If a pregnant woman is having multiple relationships, the best move would probably be to be honest with all of the potential fathers about the situation. Especially when there are traits that would be a dead giveaway such as fathers of a different race, you're playing with fire if you don't confess to an affair. In the words of Kanye West, "Eighteen years, eighteen years, And on the 18th birthday, he found out it wasn't his?" Probably the only wise thing he ever said...
Sometimes, though, mothers just want to take the risk. If you can imagine how awkward it must be to be a father watching what you think is your new baby being born only to find out your partner has been having an affair and that baby is 100% not yours, the doctors and nurses are also there to experience the discomfort. And they never forget.