Frozen embryos travel inside a liquid nitrogen dry shipper that keeps them below −150°C for several days. The releasing clinic loads and seals the shipper, a courier carries it to the destination, and the receiving clinic moves the embryos into its own storage tanks. Signed paperwork records who had custody at every step.
How embryos are kept frozen
Most embryos today are frozen by vitrification, a fast-freezing method that turns the embryo and its surrounding solution into a glass-like solid without forming ice crystals. Once vitrified, embryos are stored in liquid nitrogen at about −196°C, where biological activity effectively stops. Moving them at that temperature is known as cryoshipping, or cryogenic transport.
The goal during transport is simple: keep them at cryogenic temperature from the moment they leave one storage tank until they enter the next. As long as that happens, the journey itself doesn't change the embryos.
What a dry shipper is
Embryos don't travel in a tank of sloshing liquid nitrogen. They travel in a dry shipper: an insulated vacuum flask lined with an absorbent material that soaks up liquid nitrogen. The clinic "charges" the shipper by filling it with liquid nitrogen and pouring off the excess. The absorbed nitrogen then slowly evaporates, keeping the inner chamber well below −150°C.
- It holds temperature for days. A properly charged, validated shipper keeps its contents at cryogenic temperature for several days, which leaves a wide safety margin for delays.
- There's no free liquid. Because the nitrogen is absorbed, a correctly prepared dry shipper isn't classed as dangerous goods for air travel.
- It must stay upright. Keeping the shipper upright and steady helps it hold temperature for as long as it's designed to. That's one reason a courier keeps it with them rather than in a baggage hold.
- It carries a data logger. A temperature logger records conditions inside the shipper throughout the journey. Vessel monitors every shipment this way.
A hand-carried transfer, step by step
Enquiry and quote
You tell us where the embryos are, where they're going and roughly when. We explain the process and send a personalised quote. We reply to every new enquiry the same business day.
Paperwork between clinics
The releasing clinic needs signed release consent from the patients. The receiving clinic confirms it will accept the embryos. International routes may need extra documents. We coordinate this with both teams.
Scheduling
We agree a collection and delivery date that works for both laboratories, including opening hours and staff availability on each side.
Collection
The releasing clinic's embryology team loads and seals the dry shipper. Your specialist checks the paperwork, confirms the temperature logger is running and signs custody into a documented chain.
The journey
Your specialist carries the shipper personally, in the aircraft cabin or by road. It's never checked as baggage and never goes through airport X-ray screening. You get an update when it's on its way.
Handover and confirmation
At the receiving clinic, custody is formally signed over and the embryology team moves the embryos into storage. Every party receives written confirmation of delivery, and the temperature record can be shared on request.
What happens at the airport
The shipper stays with your specialist at all times. It travels as cabin baggage, so it's never handed to airline staff, loaded into the hold or left on a carousel. It also never goes through airport X-ray screening. Our specialists follow established procedures for travelling with cryogenic shippers, so screening is handled without the shipper leaving their care.
For more on this, read can frozen embryos go through airport security?
Chain of custody
Chain of custody is the written record of who was responsible for the embryos at every moment. With Vessel, the releasing clinic signs the shipper over to your specialist at collection, and the receiving clinic signs for it at delivery. Clinics keep these records with the patient file, and they give intended parents a clear answer to the question "who had them, and when?"
What can cause delays
The journey is rarely the slow part. Delays usually come from paperwork or scheduling:
- Release consent forms that aren't fully signed, or need notarising.
- Outstanding storage fees at the releasing clinic.
- The receiving clinic not yet confirming it can accept the embryos.
- For international routes, waiting on an import approval or document from the destination country.
- Laboratory closures around weekends and public holidays.
Our guide to moving embryos between clinics includes a checklist that helps you avoid most of these.
Frequently asked questions
How long can embryos stay in a dry shipper?
A properly charged, validated dry shipper keeps its contents at cryogenic temperature for several days. Journeys are planned to finish well within that window, leaving a margin for flight delays.
Does transport affect embryo quality?
Embryos that stay at cryogenic temperature throughout aren't affected by the journey itself. That's why the focus is on a validated shipper, careful handling and documented custody from tank to tank.
What temperature are embryos kept at during transport?
Embryos are stored in liquid nitrogen at about −196°C. Inside a dry shipper, the absorbed nitrogen keeps the chamber below −150°C, which is cold enough to keep vitrified embryos stable.
Who loads the embryos into the shipper?
The embryology team at the releasing clinic. Your courier doesn't handle the embryos themselves; they take custody of the sealed shipper and deliver it to the receiving clinic's team.
Can I get a temperature record for the journey?
Yes. Every Vessel shipment is temperature monitored with a data logger, and the record can be shared with you and both clinics.
