Twin-twin transfusion syndrome: a frequently missed diagnosis with important consequences.

OBJECTIVE To evaluate the incidence and consequences of 'misdiagnosed' cases of twin-twin transfusion syndrome (TTTS). METHODS Chorionicity and referral diagnoses were reviewed in pregnant women with monochorionic twin pregnancies complicated by TTTS treated with fetoscopic laser ablation. 'Misdiagnosed' cases, defined as failure to correctly identify chorionicity and/or to diagnose TTTS prior to referral, were compared with cases in whom chorionicity and TTTS were diagnosed correctly. TTTS stage, gestational age at referral, overall survival, fetal and perinatal mortality, gestational age at delivery, operating time and maternal complications were compared. RESULTS Failure to identify monochorionicity and/or TTTS was observed in 33% (107/323) of referrals to our center. Compared with cases in whom chorionicity and TTTS were correctly diagnosed, misdiagnosed patients were referred at a more advanced stage of disease (Stage IV TTTS: 16.8% vs 7.9%, P = 0.014) and later in pregnancy (gestational age at laser: 20.9 weeks vs 20.1 weeks, P = 0.018). They also delivered more prematurely (30.3 weeks' gestation vs 31.5 weeks' gestation, P = 0.04) and fetal and neonatal mortality were higher (neonatal death within 7 days: 19.6% vs 6.0%, P < 0.001). When the diagnosis was incorrect, major maternal complications and intensive care unit admissions were increased. CONCLUSIONS Poor recognition of chorionicity in the first trimester of pregnancy might lead to inadequate ultrasound follow up (failure to assess every 2 weeks) and patient education. Early accurate recognition of both chorionicity and TTTS, with timely referral to a fetal therapy center, are key to ensuring optimal maternal and fetal outcomes.