Stressful situations in early pregnancy can lead to the birth of babies who are underweight or born too early, new research from China shows. Timing of the stress, the researchers found, was the key.

“The findings are modest, but significant,” the authors write in the American Journal of Obstetrics and Gynecology.

The risks of premature births increased two-fold in women who were exposed to severe life events during their first and second trimesters - weeks 1-12 and 13-24, respectively. Premature birth, the authors note, is the single largest contributing factor in infant deaths in the developing world.

Researchers from Anhui Medical University, led by Dr. Peng Zhu, followed 1,800 pregnant women receiving prenatal treatment in 2008 at one hospital. The participants were surveyed on financial conditions, emotional support, traumatic events and their relationships with their spouses. Were jobs or fortunes lost, were family members cheated, did the family move, did a family member die or suffer an illness, or was there fighting or divorce?

There were 96 (5.3 percent) premature births and 55 (3.1 percent) low birth-weight babies.

Earlier studies have found that future moms with stressful lives were at greater risk of delivering preterm or low birth-weight babies. This study - looking at a long list of potentially stressful events experienced during pregnancy only - concluded that the earlier in pregnancy the stress occurred, the greater the risk.

The Zhu team found that premature birth was more than twice as likely if severely stressful events occurred during the first and second trimesters, but not the third. Low birthweight was nearly three times more likely if stress happened during the first trimester, compared to if it happened during the second or third trimester.

While for the most part consistent with earlier research, the Chinese researchers caution that the reach of their findings could be limited.

For instance, they warn that faulty memories, the small number of women in some of the stress categories, and the possibility that the list of stress events was flawed could weaken the power of the results.

The Zhu team concluded that health planners seeking to reduce the incidence of pre-term and low-weight births must take maternal stress into account when designing intervention programs.

However, Drexel University’s Dr. Robert L. Goldenberg, who was not involved in the study, said the findings will not change current practice.

“There aren’t even any hints about what those interventions might be,” Goldenberg told Reuters Health. “While they suggest the need for interventions, they do nothing to move knowledge forward.”

Interventions that have been tested in well-designed clinical trials, such as counseling and home care assistance, have not demonstrated any benefit, Goldenberg said.

“If we want to improve outcomes, we must now figure out interventions that will reduce the effects of the problem,” he said.

SOURCE: American Journal of Obstetrics and Gynecology, online April 26, 2010.