It was baby gridlock yesterday at the Greater Baltimore Medical Center, where hundreds of babies, young children and their immensely proud parents paid tribute to one of the nation's most successful test-tube baby programs.

Toddlers toddled with impunity among their elders' legs. Beaming dads with video cameras blocked hallways in their attempts to catch every moment on film. Moms filled the chairs as they fed the infants cradled in their arms.

No one seemed to mind the commotion.

"Mind? This is my miracle baby, they are all miracle babies," said Debbie Ingate, who tried to have children for almost four years before the in vitro program brought her Steven, her 22-month-old son.

"It makes you realize a lot of people need help like this," added her husband, Steven Ingate.

Nor did the parents of the many twins or triplets on parade utter a word of regret about their instant families. Almost a third of all women taking advantage of the in vitro procedure have multiple births.

"We had to get a bigger car . . . but you can't put a price on what they mean to us," said Donna Lenz, who had twin girls through the program, bringing the number of children in her family to four.

About 530 test-tube babies have been born through the medical center's Women's Hospital Fertility Program since it opened in 1985, making it one of only three programs in the nation to have more than 500 babies. More than 250 families showed up for yesterday's reunion.

In vitro fertilization has been in use for a dozen years, ever since the birth of Louise Brown in England, the first baby to start life outside a woman's womb. Since then, more than 200 clinics have opened in the United States; about 10,000 children worldwide owe their births to the procedure, according to Santiago Padilla, associate director of the Baltimore area center.

The procedure is often the last resort for couples who have struggled for years to have children.

The in vitro procedure involves retrieving eggs from a woman's ovaries, mixing them with sperm outside the body until they are fertilized, and then reimplanting the fertilized eggs inside a woman's uterus.

About one-third of all the women who undergo the procedure at the center get pregnant; about 24 percent carry to term, said center director Jalro E. Garcia. Multiple births are common because more than one egg is usually implanted to increase the chances of success.

Each attempt costs about $6,700, and while a woman can conceive on her first try, there's a 90 percent chance of success after six consecutive attempts, Garcia said.

Maryland is one of only five or six states in the country that require insurance companies to cover the costs of the procedure as they would cover other maternity costs.

Without insurance, said Bob Lenz, a Carroll County schoolteacher, it would have been hard to justify the cost. It took four tries to conceive his son Chad, now 2. His twins were conceived on the first try. He also has a son, Brian, 8, who was conceived naturally.

William T. Bunk Jr., who owns several auto parts stores in Pennsylvania, said he has no regrets about picking up the cost of three in vitro tries. The result: 8-month-old twins, William III and Elizabeth.

"I could afford it. But why should anybody be denied this?" he asked.

Yesterday's reunion was an especially proud moment for Garcia, who served on the team responsible for the first test-tube baby in the United States in Norfolk.

Garcia was surrounded by parents who wanted to shake his hand and to show off their children.

He said, "I still enjoy every single birth."