She went into labor that night. Other couples reported a loss of sexual drive as well. Some things I've read also cite a lack of drive in the male, because he finds his wife unattractive. Perhaps the women also find themselves unattractive, and certainly the size of a pregnant belly introduces logistical problems into the act. But it's important to note that not everyone has this problem.
Some people have the opposite problem, namely that the woman's sex drive is actually increased.
I have read no articles on this problem, I have seen no chapters in books on this trouble. I have heard no doctors discuss it and seen no public broadcasting shows devoted to it. But it happens. I know, because it happened to us. We had to sit in Bradley class as one couple or another would complain that one half or the other of them had lost interest in sex.