Dr. Marieke Lambers of VUMC, Gynaecology Obstetrics and Reproductive Medicine in Amsterdam, the Netherlands, and colleagues studied data from the 19,840 Dutch women who underwent in vitro fertilization between 1983 and 1995.
The researchers selected all first fresh -- unfrozen -- IVF and Intra Cytoplasmic Sperm Injection cycles using double embryo transfer that resulted in the delivery of a single or twin baby, both living and stillborn.
Excluded from the analysis were cases where there were insufficient data from medical files, patients who used donated oocytes -- egg cell -- or who had undertaken fertility treatment besides IVF and Intra Cytoplasmic Sperm Injection -- injecting a single sperm into an egg -- those who had had an abortion, an ectopic pregnancy or a miscarriage.
The remaining group was analyzed for single or multiple pregnancies, and a number of independent variables, including body mass index, weight, height, maternal age, number of oocytes retrieved, use of alcohol, level of education and parity.
Of the 6,589 patients who completed their first IVF cycle, 2,357 women had double embryo transfer, resulting in 371 single and 125 twin pregnancies.