The relative contribution of assisted reproductive technologies and ovulation induction to multiple births in the United States 5 years after the Society for Assisted Reproductive Technology/American Society for Reproductive Medicine recommendation to limit the number of embryos transferred.

OBJECTIVE: To examine the effect of the 1998 Society for Assisted Reproductive Technology/American Society for Reproductive Medicine (SART/ASRM) Practice Committee recommendation to limit the number of embryos transferred on high order multiple births (HOMB) due to assisted reproduction technology (ART) and ovulation induction (OI) in the United States.

SETTING: None.

DESIGN: Analysis of U.S. natality files, and U.S. Centers for Disease Control and Prevention (CDC) and ASRM/SART registry reports.

SETTING: None.

PATIENT(S): None.

INTERVENTION(S): None.

MAIN OUTCOME MEASURE(S): Number and ratio of twin, triplet, and quadruplet or higher order (quadruplet/+) multiple births. Percentage of HOMB due to ART, OI, natural conception, and unexplained.

RESULT(S): Between 1998 and 2003, the number of twin births (number of live-born infants in twin deliveries) in the United States increased 17%, and the number of HOMB was unchanged. Since 1998, total births due to ART increased 67%, twin births increased 65%, triplet births deceased 8%, and quadruplet/+ births decreased 35%. The ratio of twin, triplet, and quadruplet/+ births to total ART births decreased 2%, 45%, and 61% respectively. In 2003, the estimated percentages of multiple births due to ART and OI were twins 16% and 21%, triplets 45% and 37%, and quadruplets/+ 30% and 62%, respectively.

CONCLUSION(S): Following publication of the SART/ASRM recommended limits on number of embryos transferred, the ratio of HOMB births to total ART births decreased substantially; however, U.S. HOMB did not decrease due to a 67% increase in total ART births and an increase in triplet births from OI.