Infertility

Laura A.

Schieve of the National Center for Birth Defects and Developmental Disabilities, who wrote the editorial, noted that about 35 percent of U.S.

births in 2002 resulting from assisted reproduction technology "included twin or higher-order multiple gestations." In contrast, Ms.

Schieve said, "the incidence of multiple births after natural conception is less than 2 percent." But in the Belgian study, led by Dr.

Evangelos G.

Papanikolaou, a reproduction specialist at Vrije University in Brussels, the multiple-birth rate was equivalent: about 2 percent.

Of the 94 deliveries that resulted among study participants, just two involved twins, both of them identical pairs.

All women in the Belgian study received only one embryo.

Half got embryos that had been cultured for three days, a stage described as "cleavage-stage," while the other half got embryos cultured for five days, which are called "blastocyst-stage." The purpose of the research was to compare the rates of continued pregnancy and live delivery in women who received the older versus the younger embryos.

Transferring cleavage-stage embryos is far more common than implanting blastocyst-stage embryos.

"As compared with the cleavage-stage group, the blastocyst-stage group had a signifi...

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