Monozygotic pregnancy after the treatment for infertility by transfer of frozen-thawed embryos]

OBJECTIVES: It has been suggested that monozygotic pregnancies occur more frequently after in vitro fertilisation. This phenomenon is attributed to a number of factors including in vitro culture conditions, malformation of the zona pellucida due to manipulation on the oocytes and artificial opening of the zona pellucida. DESIGN: Retrospective analysis of monozygotic pregnancies in an IVF-ET procedures and obstetrical these pregnancies outcome. MATERIALS AND METHODS: A total of 2254 IVF-ET procedures were analysed. Three protocols were used for ovarian stimulation: short or long protocols with gonadotropins releasing hormone analogue or clomiphene citrate with hMG. In 811 cases male factor was diagnosed and intracitoplasmatic sperm injections were performed. RESULTS: 549 clinical pregnancies were achieved in analysed group. In six cases ultrasound examination 5 weeks after embryo transfer showed a greater number of foetus than the number of embryo transferred. In three of those cases the embryos were obtained after ICSI. Age and average thickness of zona pellucida were similar in group of patients with monozygotic pregnancies when compared with all pregnant patients after IVF treatment. CONCLUSIONS: The incidence of monozygotic pregnancy is increased in group pregnancies resulting from IVF ET. No single risk factor can explain this phenomena. This type of pregnancy needs special obstetrical attention.