Using biosensors, or devices that provide biological information to users about their own bodies, to map ovulation and time intercourse is a practice of rising significance in economically privileged countries. Based on an ethnographic study of ovulation biosensing, this paper explores the contradictions between device manufacturers' figurations of reproductive heterosex as a natural and pleasurable experience facilitated by fertility monitoring technology, and heterosexual women users' accounts of the pleasures and difficulties of ovulation monitoring and associated sexual encounters. Drawing on Science and Technology Studies and the concept of 'script', we examine the frameworks of action defined by makers of ovulation biosensors and how these are accepted, refused or remade by users. Within the scientific romance configured by manufacturers, reproductive heterosex emerges as exciting and fun, whilst the hard, 'technical' work of conception is done by ovulation technologies. Yet ovulation monitoring is described by many heterosexual women users as an exciting and yet anxiety-producing practice through which they come to know their bodies differently, often through online discussions with other women. Living a 'conceptive imperative', women engaging with ovulation sensing reconfigure their reproductive embodiment and shift their relationship to male partners in ways that reveal heterosexual 'baby-making' as a complex and nuanced practice worthy of critical engagement.