OC224: First trimester intertwin size discordance

Abstract

What is the clinical significance of first trimester discordance in the crown-rump lengths (CRL) in twin pregnancies. During a 40 months period, interfetal age differences were analyzed in 205 consecutive twin pregnancies by CRL measurements between 21–79 mm. Eight patients were lost for follow-up and hence excluded. Discordant fetal size was defined as a difference in CRL equal to 5 or more days. Differences in chorionicity, pregnancy and fetal loss rates, mean gestational ages at birth, mean birth weights and congenital malformations were analyzed and compared with concordant pregnancies. Statistical analysis was carried out by Fisher exact or c2 tests. Fetal size was concordant in 179/197 twin pregnancies (91%) (group A) and discordant in 18/197 twin pregnancies (9%) (group B). Significantly more monochorionic pregnancies than dichorionic pregnancies showed a first trimester discordant twin size (9/35 versus 9/162: p < 0.001). Compared with group A, group B revealed significantly more intentional pregnancy (4/18 versus 12/179: p = 0.0216) and fetal (10/36 versus 28/358 p = 0.0001) losses and more congenital malformations (9/36 versus 16/358: p < 0.0001). The risk of spontaneous pregnancy loss (1/18 versus 4/179: p = 0.29) and fetal demise (2/36 versus 9/358: p = 0.4) were not significantly different in both groups. Mean birth weights and mean gestational ages at the time of delivery in both groups were comparable. Discordant fetal size is more frequently found in monochorionic twin pregnancies. The presence of a CRL discordance is related with an increased risk for congenital anomalies. However abnormalities excluded, there is no further negative effect on pregnancy outcome.