Elevated incidence of monozygotic twinning is associated with extended embryo culture, but not with zona pellucida manipulation or freeze-thaw procedure

ObjectiveTo identify the incidence and risk factors associated with IVF-conceived monozygotic twinning (MZT).DesignRetrospective study.SettingAcademic hospital.Patient(s)A total of 3,463 women with clinical pregnancies between January 2014 and February 2015 were analyzed.Intervention(s)None.Main Outcome Measure(s)The measures were the incidence of MZT based on the number of embryos that were replaced, type of insemination method (conventional...