Fresh and Frozen Embryo Transfer

Embryo transfer is the procedure of placing your healthy embryos into the uterus of the surrogate. The actual transfer itself is not complicated, but preparing the surrogate’s womb for the transfer requires great skill by the Reproductive Endocrinologist. For many couples trying to have children, this is a special moment when the pregnancy will succeed or fail.

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Preparing for the Embryo Transfer

For most surrogates, the preparation of her endometrium is the most critical part of the surrogacy process. The endometrium is the nutrient-rich wall of the uterus that the embryo will connect with to form a fetus. Properly preparing the endometrium takes an artful balance of medications, dosages and durations.


Different clinics have their favored medical protocols to prepare for an embryo transfer. In many cases, the protocol begins with an injection of Lupron (the brand name of Leuprolide acetate). Lupron is given as one or more injection to suppress pituitary gland activity and decrease the chance of unexpected ovulation. This sets the stage for the start of endometrium preparation, which begins on the first day of the surrogate’s menstrual cycle.

Using Lupron at the start of the cycle is the first step, as it will reduce the risk of ovulation during the frozen embryo transfer cycle. Lupron may be a single shot, or continued throughout frozen embryo transfer (FET) cycle until just before progesterone supplements start.

Estradiol and Progesterone

Many medications can be used in different ways and with different purposes. In some protocols, Lupron is skipped altogether and the clinic may move directly to a multi-week course of estrogen (estradiol) and progesterone to stimulate the endometrium. These hormones duplicate the changes that normally occur in the uterus during a regular menstrual cycle.

Stimulation develops the thickness of the endometrium and makes it more receptive to the embryo. Stimulation consists of daily hormone injections that will boost the surrogate’s readiness to receive an embryo. Stimulation usually lasts from 15 to 20 days. Stimulation should thicken the endometrial thickness to at least 8 mm and up to 15 mm. Doctors will disagree on the “perfect” measurement, but a good target will be around 12 mm.

There are also other factors in the readiness of your surrogate, including her hormone levels and overall health. Your doctor will be monitoring all of these throughout the stimulation process.

It’s important to note that the stimulation procedure is not a single recipe for all surrogates. There are different combinations of treatments that can be used under different situations. In some cases your doctor may switch between stimulation strategies if he finds your surrogate is not responding to the first choice. Acknowledging that will help you overcome a lot of stress.

If the doctor makes adjustments to your surrogate’s stimulation protocol, that does not mean that it will be less successful or more successful. The changes are all made to reach the same ultimate goal, a healthy surrogate with a receptive uterus to carry your pregnancy.

The Embryo Transfer Procedure

Your fertilization process should have produced several viable embryos. The clinic will transfer the highest quality embryo to your surrogate’s uterus around day 15 of her cycle (more or less).

In some cases, embryos may be transferred immediately as the emerge from IVF. This is called a “Fresh Embryo Transfer”. Transfers using embryos that have been frozen are known as “Frozen Embryo Transfer”. Embryos that are not transferred will be kept frozen in case the transfer procedure doesn’t result in pregnancy and needs to be repeated.

Many parents mistakenly expect their surrogate to stay in bed after an embryo transfer. This is not necessary, and studies show that lying down after the procedure does not help the pregnancy. Many clinics even suggest that bed rest can lower the likelihood of pregnancy — they advise the surrogate to walk around and be active (after they recover from the transfer procedure). That said, while the surrogate is waiting to become pregnant, she should avoid very strenuous activity and physical exertion. The embryo typically implants within a couple of days after the transfer, so she should take a few days to relax and avoid stress.

Ten to 12 days following the embryo transfer the clinic will perform your pregnancy test. The typical test is the Beta HCG (or bHCG) test, which is a blood test that looks for hormonal changes resulting from pregnancy. A positive bHCG means that the woman is likely pregnant. A negative bHCG means that the woman is NOT pregnant. A very high bHCG test result may indicate twins. A few days after the initial bHCG test is positive, a second test will confirm the results.

Frozen vs Fresh Embryo Transfer

Your clinic may recommend either a “Fresh Transfer” or a “Frozen Transfer”. The difference is that a fresh transfer is done before the embryos are frozen for storage. A frozen transfer uses embryos that are in storage at your clinic. Frozen embryos will be thawed (and sometimes allowed to develop a bit longer) before being transferred to your surrogate’s uterus.

If you’ve requested PGS/PGD testing, then all embryos need to be frozen while you wait for the test results — so no fresh transfers are possible.

Because new embryo freezing (or ‘vitrification’) techniques are so effective, many clinics now prefer frozen transfers with embryos “vitrified” when the reach blastocyst stage (day 5). This allows the clinic to focus on the surrogate’s fertility treatments and preparation. The clinic can then perform the Frozen Embryo Transfer when the surrogate reaches her maximum fertility. (When using fresh embryos, the transfer has to happen on Day 5 whether the surrogate was ready or not.) The use of frozen embryos has generally improved pregnancy rates.

Some options exist to increase the likelihood of pregnancy. The most effective may be Preimplantation Genetic Screening (PGS or PGD), which has a proven benefit for most couples. Other treatments such as Embryo Glue or Intralipid Injections are less certain (or may have benefits only in specific cases). The best factor in achieving a success is always an experienced embryologist and a surrogate well-prepared by a committed IVF specialist.

For more on the benefits of PGD check the Surrogacy Guide: Should I perform PGS/PGD on my embryos?

The first attempt at embryo transfer is made with the highest quality embryo. Subsequent attempts are made with lower grade embryos, and the success rate may also be lower for these transfers. The pregnancy rate will depend on the quality of each embryo transferred. Each subsequent embryo transfer is typically an additional fee.

How Many Embryos to Transfer

Clinics in United States will most often transfer one embryo per transfer attempt, while transfer of 2 embryos is a common protocol in clinics overseas.

The common belief is that the chance of pregnancy is higher if you transfer more embryos. But multiple embryos produce multiple births and serious risks. Moreover, clinic data shows that transferring multiple embryos doesn’t necessarily increase the chance of pregnancy, it only increases the likelihood of twins or triplets.

Data on U.S. IVF procedures compiled by the CDC shows that transferring more embryos does NOT mean more pregnancies. In reality, there is little correlation between the use of multiple embryos and birth rates. When most IVF clinics transfer multiple embryos, they do not get more pregnancies — only more twins and more medical complications during the pregnancy. Clinics with the highest overall birth rates are NOT those that most often transfer multiple embryos.

Risks of Multiple Pregnancies

Of course what is undeniable are the potential risks of twin pregnancies. Twins pregnancies have much higher incidence of premature birth and other complications. Over 60% of twins are born premature (born before 37 weeks). Twins often don’t have a chance to reach a healthy weight before they’re born, weighing on average about 2 pounds less then singleton babies. Other conditions are more common in multiple pregnancies, including preeclampsia, gestational diabetes and placental abruption. In short, transferring more embryos does not mean you’re more likely to get pregnant, only that you’re more likely to have serious complications in the pregnancy due to multiple fetuses.

The American Society of Reproductive Medicine recommends against purposely attempting a twins pregnancy because of the health risks to the surrogate and the babies. That said, some clinics will transfer multiple embryos if the parents insist. For a more complete discussion on this topic, check out this article in the Surrogacy Guide.

Confirming Your Pregnancy

Ten to 15 days following the embryo transfer the clinic will perform your pregnancy test. Typical test is the Beta HCG (or BHCG) test, which is a blood test that looks for hormonal changes that occur as a result of pregnancy.
A positive Beta HCG means that the woman is pregnant. A negative Beta HCG means that the woman is NOT pregnant

Beta HCG (Human Chorionic Gonadotropin) is a hormone produced during pregnancy which shows up in the blood. The test result shows the concentration of the Beta HCG hormone in the blood.

A Beta HCG level over 25 miu/ml is generally considered a positive indication of pregnancy. However, the Beta HCG level usually doubles approximately every 2 days during the early weeks, so if your pregnancy test is performed on Day 10, a strong pregnancy will measure in the hundreds of BHCG miu/ml. By Day 15, a positive test should be in the thousands. A very high Beta HCG test result may indicate twins.

The fetus is usually visible on a Trans-Vaginal Ultrasound scan when the level is above 1500 units. When the level is above 4000 units, the fetus is also usually visible on a Trans-Abdominal Ultrasound scan.

Success Rates per Embryo Transfer

The success rates most often quoted by clinics reflect the standard number of embryos, and also assumes Good/Very Good quality embryos have been transferred to a fertile surrogate who has been well prepared with appropriate endometrial thickness.

Most successful clinics overseas will quote a success rate between 55% to 65%. However, published success rates are often misleading because in reality there are a wide variety of surrogacy treatment options and variables. One number cannot possibly describe the expected probability of success for all parents.

For example, for couples where the egg donor is a friend or family member (and not a “proven” donor from a thorough donation agency), the probability of success is often much lower. This reflects the reality that the donor has not received the same medical evaluation, may not be the optimal age, or may not have previously demonstrated successful fertility.

When the donor is unproven, the quality of the resulting embryos may be lower. In some cases, the embryos may carry chromosomal abnormalities that reduce the chance of pregnancy. All these factor into a different success rate for so-called “self donation” procedures.

Some clinics will quote success rate close to 85%, which generally includes transfers made with embryos that have undergone PGD analysis, and thus more likely to result in pregnancy. The number is not a foolproof measure the success of any individual cycle — but it is often a reliable gauge of the skill of the embryologist and the clinic generally. (As noted before, PGD has it’s own risks, and so is not recommended in all cases.)

If your pregnancy test is performed early (on Day 10 after the transfer), your clinic may wait for a confirmation test to prove the pregnancy is accurate. If the confirmation test on Day 15 continues to show an expected increase in Beta HCG levels, prenatal care should begin immediately.

The success of your embryo transfer will rely on the preparation of your surrogate’s uterus, the quality of your embryos, and simple good luck. There is no guarantee that a transfer will result in a pregnancy, but a good consultant can advise you of some steps to improve your chances.


About the authors

  • Bill-Houghton
  • Author: William Houghton

    Bill Houghton is the founder of Sensible Surrogacy, author of the Sensible Surrogacy Guide, 2x surrogacy dad, and a dedicated advocate for secure, legal and ethical Gestational Surrogacy. Read Bill's Biography

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