Relationship between Grade III placentas and biparietal diameter determinations.

Grade III placentas were found in 133 (12 per cent) of 1,082 pregnant women evaluated ultrasonographically after 20 weeks of gestation. Associated biparietal diameter measurements ranged from 7.2 to 10 cm. In 11 women with no complications known to accelerate fetal lung maturity or to induce premature placental maturation, grade III placentas were observed between 30 and 33 weeks of gestation. Gestational ages determined according to the growth adjusted sonographic age method of Sabbagha were accurate within one to three days. Considering the risk of hyaline membrane disease at those gestational ages, a grade III placenta cannot be equated with fetal lung maturity. Criteria other than placental grading should be used to assess the pulmonary status of the fetus.