I was not in the room for my daughter's birth. This trend was initiated during the 1970s, during the height of second-wave feminism, and I think it should be viewed with a high level of suspicion.
First, the man's presence affects the woman's ability to relax. She begins thinking about "sharing" the experience - instead of relaxing like she should be. This tension then delays the delivery. Eventually, the doctor has to call in for a C-section because he doesn't have all day. The subsequent C-section is more painful and requires a longer recovery time before she can have a child again (roughly two years). There are now a wide variety of magazines, both conservative and liberal, that agree on this point. Here is one written by Michale Odent, who was an obstetrician for nearly fifty years. He is adamant that it has a negative affect on the delivery.
http://www.dailymail.co.uk/femail/articl...child.html
Secondly, it is widely believed that watching a woman give birth during the delivery can harm the intimacy of the marriage. This is not something I would want to mess with. I know there are many people today who scoff at the knowledge of our forefathers. But I believe if there is one thing that previous generations knew about - if anything - it was interpersonal, sexual relations.
And finally, on a side note, I believe that some women want a man in the delivery room for dubious reasons. She wants the man to see this massacre, hoping that he will lose interest in her sexually. That way, she can later blame him when the sex dries up. A good example of this would be a woman in her early forties who has baby rabies, and gets some beta shlub to knock her up. She doesn't want to go the long haul with the guy, so she starts doing things to sabotage the relationship. One way to sabotage said relationship is to kill the intimacy. So she encourages Beta Joe into the delivery room, hoping that he will become nauseous. Then when the relationship dies, she can blame him for the demise. It wasn't her fault after all...it was HIM that lost interest. Meanwhile, the bitch knew what she was doing all along. Then, she catches the next open seat on the cock carousel, like she was doing for the last twenty years.