The embryo transfer is the medical stage where a fertility clinic places an embryo created by the intended parents (or their donors) into your uterus. It comes after screening, matching and a signed legal agreement, and before the pregnancy is confirmed and handed to an OB. Preparation usually takes several weeks of medication and monitoring. The transfer itself takes minutes. As an estimate, the time from starting medications to a first pregnancy blood test often runs four to six weeks, and it varies by clinic and by how your body responds.
If you are close to passing agency screening, or already past it, you may now want a precise picture of what happens to your body and in what order. This guide lays that out from your side: what you do, what the clinic does, what the intended parents decide, and where the waiting happens. Surrogate Compass is an independent platform that explains the process and connects candidates with agencies. Agencies screen, match, contract and pay. Clinics run the medical protocol.
Before the Transfer Begins: Prerequisites and Decisions Already Made
The transfer is not the first step. Several things are normally complete before any transfer medication starts, and none of them are formalities.
A signed gestational surrogacy agreement. Clinics typically will not begin a transfer protocol until the legal agreement is signed and each side's attorney has cleared it. This is a firm prerequisite. The agreement sets out matters like how many embryos may be transferred, how many transfer attempts are covered, and how compensation is structured, including what happens if a transfer does not result in pregnancy. An independent attorney who represents you reviews it.
Medical and psychological clearance. The fertility clinic reviews your records, evaluates your uterus (often with an ultrasound or saline sonogram) and runs bloodwork, including an infectious disease panel. Most programmes also require a psychological evaluation. The guides to surrogate medical screening and surrogate psychological screening cover these in detail. A physician decides medical clearance, and that decision is never automatic.
Embryos ready to transfer. Your cycle has to line up with the intended parents' embryos. Usually that means frozen embryos already exist. Sometimes the intended parents are still completing an IVF cycle, and your preparation is timed around theirs.
Federal testing rules. Federal regulations on human cells and tissues, 21 CFR Part 1271, set infectious disease screening and testing requirements for the people whose eggs and sperm create the embryo, with timing rules attached. Your clinic will also run its own tests on you. These requirements create real scheduling constraints, and your clinic can explain the specific windows that apply.
One more point matters here. Meeting common criteria on paper, or in a preliminary eligibility check, is not the same as being cleared. Agency, medical and legal screening decide readiness.
Step 1: Uterine Lining Preparation and What the Medications Actually Do
Most gestational surrogacy transfers use a medicated cycle. The goal is a uterine lining that is thick and receptive at the moment the embryo arrives. The clinic prescribes the protocol, sets the doses and adjusts them. You follow it.
Possible suppression phase. Some clinics start with medication that quiets your natural cycle so they can control timing. Others skip this. Birth control pills are sometimes used at this stage to help schedule the cycle.
Estrogen phase. Estrogen thickens the uterine lining. Depending on the clinic, it may come as oral tablets, skin patches, vaginal tablets or injections. This phase commonly lasts around two weeks, sometimes longer. Side effects can include headaches, mood changes, bloating and breast tenderness.
Monitoring appointments. During the estrogen phase you return to the clinic, or a local monitoring clinic, for transvaginal ultrasounds and blood draws. The ultrasound measures the thickness and pattern of your lining. Bloodwork checks hormone levels. This "lining check" tells the clinic whether your lining has reached the thickness and appearance they want before moving forward. If it has not, they may extend the estrogen phase or change the dose.
Progesterone phase. Once the lining looks ready, progesterone begins. Progesterone changes the lining so it can receive an embryo, and the transfer is timed to a set number of days after it starts. Many clinics use intramuscular progesterone injections, often daily, given into the upper buttock with a fairly long needle. Many surrogates describe these as the most physically demanding part of the process: soreness, lumps at injection sites and some bruising are common. A partner or friend often learns to give them. Some clinics use vaginal progesterone instead of, or alongside, injections. The full picture is covered in the guide to surrogate medication requirements.
Natural or modified natural cycles. A smaller number of clinics time the transfer to your own ovulation, with little or no estrogen. Which approach applies is the clinic's decision based on your history.
The timeline in this step is set by monitoring results. You do not control it, and an extra week of estrogen is a normal adjustment, not a sign of a problem.
Step 2: Embryo Selection and Grading, Which the Intended Parents' Clinic Decides
While you prepare, the embryo side is handled by the intended parents and their reproductive endocrinologist. You are not part of these decisions.
Day 3 versus day 5 embryos. Embryos can be transferred around day 3 after fertilisation or at the blastocyst stage, around day 5 or 6. Blastocyst transfer is common because embryos that reach this stage have shown more development.
What the grades mean. Many clinics grade blastocysts on the Gardner scale, which reads like "4AA" or "5BB". The number (1 to 6) describes how expanded the blastocyst is. The first letter grades the inner cell mass, which becomes the fetus. The second letter grades the outer layer, which becomes the placenta. A is the highest grade and C the lowest. Grades describe appearance, not a guarantee of outcome.
Frozen embryo transfer. Most gestational surrogacy transfers today use frozen embryos. Freezing allows time for genetic testing, lets the clinic schedule around your cycle, and gives time for legal clearance to finish before anything is transferred.
Genetic testing. Some intended parents use preimplantation genetic testing for aneuploidy (PGT-A), which screens embryos for an abnormal number of chromosomes. Whether to test is their decision with their doctor.
Number of embryos. Single embryo transfer is typical in gestational surrogacy. The American Society for Reproductive Medicine (ASRM) publishes guidance supporting limits on embryo numbers because twins and higher multiples carry greater medical risk for you and for the babies. The agreement usually states how many embryos may be transferred, so it is worth reading that clause closely.
Your role in this step is to be medically ready.
Step 3: Transfer Day and What to Expect at the Clinic
Picture a short appointment at the fertility clinic, not your regular doctor's office. A reproductive endocrinologist usually performs the transfer.
Full bladder. Many clinics ask you to arrive with a moderately full bladder. A full bladder helps the abdominal ultrasound show the uterus clearly and can straighten its angle. Being asked not to empty it while lying on the table is uncomfortable, and many surrogates say this is the hardest part of the day.
The procedure. You lie back with your feet in supports. A speculum is placed, much like a Pap smear. A nurse or technician holds an ultrasound probe on your abdomen. The doctor passes a very thin, flexible catheter through your cervix into the uterus, guided by the ultrasound screen, and releases the embryo. The embryo itself is too small to see. The small bright "flash" on the screen is a tiny air bubble that marks where it was placed. The catheter is then checked under a microscope to confirm the embryo left it.
Duration and sensation. The procedure usually takes a few minutes. Anaesthesia is not typically needed. Pressure and some mild cramping are common during and afterward.
Afterward. Many clinics have you rest briefly before leaving. Instructions for the rest of the day vary: some clinics suggest taking it easy, others place few limits. Follow your own clinic's instructions.
Who is there. Usually you, clinic staff and sometimes a support person. Whether the intended parents attend depends on clinic policy, distance and what everyone has agreed.