NEW YORK (Reuters Health) - There are about twice as many sets of triplets born in Norway every year compared to 40 years ago -- not including babies conceived with assisted reproductive technology (ART), new research shows.
Once ART babies were added to the mix, the rate of triplet births roughly tripled, Dr. A. Tandberg of Haukeland University Hospital in Bergen and colleagues found.
While the study wasn’t designed to investigate the reasons behind the increase in non-ART births, the researchers suggest that a sharp increase in use of the ovulation-stimulating drug clomiphene citrate since the early 1970s was likely a factor.
In countries where ART is widely used, the researchers say, the rate of triplet births climbed slowly beginning in the 1980s, and then started to decline at the beginning of the current century. However, they say, the role of ART in this pattern has not been clear.
To investigate, they looked at 2.2 million pregnancies in Norway between 1967 and 2006, including 448 triplet sets and 27,575 twin pairs. After 1988, when ART was introduced, the country introduced a separate registry for artificially conceived births.
Before 1988, one set of triplets was born for every 10,000 births; after 1988, there were 3.3 triplet births per 10,000 pregnancies. The rate of triplet births peaked at 3.5 per 10,000 in 1987-1991, but had declined to 2.7 per 10,000 by 2002-2006. During both time periods, triplet births were more common among older women.
The recent decline in ART triplet births shows that efforts to discourage the transfer of multiple embryos have been successful, the researchers say.
Throughout the course of the study, triplets had a 10-fold greater risk of dying shortly after birth than single infants; ART did not change this risk.
SOURCE: BJOG, online March 17, 2010.
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