This is a good question, and it doesn't have a simple answer. I'll do my best to answer what I think based on first principles.
I checked in a rather extensive reference (Kulund, DN: The Injured Athlete). There were lots of references to various intestinal injuries, injuries to the bladder, kidney, pancreas, and even penis and testicles. NOTHING on the ovaries - probably the most vulnerable point. My guess is that women have not been involved in contact sports long enough to have a history of the problems that are possible.
When you talk about conditioning, you are talking about repetitive, low force blows to the abdomen. Individual low force blows done to a relatively toned and properly flexed abdomen are not likely to give problems. Repeated blows over time are another story.
I'm sure some might like to attribute fibroids to trauma. As far as I know, there is no connection.
This reminds me of when my wife was preganant with he first child, and wanted to know if she could continue her weight lifting. Everyone gave her blank stares, and then said something like "Why would you want to?" There was little data on the issue, so she was on her own. I spotted her as she weight trained through the entire pregnancy, except for the last week. I was (inside) a bit concerned when I saw her benching 150 while 5 months pregnant, but I kept my concerns to myself. She was checking her pulse and she was breathing properly. She was not experiencing any bleeding. The only problem she got was a split of the abdominal muscle wall (very common), possibly due to the fact that she kept doing situps through the pregnancy to keep toned. This corrected itself within 6 months after delivery. She delivered a 9 lb 5 oz boy that was healthy beyond our wildest expectations. If anything, he might have appeared a bit precocious for a newborn.
So what am I telling you? There's little data on it. Your ovaries are the biggest concern. My recommendations are the following:
1) Take your time with abdominal conditioning. You are in it for the long haul.
2) Pain is an important tool in conditioning. Learn to pay attention to it.
3) The solar plexus is the biggest achilles heel in the abdomen. You can condition that reflex without going near any of the female reproductive organs. Do you really feel a need to condition elsewhere on the abdomen? Think about it.
4) If you are going to condition elsewhere on the abdomen, go for quantity of strikes and frequency of sessions over magnitude of impact.
5) Pay attention to any unusual bleeding (vaginal) and make sure you never see blood in the urine or stool.
6) Stay away from areas below your karate belt.
To some extent you are on your own. Proceed cautiously.
[This message has been edited by Bill Glasheen (edited 02-05-99).]