Tall Women Twice as Likely to Conceive Twins After IVF

After a double embryo transfer, women who are 5’7" or taller are twice as likely to carry dizygotic twins as are shorter women.

The incidence of twinning also significantly increased with an increasing number of retrieved oocytes, according to a retrospective database review.

The findings may help reproductive specialists develop a "tailor-made, personalized in vitro fertilization treatment," Dr. Marieke Lambers said during a press briefing at the annual meeting of the European Society of Human Reproduction and Embryology.

Dr. Lambers of Vrije Universiteit Medisch Centrum, Amsterdam, used information from the OMEGA database, a Dutch cohort study of ovarian stimulation for in vitro fertilization (IVF) and subsequent gynecologic diseases. The study comprised 19,840 women who underwent IVF or intracytoplasmic sperm injection from 1983 to 1995. Women received health questionnaires from 1997 to 1999, which were combined with data from their medical records.

Dr. Lambers’s analysis included 2,357 women who completed a first fresh – not cryopreserved – IVF cycle with a double embryo transfer. These resulted in 371 singleton pregnancies and 125 twin pregnancies.

The investigators conducted a multifactorial regression analysis to determine what factors, if any, influenced twinning in the mothers. These included body mass index, weight and height, maternal age, number of retrieved oocytes, alcohol use, education, and parity.

Two factors – maternal height and the number of eggs retrieved – were significantly associated with twinning, Dr. Lambers said. Women taller than 174 cm (5’7") were twice as likely to have twins as were shorter women. Those who had more than 11 oocytes retrieved were 2.4 times more likely to have twins than were those with fewer eggs retrieved.

Since the data were observational, it’s not possible to draw any causal relationships, but Dr. Lambers suggested that the higher number of oocytes could be an indication of egg quality. "The positive relationship between a higher number of oocytes retrieved and a twin pregnancy probably reflects the fact that these women would have had a larger choice of good quality embryos," she said.

However, "the association between increased height and pregnancy is more difficult to explain." Vascular endothelial growth factor (VEG-F) could play a part, she suggested. "Previous studies have shown that women who are prone to conceive twins after IVF had a higher level of [the growth factor], which promotes the growth of blood vessels at the site of implantation. Perhaps there is also an association between tall stature and increased VEG-F levels."

Theory aside, the findings could help refine IVF strategies for both doctors and patients.

"Doctors working in IVF are faced with a constant balancing act between giving the best chance of achieving a pregnancy without incurring all the problems associated with multiple births. We hope this work could be used in the future as a basis for predictive models that assist in the choice between single and double embryo transfer. This is important, because multiple pregnancies involved a higher risk of problems for the mother, such as preeclampsia, and also for the baby, [because of] preterm or immature delivery."

Dr. Lambers did not have any relevant financial disclosures.

After a double embryo transfer, women who are 5’7" or taller are twice as likely to carry dizygotic twins as are shorter women.

The incidence of twinning also significantly increased with an increasing number of retrieved oocytes, according to a retrospective database review.

The findings may help reproductive specialists develop a "tailor-made, personalized in vitro fertilization treatment," Dr. Marieke Lambers said during a press briefing at the annual meeting of the European Society of Human Reproduction and Embryology.

Dr. Lambers of Vrije Universiteit Medisch Centrum, Amsterdam, used information from the OMEGA database, a Dutch cohort study of ovarian stimulation for in vitro fertilization (IVF) and subsequent gynecologic diseases. The study comprised 19,840 women who underwent IVF or intracytoplasmic sperm injection from 1983 to 1995. Women received health questionnaires from 1997 to 1999, which were combined with data from their medical records.

Dr. Lambers’s analysis included 2,357 women who completed a first fresh – not cryopreserved – IVF cycle with a double embryo transfer. These resulted in 371 singleton pregnancies and 125 twin pregnancies.

The investigators conducted a multifactorial regression analysis to determine what factors, if any, influenced twinning in the mothers. These included body mass index, weight and height, maternal age, number of retrieved oocytes, alcohol use, education, and parity.

Two factors – maternal height and the number of eggs retrieved – were significantly associated with twinning, Dr. Lambers said. Women taller than 174 cm (5’7") were twice as likely to have twins as were shorter women. Those who had more than 11 oocytes retrieved were 2.4 times more likely to have twins than were those with fewer eggs retrieved.

Since the data were observational, it’s not possible to draw any causal relationships, but Dr. Lambers suggested that the higher number of oocytes could be an indication of egg quality. "The positive relationship between a higher number of oocytes retrieved and a twin pregnancy probably reflects the fact that these women would have had a larger choice of good quality embryos," she said.

However, "the association between increased height and pregnancy is more difficult to explain." Vascular endothelial growth factor (VEG-F) could play a part, she suggested. "Previous studies have shown that women who are prone to conceive twins after IVF had a higher level of [the growth factor], which promotes the growth of blood vessels at the site of implantation. Perhaps there is also an association between tall stature and increased VEG-F levels."

Theory aside, the findings could help refine IVF strategies for both doctors and patients.

"Doctors working in IVF are faced with a constant balancing act between giving the best chance of achieving a pregnancy without incurring all the problems associated with multiple births. We hope this work could be used in the future as a basis for predictive models that assist in the choice between single and double embryo transfer. This is important, because multiple pregnancies involved a higher risk of problems for the mother, such as preeclampsia, and also for the baby, [because of] preterm or immature delivery."

Dr. Lambers did not have any relevant financial disclosures.

After a double embryo transfer, women who are 5’7" or taller are twice as likely to carry dizygotic twins as are shorter women.

The incidence of twinning also significantly increased with an increasing number of retrieved oocytes, according to a retrospective database review.

The findings may help reproductive specialists develop a "tailor-made, personalized in vitro fertilization treatment," Dr. Marieke Lambers said during a press briefing at the annual meeting of the European Society of Human Reproduction and Embryology.

Dr. Lambers of Vrije Universiteit Medisch Centrum, Amsterdam, used information from the OMEGA database, a Dutch cohort study of ovarian stimulation for in vitro fertilization (IVF) and subsequent gynecologic diseases. The study comprised 19,840 women who underwent IVF or intracytoplasmic sperm injection from 1983 to 1995. Women received health questionnaires from 1997 to 1999, which were combined with data from their medical records.

Dr. Lambers’s analysis included 2,357 women who completed a first fresh – not cryopreserved – IVF cycle with a double embryo transfer. These resulted in 371 singleton pregnancies and 125 twin pregnancies.

The investigators conducted a multifactorial regression analysis to determine what factors, if any, influenced twinning in the mothers. These included body mass index, weight and height, maternal age, number of retrieved oocytes, alcohol use, education, and parity.

Two factors – maternal height and the number of eggs retrieved – were significantly associated with twinning, Dr. Lambers said. Women taller than 174 cm (5’7") were twice as likely to have twins as were shorter women. Those who had more than 11 oocytes retrieved were 2.4 times more likely to have twins than were those with fewer eggs retrieved.

Since the data were observational, it’s not possible to draw any causal relationships, but Dr. Lambers suggested that the higher number of oocytes could be an indication of egg quality. "The positive relationship between a higher number of oocytes retrieved and a twin pregnancy probably reflects the fact that these women would have had a larger choice of good quality embryos," she said.

However, "the association between increased height and pregnancy is more difficult to explain." Vascular endothelial growth factor (VEG-F) could play a part, she suggested. "Previous studies have shown that women who are prone to conceive twins after IVF had a higher level of [the growth factor], which promotes the growth of blood vessels at the site of implantation. Perhaps there is also an association between tall stature and increased VEG-F levels."

Theory aside, the findings could help refine IVF strategies for both doctors and patients.

"Doctors working in IVF are faced with a constant balancing act between giving the best chance of achieving a pregnancy without incurring all the problems associated with multiple births. We hope this work could be used in the future as a basis for predictive models that assist in the choice between single and double embryo transfer. This is important, because multiple pregnancies involved a higher risk of problems for the mother, such as preeclampsia, and also for the baby, [because of] preterm or immature delivery."

Dr. Lambers did not have any relevant financial disclosures.