Transfer of Blastocyst-Stage Embryo Better for IVF

Study halted early after pregnancy, delivery rates higher than with cleavage-stage embryo

WEDNESDAY, March 15 (HealthDay News) -- Transfer of a single blastocyst-stage embryo leads to better rates of pregnancy and delivery in infertile women under age 36 than transfer of a single cleavage-stage embryo, researchers report in the March 16 issue of the New England Journal of Medicine.

Evangelos G. Papanikolaou, M.D., Ph.D., and colleagues from Vrije Universiteit Brussel in Belgium randomized 351 infertile women under age 36 to undergo transfer of a single cleavage-stage (day 3) embryo or transfer of a single blastocyst-stage (day 5) embryo.

The ongoing pregnancy rate was significantly higher in women with a blastocyst-stage embryo than a cleavage-stage embryo (33.1 percent versus 21.6 percent, relative risk 1.54). The results prompted the researchers to terminate the study early. The delivery rate was also significantly higher in women transferred with a blastocyst-stage embryo (32 percent versus 21.6 percent, relative risk 1.48). The authors note that the two cases of multiple births occurred in women undergoing transfer of a single-cleavage embryo.

In an accompanying editorial, Laura A. Schieve, Ph.D., of the U.S. Centers for Disease Control and Prevention in Atlanta, notes that "although the results are encouraging, they are again generalizable only to a segment of the population being treated with assisted reproductive technology," adding that "less than half of women undergoing treatment with assisted reproductive technology in the United States would meet the age criterion alone."

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