Information retrieval for systematic reviews (SRs) should include sensitive searches in several bibliographic databases. In addition to standard databases (i.e., MEDLINE, Embase and CENTRAL), researchers might consider subject-specific ones. In the fields of nursing and midwifery, a SR would typically include CINAHL as a subject-specific database. The aim of this study was to analyze the number and relevance of references retrieved from CINAHL in six SRs on maternal care.

We conducted a retrospective analysis of six SRs (e.g., benefit of intrapartum ultrasound or one-to-one care during labor). The study type was limited to randomized controlled trials (RCTs) in all but three SRs. In all cases, MEDLINE, Embase, CENTRAL and CINAHL were searched for primary studies. Further information sources (e.g., study registries and reference lists of SRs) were also considered. The proportion of the additional number of hits and studies included from CINAHL as well as the corresponding number of participants were calculated.

Overall, the reviewers screened 12,013 references from bibliographic databases and identified forty relevant studies. CINAHL contained 2,643 (22 percent) of the references. In five out of six SRs, no additional studies were identified in CINAHL. In the remaining SR on birthing positions, the reviewers included thirteen RCTs of which one was a feasibility study with 68 participants indexed only in CINAHL. This corresponds to 0.9 percent of the women participating in all thirteen RCTs (n = 7,861). However, this study was cited in a journal article on a subsequent RCT that was identified and included via MEDLINE and ClinicalTrials.gov.

It is not necessary to search CINAHL in SRs on maternal care if standard databases and further information sources are considered. An additional study from CINAHL was included in one out of six SRs, a small feasibility study that could have been identified without CINAHL via a subsequent RCT.