Mini-movies of growing embryos could help boost the success of in vitro fertilization, a new study found. But the number of women who could benefit from the time-lapse technology is unclear.
For the study, British researchers used time-lapse photography to track the earliest stage of embryonic development – a process that unfolds in womb-mimicking incubators for couples using IVF. The researchers then used an algorithm to spot the embryos most likely to grow into babies.
"Embryo selection based predominantly on specific time-lapse derived algorithms could rapidly become routine in IVF treatment," the study authors wrote in the journal Reproductive BioMedicine Online, describing how the healthiest-looking embryos had a 72.7 percent chance of leading to a pregnancy and a 61.1 percent chance of resulting in a live birth.
Embryos deemed to look less healthy by the time-lapse technique had a 25.5 percent chance of leading to a pregnancy and 19.2 percent of resulting in a live birth, according to the study.
But the study was small, with only 69 couples, and some experts say many women lack the luxury of choice when it comes to embryo implantation.
"A lot of the time, we don't have that many embryos to choose from," said Dr. James Goldfarb, director of the University Hospitals Fertility Center in Cleveland and past president of the Society for Assisted Reproductive Technologies, who was not involved in the study.
An IVF cycle starts with a woman taking drugs to stimulate the production of multiple eggs. After about two weeks, the eggs are collected and fertilized. Then, the resulting embryos are grown in a lab for up to five days, depending on how many there are and how healthy they look.
The more healthy embryos there are, the more likely an embryologist will watch them for five days to let the weakest die off, leaving the strongest behind. The pregnancy rate for women under 35 with day 5 embryo transfers is 69 percent, compared to 57 percent for women with day 3 transfers, according to data from the Cleveland Clinic's IVF Laboratory.
"For some patients, you might get 15 eggs, and maybe 13 will fertilize and you have enough embryos that look good on day 3 to go out to day 5 without a problem," said Goldfarb. "But at the other end of spectrum, you might have a patient with only six or seven eggs, only three or four get fertilized, and by day 3, you only have two that look reasonable."
In that case, Goldfarb added, "it's better to transfer them on day 3."
The number of embryos transferred depends on the woman's age. But for women 35 and under, it's typically one or two, according to Goldfarb. So if only one or two embryos are thriving on implantation day, there's not much of a choice.
But the new study raises an interesting possibility for women with multiple embryos to choose from. Based on time-lapse imaging, the researchers were able to weed out embryos with an abnormal number of chromosomes – embryos that would likely fail to implant in the womb or result in a miscarriage. None of the embryos deemed the least healthy by the time-lapse technique resulted in a pregnancy or a live birth, according to the study.
"In some ways, it's more of a negative to get pregnant and miscarry," said Goldfarb. "That rollercoaster can be much more traumatic than not getting pregnant at all."
But the study does not break down the couples' ages and explain how that might have impacted their IVF success rate, noting only that they ranged in age from 25 to 47 with an average age of 36. Nor does it detail how long the embryos were observed in culture before being transferred into the womb, instead indicating that they were "cultured until 5 or 6 days" after fertilization. And while the study does suggest that technology can help in the embryo selection process, experts say the decision to undergo IVF and the odds of being successful vary from couple to couple.
"Obviously, the goal is to pick out the best embryos, and this study is certainly not the first to look at this technique," said Goldfarb, explaining how similar studies have found mixed results. "It's something still in play, and we'll how this sorts out in long run.
"But I think the one thing patients want to hear is your best assessment of their individual chance of getting pregnant," he added. "And you can get a pretty good estimate of that based on their age and some other characteristics."