Materials and methods
The study was conducted on a multicenter material of placental probes from the Obstetrics Department of the Provincial Hospital of Przemyśl, Department of Perinatology of the Medical University Bialystok, and Obstetrics Clinic of the Medical University of Lublin. Using CinCalc.com sample size calculator the minimal sample size was established on 34 women20. The material was taken from 150 women who gave birth in the period from March 2004 to December 2012. 115 women were diagnosed with premature delivery and were included in the Study Group, 35 women had a delivery at term and were allocated to the Control Group.
The following inclusion criteria were used: spontaneous deliveries concluded with vaginal delivery or with an emergency Cesarean section between 22. gestational weeks and 36. gestational weeks and 6 days. The control group consisted of women who had a spontaneous delivery between 37 gestational weeks and 40 gestational weeks and 6 days were included. Patients with diagnosed complications during the current pregnancy, as multiple gestations, anemia, intrahepatic cholestasis of pregnancy, acute fatty liver of pregnancy, chronic kidney disease, autoimmune disorders, immunodeficiency, group of placentae previa, fetal growth restriction, oligohydramnios, polyhydramnios and other rare complications not otherwise described were excluded from the study. Fetal chromosomal abnormalities, fetuses with diagnosed anatomical abnormalities during the current pregnancy, pregnancies conceived using in vitro fertilization, and intrauterine fetal demise were also excluded from the study.
This study was in accordance with the STROBE Statement - Checklist of items of cohort studies, which can be found in the appendix of the study21.
Every patient was informed about the aim of the study, its process, and agreed to it before the involvement in the study. The study had received the approbation of the Bioethical Committee of the University of Rzeszów (Nr. 05/10/2020).