Breast cancer is the most common cancer in women of reproductive age. Many patients have not yet completed their family planning at diagnosis, making fertility a major concern.

We conducted a retrospective, multicenter observational study including women aged 18–42 years, treated for breast cancer between January 2013 and December 2019. Among 554 identified patients, those with metastatic disease, carcinoma in situ, or no systemic treatment were excluded. The primary endpoint was the rate of pregnancies after treatment.

Among 428 included patients, 35 (8.2%) had at least one pregnancy after treatment. Most conceptions were spontaneous (74%). The median time to pregnancy was 31 months (19.3–42.8) and 30 pregnancies resulted in live births. Six pregnancies (17.1%) occurred during ongoing treatment. Eighty-six patients attended a dedicated fertility consultation, and 11% underwent fertility preservation, mainly oocyte cryopreservation (60%). Nine patients temporarily interrupted endocrine therapy for a parental project: eight conceived spontaneously after a median of 7 months (4–12) and only half resumed therapy. In multivariate analysis, endocrine therapy and advanced stage significantly reduced the probability of pregnancy, whereas younger age and fertility preservation increased it.

Pregnancy after breast cancer remains possible but infrequent in real-world settings. Fertility preservation was strongly associated with pregnancy, yet access to specialized counseling remains limited. The occurrence of pregnancies during treatment highlights the need for improved contraceptive counseling.