Which factors affect dizygotic twinning after in-vitro fertilization

Content: To investigate factors associated with dizygotic twinning after in-vitro fertilization (IVF) treatment with double embryo transfer (DET). Design: Retrospective cohort study. Background: Twinning causes many risks for mother and child. Factors which affect dizygotic (DZ) twinning after IVF are associated with multiple implantation and not with multiple ovulation. Risk factors for having a twin pregnancy after IVF remain unclear. Objective: The aim of this study was to investigate factors associated with dizygotic twinning after IVF treatment with DET. Patients: This study was conducted using data from a large Dutch nationwide cohort of women who underwent IVF/ICSI treatment between 1980-1995 (OMEGA database). 496 pregnancies were included; 371 singleton- and 125 twin pregnancies.Primary outcome measure: The risk of having a twin pregnancy (odds ratio) as a function of Body Mass Index (BMI), height, weight, parity, number of oocytes, maternal age, alcohol and educational attainment. Results: Women in the tallest quartile for height (>174 cm) were 2.1 times more likely to have a DZ twin pregnancy (p=0.037). Women with a high number of oocytes (>11) were 2.4 times more likely to become pregnant with twins (p=0.001). Women older than 33 years of age were 0.5 times more likely to become pregnant with twins (p=0.05). Conclusion: Our results indicate that a high maternal height, high number of oocytes retrieved at oocyte retrieval and a young maternal age are factors that are significantly positively associated with DZ twinning after IVF treatment with DET.