Menstrual cycle mating partners during the menstrual cycle; however, those seeking a short-term relationship were more likely to choose a partner with more masculine features than usual. This was found to be the case especially during the woman's high conception risk stage and when salivary testosterone was high. However, when women are in the luteal (non-fertile) phase, they tend to prefer men (and females) with more feminine faces. A preference is also shown for self-resembling faces and apparent health in faces during the luteal phase of the cycle. Apparent health preferences were found to be strongest when progesterone levels were high. Additionally,
Breast development lactation by prolactin. Expression of the PRLR in breast tissue may increase by as much as 20-fold when estrogen and progesterone levels drop upon childbirth. With suckling from the infant, prolactin and oxytocin are secreted and mediate milk production and letdown, respectively. Prolactin suppresses the secretion of LH and FSH, which in turn results in continued low levels of estrogen and progesterone, and temporary amenorrhea (absence of menstrual cycles) occurs. In the absence of regular, episodic suckling, which keeps prolactin concentrations high, levels of prolactin will quickly drop, the menstrual cycle will resume and hence normal estrogen and progesterone levels