First‐night effect in insomnia disorder: a systematic review and meta‐analysis of polysomnographic findings

Summary Polysomnographic studies have been performed to investigate the first‐night effect in insomnia disorder. However, these studies have revealed discrepant findings. This meta‐analysis aimed to summarise and quantify the characteristics of the first‐night effect in insomnia disorder. We performed a systematic search of the PubMed, Medline, EMBASE, Web of Science and PsycINFO databases to identify studies published through October 2019. A total of 11,862 articles were identified, and seven studies with eight independent populations were included in the meta‐analysis. A total of 639 patients with insomnia disorder and 171 healthy controls underwent more than 2 consecutive nights of in‐laboratory polysomnography. Pooled results demonstrated that both variables of sleep continuity and sleep architecture, other than slow‐wave sleep were significantly altered in the first‐night effect in insomnia disorder. Furthermore, the results indicated that patients with insomnia disorder had a disruption of sleep continuity in the first‐night effect, including increased sleep onset latency and reduced total sleep time, compared to healthy controls. Overall, the findings show that patients with insomnia disorder experience the first‐night effect, rather than reverse first‐night effect, and the profiles of the first‐night effect in patients with insomnia are different from healthy controls. These indicate that an adaptation night is necessary when sleep continuity and sleep architecture is to be studied in patients with insomnia disorder. More well‐designed studies with large samples are needed to confirm the results.