To study the role of the obstetric risk factors for low birth weight and preterm birth. A case-control study was carried out in 2017 at the University Hospital – Pleven; 1212 women in childbirth and 1212 live-born babies after single pregnancies were included in the study. The live-born infants were divided into two groups. The cases included the preterm low-birth-weight (PLBW) newborns weighing less than 2500 grams (g). The controls included full-term newborns with normal birth weight (FTNBW). The role of 8 obstetric risk factors (RFs) on PLBW was studied (maternal age, type of birth, amniotic fluid deficiency and congenital abnormalities, maternal pelvic size abnormalities, placental abnormalities, abnormalities of fetal membranes, umbilical cord abnormalities, and presentation of the fetus). The obstetric RFs were significantly associated with PLBW. Risk of PLBW is significantly higher (p=0.001) in breech presentation (exp (β)=6.622), placental abnormalities (exp (β)=5.556), maternal pelvic size abnormalities (exp (β)=4.426) and amniotic fluid deficiency and congenital abnormalities (exp (β)=2.903). The results of that study can be useful for effecting prevention programing of pregnancy and prematurity.