Although considerable variation in the reporting and definition of outcomes in cardio-obstetrics studies is acknowledged, the extent of this variation has not been documented. The primary objective of this systematic review was to highlight this variation and inform the development of a Core Outcome Set for studies on Cardiac disease in Pregnancy (COSCarP).

Medline, Embase, Web of Science and Cochrane Central databases were searched from 1980 to 2018 to identify all English-language publications on pregnancy and heart disease. Title/abstract screening and data extraction which included details on the study, patient population, and all reported outcomes, was performed in duplicate by 2 reviewers. As the aim of the review was to identify variation in outcome reporting, risk-of-bias assessment was not performed. The study protocol was registered on PROSPERO (CRD42016038218).

The final analysis included 422 cardio-obstetric studies. Maternal mortality or survival were reported in 232/422 studies, with inconsistency in terms of cause of death (all-cause [n = 65], cardiac [n = 55] or obstetric [n = 10]) or timeframe (ranging from in-hospital mortality [n = 11] to mortality 5 years following pregnancy). In 95/232 (41%) studies, the cause and timeframe were not specified. Similar inconsistencies in reporting and definitions were noted for outcomes such as heart failure (n = 298), perinatal loss (n = 296), fetal growth (n = 221), bleeding (n = 205), arrhythmias (n = 202), preterm birth (n = 191), thromboembolism (n = 153) and hypertensive disorders (n = 122). Functioning / life-impact and adverse effects of treatment were sparingly reported in published cardio-obstetric studies.

This systematic review hopes to create awareness among cardio-obstetrics teams about the inconsistencies in reporting and defining outcomes which makes it difficult to compare studies and perform meta-analyses. COSCarP which is being developed through international consensus between patients and care-providers will provide cardio-obstetrics teams with a minimal set of outcomes to be reported in future cardio-obstetrics studies.