Importance Data on fertility after breast cancer (BC) relative to the general population are lacking.

Objective To compare the time-to-pregnancy between women with and without prior BC seeking to become pregnant.

Design Prospective exposed-unexposed cohort study. Women were included from March 13, 2018 to June 27, 2019. Data were collected every six months via online questionnaires for up to three years.

Setting Participants were recruited through the French collaborative network for cancer research Seintinelles*.

Participants Exposed women (cases) were women aged 18-43 years with a history of localized BC who had completed treatment, without relapse. Unexposed women (controls) were women of the same age group with no history of BC.

Exposure(s) The exposure of interest was a prior history of BC.

Main Outcome(s) and Measure(s) The primary endpoint was time-to-pregnancy. The hypothesis tested was formulated before data collection. Secondary endpoints included the use of ART, including the use of cryopreserved material, factors associated with time-to-pregnancy, and pregnancy and neonatal outcomes. Statistical analysis was based on Kaplan-Meier survival analysis and multivariate Cox proportional-hazards models with adjustment for confounding factors by inverse probability of treatment weighting (IPTW).

Results We enrolled 4351 women in this study. Follow-up data were available for 642 women (76 cases, 566 controls) who sought to become pregnant during the study period. Median time-to-pregnancy was 5 months (95% CI: 3 months to 7 months) for cases and 3 months (95% CI: 2 months to 5 months) for adjusted controls, with no significant difference between the groups (p=0.34). Cases were more likely to resort to the use of ART than controls (RR=13.9, 95% CI [2.2- 154.6]), but time-to-pregnancy was similar in cases and controls, with and without ART use. Time-to-pregnancy was influenced by factors such as age, parity, menstrual cycle regularity, BMI, and ART, but not by prior BC. Pregnancy and neonatal outcomes did not differ significantly between cases and controls.

Conclusions and Relevance Time-to-pregnancy, in women seeking to become pregnant, was similar for women with and without a history of BC, raising hopes for women with BC wishing to have children.

The authors have declared no competing interest.

This study did not receive any funding

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The Seintinelles scientific board approved the FEERIC project on December 7, 2015, and the Sud Ouest Outre Mer II ethics committee approved the project on October 5, 2017

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

Question: Does time-to-pregnancy differ between women with and without a history of breast cancer (BC) in those seeking to become pregnant?

Meaning: Time-to-pregnancy and pregnancy outcomes are similar in women with and without a history of BC, raising hope for women with BC wishing to have children.

All data produced in the present study are available upon reasonable request to the authors