Uterine receptivity is essential for successful implantation. In mice, uterine receptivity begins with the secretion of LIF from uterine glands stimulated by estrogen on the morning of day 4 pregnancy. We hypothesize that gland readiness for estrogen stimulation is indispensable for uterine receptivity. The current study reveals that uterine glands undergo a differentiation process with expanded branching during the preimplantation period. The single-cell RNA profiling of glandular cells identifies that LIF is expressed exclusively in a Prss29+ subgroup of glandular cells on day 4 of pregnancy. Interestingly, Foxa2-deficient glands lacking LIF production fail to develop branches and the functional Prss29+ subgroup. This Prss29+ subgroup develops prior to estrogen secretion. Collectively, our findings show that uterine glands undergo a FOXA2-dependent maturation process to acquire the competence, named "transitional phase", for entering the receptive phase. The "transitional phase", predicting uterine receptivity one day before implantation, is a landmark concept in uterine receptivity.