California's risky trend: an over-40 baby boom

But even in vitro fertilization rates decline with age when older women use their own eggs. (The newest fertility breakthrough, announced this year, may allow younger women to freeze eggs for use later.) According to the U.S. Centers for Disease Control and Prevention, the average chance for a 40-year-old woman undergoing assisted reproductive therapy to become pregnant using her own eggs was 23%, and to successfully carry the pregnancy through to birth, about 16%. Both rates dropped steadily with each one-year increase in age.

Using donor eggs, however, raises the chances for a successful live birth to 51% for women over 40, according to the CDC.

"Because it's so reliable, the number of women getting egg donation is going up every year," Rodi said. "And that is contributing significantly to the number of pregnancies in women in their 40s."

Donor eggs also eliminate some of the risks associated with older childbearing, said Dr. Richard Paulson, chief of the Division of Reproductive Endocrinology and Infertility at USC's Keck School of Medicine and a pioneer of egg donation. Aging eggs not only contribute to infertility and miscarriages but are more likely to have chromosomal abnormalities.

Despite the advantages of using donor eggs, admitting to doing so is one of the few remaining reproductive taboos -- among celebrity and regular moms alike.

And donor eggs aren't foolproof -- nor are they cheap. Treatment can cost from $10,000 to more than $25,000 per attempt, with high-demand donors such as Ivy League graduates and models commanding higher fees.

What's more, "virtually every complication associated with obstetrics is increased with increased maternal age, if you look at it statistically," Paulson said.

"But most of us believe that if women get good prenatal care and are carefully followed, the outcome is very good."

Dr. Alan R. Fleischman, medical director for the March of Dimes, an organization primarily concerned with the eradication of birth defects, is less optimistic.

"All of the complications of pregnancy -- high blood pressure, preeclampsia [a rapidly progressing hypertension that affects mother and fetus], fetal death, prematurity, low birth weight -- occur at higher rates in older women than in younger women," he said. "That's true with or without assisted reproductive technologies."

A 2004 study of Swedish women found the rate of premature births for women ages 40 to 44 to be 150% higher than for women 20 to 29, Fleischman said.