HOUSTON, Jan. 19 (Xinhua) -- Infant mortality rates in the midwestern U.S. state of Texas vary dramatically, according to a news release Friday from The University of Texas System (UT System).

Some zip codes in the state have not experienced an infant death in the 2011-2014 period, whereas others have experienced more than 1 percent of their infants dying before their first birthdays.

Among just black mothers in Houston, there was an eight-fold difference in infant mortality rates across the city.

The zip code level rates were calculated for communities with 400 or more births in this four-year period, and were identified by the mother's zip code of residence at delivery. The data were obtained from the Texas Department of State Health Services (DSHS).

"What this reveals is that the infant mortality picture is dramatically more complex than we knew," said David Lakey, chief medical officer and vice chancellor for Health Affairs for UT System.

The variations, said Lakey, are both geographic and racial/ethnic. White women in Texas have a relatively low risk of their baby dying within the first year after birth. However, as with the infant mortality rate for all infants, there are significant community-level differences in infant mortality rates among this group. The highest infant mortality rates for white infants were seen outside the major metro areas.

Of the three major racial/ethnic groups in Texas, Hispanic women have the lowest rate of infant mortality. However, as with white women, infant mortality rates for Hispanic women varied greatly based on where they lived when they were pregnant.

Non-Hispanic black families in Texas and the United States are disproportionately impacted by infant mortality. However, mortality rates for infants of black mothers varied across zip codes of the same city.

Researchers with UT System will continue to work towards understanding why the variations exist and what can be done to reduce rates overall.