[Risk factors for preterm deliveries in a public hospital]

Preterm births are responsible for 75 to 80% of perinatal mortality.

To determine the factors associated with preterm births, using maternal clinical data, laboratory results and pathological placental findings.

Retrospective study of 642 preterm single births at 22-34 weeks' gestation. Four hundred and seven cases with pathological placental studies were included. Births were subdivided into preterm births as a consequence of a medical indication and spontaneous births with or without premature rupture of membranes (PROM). Risk factors for preterm births were classified as maternal, fetal, placental, indeterminable and unclassifiable.

The proportions of preterm births were spontaneous 69% (with PROM 27% and with intact membranes 42%) and medically indicated births 31%. A risk factor associated with prematurity was identified in 98 and 85% of medically indicated and spontaneous births, respectively. Ascending bacterial infection (ABI) was the most frequently associated factor with spontaneous preterm delivery in 51% of women (142/280, p < 0.01) and with preterm births of less than 30 weeks in 52% of women (82/157, p < 0.01). Vaginal or urinary infection with Group B Streptococcus, was the most common clinical condition associated with ABI related deliveries. Hypertension was present in 94 of 127 medically indicated preterm deliveries (preeclampsia in 62% and chronic hypertension in 12%), and in 29% (preeclampsia 24%) of preterm births of more than 30 weeks. Congenital anomalies were mainly associated with a maternal age over 35 years in 15% (14/92) of women. The frequency of placental diseases was higher in spontaneous preterm deliveries (14%) and in pregnancies of more than 30 weeks in (14%).

ABI was the most common factor associated with spontaneous preterm births at 2234 weeks, while preeclampsia is the most common factor associated with medically indicated preterm births.