Lactational amenorrhea and mesulleket damim-a medical halakhic analysis
Zimmerman, DR. 2002.  BH 13:173-181. CELD ID 21439

Lactational amenorrhea, or the lack of menstration during the time a woman is breastfeeding, has important implications in Jewish law. The talmudic sources and laws based on them describe a nonmenstrating time period of two years. This seems to contradict current common experience of much shorter periods of lack of menses during breastfeeding. The goal of this paper is to analyze the Jewish sources in light of modern knowledge of lactation.