Embryo glue is a specialized liquid medium used during the embryo transfer step of IVF. It contains a high concentration of hyaluronan, a naturally occurring substance found throughout the human body, designed to help an embryo stick to the uterine lining. It is not actually a glue. The product is a clear solution that replaces the standard culture medium embryos sit in just before transfer.
What Embryo Glue Contains
The most widely used product, EmbryoGlue by Vitrolife, contains 0.5 mg/ml of hyaluronan, which is four times the concentration found in standard embryo culture media. Hyaluronan is a large, gel-like molecule your body already produces in joints, skin, eyes, and critically, in the uterine lining. During the window when the uterus is most receptive to an embryo (the secretory phase of your menstrual cycle), hyaluronan levels in the uterine lining naturally rise, then drop back down at menstruation. This natural spike suggests the molecule plays a role in helping embryos implant.
How It Helps Embryos Attach
The working theory is that hyaluronan acts as a molecular bridge. Both the outer shell of the embryo and the cells lining your uterus have surface receptors called CD44 that bind to hyaluronan. When the embryo is bathed in the high-hyaluronan medium, the molecule essentially connects the two surfaces during that critical first contact, helping the embryo “dock” against the uterine wall.
Beyond simple stickiness, hyaluronan stimulates cell growth, migration, and adhesion. There is also evidence that embryos can break down the large hyaluronan molecules into smaller fragments, which then act as signaling agents that may promote further development. So it likely does more than just hold the embryo in place during those first moments.
What Happens During Transfer
The process adds very little to your IVF cycle. Before transfer, your embryos are placed into the hyaluronan-enriched medium and incubated for at least 10 minutes at body temperature. The embryos are then loaded into the transfer catheter along with this medium and placed into your uterus the same way they would be with standard media. You won’t feel any difference during the procedure itself.
Does It Improve Success Rates?
The evidence is promising but not settled. A large Cochrane systematic review covering 26 randomized controlled trials and over 6,700 participants found that adding hyaluronan to transfer media probably increases clinical pregnancy rates by about 16% relative to standard media. The review rated this as moderate-quality evidence, meaning there is reasonable confidence in the finding but some uncertainty remains.
Individual studies have reported more dramatic numbers. One large study comparing frozen embryo transfers found a live birth rate of 60.6% with embryo glue versus 47.5% without it, and a clinical pregnancy rate of 69.5% versus 57.6%. The benefit appeared across age groups: for patients under 35, live birth rates rose from 51.9% to 63.4%, and for those 35 and older, rates went from 35.6% to 52.8%.
However, these headline figures come with caveats. The Cochrane review noted considerable variation between studies, and subgroup analyses suggested the benefit may be more pronounced in fresh transfer cycles than in frozen ones. When researchers looked only at the most rigorously designed studies, some of the advantages (like reduced miscarriage rates) became inconclusive.
Who May Benefit Most
The strongest evidence points toward two groups. Patients with recurrent implantation failure (two or more failed transfer cycles) saw their implantation rate rise from 11% to 16% with embryo glue in one prospective trial. Patients whose infertility was caused by tubal factors also showed significant improvement, with clinical pregnancy rates roughly doubling from 18.8% to 38% in the same study. For patients without these specific issues, the benefit appears smaller and less consistent.
Safety Profile
No clear safety concerns have emerged. The Cochrane review found no evidence that hyaluronan-enriched media increased adverse events. One finding that initially raised eyebrows was a 45% relative increase in multiple pregnancy rates, but this was likely explained by the transfer of more than one embryo per cycle in those studies rather than a biological effect of the medium itself. With single embryo transfer, which is now standard practice in many clinics, this concern largely disappears.
Long-term data on babies born after embryo glue use remain limited. No signals of harm have appeared, but large-scale randomized trials tracking neonatal and childhood outcomes are still underway.
How Regulators View It
The UK’s Human Fertilisation and Embryology Authority (HFEA), which rates IVF add-ons using a traffic light system, gives hyaluronan-enriched transfer medium a yellow rating. That means: on balance, it is not clear whether this add-on is effective at improving treatment outcomes, because there is conflicting moderate to high-quality evidence. Some studies show a benefit, others do not.
This yellow rating doesn’t mean it’s unsafe or useless. It means the HFEA considers the evidence too mixed to recommend it as routine practice for all patients. Many clinics still offer it, typically as an optional extra costing anywhere from $50 to $300 depending on the clinic and country. If your clinic recommends it, it is reasonable to ask whether your specific situation (recurrent failure, fresh versus frozen cycle, number of embryos being transferred) aligns with the patient groups that showed the clearest benefit in clinical trials.