various groups. Causes of the state's poor rankings include politics, a high poverty rate, and the highest rate of illegal immigration in the nation. In May 2006, Texas initiated the program "code red" in response to the report the state had 25.1 percent of the population without health insurance, the largest proportion in the nation. The Trust for America's Health ranked Texas 15th highest in adult obesity, with 27.2 percent of the state's population measured as obese. The 2008 Men's Health obesity survey ranked four Texas cities among the top 25 fattest cities in America; Houston ranked 6th, Dallas 7th, El Paso 8th, and Arlington 14th. Texas had only one city (Austin, ranked 21st) in the top 25 among the "fittest cities" in America. The same survey has evaluated the state's obesity initiatives favorably with a "B+". The state is ranked forty-second in the percentage of residents who engage in regular exercise according to a 2007 study. Texas has the highest maternal mortality rate in the developed world, and the rate by which Texas women died from pregnancy-related complications doubled from 2010 to 2014, to 23.8 per 100,000 — a rate unmatched in any other U.S. state or economically developed country. In May 2021, the state legislature passed the Texas Heartbeat Act, which banned abortion from as early as six weeks of pregnancy, except to save the life of the mother. The Act allows private citizens to sue abortion providers and anyone else who assists in an abortion, except for the woman on whom the abortion is performed. The Act applies to pregnancies caused by incest or rape, although a clause prohibits the perpetrators from enforcing it with civil lawsuits. On August 25, 2022, another law took effect that made committing abortion at any stage of pregnancy a felony punishable by life in prison. Medical research Texas has many elite research medical centers. The state has 15 medical schools, four dental schools, and two optometry schools. Texas has two Biosafety Level 4 (BSL-4) laboratories: one at The University of Texas Medical Branch (UTMB) in Galveston, and the other at the Southwest Foundation for Biomedical Research in San Antonio—the first privately owned BSL-4 lab in the United States. The Texas Medical Center in Houston, holds the world's largest concentration of research and healthcare institutions, with over 50 member institutions. Texas Medical Center performs the most heart transplants in the world. The