Abstract Study question Can we monitor post-oocyte retrieval ovarian hyperstimulation syndrome (OHSS) in the French national health data system to complement the French ART vigilance system? Summary answer Medico-administrative databases offer a more comprehensive view of post-oocyte retrieval complications and can be used to detect abnormal increases in frequency and outlier ART centers. What is known already Assisted reproductive technology (ART), widely used in Europe, accounts for about 3% of births in France. The various studies of ART complications are reassuring, showing relatively low overall complication rates. Nonetheless, the European Union has established a vigilance system to monitor these complications. However, this system is not an exhaustive source of information and does not provide a complete overview of post-ART complications. Study design, size, duration The study population was identified from the comprehensive French National Hospital discharge database and included 53,490 women under 46 years old who underwent 65,924 oocyte retrievals in 2022. Women were classified into three population subgroups according to the indication of oocyte retrieval: infertility (IF), fertility preservation (FP), and oocyte donation (OD). Participants/materials, setting, methods Hospital stays for OHSS within two months post-retrieval were analyzed and characterized according to various characteristics (age, comorbidities, indication of oocyte retrieval, type of hospital stay, length of hospital stay...). Multivariate analysis was performed to determine the relation between the occurrence of OHSS and women’s characteristics, and results are expressed as odds ratios (ORs) and 95% CI. A funnel plot was used to compare the OHSS rate per center with the national average. Main results and the role of chance Hospitalized OHSS accounted for 1.1% of retrievals in 2022 (n = 718). The mean age of the women was 31.6 years (SD 4.5). Women with Polycystic Ovary Syndrome (PCOS) accounted for about 4% of the women with OHSS. More than half of OHSS hospital stays lasted less than two days (54%). Of these stays, 2% of women were in intensive care. Multivariate analysis showed a significantly higher OHSS risk in women under 30 and those with PCOS. Other risk factors are currently introduced into the model, such as a history of OHSS or pregnancy. Funnel plot analysis showed that one ART center has an OHSS rate significantly higher than the national average. In the centers that stand out from all the others, the objective is to return to these centers to understand the possible reasons for this observed rate and to implement corrective measures. Limitations, reasons for caution Despite all its advantages, the French national health data system presents some limitations, such as the risk of inappropriate coding. Moreover, the unavailability of personal or clinical information prevented us from considering certain risk factors. Wider implications of the findings Despite the limits of using medico-administrative databases, this approach provides a better representation of post-ART complications and is a promising way to complement the ART vigilance reporting system. This concept will also be generalized to other complications with regular feedback to professionals. Trial registration number not applicable