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.

This is a study to assess the potential for sulfasalazine to prevent recurrent preterm birth. The investigators' main objective is to assess the effects of sulfasalazine on the maternal serum biomarker CRH, which is associated with preterm birth.

The will be a pilot randomized controlled trial of pregnant multiparous patients who have had a prior preterm delivery. Pregnant women with a prior preterm birth are at high risk (about 20-30%) of having a recurrent preterm birth. The goal of the study will be to evaluate the effect of sulfasalazine on the maternal serum biomarker CRH at 28, 32, and 36 weeks gestation after randomization of patients to the study drug.

Secondary objectives include evaluating the effect of sulfasalazine on the outcome of delivery less than 37 weeks gestation in this group of high risk pregnant women. Additional composite neonatal outcomes will be assessed.

The proposed study has the potential to identify a novel, low-cost, orally available treatment for preterm delivery based on in vitro evidence and epidemiologic studies suggesting that sulfasalazine may be an effective intervention to prevent preterm birth. If the hypothesis put forth by the investigators is confirmed, sulfasalazine would be an attractive therapeutic intervention that could be implemented for the prevention of preterm birth in both developed and developing nations.

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.

Deidentified data will be provided to those inquire to the corresponding author of the manuscript if published. If no manuscript is published, inquiries can be directed to the principal investigator of the study.

Data will be available on publication and remain available for two years.

The principal investigator will individually assess all requests for data.