I'm still a nursing student, but I'm also a mother, so I'll give you my $0.02.
Personally, I prefer female physicians. Our family doctor is a woman, as is my OB and our family dentist. The ARNP who does my routine GYN care is female, as well. It's partly personal preference (especially with the OB/GYN--the old mechanic/car adage) but also coincidence--the vast majority of family practise physicians in our area happen to be female.
However, as far as the actual labour and delivery process goes, I found out fast that it doesn't matter what sex your OB is...he/she won't be there for most of the labour. Mine ended up being on vacation, and one of her partners (female) barely made it into the delivery room, even though the nurse was screaming into the phone that I was crowning and she'd better get here if she didn't want a nurse delivery (I was an unmedicated primipara, and the doc underestimated my desire to be done being pregnant). You probably know all about this, being a dad.
I now believe that a CNM, male or female, would be a better choice than an absent female OB doctor. Certainly, the LDRP nurse who was with me through delivery could have been any sex at all as long as she kept the pudding cups coming and kept the poking and prodding to a minimum. Postpartum care was an embarassment-inducing time, and I doubt a male nurse would have made it much worse.
As Mark said, it's all about your presentation of yourself. Be confident and professional, and I'd be surprised if your patients even give your sex a second thought. Good luck!