The idea for the study came from Thornton's own lifelong struggle with weight. During her first pregnancy in the late 1970s, she gained 67 pounds and hit a peak weight of 225 pounds.
After the pregnancy, she signed up for Weight Watchers and lost 20 pounds, only to become pregnant again.
But with her second child, she continued the focus on nutrition and gained less than a half-pound.
"I was the first test case,'' Thornton said.
The American College of Obstetricians and Gynecologists has more on nutrition and weight gain during pregnancy.
SOURCES: Yvonne Thornton, M.D., M.P.H., clinical professor, obstetrics and gynecology, New York Medical College, Valhalla, N.Y.; Robin Kalish, M.D. director, clinical maternal fetal medicine, New York Presbyterian Hospital/Weill Cornell Medical Center, New York City; June 2009, Journal of the National Medical Association