RESUMO
OBJECTIVE: To analysis the incidence and management of monozygotic twin (MZT) conceived by assisted reproductive techniques (ART). METHODS: A retrospective analysis of clinical pregnancies and MZT that resulted from ART was performed in Reproductive Medical Center, the First Affiliated Hospital, Wenzhou Medical University between January 2011 and January 2014. RESULTS: A total of 5 908 pregnancies were diagnosed: 2 012 twins, 157 high-order multiple pregnancy (HOMP), including 4 quadruplets. Overall, 51 MZT pregnancies were identified of them including 32 cases HOMP and 19 cases MZT. The incidence of MZT resulting from cleavage-stage embryo transfer was similar to blastocyst transfer (P = 0.960). The percent of MZT resulting from in vitro fertilization [0.93% (28/3 022)], frozen-thawed embryo transfer [0.87% (13/1 502)] and intracytoplamic sperm injection [0.72% (10/1 384)] did not show statistical significance (P = 0.794). The expectantly managed MZT was associated with a significantly greater likelihood of miscarriage [6/19 vs 5.11% (101/1 976)], and low birth weight infant [73.91% (17/23) vs 42.89% (1 453/3 388), P < 0.01], when compared with dizygotic twin (DZT) did not undergo selective embryo reduction (SER). In monozygotic (MZ)-triplets with SER to 2 fetuses or to 1 fetus, there was no cases of preterm birth or low birth weight infant observed in MZ-triplets with SER to 1 fetus; when compared with MZ-triplets with SER to 2 fetuses, the low birth weight infant [56.00% (14/25), P = 0.021] has statistical significance. The likelihood of the survival of two babies was lower in MZ-triplets with SER to 2 fetuses when compared with non-MZ triplets with SER to 2 fetuses [42.86% (9/21) vs 75.21% (91/121), P = 0.003]. CONCLUSIONS: The incidence of MZT pregnancies following ART is high. It plays a significant role in the occurrence of HOMP. MZT pregnancies are at an increased risk of adverse outcomes, it should transform to a single embryo thansfer (SET) program to reduce them incideuce. Reduction of MZT contained in multiple pregnancies appears to be a safe option.