The following Healthcast report by medical editor Marilyn Brooks first aired Sept. 28, 2004, on Channel 4 Action News at 5 p.m.

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Weight-loss surgery has become the technique of choice to prevent serious health problems in the obese, but women who have the operation are finding an unexpected side effect.

Women aren't having the operation to get pregnant, but they are getting pregnant because they had the operation -- and that pregnancy often comes as quite a surprise.

At 39, Karen Friday had no intention of having a baby. In fact, she didn't think she could. All she wanted to do was lose the weight that broke her ankles and an arm.

Friday: "I decided that the best thing to do was to do this (surgery). I want to live. I want to see my kids grow up. I want to have grandkids. I want to be around. If I don't do this, I'm not going to make it."

She weighed 312 pounds, and nothing helped, so she opted for gastric bypass surgery last November.

Dr. Joseph Colella, Allegheny General Hospital: "Most of the weight loss that occurs after gastric bypass occurs in the first 18 months to two years."

Friday began to drop weight, as expected. What she did not expect was pregnancy. What happened?

Dr. Ronald Thomas, AGH: "They have the surgery and all of sudden, their body comes down to a more normal metabolic function. The ovaries begin to work, they get pregnant, they're surprised."

Gastric bypass is considered routine today, but it is major surgery. While it is one solution for obesity, it can be one problem for pregnancy, especially if that pregnancy comes too soon after the operation. Timing is everything.

Thomas: "Those pregnancies are at major risk, in terms of the baby not growing well, nutrients not coming in, mom continuing to lose weight, electrolyte issues, fluid issues."

Friday's weight loss was literally starving her unborn baby. She had to eat every two hours and spend three weeks in the hospital. Doctors delivered a healthy baby by C-section five weeks early.

Colella: "If you have gastric bypass surgery and you manage to wait two years to become pregnant, that is the best-case scenario."

It's an incredible story, but not at all unusual. Doctors say it's happening all the time.

Obese women don't ovulate normally, so they think they can't get pregnant. They're warned about that when they consider gastric bypass. Take the warning to heart, doctors say. It will be easier on you and the baby.