Abstract: Menstrual synchrony is when the menstrual cycles of friends or family members coincide, such that women conform to the same cycle. In this paper, we propose for the existence of synchronous pregnancies, which may be analogous to menstrual synchrony. Menstrual synchrony is a well studied topic, whereas synchronous pregnancies among friends or family members is an overlooked area of investigation. In this exploratory study of 81 pregnant women, we hypothesize that women's pregnancies are synchronized with those of friends or family members. We also examine whether women intentionally plan their pregnancies in accordance with these individuals. Finally, we investigate the sharing of resources among women who have simultaneous pregnancies. Our findings suggest that the pregnancies of women are more synchronized with friends than family members, and often the synchronicity is unplanned. The majority of women indicated that they intend to share resources (including parenting) with others who are pregnant at the same time, or who have recently given birth. Using an evolutionary framework, we propose that the sharing of resources is highly valuable and might represent a reason for women to, albeit inadvertently, have synchronized pregnancies. Keywords: pregnancy; sharing behavior; mothering; women's sexuality; menstrual synchrony AN INVESTIGATION OF SYNCHRONOUS PREGNANCIES IN WOMEN The phenomenon that groups of women in close relationships (e.g., sisters, close friends) appear to get or be pregnant simultaneously is an unexplored and potentially unnoticed area of science, despite its implications from both health and medical perspectives. Furthermore, the topic has academic appeal, at least to those in evolutionary psychology, because synchronous pregnancy represents a potentially adaptive behavior for women. Here we investigate the relationships in which synchronous pregnancy occurs and document some of the potential evolutionary bene-
