The rate of triplet and higher-order births in the United States has declined since 1998, coincident with efforts to limit the number of embryos transferred during IVF procedures, according to a report published online Dec. 4 in the New England Journal of Medicine.
A similar effort to reduce multiple births resulting from non-IVF fertility treatments would decrease the rate even further, bringing it more into line with the "natural" rate of multiple births that occurred before fertility treatments became available in 1971, said Dr. Aniket D. Kulkarni of the women’s health and fertility branch at the Centers for Disease Control and Prevention, Atlanta, and her associates.
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The rate of triplet and higher-order births in the United States has declined since 1998, coincident with efforts to limit the number of embryos transferred during IVF procedures, according to the report.
The investigators wanted to examine time trends in multiple births across the country, in particular the contribution that fertility treatments make to multiple births, but statistics regarding births that result from non-IVF fertility treatments are "not directly ascertainable" because there is no legal mandate to report those births, they noted. In contrast, multiple births resulting from IVF can be ascertained from a national registry of those births.
Dr. Kulkarni and her colleagues analyzed data on all live births that occurred from 1971 to 2011, then used statistical methods to estimate the proportion that occurred from natural conception, IVF, and non-IVF fertility treatments. They also used statistical methods to account for the effect of maternal age on multiple births.
The overall proportion of national births that were multiple births rose from 1.8% in 1971 to 3.5% in 2011.
This rate, however, did not show a continuous increase over the 4-decade study period, but rather showed a rise until approximately the last decade, followed by a steady decline.
By 2011, they estimated, 36% of twin births and 77% of triplet and higher-order births in the United States resulted from fertility treatments.
The rate of triplet and higher-order births increased from 1971 and reached its peak in 1998, the year that the Society for Assisted Reproductive Technology first issued practice guidelines designed to limit the number of embryos transferred during IVF cycles. The national rate of triplet and higher-order births then began to decline, going from 1.94 per 1,000 live births in 1998 to 1.37 per 1,000 in 2011.
This represents a 29% reduction, Dr. Kulkarni and her associates said (N. Engl. J. Med. 2013 [doi:10.1056/NEJMoa1301467]). The decline coincided with a 70% reduction in transfers of three or more embryos during IVF.
The trends for non-IVF fertility treatments were "less favorable," the researchers noted. In particular, ovulation induction and ovarian stimulation continue to contribute heavily to the national rate of triplet and higher-order multiple births.
Adherence to more prudent practice patterns, such as the use of low-dose gonadotropins, could reduce the rate of multiple births "while maintaining acceptable per-cycle pregnancy rates," they said, adding that mandating the public reporting of births resulting from non-IVF fertility treatments also would help by facilitating data analysis.
This study was supported by the U.S. Centers for Disease Control and Prevention. Dr. Kulkarni reported no financial conflicts of interest; an associate reported ties to Alere.