After the informed consent process and study enrollment, study participation will begin with a baseline cycle. The main goal of the baseline cycle is to identify the occurrence and the timing of ovulation. Starting at about day 6 of the baseline cycle, participants will undergo blood sampling for progesterone (P4) levels at intervals of every 2-3 days. An increase of P4 to greater than 3 ng/mL, confirmed by a second such value, will indicate ovulation and eligibility to continue in the study. The participant's baseline breast MRI and biopsy (see below) will be scheduled to occur in the mid luteal phase, about 7 days after the first increase (>3 ng/mL) in P4. The investigators will randomly assign which breast has the first biopsy, and women will return for a post-biopsy visit about 7 days later. At the post-biopsy visit, the investigators will assess acceptability of the MRI and biopsy to the participants using visual analog scales (VAS) as well as interview.