A classification system for selective intrauterine growth restriction in monochorionic pregnancies according to umbilical artery Doppler flow in the smaller twin.

Objectives: To evaluate a classification of selective intrauterine growth restriction (sIUGR) in monochorionic (MC) twins based on the characteristics of umbilical artery (UA) Doppler flow in the smaller twin, in terms of association with clinical outcome and with the pattern of placental anastomoses.
Methods: One hundred and thirty-four MC twins diagnosed with sIUGR at 18-26 weeks were classified as Type I (UA Doppler with positive diastolic flow, n = 39), Type II (persistent absent or reversed end-diastolic flow, n = 30) and Type III (intermittent absent or reversed end-diastolic flow, n = 65). Perinatal outcome, placental sharing and the pattern of anastomoses were compared with those in 76 uncomplicated MC twins.
Results: Mean gestational age at delivery was 35.5 (range, 30-38) weeks in controls, 35.4 (range, 16-38) weeks in Type I, 30.7 (range, 27-40) weeks in Type II (P < 0.0001) and 31.6 (range, 23-39) weeks in Type III (P < 0.0001) pregnancies. Fetal weight discordance was significantly higher in Type II (38%) and Type III (36%) than in Type I (29%) (P < 0.0001) pregnancies. Deterioration of the growth-restricted fetus occurred in 90% of Type II cases, compared with 0% and 10.8% of Types I and III, respectively (P < 0.001). Unexpected intrauterine fetal death of the smaller twin occurred in 15.4% of Type III cases, compared with 2.6% and 0% of Types I and II respectively (P < 0.05). Parenchymal brain lesions in the larger twin were observed in 19.7% of Type III cases and less than 5% in the other groups (P < 0.05). Placental discordance (larger/smaller) was 1.3 in controls, compared with 1.8, 2.6 and 4.4 in Types I, II and III, respectively (P < 0.01). The proportion of cases with arterioarterial anastomoses > 2 mm in diameter was 55% in controls, 70% in Type I, 18% in Type II (P < 0.01) and 98% in Type III (P < 0.01).
Conclusion: sIUGR can be classified on the basis of umbilical artery Doppler into three types that correlate with different clinical behavior and different patterns of placental anastomoses. This classification may be of help in clinical decision-making and when comparing clinical studies.