A mаre presented fоr trаnsrectаl palpatiоn and ultrasоnography pregnancy check and showed a tightly closed cervix with a discrete fluid swelling at the base of the right uterine horn. Transrectal ultrasonography showed an embryonic vesicle with 55 mm in diameter, similar proportion of yolk sac and allantoic sac, and an embryo proper located at the center of the vesicle, between the allantoic and yolk sacs. Select the option that best estimates this mare's pregnancy stage: