The Effect of Sulfasalazine on CRH Levels in Pregnant Women

The goal of this randomized clinical trial is to assess sulfasalazine as a potential treatment to prevent recurrent preterm birth. The main questions it aims to answer are: * Does sulfasalazine down regulate corticotropin releasing hormone (CRH) levels in pregnant persons with a prior history of preterm birth? * Does sulfasalazine reduce the incidence of recurrent preterm birth in pregnant persons given drug vs. controls? Consenting participants will be randomized to receive sulfasalazine or to a control group and will undergo serial blood draws to assess plasma CRH levels.

Inclusion Criteria: * \> 18 years of age * Singleton pregnancy * Participants with a history of prior preterm birth in a previous pregnancy * Participants must be between 12 and 22 weeks gestation. * Participants must have their pregnancy dates confirmed by ultrasound. Exclusion Criteria: * Participants \< 18 years old * Participants with a cervical length \< 25 mm * Participants with a multiple gestation * Cerclage * Progesterone administration * Unwilling or unable to swallow the study agent capsule or consume an inert ingredient in the study agent capsule * Acute liver disease or known liver abnormalities * Other significant chronic medical or psychiatric illness that, in the investigator's opinion, would prevent participation in the study * Known hypersensitivity to sulfasalazine * Known glucose-6-phosphate dehydrogenase (G6PD) deficiency * History of severe asthma * Digoxin use * Porphyria * Intestinal obstruction * Urinary tract obstruction * Hepatic dysfunction * Renal dysfunction * Blood dyscrasia such as agranulocytosis, aplastic anemia.