It's more likely an ovarian cyst than a pregnancy. You could always take a home pregnancy test, or check in with your doctor for a blood test.
About your bigger problem, which is, how to reliably prevent pregnancy so you will never ever be worried that you are pregnant, if it would be a life-and-death situation to get pregnant, you might also consider either getting your tubes tied (if you are sure you will NEVER want kids even if you lost your husband and got remarried), or getting an IUD and taking the pill on top of it. Another option that is simpler is for your husband to get a vasectomy. Again, that's a permanent solution, but if he is sure he never will want kids even if his life changes in unexpected ways, it would be the easiest thing to do. (And a vasectomy is actually more reversible in the event someone changes their mind than a tubal ligation is.)
Good luck, see your doc if you are freaking out.
Not to be snoopy, but what condition can a man have that would make his wife and child ill if she were to get pregnant, but would not make his wife ill if they have sex? I assume there are diseases a man can pass to his wife, but one specific to pregnancy and childbirth is new to me. I have also heard of women with heart conditions who are advised not to get pregnant, but didn't know something a male has could make his wife ill if she were to get pregnant and have a baby but not make her ill if they had sex.) Maybe you could mention the condition so other women married to men who have it, could be sure they were forewarned before getting pregnant.