"Now we see that the daughters of foreign-born women have similar issues," said Packard Children's neonatologist Ashima Madan, MD, "and that the indicators we have traditionally used to predict pregnancy outcomes - maternal educational level and age, and access to early prenatal care, for example - aren't reliable for every population." Madan is the lead author of the research, to be published in the March issue of the Journal of Pediatrics.
Researchers call the previously identified differences in pregnancy outcomes between Indian and Mexican immigrants the "dual paradox." That's because Mexican women giving birth in the United States are more likely than women from India to have healthy-sized newborns, even though they are less likely to have completed high school or to have initiated prenatal care during the first trimester of their pregnancy. In contrast, newborns of Indian immigrants, most of whom have completed college and begun prenatal care early, are more likely to deliver a low birth weight infant.
Madan, associate professor of pediatrics at the medical school, and her colleagues set out to determine for the first time whether this pattern persisted in the U.S.-born daughters of these immigrants. They surveyed more than 6 million births that occurred in 11 states between 1995 and 2000 to white, foreign and U.S.-born Asian-Indian and Mexican women. In addition to collecting data about the mother's birthplace and ethnic group, the birth records documented maternal age, history of prenatal care, maternal use of alcohol or tobacco, maternal educational level, and common complications of pregnancy and labor.
They found that Asian-Indian women were more than twice as likely to have low birth weight infants as were white women. These infants weigh 2,500 grams (about 5.5 pounds) or less at birth, either because they grew poorly in the womb or were born prematurely. They were also more than twice as likely to have babies that were small for their gestational age, regardless of whether they were premature. In other words, a generation in America didn't significantly improve or worsen the outcome for the Asian-Indian infants.
In contrast, although infants of foreign-born Mexican-American women closely mirror white infants in weight, the infants of U.S.-born Mexican-American women didn't fare as well, despite the fact that their mothers were more likely to have completed high school and tended to initiate prenatal care earlier. But even though they were more likely to be premature or smaller than infants of foreign-born Mexican-American mothers, they still weighed more, on average, than the infants of Asian Indians.
"You might ask, 'What's so bad about being small?'" said Madan, who points out that the growth curves used for this and other similar studies are based on white infants. "Is this just normal for Asian Indians? But we're concerned because we know that abnormally small babies run a higher risk of fetal distress and often require more intensive medical care and longer hospital stays after birth."
In addition, unusually small babies are known to be at higher risk for a variety of medical problems in adulthood, including diabetes, hypertension and an increased risk of heart disease - conditions that some studies have reported to be higher in Asian Indians.
Madan and her colleagues speculate that, among other things, maternal birth weight, stress, attitudes toward pregnancy and family support or other biological risk factors may play a role in fetal growth. In addition, Indian mothers were more likely than either Mexican Americans or whites to have diabetes, which in severe cases can restrict fetal growth.
"Our findings point out how much more we have to learn about fetal growth and well-being," said Madan. "Hopefully by continuing to study these populations we may identify new interventions that improve perinatal outcomes for women of all ethnic backgrounds."
The paper's senior author is Jeff Gould, MD, professor of pediatrics. Other researchers from the Stanford Prevention Research Center include instructor Latha Palaniappan, MD; research associate Guido Urizar, PhD; Yan Wang; and Stephen Fortmann, MD, professor of medicine.
Stanford University Medical Center integrates research, medical education and patient care at its three institutions - Stanford University School of Medicine, Stanford Hospital & Clinics and Lucile Packard Children's Hospital at Stanford. For more information, please visit the Web site of the medical center's Office of Communication & Public Affairs at http://mednews.stanford.edu.
Ranked as one of the nation's top 10 pediatric hospitals by U.S. News & World Report, Lucile Packard Children's Hospital at Stanford is a 264-bed hospital devoted to the care of children and expectant mothers. Providing pediatric and obstetric medical and surgical services and associated with Stanford School of Medicine, Packard Children's offers patients locally, regionally and nationally the full range of health-care programs and services - from preventive and routine care to the diagnosis and treatment of serious illness and injury. For more information, visit http://www.lpch.org
Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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