable about it, especially regarding the yellow fever.

If you are aware of or have a recommendation for an insurance carrier with whom cancellation would be possible if I were to become pregnant between when I purchase the coverage and when I am due to travel, please let me know. I realize I would need to contact any insurer directly for definitive answers, but since I've never had travel insurance, I thought recommendations here would be a good place to start to help me narrow down the possibilities. I live in the United States.

Thank you for the suggestions.