Conception rate still good with fewer IVF embryos

It seems that one of the dilemmas facing women undergoing in vitro fertilization need not be a bar to a successful outcome.

Usually, IVF produces more embryos than are need for implantation in the womb. The surplus is discarded or frozen, but many women find this objectionable. Now researchers report that the obstacle can be overcome by fertilizing fewer eggs, or oocytes.

Although this means that the likely number of embryos available for transfer is limited, it apparently does not adversely affect pregnancy rates, the investigators report.

To determine the effect of inseminating no more than four oocytes during IVF, Dr. John Nulsen and his team looked at outcomes for 16 women who had chosen this path.

This study group was compared with 150 women who had excess embryos cryopreserved (a group with a good prognosis) and with 37 women who produced only four or fewer oocytes because of underlying fertility problems (a poor-prognostic group).

All the women were undergoing their first cycle of standard IVF treatment.

The research team, based at the University of Connecticut Health Center in Farmington, reports the results in the medical journal Fertility and Sterility.

The clinical pregnancy rates were similar in the study group and good-prognostic group (63 percent versus 64 percent), and higher than in the poor prognostic group (30 percent). Corresponding rates for ongoing pregnancy rates followed a similar pattern - 56 percent, 61 percent, and 24 percent.

Summing up, the investigators write: "Patients who respond well to treatment but have fewer oocytes inseminated by choice behave like the good-prognostic patients and produce a cohort of good-quality oocytes that become good-quality embryos capable of implanting."

In counseling women who are thinking about this approach to IVF, Nulsen and his team recommend that they consider the fact that they forego the advantages of a frozen replacement cycle if the "fresh" cycle fails; that they may still produce more embryos than would normally be transferred; or that "there is a risk that no embryos will be transferred because of failure of fertilization or embryo development."

SOURCE: Fertility and Sterility, November 2005.