Here is a paragraph from the book, A Gynecologist's Second Opinion: The Questions and Answers You Need to Take Charge of Your Health by William H. Parker, M.D., with Rachel L. Parker, Contributions by Ingrid A. Rodi, M.D. and Amy E. Rosenman, M.D.
"Once the lining cells of the uterus are destroyed by the procedure, there is no place for a developing fetus to attach within the uterus. If some cells remain following an ablation, there exists the rare possibility of pregnancy occuring. If pregnancy were to occur, termination would most likely be recommended as doctors are concerned that without adequate cells lining the inside of the uterus, the placenta would grow directly into the muscle wall of the uterus and take hold like the roots of a tree. As a result, the placenta would not be able to separate at the time of delivery, and hemorrhage could occur. This procedure is not a form of birth control and another method of birth control must still be used to avoid pregnancy."
"Ablation does NOT provide reliable birth control, since ovulation still takes place as before, and the uterine lining may be receptive to a pregnancy. Second, pregnancy in general should not be elected after an ablation; in fact, it can be dangerous. The procedure can cause changes in the uterus that make pregnancy potentially hazardous to the mother, including possible complications such as uterine rupture and placenta accreta (a placenta that becomes "stuck" to the uterus and cannot be removed, causing potentially life-threatening bleeding). Because of the potential problems with future pregnancies, it is generally recommended that reliable birth control, including male or female sterilization, be considered in women who undergo ablations. Please discuss this further with your doctor."