OvidSP added a new field, Other ID (OI), to note the PubMed Central reference number (PMCID):

“The Other ID (OI) is a unique alpha-numeric code. In particular, it will contain the PubMed Central Identifier (PMCID), where the alphabetical prefix ‘PMC’ precedes the identifier. If the publisher has embargoed access to the full text, the date of availability in PubMed Central will be noted. When the embargo is lifted, a revised record with the date of availability removed will be released.”

The new field will be available around the end of January after OVID completes its annual reloading of MEDLINE data.