Laurens Schattenkerk

128 Chapter 5 Search strategy The electronic databases of the National Institutes of Health PubMed and EMBASE were systematically searched in February 2020 using both simple search terms as well as hierarchical family forms (e.g. MESH). The clinical data expert (RV) aided in the formation of the search strategy. The search combined four groups of search terms and their equivalents: (1) terms related to the age at the moment of surgery (e.g. neonate); (2) terms related to the location of surgery (e.g. abdominal surgery); (3) terms related to congenital abdominal defects (e.g. omphalocele); (4) terms related to incisional hernia (e.g. cicatricial hernia). Mesh and search terms used in PubMed are included in Appendix 1. Primary and secondary outcomes The primary endpoint was the pooled percentage of IH. Secondary endpoint included the pooled percentage per congenital anomaly and identification of possible risk factors such as surgical procedure and disease severity by means. A Forest plot, containing the estimated overall pooled proportion of IH and the corresponding 95%-CI, was created using Graphpad Prism version 8. In the Forest plot we also reported the pooled proportion and CI per anomaly if; (1) IH was reported in at least three studies for the anomaly OR (2) if the total number of patients all studies on an anomaly combined was ≥ 100 patients; (3) there was at least one event of IH present all studies on a specific anomaly combined. If these criteria were not met the anomaly was reported under the forest plot as residual. These residuals were still included in the analysis for overall pooled proportions For all studies with multiple arms, data of both trial-arms were combined or, if only one arm matched the inclusion criteria, the appropriate arm was used. Additional extracted parameters were: author, country of conduct, year of publication, journal, study design, duration of follow-up, duration of study, number of participants, type of congenital anomaly, subdivision within anomaly, time to IH, repeat surgery because of IH, history of stoma data was extracted on. Duration of follow up was described as median with range, mean with/without standard deviation or citated text following each article’s own description. Duration was either reported in month or years recalculated from the reported value if necessary. For studies describing gastroschisis, type of closure (by SILO or primary) and severity of disease (complex or simple) was noted following definitions used by the author. Studies deemed gastroschisis complex when a patient had additional anomalies, such as intestinal atresia. If the patient only suffered from a gastroschisis, it was accepted as simple gastroschisis.

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