Objective: To study whether spontaneous preterm birth (SPB) is associated with maternal-newborn ABO blood phenotype pairs.
Methods: We conducted a retrospective case-control study in the Department of Pediatrics, King Abdulaziz Hospital, Al-Ahsa, Kingdom of Saudi Arabia. A total of 631 live singleton SPBs (less than 37 weeks) between August 2005 and May 2011 formed the case group.