Analysis of 122 triplet and one quadruplet pregnancies after single embryo transfer in Japan.

Research Question: What is the prevalence of triplet and quadruplet pregnancies after single embryo transfer (SET) in Japan.

Design: A retrospective observational study was conducted on 274,605 pregnancies after 937,848 SET cycles in registered assisted reproductive technology (ART) data from the Japanese ART national registry database between 2007 and 2014. A questionnaire survey of ART centres was also conducted. Data on pregnancies with embryo division into three or more after SET were analysed.

Results: According to the Japanese ART national registry database, SET resulted in 109 triplet pregnancies (0.04% of pregnancies), and the questionnaire reports from 31 centres revealed 33 triplet and one quadruplet pregnancies. After exclusion of 20 duplicated cases, 122 triplet and one quadruplet pregnancies included 46 monochorionic (one gestational sac [37.4%]), 18 dichorionic (two gestational sacs [14.6%]) and 59 trichorionic pregnancies (three gestational sacs [48.0%]). Compared with singleton pregnancies, patients with monozygotic triplet or quadruplet pregnancies were less frequently diagnosed with unexplained infertility (P = 0.004), more often received gonadotrophin injections for ovarian stimulation in 39 cases with information available (P = 0.021) and underwent more blastocyst transfers and assisted hatching (P = 0.002 and P < 0.001, respectively). The proportion of live birth, defined as at least one baby born, excluding induced abortion, was 64.6% (73/116 pregnancies) of monozygotic triplet or quadruplet pregnancies.

Conclusions: Combined Japanese ART national registry and survey data revealed 122 triplet and one quadruplet pregnancies, the majority after cryopreserved embryo transfer. Most were conceived after blastocyst transfer and often after assisted hatching, which are potential risk factors for zygotic splitting.