in vitro fertilization

, the largest risk that a couple faces is that of multiple pregnancy. Doctors can increase the chance for pregnancy by increasing the number of embryos transferred in an IVF cycle. Doing this however, increases the chances for a multiple pregnancy.

A multiple pregnancy, even if it is only a twin pregnancy, is associated with a large number of problems for both mother and babies. The incidence of IVF success

pregnancy complications is higher compared to singleton pregnancies. Problems as gestational diabetes, pre-eclampsia, preterm labor and cesarean section occur more commonly with twin pregnancies. These complications result in a rate of fetal death rate before delivery that is five times higher in twins than singletons. Preterm delivery leads to significant problems for babies such as respiratory distress and low birth weight. Prematurity is one of the primary reasons that seven times more twin babies die in the first month of life than singleton babies and why they have almost double the rate of severe handicaps. Babies that are born as multiples also experience a higher rate of birth defects and have a four times greater rate of cerebral palsy compared to singletons.

In sum, avoiding multiple pregnancy in in-vitro fertilization is a very desirable goal. The problem is how to accomplish this goal without reducing the chance for pregnancy overall.

Several IVF studies have looked at transfer of a single embryo to the uterus compared to two embryos. These studies have compared the overall pregnancy rate and the multiple pregnancy rates. In most cases, these studies looked at a very select group of women who were thought to have a very good chance for pregnancy. They were young, had a large number of high quality embryos (as assessed under the microscope), and usually were on their first in vitro fertilization attempt. As a whole, these studies showed a lowering of the risk of multiple pregnancies but also a lowering of the overall IVF pregnancy rate.

One recent study looked at an unselected in vitro fertilization population and found the same to be true but to a larger extent. There was a greater difference in pregnancy rates between those women that had two embryos transferred compared to those that had one embryo transferred.

Some programs persist on transferring embryos after only two or three days in the laboratory. These are known as cleavage stage embryo transfers. Studies comparing single embryo transfer to double embryo transfer at the cleavage stage have uniformly shown a lower pregnancy rate for the single embryo transfer. Although many studies using blastocyst transfer have not shown a difference in pregnancy rates, more studies are needed before definite conclusions can be drawn. It also has yet to be seen whether greater use of such methods as preimplantation genetic diagnosis can narrow or eliminate the difference in pregnancy rates and make single embryo transfer a more widely used practice.

Patients undergoing IVF have an interesting perspective on IVF risks. Most studies assessing the preferences of IVF patients have concluded that they would actually prefer to have twin pregnancies than singletons. A survey of 81 Scottish couples found that the majority of couples would prefer dealing with twin related complications than risk treatment failure and childlessness. A study of British couples found that even if these patients were given extra information and counseling about the risks of multiple pregnancy, only 25-30% would accept a single embryo transfer if they thought there was even a slight chance of a lower IVF pregnancy rate.

Last Updated ( Friday, 26 October 2007 )