[Incidence and management of monozygotic twin conceived by assisted reproductive techniques]

To analysis the incidence and management of monozygotic twin (MZT) conceived by assisted reproductive techniques (ART).

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.

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].

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.