More than 30 years after the world's first test-tube baby was born and despite modest advances, scientists are still struggling to dramatically improve the odds for infertile couples trying to have children.
Though new techniques have been introduced in recent years, in-vitro fertilization remains a costly, stressful process, with only about a 25 percent chance of success in most cases.
At a meeting this week of the European Society for Human Reproduction and Embryology in Stockholm, scientists discussed new research into how eggs and embryos develop and how to predict and possibly prevent miscarriages in infertile women.
But even that knowledge is unlikely to radically boost the chances of most infertile couples trying for a baby.
"IVF isn't a perfect technology," said Dr. James Grifo, director of the NYU Fertility Center. He was not connected to any of the studies presented in Stockholm. "We're still limited by nature and most embryos in nature don't make babies," he said.
Grifo said IVF success rates have risen from about 10 percent about 15 years ago to about 25 percent for most infertile couples these days. He also added that for healthy women under 40, the rate can be as high as 50 percent.
"For many patients, the technology is the difference between having a baby and not having a baby," he said. "I'm very hopeful about the future, but it isn't for everybody. Not everybody has the money or the stomach for it."
Women undergoing IVF must take drugs to dampen down and then to stimulate their reproductive systems, which involves taking pills and giving themselves shots every day. For several weeks, women typically have daily blood and ultrasound tests to monitor their hormone levels and ovaries before having a procedure to retrieve their eggs. Scientists then add sperm to the eggs in a laboratory and embryos develop for three to five days before either being implanted into the womb or being frozen for later use.
Many infertile couples undergo more than one IVF cycle, which on average costs more than $12,000. In most European countries, at least one cycle is paid for by national health insurance but not all U.S. insurance providers cover it.
Even supposed breakthroughs like preimplantation genetic diagnosis, a test done to pick the best embryos, haven't panned out as scientists hoped. Doctors had assumed the test would improve pregnancy rates, but studies showed women who had their embryos tested were actually less likely to become pregnant _ probably because scientists still can't accurately predict which embryos will succeed.
A study in its early stages presented this week at the European fertility conference suggested embryos that look problematic at day three can fix themselves by day five. Many embryos created by IVF are implanted after three days, though doctors are increasingly waiting until day five if possible.
"The research suggests you can have abnormal cells in an embryo, but that doesn't necessarily condemn embryo development," said Dr. Stuart Lavery, an IVF specialist at London's Hammersmith hospital and a spokesman for the British Fertility Society.
He warned that science is still a long way from having accurate tests to substantially improve IVF live birth rates. "Don't think that all these new-fangled genetic tests are really working," he said. "We're still searching for the best way to pick the best embryo."
Other experts said improving success rates isn't just about the technology.
"If there are abnormal embryos, there is nothing we can do about that," said Alan Handyside, director of the London Bridge Fertility Centre. "This is ultimately about identifying the right patients and preventing women from going through the stress of multiple failed IVF cycles."
Still, doctors have made progress in reducing the risk of multiple births in recent years. Women having IVF previously had up to a 25 percent chance of having twins or triplets because scientists implanted numerous embryos, increasing the health risks for both the mother and children.
But in the last few years, doctors in many countries including Britain, Sweden, and the U.S. have aimed to only implant one or two embryos in most women, cutting the risk of multiple births to about 2 percent, the same risk in the general population.
Doctors still say the most important factors influencing fertility are a woman's age and things like smoking and being obese.
Clare Lewis-Jones, who endured three failed IVF cycles before adopting two children, said anything scientists could do to improve the technology would make a big difference.
"IVF is very physically tiring and stressful because it goes on for weeks, and you know that, at any stage, something could go wrong," Lewis-Jones said. "Your ovaries might not produce enough eggs, and even if you get the eggs, will the sperm fertilize them and how will the embryos do?"
"It was a great relief to finally be off the emotional roller coaster of fertility treatment," she said.
After her IVF experience, Lewis-Jones became the chief executive of the charity Infertility Network U.K. to raise awareness of the issue.
"By the time people get to IVF, they have already experienced a lot of failure," she said. "It's very reassuring for patients to know there's continued research to improve success rates. This is not a treatment that you want to go through more than once."