An IVF transfer is the final step of in vitro fertilization, where an embryo that was created in a laboratory is placed directly into the uterus through a thin catheter. The procedure itself takes only a few minutes, requires no anesthesia, and you can walk out of the clinic immediately afterward. But the preparation leading up to it, the choices involved, and the waiting period that follows are where most of the complexity lives.
What Happens During the Procedure
The transfer is surprisingly simple compared to the egg retrieval that came before it. You’ll lie on an exam table, similar to a routine pelvic exam. The doctor inserts a speculum, then cleans the cervix to remove mucus, which can block the catheter tip or pull embryos away from where they’re placed. Studies show that this cleaning step alone improves clinical outcomes.
Next, a thin, flexible catheter is threaded through the cervix and into the uterus. In most clinics, this is done under ultrasound guidance so the doctor can see exactly where the catheter tip sits. The embryo is loaded into the catheter by the embryology team and gently deposited in the upper or middle portion of the uterine cavity, ideally about 2 cm from the top wall of the uterus. Placement matters: pregnancy rates are significantly higher when embryos are placed 1.5 to 2 cm from the top of the uterus compared with 1 cm away. The catheter is then withdrawn immediately, and the embryologist checks it under a microscope to confirm the embryo was successfully released.
Most clinics use transabdominal ultrasound to guide the process, which means you’ll be asked to arrive with a full bladder. The fluid acts as a window, giving the doctor a clear view of the uterus on the screen. Some clinics use transvaginal ultrasound instead, which eliminates the full-bladder requirement and causes less discomfort, though it requires specialized equipment. About 1% of women report moderate to severe discomfort with the transvaginal approach, compared to 20% with the full-bladder method.
Day 3 vs. Day 5 Embryos
Embryos can be transferred at two main stages of development. A Day 3 transfer uses a “cleavage-stage” embryo, which contains roughly 6 to 8 cells. A Day 5 transfer uses a blastocyst, a more developed embryo with 100 or more cells that has begun to differentiate into distinct structures.
Most clinics now favor Day 5 transfers, and the reasoning comes down to biology. In a natural conception, an embryo doesn’t even reach the uterus until about Day 4. Placing a Day 3 embryo into the uterus exposes it to the uterine environment earlier than nature intended, particularly one affected by the high estrogen levels from fertility medications. By Day 5, the embryo has also passed a natural selection checkpoint. A large proportion of normal-looking Day 3 embryos carry chromosomal abnormalities (as high as 59% in women over 36), but by Day 5 that rate drops to around 35%, because many abnormal embryos stop developing before reaching the blastocyst stage.
The clinical difference is measurable. Live birth rates following fresh blastocyst transfers are roughly 27% higher than after cleavage-stage transfers. If 31% of women achieve a live birth after a Day 3 transfer, somewhere between 32% and 41% would after a Day 5 transfer. The tradeoff is that some women end up with no embryos to transfer at all, because none survive to Day 5 in the lab. This risk of cycle cancellation is why Day 3 transfers are still sometimes recommended for patients with fewer embryos.
Fresh vs. Frozen Transfers
A fresh transfer happens in the same cycle as egg retrieval, typically 3 to 5 days later. A frozen embryo transfer (FET) uses an embryo that was cryopreserved from a previous cycle, thawed, and transferred in a separate, later cycle.
Frozen transfers have become increasingly common, and the outcomes tell a clear story. In one large study, the clinical pregnancy rate was 47.5% for frozen transfers compared to 35.5% for fresh. Live birth rates showed an even starker gap: 38.8% for frozen versus 15.7% for fresh. Frozen transfers also had lower rates of preterm delivery (3.9% vs. 8.3%), low birth weight (5.6% vs. 10.5%), and first-trimester miscarriage (17.7% vs. 23.0%). Babies born from frozen transfers had higher average birth weights as well.
The likely explanation is timing. After egg retrieval, the uterine lining has been exposed to high levels of hormones from ovarian stimulation, which can throw off the synchrony between the embryo and the endometrium. A frozen transfer allows the lining to develop in a more controlled, natural hormonal environment, giving the embryo a better chance of implanting.
Preparing Your Uterine Lining
Before a transfer can go forward, your doctor will monitor the thickness of your uterine lining using ultrasound. Lining thickness is one of the strongest predictors of whether an embryo will implant. A thickness below 6 mm is associated with a dramatic drop in live birth rates for both fresh and frozen cycles.
For fresh transfers, live birth rates climb steadily as the lining thickens, plateauing once it reaches 10 to 12 mm. For frozen transfers, the plateau comes earlier, around 7 to 10 mm. If your lining isn’t thick enough, your doctor may adjust your medication protocol or delay the transfer to a future cycle. This is one reason frozen transfers offer more flexibility: there’s time to optimize the lining without the pressure of a developing embryo waiting in the lab.
How Many Embryos Are Transferred
The strong trend in reproductive medicine is toward transferring a single embryo, especially when the embryo has been genetically tested and found to have a normal chromosome count. For women 42 and under, transferring one genetically tested blastocyst produces pregnancy rates comparable to transferring two untested blastocysts, while dramatically reducing the risk of twins.
Multiple pregnancies carry substantially higher risks of preterm birth, low birth weight, and complications for both the pregnant person and the babies. The American Society for Reproductive Medicine recommends single embryo transfer as the default for most patients, with any decision to transfer more than one embryo documented along with the specific clinical reasoning.
After the Transfer
One of the most persistent myths in IVF is that you need bed rest after a transfer. The evidence says the opposite. The ASRM guidelines specifically support immediate ambulation, meaning you can get up and walk right after the procedure. Prolonged bed rest has not been shown to improve outcomes and may even be counterproductive.
What follows is commonly called the “two-week wait,” though the actual timeline to your pregnancy test varies. Most clinics schedule a blood test to measure hCG (the pregnancy hormone) about 9 to 14 days after transfer. Research has shown that hCG can be reliably detected in the blood as early as 5 days after a frozen blastocyst transfer, with levels at or above 4.0 IU/L serving as an accurate early marker of pregnancy. However, most clinics wait longer to reduce the chance of ambiguous results and to let hCG levels rise to a clearly measurable range.
During this waiting period, you’ll typically continue hormone support (usually progesterone) as prescribed by your clinic. Normal daily activities, including walking and light exercise, are generally fine. The embryo does not “fall out” from movement; by the time it’s placed in the uterus, it’s microscopic and nestled against the lining, held in place by the same biological mechanisms that support any early pregnancy.
Success Rates by Age
Success rates for IVF transfers vary significantly based on age, embryo quality, and whether the embryo was genetically tested. The CDC tracks outcomes for every fertility clinic in the United States, and the most recent national data (from 2022 cycles) is publicly available and searchable by clinic.
As a general pattern, live birth rates per transfer are highest for women under 35 and decline progressively with age. Women using donor eggs see more consistent success rates regardless of their own age, because the egg donor’s age is what primarily determines embryo quality. The specific numbers at your clinic may differ from national averages depending on the patient population they serve and the lab protocols they use, so the CDC’s clinic-level data is worth reviewing when comparing programs.