OBJECTIVE To investigate clinic-specific risk factors for monozygotic twinning (MZT) using a large, electronic database. DESIGN Retrospective case-control study. SETTING Infertility clinics. PATIENT(S) Using an electronic medical record system, viable clinical pregnancy (confirmation of a gestational sac(s) and presence of at least one fetal pole with a heartbeat on first trimester ultrasound), data were obtained from homologous in vitro fertilization (IVF) cycles after single ET from June 1, 2004, to December 31, 2016. Monozygotic twinning was defined as a pregnancy with two fetal heartbeats on ultrasound with sex concordance at birth. INTERVENTION(S) None. MAIN OUTCOME MEASURE(S) Risk factors for MZT including cycle type, method of insemination, and method of cryopreservation. RESULT(S) Of the 28,265 IVF cycles that met inclusion criteria over the study period, 8,749 (31.0%) resulted in a viable intrauterine clinical pregnancy. There were 102 (2.7%) MZT in the fresh cycle cohort and 133 (2.7%) in the frozen cycle cohort. Neither cryopreservation nor the method of cryopreservation was a significant risk factor for MZT. However, the use of sequential media was an independent risk factor for MZT in fresh, but not frozen, ETs (odds ratio = 1.72, 95% confidence interval, 1.10-2.68). Significant differences were seen in the incidence of MZT between clinics, and this difference persisted after controlling for known risk factors (clinic 0, reference; clinic 2, odds ratio = 2.22; 95% confidence interval, 1.48-3.32; clinic 3, odds ratio = 1.93; 95% confidence interval, 1.30-2.87). CONCLUSION(S) Differences in MZT rates exist between individual IVF clinics, suggesting that variations in practice patterns may contribute to this event. The present study noted the use of sequential media was an independent risk factor for fresh but not frozen cycles.

中文翻译：

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双重麻烦？单卵双胞胎的临床特异性风险因素

目的 使用大型电子数据库调查单卵双胞胎 (MZT) 的临床特异性危险因素。设计 回顾性病例对照研究。设置不孕症诊所。患者（S）使用电子病历系统、可行的临床妊娠（确认妊娠囊和至少一个胎极在头三个月的超声检查中有心跳），从同源体外受精 (IVF) 中获得数据) 从 2004 年 6 月 1 日到 2016 年 12 月 31 日的单次 ET 后的周期。单卵双胞胎被定义为在超声检查中出现两个胎儿心跳且出生时性别一致的妊娠。干预措施 无。主要结果测量 MZT 的危险因素，包括周期类型、授精方法和冷冻保存方法。结果(S) 28, 在研究期间符合纳入标准的 265 个 IVF 周期中，8,749 个（31.0%）导致可行的宫内临床妊娠。新鲜周期队列中有 102 (2.7%) 个 MZT，冷冻周期队列中有 133 (2.7%) 个 MZT。冷冻保存和冷冻保存方法都不是 MZT 的重要危险因素。然而，使用连续培养基是新鲜但非冷冻 ET 中 MZT 的独立危险因素（优势比 = 1.72，95% 置信区间，1.10-2.68）。诊所之间的 MZT 发生率存在显着差异，并且在控制已知危险因素后这种差异仍然存在（诊所 0，参考；诊所 2，优势比 = 2.22；95% 置信区间，1.48-3.32；诊所 3，优势比） = 1.93；95% 置信区间，1.30-2.87)。结论 (S) 各个 IVF 诊所之间的 MZT 率存在差异，这表明实践模式的差异可能导致这一事件。本研究指出，使用连续培养基是新鲜但非冷冻周期的独立危险因素。