Ellen Hodgson never had the classic symptoms of elevated blood pressure and swelling. Still, she needed an emergency C-section. Daughter Peri arrived in December 1998, fully developed and healthy. Hodgson has had two babies since, both healthy, with no sign of the syndrome, she says, although they were deliberately taken a week early to avoid late-onset HELLP.

"You really have to be on your toes if someone has had it with a first pregnancy," Anderson says. "If there's toxemia again in subsequent pregnancies, it's very likely."

The good news is that most pregnant women won't ever experience HELLP. While well-characterized eclampsia (also called toxemia) occurs in about 3 percent of pregnancies, HELLP accounts for only about 5 percent of those cases, according to Dr. Michael Varner, professor of maternal-fetal medicine at the University of Utah. The national HELLP Syndrome Society estimates about 27,000 women experienced the syndrome in 2000. It's hard to get a clear count, though, because it is often missed, and there's some debate about which lab values actually mean HELLP.

Varner notes that obstetricians are generally familiar with the condition and family practitioners are not far behind. Nevertheless, every couple of years a pregnant woman dies because it was not properly diagnosed, he says.

The symptoms and where a woman seeks care for them may make the difference, since the complaint may not seem to be related to the pregnancy. A woman goes to an emergency room with a killer migraine, for instance, and a doctor unfamiliar with HELLP never considers it. Plus, trademark symptoms like high blood pressure and protein in the urine may be mild or delayed, further complicating diagnosis.

By the time gall stones were ruled out and Tracy was diagnosed a couple of days later, her body was shutting down. Her blood wasn't clotting. Son Ryker, taken by emerency C-section, was small — 4 pounds 5 ounces — but fine. His mom still has her kidneys tested periodically, but she has recovered well. And when she got pregnant a second time, she had some toxemia, but she was able to deliver Regan in 2001 without major complications or C-section.

Thunell ignored the "don't worry" advice and kept complaining about the swelling. Her routine appointment was bumped up a few days, and she left it not in her car, but in an air ambulance headed to a hospital that could deal with her dire situation.

It's hard to pinpoint the cause. Preeclampsia itself is rather mysterious. Varner says that's called a "disease of theories about what causes it." Even less is known about the less common HELLP.

With HELLP, there's no guesswork, though, about the cure. Delivery — and quickly.