"In examining the causes of problem pregnancies, medical researchers increasingly study lifetime stress, not only stress during pregnancy... Many experts now conclude that stress causes release of hormones that weaken the uterus, leading to premature delivery or mortality. The hormone changes can occur over a lifetime, not only in pregnancy. They may build up from fear of violence, from worries about paying for food or housing, from job insecurity or from having to stand for long periods at work. One study found that problem pregnancies were more frequent among black women who reported more experiences with racial discrimination in employment or housing."  Richard Rothstein, The New York Times.