According to researchers in the Netherlands, tall women are more likely to conceive twins after double embryo transfer than shorter women. The study included nearly 20,000 women undergoing in-vitro fertilization. Women received the embryo transfers between 1983 and 1995. All transfers included fresh embryos resulting in births, single and twin. Both stillborn and live births were taken into consideration for the study. 

Variables of the study included height, weight, age of mother at implantation, education level and certain lifestyle factors. Of the 20,000 case studies, about 2,300 women received a double embryo transfer (DET). The resulting births included 371 singles and 125 twins. Women in the twin group were nearly 2 cm taller than women in the single group. Women with insufficient personal and health information present in the medical file were excluded from the study. 

Doctors have noted a connection between in-vitro fertilization success and VEGF-A. VEGF-A stands for vascular endothelial growth factor – A. This growth factor is typically responsible for promoting blood vessel growth at the time of implantation, but experts believe it could also have something to do with height. Women giving birth to twins had more VEGF-A than shorter women giving birth to singlets. 

Researchers are still in awe over the exact connection between VEGF-A, height and twin birth. One theory explains that women with higher VEGF-A levels may have more viable embryos and thus the increased number of twin pregnancies and subsequent twin births may be associated with embryo quality as opposed to height, but the taller stature is still a common factor in twin births – so this theory leaves much to be discovered. 

IVF doctors are constantly trying to increase viability of implanted embryos and increased chances of live birth. Multiple pregnancies are associated with an increased number of risk factors and risk factors of increased severity. If IVF doctors could pinpoint the sector of the female population more likely to conceive twins, they could prepare women for the possibility of twin pregnancy before implantation or implant only one embryo in women more likely to conceive twins. Double embryo transfer is used to increase the chances of conception. 

Source: European Society of Human Reproduction and Embryology. 5 July, 2011.