MADISON, Wis.  Seven and a half months into Ta-Shai Pendleton’s first pregnancy, her child was stillborn. Then in early 2008, she bore a daughter prematurely.

Soon after, Ms. Pendleton moved from a community in Racine that was thick with poverty to a better neighborhood in Madison. Here, for the first time, she had a full-term pregnancy.

As she cradled her 2-month-old daughter recently, she described the fear and isolation she had experienced during her first two pregnancies, and the more embracing help she found 100 miles away with her third. In Madison, county nurses made frequent home visits, and she got more help from her new church.

The lives and pregnancies of black mothers like Ms. Pendleton, 21, are now the subject of intense study as researchers confront one of the country’s most intractable health problems: the large racial gap in infant deaths, primarily due to a higher incidence among blacks of very premature births.