Every year about this time, the National Library of Medicine (NLM) performs additional maintenance to MEDLINE data, known as year-end processing. This involves changes to the Medical Subject Headings (MeSH) on existing MEDLINE citations to conform to next year’s version of MeSH, and other global changes.
What does this mean to you? Starting about mid-November, records will be added to MEDLINE without the MeSH headings. These are referred to as “in-process” citations and will occur in both PubMed and Ovid MEDLINE. This year-end processing should conclude by mid-December. During this period, any searching you do using MeSH will not retrieve the newest citations. To retrieve new, “in process” records during this time, you should use searches that do not limit to MeSH, such as textword searching.