Sociomedical trends are giving new meaning to the phrase "dear old mom". Statistics confirm that first-time births to women in their 30s and 40s are fast becoming the norm.

Massachusetts has become the first state in which there are more births to women 30 and older than to those younger than 30, according to new statistics from the Department of Public Health. Of the 81,406 births in the state in 1998 -- the most recent year for which data are available -- women 30 and older accounted for 42,749 births, and women younger than 30 accounted for 38,657.

Twenty years ago, there were nearly three times as many new mothers younger than 30 than older than 30. Between 1994 and 1998, births to women 40 and older rose 41 percent.

Nationally, birth rates for women 30 to 34 rose 2 percent -- to 87.4 births per 1,000 women -- and increased 4 percent for women 35 to 39 -- to 37.4 births per 1,000 women. The rate for mid- to late-30s women was almost double the 1978 rate and set a record high, according to the National Center for Health Statistics. The birth rate for women 40 to 44 increased in 1998 to 7.3 per 1,000, a 92 percent increase over the 1981 rate. The median age at first birth, which has been rising slowly but steadily since 1972, increased to 24.3 years.

The news behind these numbers is that obstetric medicine will have to meet the needs of a changing population.

"Physicians need to become accustomed to taking care of the older gravida patient," said Jill Maura Rabin, M.D., clinical associate professor of obstetrics and gynecology at the Long Island (N.Y.) Jewish Medical Center campus of the Albert Einstein College of Medicine. (A gravida patient is simply a pregnant woman.)

"People are living better and living longer. This is more than a trend; it's the wave of the future," Rabin said.

Higher birth rates among Massachusetts women in their 30s and 40s could be explained in part by a concentration of highly educated career women. Massachusetts also requires insurers to cover infertility treatments -- one of 13 states to do so.

"It definitely has to do with demographics," said Deborah Klein Walker, Ed.D., Massachusetts associate commissioner of public health. "We have many educated women, and when there are career opportunities, women decide to delay having a family. Many of the women having babies over 30 are first-time mothers."

Experts speculate that a rise in divorces and second marriages also could be fueling the trend.

But there are risks.

Babies born to older women generally experience more problems, including prematurity and low birth weight. Massachusetts has had an increase in low-birth-weight babies. But the state's infant mortality rate fell 27 percent between 1990 and 1998 and is lower than the national average.

There are other problems associated with delaying childbirth. Fertility problems increase after about age 35. Miscarriage rates double. And the older a women gets, the higher the risk of chromosomal abnormalities, such as Down syndrome.

A 35-year-old woman has a 1-in-2,000 chance of carrying a child with chromosomal abnormalities. The risk rises to 1 in 100 for a 39-year-old and 1 in 20 for a 44-year-old. Birth defects rise from 5.2 per 1,000 for a 35-year-old to 15.2 per 1,000 for a 40-year-old and 47.6 per 1,000 by age 45.

Older patients are also at greater risk of developing conditions during pregnancy such as hypertension and diabetes -- illnesses also associated with general aging, said Owen Montgomery, M.D., assistant professor of obstetrics-gynecology at the University of Pennsylvania School of Medicine in Philadelphia.

But he said there are few conditions for which he would counsel against pregnancy after a certain age. Half the women in his obstetrics practice are older than 30, and "most do beautifully," he said. "The tradeoff for youthful enthusiasm is maturity. (Women in their 30s and 40s) want the pregnancy to be successful. They tend to take good care of themselves and follow instructions."

Countering the risks of later childbirth are other demographic factors: Older mothers tend to be married and better educated and have higher incomes.

"Preconception counseling is the single most important thing a doctor can provide to maximize a woman's chances of having a healthy pregnancy and delivery," Rabin said. It's recommended that women older than 35 receive genetic counseling as well as amniocentesis or a chorionic villus sampling test.