T

he different types of goop that embryos are grown in during in vitro fertilization could play a part in how well the process works — and how babies conceived through IVF fare after birth, too.

A new study — the first to randomly assign embryos to culture media — finds that the substrate used could affect the number of viable embryos created, pregnancy rates, and birth weight. There are around 20 different substrates used in clinics around the world. Fertility experts now say they want companies who make those compounds to clearly label the ingredients so scientists can parse out the differences.

During IVF, eggs and sperm are put together in a Petri dish filled with a culture media, which creates an environment to help embryos grow. Around three to five days later, one or more of those fertilized eggs are put into a woman’s uterus.

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The randomized, controlled trial divided up 836 couples undergoing an initial IVF treatment to have their embryos developed in one of two cultures, known as HTF and G5. Couples who had their embryos cultured in G5 had a higher pregnancy rate, slightly higher rate of live births, and more utilizable embryos than those who had embryos cultured in HTF. But babies born after fertilization in HTF did weigh about one-third of a pound more, on average, than babies born after fertilization in G5. The findings were published Tuesday in Human Reproduction.

“I would see these differences as relatively minor, but it’s reasonable to believe that different media compositions can affect embryo development,” said David Ball, an embryology lab director in Seattle who wasn’t affiliated with the study.

But it’s not really the difference between the two that matters, experts said — it’s that there’s a variation between the two at all.

“What’s important for me is there is a difference,” said study author John Dumoulin, an IVF researcher at Maastricht University Medical Center in the Netherlands. “The culture media has an influence on the embryo that is visible nine months later.”

Previous studies have come down on both sides of the question of whether media impacts IVF outcomes, but have been retrospective in design. This is the first study to prospectively set out to answer the question.

But it’s only the tip of the iceberg. There are about 20 commercially available culture media used in IVF, Dumoulin said, and there could be variations among all of them. His team is currently working on comparing more of those mediums.

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Hans Evers, editor in chief of the journal that published the paper, said that the finding suggests that IVF culture media need to be more clearly labeled in order for embryologists to make an informed decision about which culture to use.

“For me, as a doctor, it is a great concern that companies marketing culture media do not have to disclose the exact composition of their media,” he said in an interview. “This is in stark contrast to new medicines.”

Currently, the labels have general descriptors, which Evers compares to a nutrition label not having any actual nutritional information.

“Not knowing the exact composition of their IVF culture media is no longer an option for clinical embryologists,” Evers wrote in an editorial that accompanied the paper. 

But without research into the nitty gritty of those ingredients, embryologists won’t be equipped to fully understand what the exact composition of a media actually means for embryos, Ball pointed out.

“The problem is, how are we going to know what’s best just based on the composition of media?” Ball said. “It’s going to be a huge list of chemicals.”

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