By Suzanne Rostler 

NEW YORK, Feb 21 (Reuters Health) -The good news is that more women nationwide got prenatal care, and fewer pregnant women smoked during the past decade.  

And the bad news? The percent of women in the US who gave birth to babies weighing less than 5.5 pounds slightly increased, and a greater percentage of children were born to unmarried women. What's more, a report on pregnancy trends released this week also shows that, on average, babies born to women in America's 50 largest cities begin life at a greater disadvantage than babies born elsewhere in the country. 

"There is no definite explanation, but we suspect it is due to the greater concentration of poverty in cities and the greater concentration of minorities," said Dr. Richard Wertheimer, a senior research associate for Child Trends, one of the groups that conducted the study. 

The percentage of children born to mothers with less than 12 years of education fell to 22% in 1998 from 24% in 1990 in the US as a whole, but stood at 27% in cities by the end of the decade.  

Mothers with less than a high school education are more likely to smoke during pregnancy and receive inadequate prenatal care, putting their babies at risk for illness and death in the first year of life. 

And 33% of children nationwide were born to unmarried mothers compared with 43% in cities in 1998. Unmarried women are less likely to get prenatal care and their children have a higher infant mortality rate.  

Wertheimer noted that the study found a lower rate of smoking during pregnancy in cities compared with the nation as a whole, and said that white women are more likely to smoke during pregnancy than black or Hispanic women. Smoking can stunt a baby's growth in the womb and increase the infant's risk of developing health problems.  

On the other hand, blacks and Hispanics were more likely to give birth during their teens, be unmarried, have low levels of education and receive late or no prenatal care compared with whites, the study reveals.  

Wertheimer said that efforts at the community, state and national levels are needed to reverse some of the negative trends that endanger the health of babies. 

In other findings, the rate of women who received inadequate prenatal care in the US declined to 4% from 6% over the study period and stood at 5% in cities in 1998. Failing to get prenatal care early on in pregnancy can increase the risk of a baby being born with health problems. 

The percentage of babies born weighing less than 5.5 pounds rose to 8% from 7% across the country and remained steady at 9% in the cities. An infant's weight at birth has been shown to predict the likelihood of dying in the first year of life and experiencing developmental and health problems during the course of life. 

The data from the National Center for Health Statistics was analyzed by Child Trends, a non-profit research group, and Kids Count, a project of a private charitable organization, the Annie E. Casey Foundation. The groups looked at eight variables that reflect a baby's health at the time of birth and social conditions prior to birth, which can influence a child's health throughout life.