RELATIONSHIP BETWEEN PLACENTAL HISTOLOGIC FEATURES AND UMBILICAL-CORDBLOOD-GASES IN PRETERM GESTATIONS

OBJECTIVE: Our purpose was to test the hypothesis that placental histo logic lesions reflect abnormal placental respiratory function in prete rm gestations. STUDY DESIGN: A retrospective study of preterm deliveri es from 22 to 32 weeks revealed 431 patients with umbilical venous or arterial blood gas values. Excluded were stillbirth, multiple gestatio ns, placenta previa, maternal medical diseases, and fetal anomalies. C harts were reviewed for principal indication of delivery, diagnosis of labor, and mode of delivery. Blood gases were studied within 10 minut es of delivery on a model 178 automatic pH analyzer (Coming Med, Bosto n). Placental data included uteroplacental vascular lesions and relate d villous lesions, lesions of acute inflammation, chronic inflammation , and coagulation. Contingency tables and analysis of variance conside red p < 0.05 as significant. RESULTS: Mean +/- SD umbilical vein pH wa s 7.36 +/- 0.07 (range 6.94 to 7.56) and umbilical artery pH was 7.30 +/- 0.08 (range 6.83 to 7.55). Increasing severity of uteroplacental t hrombosis, villous lesions reflective of uteroplacental vascular patho logic mechanisms, avascular villi, histologic evidence of abruptio pla centae, chronic villitis, and increased circulating erythrocytes were associated with decrease in umbilical vein and artery pH, increase in umbilical vein and artery Pco(2), and decrease in umbilical vein and a rtery Po-2. Histologic evidence of acute infection and villous edema w ere associated with a higher pH and Po-2 and a lower Pco(2) in both um bilical vein and artery. Umbilical vein or artery base excess was not related to placental lesions. Labor was not related to blood gas value s in this data set, although a subset of cases of extremely preterm pr emature rupture of membranes and preterm labor who labored and were de livered by cesarean section had significantly poorer umbilical Venous and fetal arterial blood gas values (all p < 0.005). lesions related t o poorer blood gas values were significantly more frequent in preterm preeclampsia and nonhypertensive abruptio placentae than in premature rupture of membranes or preterm labor. CONCLUSIONS: Changes in umbilic al vein and artery pH, Po-2 and Pco(2) are significantly related to le sions of uteroplacental vascular pathologic mechanisms and intraplacen tal thrombosis. Placental lesions may be associated with chronic fetal distress by altering fetal oxygen availability and acid-base status. Placental immaturity resulting from prematurity may be associated with inefficient placental respiratory function and an increased likelihoo d of cesarean delivery in cases of premature rupture of membranes or p reterm labor. Altered fetal acid-base balance plus excess numbers of c irculating nucleated erythrocytes suggests that placental respiratory function is functionally abnormal when these lesions are present and l eads to fetal tissue hypoxia.