foreach (var item in Data)
{
    Table table = new Table();
    flowDoc.Blocks.Add(table);
    paginatorSource.DocumentPaginator.ComputePageCount();
    pagecount = paginatorSource.DocumentPaginator.PageCount;

    //do some work populating the table details...
    TableColumn t = new TableColumn(); //etc...

    paginatorSource.DocumentPaginator.ComputePageCount();
    int newPagecount = paginatorSource.DocumentPaginator.PageCount;

    if (newPagecount != pagecount)
    {
        //The table has spanned a new page so set the page break!
        table.BreakPageBefore = true;
    }
}