@Sunch Be careful with Googling stuff like this. This isn't clinical information, it's here-say on the internet, and the question it comes under is whether Pregnacare can give you a false positive, which is obviously absurd. I can't see the actual question Google was asked, but that can also provide biased answers. If you're looking for a specific answer that something is bad, Google will show that. If you look for clinical evidence, it will show you something closer to fact. I work in pharmacology medical research and publishing, so this is my bread and butter.
Pregnacare is just a vitamin tablet with relatively minor amounts of fertility boosting vitamins. There is nothing harmful in it, or it would not be available on the U.K. market. Yes, it can affect some peoples cycles, as it says in the box, but that is the case for any vitamin really depends on each person. It's why all guidelines recommend talking to a doctor before adding a vitamin to your regime that can cause changes. There was an article about vitamin B6 causing nerve damage and hand/foot cramps this week because people were taking too much of it without realising. Multivitamins are designed to have a safe balance so those kinds of things don't happen. Pregnacare can't cause damage to sperm if he's taking the one designed for men, so please don't panic about that, lovely.
As an outside example, Papaya can cause uterine contractions, but you don't see everyone currently trying to conceive panic about eating a fruit salad that might contain a bit of papaya because the effect would be minimal.
By all means, change to something else you feel more comfortable with, but don't be panicked. Bear in mind, other multivitamins with similar compositions may have the same effect, or they could have no effect at all, it's all down to your own body and how you react to the combination. Hope this helps you :)