Methods
PTD, PPROM, vasculitis, lupus, abortion, hypertension, fetal malformations, diabetes
HELLP SYNDROME, PRE-ECLAMPSIA, THROMBOCYTOPENIA, IUGR, VASCULITIS, ANTIPHOSPHOLIPID SYNDROME, INTRAUTERINE GROWTH RESTRICTION, LUPUS, HYPERTENSION, DISEASES, DIABETES
The present randomized clinical trial was conducted as a pilot study on pregnant women with a history of PTD who were referred to the Mahdieh and Shohada Tajrish hospitals in Tehran, Iran, in 2019 and 2020. The inclusion criteria consisted of age > 18 years old, singleton pregnancy, gestational age of 8 to 16 weeks, and a history of spontaneous PTD. The exclusion criteria were the following: twin or multiple pregnancies, history of non-spontaneous PTD due to maternal problems such as pre-eclampsia, HELLP syndrome, or fetal problems such as intrauterine growth restriction (IUGR), taking aspirin for treating other diseases, including vasculitis, lupus, type 1 and 2 diabetes, hypertension kidney problems, and antiphospholipid syndrome. Thrombocytopenia, fetal malformations in the current pregnancy or previous PTD, and simultaneous participation in another trial were other exclusion criteria.Using the following formula and considering the likely incidence of PTD of 15%, α = 0.05, and d = 0.1 (10% accuracy), the calculated sample size was 50 people in each group
Considering a patient dropout of 30%, the required sample size for each group increased to 66 patients in each group. Eligible patients were selected via convenience sampling in the order of referral, and after explaining the study method and obtaining written consent, the subjects were enrolled in the study. Utilizing a random number table, the patients were divided into two groups: the intervention group, taking aspirin with a dosage of 80 mg daily, and the control group, without intervention. During the study, 12 patients in the aspirin group and 13 patients in the control group withdrew, and eventually, 54 patients in the aspirin group and 53 patients in the control group completed the study, and their data were analyzed (

Consort algorithm of our study.

Using a form, we collected the data on patients, including age, history of pregnancy (gravidity, parity, history of abortion and stillbirth, number of alive and dead children), etiology for previous spontaneous PTD (spontaneous labor, PPROM), and PTD category based on the fetal age (early: < 34 weeks, late: from 34 to 37 weeks). Then, the patients were randomly divided into two groups. Patients in the aspirin group took an 80 mg tablet, manufactured by Hakim Pharmaceutical Company, Iran, daily and preferably in the evening until the 36

All methods used in the present study are based on the principles of Helsinki Human Studies. Patient information will be kept entirely confidential during and after the study. The study was approved by the ethics committee of Shahid Beheshti University of Medical Sciences (Registration code: IR.SBMU.MSP.REC.1398.528) and was registered in the site of the Iranian registry of clinical trials (
