Length of residence in the U.S. increases risk of PTB among Hispanic women

The longer a Hispanic woman lives in the United States, the higher her risk of preterm birth (PTB), with nearly half of PTBs among Hispanic women occurring in those who were born in the U.S.

This is the main finding of a study by researchers at the University of Texas Medical Branch (UTMB) at Galveston who sought to shed light on possible environmental factors in PTB. It is one of several studies from UTMB presented this week at the Society for Maternal-Fetal Medicine's (SMFM) 32nd Annual Meeting in Dallas.

"Though we don't know whether preterm birth is predominately related to genetic or environmental factors, our research shows that preterm birth is at least strongly related to our environment in ways that are potentially preventable," said principal investigator Dr. Radek Bukowski, professor of obstetrics and gynecology in the Division of Maternal-Fetal Medicine at UTMB.

More than half a million babies are born prematurely each year in the U.S.; the cause is unknown in as many as 40 percent of cases.

Using data from a population study of more than 2,140 Hispanic women with a prior live birth who participated in the National Health and Nutrition Examination Survey (1999-2006), the researchers observed that the PTB prevalence rate for women residing in the U.S. for fewer than 10 years was four percent; after 10 years, that rate rose to 7.4 percent. Hispanic women born in the U.S. had a PTB prevalence rate of 9.5 percent.

The researchers adjusted for age, body mass index, education, marital status, income, current and prior smoking, diabetes and hypertension, among other potential factors.

"We were surprised to find that the risk was nearly twice as high for women living in the U.S. for more than 10 years and was almost three times higher for women born here," said Bukowski. "These findings confirm the link between preterm birth and environmental factors. However, it remains unclear what specific environmental features may predispose or protect women from preterm birth. That said, because the risk factors appear to have been acquired while living in the U.S., it is likely that they are modifiable," added Bukowski.

Additional UTMB research presented at the SMFM meeting includes:

• Immune and biochemical pathways of preterm labor vary in response to specific bacteria associated with amniotic fluid infection and differ between races. Led by Dr. Ramkumar Menon, assistant professor, Division of Maternal-Fetal Medicine, researchers tested normal-term fetal membranes exposed to a range of pathogens linked to spontaneous PTB for differences in immune response and between African American and Caucasian women. They found that pathogens associated with PTB have different cytokine signatures and that those with lipopolysaccharides (LPS; lipids containing endotoxins) provide maximum immune response. Further, pathogens such as E. coli may play a role in racial disparities associated with infection-mediated PTB. Menon notes that the findings reiterate that the pathways of PTB associated with bacterial infection are not universal and that interventions should take into account the type of infection and the patient's race/ethnicity.
• Babies born to obese mothers are at risk for metabolic syndrome as adults. Dr. Arshag Kalanderian, also from the Division of Maternal-Fetal Medicine, and his team explored whether they could activate a known biological pathway with a diabetic drug to improve the metabolic status of mouse offspring exposed to maternal obesity. They found that short-term therapy with the drug pioglitazone (PL) significantly reduced the offsprings' body weight and other metabolic changes associated with developmental programming. According to Kalanderian, this research is novel and points to a potential new role for PL and similar drugs.
• Other UTMB researchers presented data on late-preterm birth and optimal timing of repeat cesarean sections; the novel use of statins to prevent preeclampsia and PTB; and the effects of nicotine exposure on long-term cardiovascular health of babies, among others.