The number of women giving birth early - often for no medical reason - has increased dramatically during the past two decades, altering the way we bear children and posing new health risks, experts say.

The average time a fetus spends in the womb has decreased by seven days in the United States since 1992, according to researchers and data from the Centers for Disease Control and Prevention.

Researchers say shorter pregnancies coincide with a large number of women and doctors now scheduling childbirth for convenience. One study of nearly 18,000 deliveries in 2007 showed that 9.6 percent were early births - through scheduled inductions or C-sections - for nonmedical reasons.

Shortening a pregnancy could affect a baby's lung development, vision, weight and some fine-tuning of the brain, experts say. Babies born too early often sleep longer than normal and have trouble learning how to breast-feed, causing dehydration and jaundice.

"For every day and every week before 39 weeks, it's an increasing risk to the baby," said Dr. Bryan Oshiro, vice chairman of obstetrics and gynecology at Loma Linda University. "The vast majority of early-term babies do fine, but it's like playing Russian roulette."

California Watch reported in September that women are significantly more likely to experience C-sections at for-profit hospitals across the state. In February, California Watch reported that the number of women who die each year from causes directly related to childbirth had more than doubled in California since 1996.

The rise in deaths during childbirth is an indicator that obstetric health has deteriorated in many important ways, according to the California Maternal Quality Care Collaborative, a task force of medical researchers.

Normal pregnancies are 40 weeks long, although researchers believe induced delivery at a full 39 weeks is probably safe. Women often naturally give birth earlier than this, and in some cases, medical problems require an early delivery. The problems come when babies are born before they are ready.

Of all births between 1990 and 2006, the number of babies born at 36 weeks increased by about 30 percent, and babies born at 37 and 38 weeks rose more than 40 percent, according to national vital statistics.

Unmistakable trend

There was a corresponding drop in the number of babies born in later weeks. There are now more babies born at 39 weeks than at full-term. The data examined is considered fresh by academic standards and covers such a long period of time - 16 years - that experts say the trend is unmistakable.

"The entire bell curve has shifted," said Dr. Jeanne Conry, California district chairwoman of the American Congress of Obstetricians and Gynecologists.

Some early births are scheduled for the convenience of the mother or doctor; some are judgment calls that require weighing relative risks.

A California Watch inquiry through the Public Insight Network, which solicits observations from people around the nation, asked mothers about their experiences with early deliveries. The questionnaire elicited responses from more than 300 women and produced several cases in which mothers said their doctors had pushed for early births.

One mother, Michelle Van Norman, gave birth to her second child, Christian, 11 days early in 2006, despite no urgency noted on her medical records. The doctor wrote on her chart: "This is a pleasant white female in no apparent distress."

Van Norman, 31, of Las Vegas, said her doctor didn't seem worried about the date.

"There were no medical reasons for the delivery being early," Van Norman said. "He told me the week he could do it and asked me to choose which day was best for us."

After his birth by C-section, one of Christian's lungs collapsed. He spent three weeks in intensive care and 10 days on a ventilator with six tubes going into his chest. It's unclear what caused Christian's lung to collapse but the condition is strongly associated with early childbirth.

"The whole experience was horrific," Van Norman said. "It didn't end with the birth, it continued for the first year of his life, and we still don't know if the oxygen deprivation has had any affect on him."

When Van Norman's surgeon cut the cord, Christian seemed robust. The doctor declined to comment about the case.

"The doctor came in the day after and asked where the baby was," Van Norman said. "When I told him, he asked me if I was joking. ... I swore from that day on I would never put another baby through that kind of torture for any reason."

Raising awareness

In California, the state Department of Public Health, March of Dimes and California Maternal Quality Care Collaborative have released what its authors call the "Toolkit." The authors note that deliveries at 37 and 38 weeks account for about 17.5 percent of total births in the United States.

Babies born early through induction or C-section without a medical reason are nearly twice as likely to spend time in the neonatal intensive care unit, researchers say. They also are more likely to contract infections and need the assistance of breathing machines, according to a 2009 study in the New England Journal of Medicine and a number of other reports.

"We are finding out that the last weeks of pregnancy really do count," said Leslie Kowalewski, an associate state director for the March of Dimes. "At 35 weeks, the brain is only two-thirds of what it will weigh at 40 weeks."

Many organizations are responding with programs designed to eliminate early elective deliveries. Most significantly, chapters of the American Congress of Obstetricians and Gynecologists have begun to notify doctors about the serious consequences of performing early elective births.

Authors of the "Toolkit" argue that cesarean sections and artificial induction of labor before full gestation should be eliminated, unless they are medically necessary.

The state chapter of the American Congress of Obstetricians and Gynecologists has thrown its weight behind this recommendation and is taking measures to see that it is carried out, holding teaching sessions and reaching out to obstetrics leaders at every hospital in the state.

"Nothing on this scale has ever been done before in California," Conry said. At the same time, physicians groups are rolling out the "Toolkit's" guidelines in New York, Florida, Illinois and Texas.

Medical interventions

The authors of the "Toolkit" note that rates of medically induced labor more than doubled between 1989 and 2004. The increase in deliveries between 37 and 39 weeks "has been associated with an increase in obstetrical interventions such as induction of labor and cesarean sections," the "Toolkit" authors said.

Lack of knowledge among clinicians and patients seems to have driven this trend.

To complicate matters, doctors start the pregnancy clock at a woman's last menstrual period before becoming pregnant, which is usually about two weeks before conception. All this is confusing enough that when doctors tell women they are at 36 weeks gestation and must wait at least a month before starting labor, they can grow impatient, Conry said.

"We call it tired of being pregnant," she said. "Some women have 36 weeks in their heads as the end point."

Societal changes also push women to seek an early delivery. Some women schedule births before their due date so they can better plan for taking time off work and flying in family members, Kowalewski said.

A little information can change this.

"I haven't met a woman who wasn't willing to continue her pregnancy if given information," said Debra Bingham, an author of the "Toolkit" and vice president of the Association of Women's Health, Obstetric & Neonatal Nurses in Washington, D.C.

"I've had experience with women who clearly didn't understand the risks of an elective induction, but it's also fair to say that there are a lot of doctors, nurses and childbirth educators who aren't aware of the risks."