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.

中文翻译：

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在日本进行单胚胎移植后，分析了122个三胞胎和1个四胞胎妊娠。

研究问题日本单胎移植（SET）后三胞胎和四胞胎妊娠的患病率是多少？设计在2007年至2014年之间，对日本ART国家注册数据库中已注册的辅助生殖技术（ART）数据中的937,848个SET周期后的274,605例妊娠进行了回顾性观察研究。还对ART中心进行了问卷调查。分析了SET后胚胎分裂为三个或更多的妊娠数据。结果根据日本ART国家注册数据库，SET导致109例三胞胎妊娠（占妊娠的0.04％），来自31个中心的问卷调查报告显示，有33例三胞胎妊娠和1例四胞胎妊娠。在排除20个重复的案例之后，122三胞胎和1四胞胎妊娠包括46个单绒毛膜性妊娠（1个胎囊[37.4％]），18个绒毛膜性妊娠（2个胎囊[14.6％]）和59个三甲胎妊娠（3个胎囊[48.0％]）。与单胎妊娠相比，单卵三胞胎或四胞胎妊娠的患者被诊断为无法解释的不育症的频率较低（P = 0.004），在39例有相关信息的病例中，更经常接受促性腺激素注射以刺激卵巢（P = 0.021），并进行了更多的囊胚转移和辅助孵化（分别为P = 0.002和P <0.001）。不包括人工流产的活产比例定义为至少一个婴儿出生，是单卵三胎或四胎妊娠的64.6％（73/116胎）。结论结合日本抗逆转录病毒疗法国家注册和调查数据，发现122例三胞胎和1例四胞胎妊娠，大多数是冷冻保存胚胎移植后的。多数是在胚泡转移后和通常在辅助孵化后才受孕的，这是合子分裂的潜在危险因素。