How about the contraceptive pill that allows fertilization of the egg, but prevents it from attaching to the uterus wall, thus being flushed during menstration. Commonly used contraceptive by thousands if not millions of women who would no sooner enter an abortion clinic than to....well date me. Yet month after month, a fertilized egg already beginning the process of life and cell division cannot attach itself to the uternine wall. And slowly the life drifts down the canal and finds it's final resting place.... well it gets graphic.
Technically a dalcon shield does exactly that.