Liu H, et al. - The incidence and risk factors associated with IVF-conceived monozygotic twinning (MZT) were investigated. As per observations, there appeared an association of extended culture (advanced embryo stage) in fresh and frozen cycles with increased rates of MZT. Findings provided no evidence supporting the effect of the number of embryos transferred, intracytoplasmic sperm injection (ICSI) and assisted hatching (AH), and freeze-thaw procedures on the risk for MZT.

Methods

• Researchers performed a retrospective study at an academic hospital analyzing a total of 3463 women with clinical pregnancies between January 2014 and February 2015.
• They determined the incidence of MZT based on the number of embryos that were replaced, type of insemination method (conventional IVF or ICSI), with or without the use of assisted hatching (AH), and day of embryo transferred in fresh and frozen cycles.

Results

• MZT was noted in 93 women (2.69%).
• The cycle parameters of fresh or frozen cycles between MZT and other non-MZT pregnancies were not statistically significantly different.
• The rate of MZT did not significantly increase in relation to specific IVF procedures or techniques, such as the number of embryo replaced, zona pellucida manipulation (ICSI and AH), and freeze-thaw procedure, except for the day of embryo transferred.
• An increased probability of MZT was observed with day 4 and 5/6 transferred compared with day 3 transferred (odds ratio [OR], 2.73; 95% confidence interval [CI], 1.16–6.42 for day 4 transferred and OR, 3.68; 95% CI, 2.29–5.93 for day 5/6 transferred).