Data collection
Medical records was obtained from the computerized
database of the Statistical Unit of the Department of
Obstetrics and Gynecology at Chaiyaphum Hospital. Of
16225 eligible medical records in the study period, 594
records met the criteria for being case and 2406 for
being control. The controls were randomly selected from
women who delivered at the same period with preterm
cases by computer-generated random numbers with
simple random sampling. Their records were reviewed.
Preterm delivery