Purpose: Breast cancer is the primary cause of cancer-related death in women. Women diagnosed with estrogen receptor (ER)-positive breast cancer have prolonged treatment durations. Owing to the paucity of research and lack of consensus regarding conception planning and pregnancy for patients with ER-positive breast cancer, we aimed to assess pregnancy and survival outcomes in women with ER-positive breast cancer during and after treatment. Methods: We conducted a systematic review of the available studies on pregnancy after ERpositive breast cancer. The assessed outcomes included overall survival (OS), disease-free survival (DFS), hormonal therapy duration, and pregnancy outcomes. Results: Ultimately, 2,669 patients from five studies were included in this study. When all breast cancer receptor subtypes were included in the analysis, pregnancy after breast cancer was associated with a time-dependent protective effect on both DFS and OS. This protective effect was not evident when examining ER-positive patients with subsequent pregnancies, and no significant differences in DFS were observed. ER-positive patients who became pregnant received significantly lower rates of hormonal therapy. Hormonal treatment at the time of pregnancy was correlated with increased rates of termination owing to concerns about teratogenic effects. Conclusions Pregnancy after breast cancer did not significantly affect DFS in ER-positive patients over a follow-up period of 5–10 years from diagnosis, although did significantly affect hormonal treatment duration in the reviewed studies. Further analysis and in-depth studies are required to assess the effects of altered hormonal treatment times, as well as patient management related to pregnancy planning after breast cancer.