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Using One Embryo in IVF Doesn't Lower Birth Rate

In the News: New Study on IVF and Number of Embryos vs. Birth Rate

 IVF traditionally "hedged the bet" for a successful pregnancy by transferring several embryos, increasing a woman's chances of having twins and other multiple births.Carrying multiples could raise the number of risks to the mother and babies. Conditions can include diabetes during pregnancy, premature birth and cerebral palsy.

"Babies conceived through IVF account for just one percent of births each year, but IVF is responsible for 17 percent of twins," said Jessica Kresowik at the University of Iowa in Iowa City, who led the study.

One Embryo, One Healthy Baby

"Improved technology, has helped increase births if single embryos are used in younger women judged to have a good chance of getting pregnant," Kresowik added.

DNA fingerprinting, a comprehensive chromosomal screening, helps doctors know if the embryo has the right number of chromosomes. This allows the transfer of more genetically sound embryos. The result? An increase in pregnancy rates while the possibility of miscarriage or multiple births decreases. On the fifth day, they examine a few cells from a placental portion of the embryo (avoiding potential damage to the embryo).

What's on the Research Horizon?

Future changes in technique might include making the baby feel at home. Researchers at the University of Michigan are rocking the cradle. They've built a device that imitates the motion that an embryo experiences as they journey from woman's Fallopian tube to the uterus. Currently in IVF, eggs are fertilized with sperm and left to grow for several days in a culture dish that remains still and then the embryos are transferred to the uterus.

Shu Takayama and Gary Smith, built a thimble-sized device that pulses and moves the fluid holding the embryos. In animal studies, embryos grown in this dynamic device were healthier and more robust. The embryos at this stage are the size of a period.

About the studies: Jessica D. Kresowik, "Five-years of a mandatory single-embryo transfer (mSET) policy dramatically reduces twinning rate without lowering pregnancy rates." Among 364 women who fit the criteria and had a single-embryo transfer from 2004 on, 65 percent gave birth to a live baby and just over 3 percent had twins or other multiple births. Before the single embryo policy, 51 percent of all women younger than 38 got pregnant and gave birth to a live baby, compared with 56 percent afterwards. The proportion of women with multiple births dropped from 35 percent to less than 18 percent.

Takayama and Smith, "Dynamic Microfunnel Culture Enhances Embryo Development and Pregnancy Rates."

Human Reproduction, Vol.25, No.3 pp. 613–622, 201. Gently rocking embryos while they grow during in vitro fertilization (IVF) improves pregnancy rates in mice by 22 percent. The procedure could one day lead to significantly higher IVF success rates in humans.