Gestational sac diameter in very early pregnancy as a predictor of fetal outcome.

OBJECTIVE: To determine whether transvaginal sonographic measurement of gestational sac diameter in pregnancies 28-42 days from the last menstrual period can predict whether a pregnancy results in a normal term birth or a spontaneous miscarriage.

DESIGN: Gestational sac diameter was measured during the 4th and 5th weeks of gestation from the last menstrual period in 67 women who had a total of 102 ultrasound scans. These pregnancies were followed until one of two outcomes occurred: term gestation (n = 32) or spontaneous miscarriage (n = 35). Gestational sac diameter as a function of gestational age was compared in each of the groups.

RESULTS: The mean diameter of the gestational sac at 28-35 days from the last menstrual period among normal pregnancies did not differ significantly from that in those that subsequently miscarried (2.6 mm vs. 2.7 mm; P = 1.00). In pregnancies 36-42 days from the last menstrual period, the mean sac diameter was significantly different between the two groups (normal group, mean sac diameter, 8.2 mm and miscarriage group, mean sac diameter, 4.5 mm; P < 0.001).

CONCLUSION: There is no difference in gestational sac diameter at 28-35 days from the last menstrual period in normal and abnormal pregnancies. However, smaller than expected sac diameter in pregnancies 36-42 days from the last menstrual period is predictive of spontaneous miscarriage.