Objectives To study the incidence and potential causes of monozygotic twins after in vitro fertilization and embryo transfer （IVF-ET）. Methods A retrospective study was performed on women carrying monozygotic twins ...Objectives To study the incidence and potential causes of monozygotic twins after in vitro fertilization and embryo transfer （IVF-ET）. Methods A retrospective study was performed on women carrying monozygotic twins （MZTs） after conventional IVF-ET treatment at the Third Affiliated Hospital of Guangzhou Medical College in China from January 2003 to May 2009. The incidence and the miscarriage rate for MZTs following IVF-ET were examined iin relation to maternal age, duration of infertility, type and dose of hormone treatment, conventional IVF-ET cycles versus intracytoplasmic sperm injection （ICSI） cycles, the use of fresh or frozen-thawed embryos, and day （post-fertilization） of embryo transfer. Results Sixteen MZT pregnancies occurred in 2 161 patients （incidence of 0.74%）, of which 5 miscarried （31.25%）. No significant difference was found between MZT and non-MZT groups in terms of maternal age, duration of infertilit）, duration of gonadotropin （Gn） administration, dosage of Gn, number of oocytes retrieved, number of oocytes fertilized, or number of embryos transferred （P〉O.05）. The incidence of MZT was not statistically different between conventional IVF-ET cycles and ICSI cycles, between fresh embryos transfer cycles and frozen-thawed embryo cycles, or between different transfer days （P〉0.05）. Conclusion The incidence of MZTs following IVF-ET treatment greatly exceeds that observed following spontaneous conception. Intracytoplasmic sperm injection, frozenthawed procedures, and embryo transfer on different days were not correlated with an increased incidence of MZT pregnancies.展开更多
为研究特高压气体绝缘开关设备的隔离开关残余电荷电压特性及其仿真方法,首先分析了残余电荷电压的几种影响因素;并在真型试验平台上开展了大量试验研究,对气体绝缘开关设备隔离开关分闸空载短母线所产生的触头间隙重复击穿过程进行了...为研究特高压气体绝缘开关设备的隔离开关残余电荷电压特性及其仿真方法,首先分析了残余电荷电压的几种影响因素;并在真型试验平台上开展了大量试验研究,对气体绝缘开关设备隔离开关分闸空载短母线所产生的触头间隙重复击穿过程进行了分析。基于试验结果,采用一元线性回归法得到触头间隙的击穿特性表达式,并在此基础上得到了残余电荷电压统计特性的仿真方法。结果表明,触头间隙正、负极性击穿电压之比约为1.3：1;正极性击穿电场强度在22~26 k V/mm之间。减小隔离开关开断速度,增大正、负极性击穿电压之差,降低SF6绝缘耐受强度都可以降低高幅值残余电荷电压的出现概率。展开更多
文摘Objectives To study the incidence and potential causes of monozygotic twins after in vitro fertilization and embryo transfer （IVF-ET）. Methods A retrospective study was performed on women carrying monozygotic twins （MZTs） after conventional IVF-ET treatment at the Third Affiliated Hospital of Guangzhou Medical College in China from January 2003 to May 2009. The incidence and the miscarriage rate for MZTs following IVF-ET were examined iin relation to maternal age, duration of infertility, type and dose of hormone treatment, conventional IVF-ET cycles versus intracytoplasmic sperm injection （ICSI） cycles, the use of fresh or frozen-thawed embryos, and day （post-fertilization） of embryo transfer. Results Sixteen MZT pregnancies occurred in 2 161 patients （incidence of 0.74%）, of which 5 miscarried （31.25%）. No significant difference was found between MZT and non-MZT groups in terms of maternal age, duration of infertilit）, duration of gonadotropin （Gn） administration, dosage of Gn, number of oocytes retrieved, number of oocytes fertilized, or number of embryos transferred （P〉O.05）. The incidence of MZT was not statistically different between conventional IVF-ET cycles and ICSI cycles, between fresh embryos transfer cycles and frozen-thawed embryo cycles, or between different transfer days （P〉0.05）. Conclusion The incidence of MZTs following IVF-ET treatment greatly exceeds that observed following spontaneous conception. Intracytoplasmic sperm injection, frozenthawed procedures, and embryo transfer on different days were not correlated with an increased incidence of MZT pregnancies.
文摘为研究特高压气体绝缘开关设备的隔离开关残余电荷电压特性及其仿真方法,首先分析了残余电荷电压的几种影响因素;并在真型试验平台上开展了大量试验研究,对气体绝缘开关设备隔离开关分闸空载短母线所产生的触头间隙重复击穿过程进行了分析。基于试验结果,采用一元线性回归法得到触头间隙的击穿特性表达式,并在此基础上得到了残余电荷电压统计特性的仿真方法。结果表明,触头间隙正、负极性击穿电压之比约为1.3：1;正极性击穿电场强度在22~26 k V/mm之间。减小隔离开关开断速度,增大正、负极性击穿电压之差,降低SF6绝缘耐受强度都可以降低高幅值残余电荷电压的出现概率。
