The rate of cerebral palsy among very preterm infants may be much lower now compared with 20 years ago, a study at one large medical center suggests.

Cerebral palsy refers to a group of conditions, usually present at birth, that permanently damage movement, balance and posture. The impairments range from mild to more severe, such as mental retardation and an inability to walk.

The precise cause of cerebral palsy is unknown, but it’s thought to involve a disruption in normal fetal brain development. Premature and low-birthweight infants have a higher risk than full-term, normal-weight babies.

Studies on the rate of cerebral palsy among preterm infants have come to conflicting conclusions, with some suggesting it has remained stable and others finding a decline.

In the new study, researchers at the University Medical Center Utrecht, in the Netherlands, found that between 1990 and 2005 cerebral palsy rates fell among preterm infants treated in their neonatal intensive care unit (NICU).

From 1990 to 1993, 6.5 percent of 755 infants were diagnosed with cerebral palsy. That rate fell to 2.2 percent of 913 newborns admitted to the NICU between 2002 and 2005 according to the findings, which are published in The Journal of Pediatrics.

Much of the decline seemed to be related to a 93 percent drop in the number of preterm infants with severe damage to the white matter of the newborn’s brain, called cystic periventricular leukomalacia. The condition is commonly caused by infections in the mother.

One of the factors found to be protective against cerebral palsy was giving antibiotics to mothers in preterm labor, lead researcher Dr. Linda de Vries told Reuters Health in an email.

In general, the researchers say, improvements in prenatal care in recent years likely deserve the credit for the declining rate of cerebral palsy. Those include giving corticosteroids to mothers who are at risk of preterm labor, in order to speed fetal lung development.

“Over the years we have seen a decline in the number of infants needing ventilation after delivery,” de Vries said. And as fewer newborn preemies have needed to be placed on ventilators, fewer have been developing brain damage resulting in cerebral palsy.

The findings, de Vries said, are “indeed good news.”

“Parents and their children can therefore benefit from being born in a developed country with access to good (prenatal) and neonatal care with experienced members of staff,” she said.

While the findings are from one medical center, de Vries said that there is similar evidence from other countries. A recent Canadian study found a declining prevalence of cerebral palsy over 30 years, she noted. And a study at the University of California, San Francisco, found a falling rate of cystic periventricular leukomalacia after the early 1990s.

It’s not clear why some past studies have failed to show a decline in cerebral palsy. But one reason, according to de Vries, may be that some have included the most extreme preemies - born during the 23rd or 24th week of pregnancy; the infants in the current study were born at week 25 or later.

A U.S. study published last month highlighted the importance of preterm birth - and possibly prenatal care - in children’s risk of cerebral palsy.

Researchers found that among 6.2 million births in California between 1991 and 2001, black infants were about 30 percent more likely than white babies to have cerebral palsy. And the extra risk appeared to be explained by their greater risk of being born underweight.

The overall prevalence of cerebral palsy was 1.4 cases for every 1,000 live births.

The researchers speculated that better prenatal care for black mothers, especially teenagers, might help close the racial gap in low birthweight - and possibly cerebral palsy as well.

SOURCE: The Journal of Pediatrics, online March 3, 2011.