Pregnant with her third child, Placida Blackwood first heard about cord blood banks in her obstetrician's waiting room. The pamphlet didn't leave much of an impression. What's the point of paying some company hundreds of dollars to store a little blood from her baby's umbilical cord?

"I didn't think I would need it, and I certainly couldn't afford it," says Blackwood, who is 28 and lives in Cockeysville.

The next time she heard about cord blood was a few months later, when doctors told her that her oldest son had leukemia. Cord blood, they said, might save his life.

Once tossed in the trash along with the placenta and other delivery-room debris, the umbilical cord - along with the blood it contains - has become the focus of growing interest among scientists, entrepreneurs and especially expectant parents.

Cord blood, it turns out, is rich with stem cells. Since 1988, doctors have increasingly turned to these cells as a life-saving alternative to bone marrow transplants for people with leukemia, sickle cell anemia and other blood-borne diseases.

As a consequence, roughly a dozen for-profit companies have sprung up offering to store cord blood for new parents. Pitching the service as "biological insurance," they blitz mailboxes and maternity wards with glossy pamphlets.

Although not all physicians believe it's worthwhile - and cord blood still accounts for only a tiny proportion of transplants - more parents are deciding to do it.

"It's definitely getting asked about more and more," says Adriane Burgess, a labor and delivery nurse at St. Joseph Medical Center in Towson who also teaches childbirth classes at the hospital.

Burgess and others say one of the big questions parents have concerns the often-confusing science of stem cells.

Stem cells are the precursors for every other cell type in the human body. Scientists hope someday to cure all sorts of diseases by transplanting stem cells - which would then become brain cells or liver cells or heart muscle cells, for example - or manipulating them to grow entire new organs to replace damaged ones.

But some stem cells are not as flexible as others. Those from embryos hold the most promise because of their ability to develop into every cell type, but research using them has been limited because of ethical concerns.

Stem cells from bone marrow and umbilical cords are used mostly for their ability to turn into blood and disease-fighting immune cells, but scientists are trying to coax them into other cell types.

Today, cord blood is used mostly in cases where bone marrow is unavailable.

Advantages of blood

Still, it has several advantages, experts say.

For one, stem cells from cord blood often don't require as close a biological match as those from bone marrow, meaning there's more of a chance the transplanted cells will "engraft" or thrive and manufacture blood cells in their new home.

Another advantage is that, because cord blood can be frozen, doctors can get it quickly - often within a day or so, says Dr. Dennis Confer, chief medical officer of the National Marrow Donor Program.

Marrow, in contrast, can take weeks to collect because doctors have to find a biologically matched donor, who must undergo an unpleasant procedure to extract it.

Finally, cord blood recipients might be less at risk of what is called "graft-vs.-host" disease, a condition that occurs when transplanted immune cells declare war on their new host.

Despite these advantages, experts disagree over whether storing cord blood is worth the expense. After reviewing the issue several years ago, the American Academy of Pediatricians deemed it "unwise" unless parents had genetic disease in the family.

One of the most common diseases that cord blood is used to treat is leukemia, a condition that killed 20 Marylanders ages 24 and younger last year, according to the state Department of Health.

"It's rare," says Dr. Allen Chen, a pediatric oncologist at Johns Hopkins' Kimmel Cancer Center.

Still, a growing number of parents are deciding that it's insurance worth having - for the child or other family members.

Before the birth of their first child, Ethan, in September, Ron Samuelson and his wife, Laura, asked an obstetrician friend whether they should store their baby's cord blood.

He told them there's really no downside.

So the couple signed up with Cord Blood Registry, an Arizona company that charges $1,295 up front and $95 a year to freeze and store the blood. The company says it has 1,200 clients in Maryland and more than 40,000 across the country.

Minutes after birth

Collecting cord blood is painless. Most banks send their clients a kit containing a blood bag, syringe and anticoagulants to hand over to delivery room doctors.

The blood is collected minutes after birth when the umbilical cord is snipped. Then the sample - ranging from a few tablespoons to a half-cup - is shipped overnight to the bank, where it's frozen in liquid nitrogen.

"You only have one shot to get the stem cells," says Samuelson, who owns Boston Loan, a pawnshop and jewelry store on West Baltimore Street. "In 30 years if, God forbid, something happens, they'll probably be able to generate an organ out of it.

"This is the future of medicine."

But not all parents are swayed by the science - or the sales pitches.

Linda Lane, a 35-year-old mother of two toddlers in suburban Boston, said she researched the banks when she was pregnant and concluded they are a "rip-off." Most of her female friends, she said, feel the same way.

For her, one big turnoff is the subtle psychology many banks employ: "Don't you want to do the best for your child?"

A self-described worrier, she said that if she thought there was even a slight chance that cord blood stem cells would someday help her children, "I'd have opened my checkbook right there."

But in the end, she decided, "the possibility of using it was just so remote. I'd rather spend the money on their future, like college."

David Harris, scientific director of the Cord Blood Registry, argues that it's not rare diseases such as leukemia that make banking cord blood worth it, but the hope that it can used far more widely in the future. Research in Japan has hinted that cord blood stem cells can turn into nerve cells.

Bone marrow, though, might be even more promising.

Scientists at the University of Minnesota have amassed evidence that bone marrow stem cells can be coaxed to turn into nerve, liver, lung and pancreas cells in addition to blood cells, says Dr. John Wagner, clinical director of the university's Stem Cell Institute.

If marrow turns out to be that flexible, he says, saving cord blood would be unnecessary.

Still, since 1988 more than 2,000 people have received cord blood transplants. Some have been lifesaving, as it turned out to be for Placida Blackwood's family.

Frightening diagnosis

In August of last year, a routine blood test for her oldest child, Casey, came back abnormal, indicating the boy's white blood cell count had skyrocketed.

The pediatrician sent Casey to Johns Hopkins Hospital. There, doctors confirmed the worst: The 4-year-old had leukemia.

Doctors told Blackwood and her partner, Shawn Collins, a 28-year-old accountant at Sylvan Learning Systems, that chemotherapy was the best hope for Casey.

One physician offhandedly advised Blackwood, who was due to deliver the couple's third child within days, that she still might want to save her baby's umbilical cord blood, just in case.

Later that evening, as her son was being treated, Blackwood went into labor.

Things were happening so fast that it was unclear whether the delivery team was even told by oncologists to save the umbilical cord. Worried, Blackwood never let them forget.

"I was on the table pushing the baby out saying: 'You have to save the cord blood! You have to save the cord blood!'"

That saved Casey's life.

Chemotherapy later failed, and Blackwood says doctors told her, "If we don't get him a transplant, he'll be gone in nine months."

Despite testing family members and combing bone marrow registries for a match, doctors couldn't find a donor. A stem cell transplant turned out to be the couple's only hope.

Sister's donation

So doctors sent for Casey's little sister's stored blood.

Unlike organ transplants, a stem cell transplant is fairly mundane. Doctors typically hang the blood by the bedside, insert a tube into the patient's arm and let it drip in.

After the transplant, Casey developed graft-vs.-host disease, causing his skin to blacken and his body to shed nearly a third of its weight.

"He wasted away to nothing," his mother said.

But the stem cells ultimately took and started churning out healthy blood cells.

Today Casey, 6, is in remission and back in school. Although he goes to Hopkins every other week for checkups, "he's back on track," his mother said.

The couple likes to show off a photo taken on the day they call the best and worst of their life.

Snapped just moments after their daughter, Sydni, was born, it shows their son sitting up in his hospital bed, holding his new baby sister against his hospital gown, beaming. Tubes snake from the boy's arms.

Below the image, a caption reads: "I love my baby sister!"

"When I look back at that picture," said Collins, "it kind of tells the story best."