"Pseudo" twin-to-twin transfusion syndrome and fetal outcome.

OBJECTIVE

To assess the fetal outcome, in a tertiary center, in pregnancies with suspected twin-to-twin transfusion syndrome (TTTS) not confirmed using ultrasonographic examination, diagnosis of pathology, or both.

STUDY DESIGN

Forty-four pregnancies with suspected TTTS were followed longitudinally using ultrasonographic examination until delivery. The minimal criteria for the diagnosis of TTTS were: (1) suspicion of monochorionicity gleaned from ultrasound examination (to be confirmed at birth); (2) presence of polyhydramnios in one gestational sac (either assessed subjectively--or, finding that the largest vertical pocket of amniotic fluid was >8 cm in diameter before 20 weeks' gestation and >10 cm in diameter thereafter); and (3) presence of oligohydramnios in the other gestational sac (finding either that there was a "stuck" twin complication or that the largest vertical pocket of amniotic fluid was <1 cm in diameter). When one of the above criteria was not present, the pregnancy was defined as "pseudo" TTTS. Fetal outcome in "pseudo" TTTS was analyzed according to the relative size of the neonate (large or small) and whether the cord insertion was normal or velamentous.

RESULTS

There were 18 cases of "pseudo" TTTS. No treatment in utero was necessary in any of the 18 pregnancies. The mean gestational age was 21.9 +/- 3.7 (1 SD) weeks at diagnosis and 33.0 +/- 3.0 weeks at delivery. The average weight discrepancy between the twins at birth was 34.3 +/- 14.8%. There were three fetal demises of the small twin and one neonatal demise of the large twin (p > 0.05). Large twins developed respiratory distress syndrome (RDS) more often than small twins (p < 0.05). Five percent of the large twins and 50% of the small twins had a velamentous insertion of the cord (p < 0.05).

CONCLUSION

In pregnancies complicated by "pseudo" TTTS our data indicate that: (1) small twins have abnormal cord insertion more frequently than large twins, (2) large twins develop RDS more frequently than small twins. Our data suggest that the perinatal mortality in these pregnancies appears to be lower than that reported for the classical TTTS.