One Embryo or Two? Why More Embryos Is Not Automatically Better IVF

The question behind "one or two?"

After months of preparation, money and a flight to Medellín, transferring two embryos can feel like doubling your odds. That intuition treats embryos like lottery tickets: two tickets, two chances, no downside. IVF doesn't work that way. When both embryos implant, the result isn't two separate chances that came good. It's a twin pregnancy, which has its own risks for both the mother and the babies.

So the real question isn't "how do I maximize my chance of a positive test?" It's "how do I maximize my chance of a healthy baby, with the least risk, across all the embryos I have?" Asked that way, the answer often changes.

What a twin pregnancy can mean

The UK fertility regulator calls multiple births the main risk of fertility treatment (HFEA, 2016). Its patient guidance says:

• At least half of twins are born premature and underweight, which can lead to serious health problems.
• Carrying more than one baby makes early or late miscarriage more likely.
• Mothers of multiples face higher risks of high blood pressure, gestational diabetes, anemia and hemorrhage.

The 2021 ASRM/SART guidance reaches the same conclusion. It says multiple gestation increases the risk of complications for both the woman and the fetuses. It also notes that reducing the number of fetuses later in pregnancy doesn't fully remove those risks (ASRM/SART, 2021).

What the professional limits say

ASRM and SART set upper limits by age and embryo type. For patients with a favorable prognosis:

These are ceilings, not targets. The same document adds several points that matter in practice:

• Donor eggs: use the donor's age, not the recipient's.
• Frozen embryos: use the age at which the embryos were frozen.
• Gestational carriers: strongly favor a single embryo.
• Medical conditions that a multiple pregnancy could worsen: no more than one embryo.
• Age 43 and over, own eggs: too little data to set a limit, so caution is advised.
• Going over the limits: requires counseling about the risk of twins or more, and a documented reason in the medical record.

Colombian clinics aren't bound by ASRM. Still, this is a well-reasoned, published reference point. A clinic recommending more than it suggests should be able to explain why.

What happened when the UK moved to single transfers

The UK offers a large natural experiment. According to the HFEA, single-embryo transfers rose from about 10% of IVF cycles in the early 2000s to 88% in 2023. Meanwhile, the multiple birth rate after IVF, roughly 28% in the early 1990s, fell to 3.4% in 2023, the lowest UK average (HFEA, 2025). The regulator's patient guidance says elective single-embryo transfer has no significant impact on success rates. It also acknowledges that it may not suit everyone, particularly older women.

The lesson isn't that one embryo is always right. It's that a whole system moved to single transfers as the default and cut multiple births sharply, without the drop in success many patients fear.

Why travel makes two embryos tempting

For international patients, the pull toward two embryos is often about logistics, not biology. Another frozen transfer means another flight, more nights in Medellín, more time off work and more fees. That cost is real and should be in your budget. But compare it honestly with the alternative: a higher chance of a twin pregnancy, which brings its own medical costs and risks once you're home.

The better fix is to plan for the trip, not to transfer more embryos. Ask the clinic what a frozen transfer involves and how long you'd need to stay. Our guides to frozen embryo transfer in Medellín and travel after embryo transfer help you price a second trip. Once the second trip is a known, budgeted item, single transfer feels much less like a gamble.

Common reasons for wanting two, and how to think about them

"I'm older, so I need to maximize my chances"

Age does change the guidance. ASRM/SART limits are higher for untested embryos in older patients, and the HFEA says single transfer may not suit everyone, particularly older women. But age also raises the risks of a twin pregnancy for the mother. Ask the clinic to weigh both sides for you specifically, not just the first.

"My embryos aren't top quality"

This is a legitimate medical conversation. Embryo quality is one of the things clinicians consider. Ask how your embryos' grading affects the clinic's view, and what the clinic's own data show for embryos like yours.

"I can't afford another trip"

This is the most understandable reason and the weakest medical one. If cost is driving the decision, look at the cost side first. Price the frozen transfer trip, ask about home monitoring for lining preparation, and compare that figure with the extra medical risk.

"We'd be happy with twins"

Many people would. The risks described above apply whatever the parents' wishes, though. Being happy with twins is a reason to discuss the risks openly, not a reason to skip that discussion.

How to have the conversation with a Medellín clinic

Raise the embryo number early, ideally at the remote consultation and well before transfer day. Useful questions:

If you're considering embryo testing, our guide on when PGT-A may or may not help explains how it connects to the one-embryo recommendation for tested embryos.

If you and your doctor do choose two

Sometimes, after a full discussion, two embryos is the agreed choice, especially for older patients with untested embryos. If so, prepare for the possibility of twins before you fly home. Tell your obstetric provider at home as soon as you have a positive test, so that early scans and pregnancy care can be planned. Ask the Medellín clinic to put the number transferred, the embryo stage and the reasoning in your treatment summary. Make sure your health insurance at home covers a higher-risk pregnancy. And keep a copy of the full transfer report with your records.

Decide before transfer day

The worst time to decide how many embryos to transfer is on the morning of the transfer, when you're anxious and hopeful. Settle it in advance with your doctor and your partner if you have one. Write the number down, ask the clinic to note it in your record, and only revisit it if something medically new comes up, such as how your embryos develop. That way the decision is made on medical grounds, not under pressure on the day.

Medical disclaimer: MedellinIVF.co is an independent educational and lead-navigation site, not a fertility clinic. Nothing on this page is diagnosis, treatment advice or a guarantee of outcome. Prices and policies change. Verify current information directly with the treating clinic and appropriate Colombian registries.