Reducing the Occurrence of Multiple Births, 10/2000 

There are a number of risk factors that increase the probability of an infant being born with cerebral palsy; four major risk factors are prematurity, low birth weight, maternal infection and multiple births (twins, triplets, etc). The May 1997 Research Fact Sheet provides information available about the relationship between multiple births and cerebral palsy. 

However, there is now additional knowledge about the methods being used for fertility enhancement, a major factor in causing multiple births. Since multiple births (sometimes referred to as a "multiple pregnancy") often occurs in women who have participated in a fertility enhancement procedure, more attention is now being given to approaches that reduce the risk of a high order multiple pregnancy (3 or more infants). There are 2 common methods of fertility enhancement in common use: 1) induction of ovarian egg production by hormone stimulation. This procedure usually results in the release of many eggs and thus the high probability of multiple births and (2) the fertilization and then the implantation of fertilized eggs into a woman's uterus (in vitro fertilization); sometimes the fertilized eggs are permitted to develop to the next stage before they are implanted. The insertion of two or more fertilized eggs is usually done to increase the probability of a successful pregnancy occurring. Of the two procedures, the more common at this time is the induction of multiple egg production by the use of hormonal stimulation. 

In a study of 3347 consecutive treatments involving 1494 infertile woman in which ovarian stimulation by hormones was used, 441 pregnancies occurred; this included 88 sets of twins, 22 triplets, 10 quadruplets, 5 quintuplets and 2 sextuplets.¹ The number of eggs available to sperm and the level of a female sex hormone in the blood are indicators of the risk of a multiple pregnancy. The age of the woman involved was also significant as a predictor of the risk of a multiple pregnancy; younger women being at higher risk of a multiple pregnancy. 

The authors suggest that the current guidelines being used by physicians as to whom and what method is to be used may no longer be adequate for reducing the occurrence of high order multiple pregnancies. One approach to reducing the risk would be to decrease the amount of ovarian stimulating hormone being used. The problem is it would also decrease the success rate of resulting pregnancies. The authors also suggest that increased consideration be given to use of in-vitro fertilization, implanting only two embryos (fertilized eggs) into the uterus. Using modern techniques, this could result in pregnancy in up to 60% of participating women. 

Comment:
The emotional situation related to a successful pregnancy and the financial costs involved for each time a fertility enhancement procedure is used are two very important factors that need to be considered when deciding upon the method to be used for fertility enhancement. On the other hand, consideration also needs to be given to the emotional burden and high economic costs of multiple births which can require special neo-natal care; in addition, the increased probability in multiple births of one or more infants having developmental brain damage (e.g. cerebral palsy) must also be considered. 

A consensus has not been reached on modern criteria that need to be established for the choice of fertility enhancement techniques in different groups of women (e.g. age groups). However, this study and others are providing the data necessary to review the present guidelines and how they need to be revised. The methods for achieving a successful pregnancy, which would result in a single full term birth, two at the most, needs to be reevaluated regularly as new knowledge about fertility enhancement methodologies become available. 

¹ Gleicher, N. et al. Reducing the Risk of High-Order Multiple Pregnancy After Ovarian Stimulation With Gonadotropins. NEJM 2000; 343:2-7 

UCP Research & Educational Foundation, October 2000

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