I took someone's advice above and reached out to Don Croft. He replied a few hours later with the following:
"I've sold hundreds of zappers to pregnant women over the years and have only gotten positive feedback from them, don't worry. It's apparently impossible to do any harm with a battery powered zapper.
Hulda Clark warned against pregnant women using zappers but most of her warnings, recommendations and protocols were off target, I'm sorry to say, and based on nothing but imagination, evidently.