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Monday 3rd May, 2004


Multiple-infant pregnancies are associated with complications for both the mother and her baby.


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  Single-Embryo Transfer reduced incidence of multiple births  

In a study published in the latest edition of The New England Journal of Medicine, a group of researchers from Boston evaluated the incidence of multiple-infant pregnancies (pregnancies involving three or more fetuses) in infertile women treated with assisted reproduction techniques (ART).

Assisted reproduction techniques, which have been around since the 70s, involve union of the egg and sperm in the lab, then placing a number of fertilized eggs back into the women. To increase the chance of implantation several embryos are transferred at once. This comes at a price however, as it also increases the risk of multiple-infant pregnancies.

Multiple-infant pregnancies are associated with complications for both the mother and her baby, including much higher rates of miscarriage, premature birth, higher need for cesarean delivery, birth defects, and higher rates of infant death. Assisted reproduction techniques are responsible for a 100-fold increase in the occurrence of multiple-infant births over the past two decades.

Study details

Tarun Jain et al. from Boston's Brigham and Women's Hospital analyzed data on assisted reproductive techniques from 1995 until 2001 by fertility clinics in the U.S. They found a decline in the incidence of pregnancies three or more fetuses by 4% in 2001. This decline reflects better technique in particular decreasing the number of transferred embryos. They also found that the pregnancy rates in those undergoing ART were on the increase which strengthens the notion that decreasing the number of transferred embryos does not affect overall pregnancy rates.

Current guidelines call for a maximum of two embryos transferred per attempt at assisted reproduction for infertile women with the most favorable prognoses for becoming pregnant. These women are usually under 35 years old. In women with a below average chance of becoming pregnant with assisted reproduction techniques, a maximum of five embryos are transferred. These are women who are 45 and older and who have had numerous failed attempts at assisted reproduction.

The study also reviewed figures on the rates of twin pregnancies in the U.S. from 1980-2001. They found, however, that the rates of twin pregnancies did not improve which may require further tightening the guidelines by decreasing the number of embryos transferred per attempt. Like higher-order births, twin births are associated with greater obstetrical and neonatal morbidity and mortality.


Tarun Jain, M.D., Stacey A. Missmer, Sc.D., and Mark D. Hornstein, M.D. Trends in Embryo-Transfer Practice and in Outcomes of the Use of Assisted Reproductive Technology in the United States. NEJM, Volume 350:1639-1645.

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