The Vatican has approved the merger of Saints Medical Center in Lowell and Lowell General Hospital. The approval came on condition that the main Saints campus will retain its Roman Catholic identity and that family planning and other women’s reproductive-health services will be handled at the Lowell General campus. The hospital merger agreed upon in March was approved by state regulators last month. Officials at both hospitals said they expect a final closing by the end of the month. The Sun of Lowell reported that a merger had been proposed as early as 2001, but was abandoned after objections by the Archdiocese of Boston. Executives said the merger will mean better patient care, expanded services, the elimination of duplicated services, and the retention of medical specialists.