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Ran Kim,1 Seung-Ah Choe,2 Eun A Park,1 Myung Joo Kim,1 Young-Sang Kim,1 You Shin Kim1 1Department of Obstetrics and Gynecology, CHA Fertility Center Seoul Station, CHA University School of Medicine, Seoul, 04637, Korea; 2Department of Preventive Medicine, Korea University College of Medicine, Seoul, 02841, KoreaCorrespondence: Seung-Ah ChoeDepartment of Preventive Medicine, Korea University College of Medicine, Department of Epidemiology & Health Informatics, Graduate School of Public Health, Korea University, 73 Goryeodae-ro, Seongbuk-gu, Seoul, 02841, KoreaTel +82-2-2286-1344Email seungah@korea.ac.krPurpose: To assess the impact of additional embryo transfer (ET) on pregnancy in young women, we used a natural-experiment approach.Patients and Methods: The design was based on the national policy of South Korea limiting the number of embryos transferred in vitro fertilization (IVF):≦2 embryos on day 2– 4 or one on day 5– 6 for patients aged < 35, with one extra embryo allowed for patients aged ≥ 35. Using the data from 1909 ET cycles of 1287 women aged ≥ 34 and ≤ 35, we calculated adjusted risk ratios (RRs) for pregnancy.Results: Half of cycles were undertaken by women aged 35, and additional ET was performed in 68.7% of them. Intrauterine pregnancy (45.2% vs 51.3%) and multiple gestation (30.5% vs 6.9%) were more common in women aged 35 than in those aged 34. The RR for intrauterine pregnancy was 1.34 (95% confidence interval: 1.12– 1.59) when comparing double ET to single ET in frozen day 5– 6 cycles.Conclusion: We observed no evidence of a higher probability of pregnancy with additional ET in fresh or frozen day 3– 4 ET, or in fresh day 5– 6 ET of women aged 35. Additional ET may not increase the successful pregnancy rate in the 35-year-old group, unless it is a frozen day 5– 6 ET cycle.Keywords: in vitro fertilization, single embryo transfer, pregnancy rate, multiple pregnancy |
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