Risk factors for monozygotic twinning after in vitro fertilization: a systematic review and meta-analysis

To establish the risk factors for monozygotic twin (MZT) and monochorionic twin (MCT) pregnancies after in vitro fertilization (IVF). Systematic review and meta-analysis. Not applicable. Women who achieved MZT and non-MZT pregnancies through IVF. Systematic search of Medline from January 1995 to October 2018 with cross-checking of references from relevant articles in English. Possible risk factors for MZT or MCT pregnancies after IVF, comprising extended embryo culture, insemination method (conventional IVF and intracytoplasmic sperm injection [ICSI]), embryo biopsy for preimplantation genetic testing for aneuploidies or for monogenic/single-gene defects (PGT-A or PGT-M) programs, assisted hatching (AH), oocytes donation, female age, and embryo cryopreservation. A total of 40 studies were included. Blastocyst transfer compared with cleavage-stage embryo transfer, and female age