Unfortunately, even though you didn't know you were pregnant when they asked, it's easy enough to date a pregnancy and know that you actually were. Even though you didn't knowingly deceive them, they have no way of knowing that and you have no way of proving it.
Not necessarily true... the ultrasound said plus or minus 5 days, which means she could have been 8 weeks, 1 day. That puts her at 2 weeks, 4 days on November 25, and it's not possible to get a positive HPT at 4 DPO. I'd push that angle if I were you, OP.
Doesn't matter. Pregnancy is dated back to CD1- the first day of your last period.
Insurance companies like loopholes and they will use that to their advantage.
This is true, but there is part of the ACA in effect that says that insurance companies can no longer drop you for honest errors made on applications. I think this situation would fall under that category, considering the OP could not have possible known she was pregnant when she applied.
It's less likely that they'll drop her completely and more likely that they're just going to refuse to cover any bills related to her pregnancy. Honest mistake or not, it's factual that she was pregnant to the medical world when she applied and they're not going to be willing to foot the bill for such a definite, well, bill. It sucks, don't get me wrong and I hope for the OPs sake that they don't do this but like a PP said, they're always looking for loopholes and they find them.
This is likely true. As much as it sucks, it's better than being dropped altogether.
Actually it's worse. They will state that everything that happens while pregnant is related to pregnancy and reject all claims. If she is outright denied coverage, that would open her up to the state exchanges that are being set up. Since she would still have coverage, she may not be eligible for those plans.
In a perfect world, they wouldn't be bastards and would be well aware that a women wouldn't know that she is pregnant at 4 dpo. But we don't live in a perfect world and insruance companies will screw you when they can. I had one plan (many years ago, well before ACA) that technically didn't hit me with pre-existing, but since I had an abnormal pap one year, they refused to cover all thing GYN related stating they could all be tied back to the abnormal pap that I had under another company's coverage. My rates went from $40 a month to just under $300 less than 6 months later as well. I could totally see that company denying maternity coverage in a case like the OP's, just because they can.