BACKGROUND: During the past decade in the United States, increasing attention has been paid to lowering the incidence of multiple gestations resulting from the use of assisted reproductive technology. To determine whether such efforts have been successful, we assessed national trends in embryo-transfer practice patterns and in outcomes after the use of assisted reproductive technology. METHODS: We analyzed data on outcomes of assisted reproductive technology procedures as reported to the Centers for Disease Control and Prevention from 1995 to 2001 by fertility clinics in the United States. We also analyzed data from the National Center for Health Statistics on the rates of twin births and triplet or higher-order multiple births. RESULTS: From 1995 to 2001 in the United States, the number of infertility clinics, the number of fresh-embryo cycles initiated, and the number of fresh-embryo transfers increased steadily. The average number of embryos transferred per cycle began decreasing in 1997, with the steepest decline (an 11.1 percent decrease) between 1998 and 1999. In contrast, the number of pregnancies and live births per cycle during the period from 1995 to 2001 steadily increased. Even though the percentage of pregnancies with twins did not change significantly between 1997 and 2001, the percentage of pregnancies with three or more fetuses significantly decreased every year, with the steepest decline (a 20.8 percent decrease) between 1998 and 1999, after the publication in 1998 of the American Society for Reproductive Medicine guidelines for embryo transfer. CONCLUSIONS: Since 1997 in the United States, there have been consistent decreases in both the number of embryos transferred per cycle and the percentage of pregnancies with three or more fetuses, as well as a consistent increase in the percentage of live births per cycle.
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