The aim of our study is to evaluate the 2010 regulations in Turkey regarding the number of embryos which can be transferred. This retrospective single center study evaluated single versus multiple births before and after the introduction of 2010 Turkish regulations. The study is based on data from Istanbul Memorial Hospital, ART and Genetics Center used to evaluate the 2010 regulations, which restricts the number of embryos to be transferred. According to the regulation; double embryo transfer (DET) is allowable after two unsuccessful attempts in cases up to maternal age of 35 and in any one cycle in cases ≥35. For the period from March 2003 to June 2019, a total of 31,459 cycles were analyzed to evaluate the overall effect of 2010 regulations. For the period from January 2014 to July 2019, a total of 4450 cycles were evaluated according to two different ages groups, patients <35 and patients from 35-42 years of age with single or double blastocyst transfer performed in compliance with current regulations. First the overall effect of the introduction of the regulations on multiple births was evaluated regardless of previous ART attempts and maternal age. Secondly, the clinical results of fresh and frozen-thawed single or double blastocyst transfer in patients <35 years with a history of 2 or 3 previous unsuccessful ART attempts and in patients ≥ 35 (35-42) years with a history of either no previous attempts or 1,2 or 3 attempts were evaluated. In the first study groups (March 2003 to July 2019), the parameter most significantly affected by the introduction of the regulations was the number of the embryos transferred. The percentage of single embryo transfer (SET ) cycle increased dramatically from 14% to 56.6%. However, despite a fall from 32.4%, the incidence of twin births remained high at 15.5%. In the second study groups from January 2014 to July 2019, in young patients <35 years with 2 or 3 previous cycles, the twin birth rate was very high at 47.26 % in the double blastocyst group whereas it was only 1.75% when a single blastocyst was transferred (p=0.0001). In patients ≥ 35 years (35-42) with zero,1,2 and 3 previous cycles, in the double blastocyst transfer group, the twin birth rate was again high at 28.4% whereas in the single blastocyst transfer group it was only 1.8% (p=0.0001). Importantly, there was no statistically significant difference in clinical pregnancy rates between these two groups (67.4% vs 67.5% in the <35 group, and 59.1% vs 54.1% in the ≥ 35 year group) (p=0.846 and p=0.055). Thus, in DET, there was a high risk of twin births and no advantage in terms of pregnancy rates. As a result of the wording of the current regulations, there has been a high demand for DET in both young and older patients. Our study strongly suggests that, especially in the light of the success of blastocyst transfer, the Turkish regulations should be amended to limit the use of DET and encourage the use of SET apart from in exceptional cases and particularly in women under 35 years old.
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