RESUMO
OBJECTIVE: To study the incidence of monozygotic twinning (MZT) in patients using in vitro fertilization, relative to their age, genetic background, ovarian function, and assisted reproductive techniques used. DESIGN: Analysis of a collected database. SETTING: Infertility treatment center. PATIENT(S): A total of 1,876 patients receiving infertility treatment between 2000 and 2012. Pregnancies with monozygotic twins (A: 23) were compared with deliveries of dizygotic twins (B: 423), singleton pregnancies (C: 880), and aborted pregnancies (D: 389). INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): A genetic survey on multiple pregnancies in the extended family. Measures were micromanipulation technique, the length of embryo cultivation, type of cultivation media, basal follicle-stimulating hormone level, estradiol level on the day of human chorionic gonadotropin administration, number of oocytes, total consumption of gonadotropins, and consumption of gonadotropins needed for recovery of 1 oocyte. RESULT(S): No differences were found between the incidence of MZT in cycles that did vs. did not use micromanipulation techniques. In addition, the length of embryo cultivation or type of cultivation media used did not affect the results. Estradiol levels and implantation rates were significantly higher in group A. The incidence of MZT in families in group A was significantly higher than that in groups B and C. CONCLUSION(S): We propose that the high incidence of MZT in infertility-clinic patients is conditioned by hereditary factors, and good ovarian function only facilitates the expression. The resulting recommendation is that young women with a positive family history and good ovarian function undergo elective single-embryo transfer, and proper counseling is advisable.
