NEW YORK — Kim Farmer grew sick of the garish yellow T-shirts her twins wore frequently after they were born in July.

Grace and Henry wore the tops incessantly because they were born six weeks early and Farmer couldn't find many clothes for premature babies.

"I wish I had some nice clothes for when I wanted to have a photo taken," said Farmer, a resident of Alpharetta, a suburb of Atlanta. "I couldn't find anything for my preemies and there is such a need."

Farmer and other mothers of preemies complain of the difficulties in finding products to meet the special needs of their children, ranging from small-sized clothes that can accommodate wires from life-support machines to tiny bottles to fortified formula.

But as the number of premature children in the United States continues to rise, businesses including hospitals, magazines and clothing manufacturers are stepping up with products and services to fill the demand.

Families with premature children aren't necessarily an easy niche to reach, however. Their needs are different from those with full-term infants and they cut across geographic, economic, ethnic and religious lines, making target marketing difficult. What's more, many stores don't want to carry items for preemies because there isn't always a steady stream of customers.

"There is a lot of education to get local shop owners to stock preemie products," said Lisa Purkerson, the owner of Preemie-Yums, a line of clothing. "Preemie sales go in spurts and sometimes the clothes may stay in the shop for a long time."

The number of children born premature — before the 37th week of pregnancy — has been rising annually since 1981 in all but two years, according to the March of Dimes. In 2003, the most recent numbers available, 12.3 percent of children — 499,008 infants — were born prematurely, up from 12.1 percent in 2002. The number of premature births has grown 16 percent since 1990 and more than 30 percent since 1981, a report by the National Center for Health Statistics and Centers for Disease Control and Prevention said.

Numerous factors contribute to the rise in premature births. More women are delaying childbirth and older moms are at greater risk for delivering early. The increased use of fertility treatments often leads to more multiple births; twins have about a 50 percent chance of being premature while triplets' likelihood jumps to 90 percent, according to Dr. Scott Berns, a vice president at the March of Dimes.

Premature infants are more likely to endure serious, multiple health problems than infants born at full term, 37 to 40 weeks. Preemies often require medical care such as feeding tubes, ventilators and oxygen monitors that mean staying in the hospital in special neonatal intensive care units.

Many hospitals are either adding or expanding such units to satisfy the need. The NICUs not only provide a much-needed service to the community but also are often profit centers for the hospital because of generous insurance reimbursement rates, said Kerry Shannon, a director at Pricewaterhouse-Coopers LLP.

Earlier this year, Ohio State University Hospital in Columbus spent $1.5 million to add eight beds to its NICU, bringing the total to 49. The unit had been running a 98 percent occupancy rate, which didn't leave much margin for a rash of emergencies, so an expansion was considered prudent, said the hospital's chief operating officer Judy Gilliam.

Reimbursement wasn't the chief consideration in the expansion decision but it was a factor, said Gilliam. And the expanded unit is a marketing bonus, she said.

"It is definitely an advantage to say to the community that you provide a full complement of women and infant services," Gilliam said.

For moms of premature babies, such specialized units are invaluable not only for the lifesaving medical services they provide but because of the advice from the doctors and nurses about how to care for the children. The hospitals also sometimes send the moms off with special formula, bottles and diapers that can be hard to find at stores.