Risky, multiple pregnancies may be a thing of the past
Scientists are on the verge of being able to tell whether or not an embryo will develop into a healthy fetus, a milestone that might allow doctors to stem the epidemic of twins and triplets from in-vitro fertilization.
By examining embryo genetics and using high-technology imaging, scientists are learning to identify signs that an embryo is healthy. If they can master this, doctors can confidently implant just one embryo rather than several as they do now to increase the chance of a viable pregnancy.
To the parents, ''having twins is not bad news after they have been searching for a pregnancy for a minimum of two or three years," said Dr. Pasquale Patrizio, director of the Yale Fertility Center.
But the risks to both mother and fetus skyrocket with multiple births. Triplets born through IVF have a 24 percent chance of having cerebral palsy. In 2000, 36 percent of triplets were born before 32 weeks of gestation, at risk for severe disabilities, or even death.
''We should have single-embryo transfer; that ought to be what every [IVF] program strives for," said Dr. Charles J. Lockwood, chairman of obstetrics and gynecology at Yale.
According to the US Centers for Disease Control and Prevention, of the 35,025 infants born using reproductive technology in 2000, more than half were twins, triplets, or higher order multiples.
In addition to worries about the children's health, multiple births also strain parents psychologically and financially, said Carol M. Warner, a professor of biology at Northeastern University who specializes in the health of preimplantation embryos. She said that premature babies can require millions of dollars in health care, and that most insurance companies have a $1 million cap.
''Single-embryo transfer is the absolute Holy Grail," she said.
Warner is among the scientists developing techniques to assess an embryo's health without harming it -- an accomplishment that is key to single-embryo transfer.
One of Warner's newest and most promising tools is an immense microscope, the product of a partnership between engineers and biologists, invented by Charles A. DiMarzio, director of the Optical Science Laboratory at Northeastern University. This microscope, called the QTM, allows Warner to view the whole embryo at once without having to dye the cells, which is a potentially toxic step.
''Our big hope for QTM," Warner said, ''is that we can noninvasively count the number of cells in an embryo."
The number of cells in an embryo is a widely-used health indicator -- the more cells, the better -- but getting an accurate count is difficult. Thus far, Warner's lab can reliably count up to 12 cells, and has had only slightly less success counting up to 23. Previously, the number of cells could never be reliably counted.
Embryos are usually implanted three days after they are retrieved, when they've grown to six or eight cells. In an effort to select the embryos that are most likely to become successful pregnancies, doctors have begun growing the cells in a culture for up to five or six days before they implant -- but that move itself could damage the embryo.
Warner said she's now trying to gain insight into the embryo's growth without having to actually wait for it to happen.
A decade ago, her laboratory discovered a gene that regulates how fast an embryo develops -- a major indicator of how likely it is to become a baby -- in addition to predicting birth weight. This gene also secretes a protein that can be measured without harming the embryo, and she is currently testing how that data predicts health.
''This explosion in technology that's occurring is improving our ability to discern abnormalities in embryos," said Lockwood of Yale.
Other procedures already exist to evaluate embryos, but parents are often reluctant to use them because they require biopsies that might harm the embryo.
The most common practice is the preimplantation genetic diagnosis available at fertility clinics: Patrizio said the diagnosis costs $2,000 to $2,500 at his clinic. He said that the procedure can be used to analyze up to nine chromosomes, looking for such genetic disorders as Down syndrome, Tay-Sachs disease, cystic fibrosis and sickle-cell anemia.
The Yale Fertility Clinic will not transfer more than two embryos, and offers single-embryo transfer, but Patrizio estimated that only 5 percent of its patients opt for just one.
The policy makers are now starting to catch up to the embryo science. The Society for Assisted Reproductive Technology, which reports national fertility data to the federal government, recently set guidelines recommending that patients under 34 consider implanting just one embryo, said Dr. Owen K. Davis, the society's president.
While guidelines can help doctors and patients, Davis cautioned against ''one-size-fits-all" legislation that would mandate the number of embryos implanted -- such as new Italian laws that do not allow more than three eggs to be fertilized and mandate that resulting embryos must be implanted. Such legislation may meet religious imperatives, but does not take into account the patient's fertility characteristics, Davis said.
In the five months since Italy instituted the restrictions, its rate of successful pregnancies has dropped from one in four to one in nine, according to the BBC.
''Italy," Davis said, ''is an extreme example of regulation gone amok."
