People often assume that once a surrogate enters the picture, the chances of pregnancy rise automatically. The idea sounds intuitive: if a woman has struggled to carry a pregnancy herself, then a healthy surrogate should “fix” the situation. Doctors at SILK Medical see the opposite every day. Surrogacy is not a workaround for embryo biology. A surrogate can only carry what the IVF lab creates, and the embryo itself remains the single most important factor in whether a transfer results in a pregnancy.
Surrogacy shifts the responsibility for the uterine environment to another person, but nothing about the process changes the genetics, the chromosomal structure, or the developmental competence of the embryo.
When lower-quality embryos are transferred, they behave exactly the same way as they would in a patient’s own uterus: some fail to implant, some arrest after implantation begins, and some stop developing early in pregnancy. That is why clinics take embryo quality very seriously in surrogacy programs, because each failed attempt carries logistical, financial, and emotional costs for intended parents and surrogate alike.
Why Embryo Quality Determines the Number of Transfers Needed
The number of available embryos also shapes the entire trajectory of a surrogacy program. Patients often ask how many embryos they “need” for one successful pregnancy. The answer depends almost entirely on the strength of the embryos themselves. One strong blastocyst can be enough. Several lower-grade or untested embryos may still lead to success, but the path becomes longer.
This is why many surrogacy programs around the world structure themselves around one, three, or unlimited transfers. SILK Medical offers the Effective, Classic, Successful, and Guaranteed programs, which align with these categories. Beneath those numbers sits a simple truth: the quality of the embryos determines how many transfers are realistically needed.
Why PGT-A Is Even More Important in Surrogacy
This is also why PGT-A plays a bigger role in surrogacy than many people expect. In standard IVF, couples sometimes skip genetic testing because they prefer a “wait and see” approach. In surrogacy, the calculus changes. Each transfer requires coordinating the surrogate’s cycle, preparing her endometrium, transporting her if she lives abroad, scheduling medical teams, and compensating her for the treatment period.
When an embryo has a chromosomal imbalance that could have been detected in advance, a failed transfer becomes a preventable loss of time and resources. This is the reason donor-egg programs at SILK Medical include PGT-A as part of the IVF workflow. The goal is simple: reduce the number of attempts needed for a healthy pregnancy by identifying embryos with the highest developmental competence. Luckily, this aligns with international good‑practice recommendations for preimplantation genetic testing (PGT).
Day-5 vs Day-6 vs Day-7 Embryos: How Surrogates Respond
The type of embryos used in a surrogacy program makes just as much difference. Most clinics strongly prefer Day-5 or Day-6 blastocysts because their development has already passed several checkpoints. A blastocyst that reaches these stages shows that the embryo has navigated the early hurdles of cell division and metabolic regulation.
Day-3 embryos provide far less information. They can still succeed, but with greater unpredictability. Day-7 embryos, while viable in some cases, usually reflect slower development and therefore more modest expectations. SILK Medical accepts all these embryo types when shipped from abroad, including Day-3 and Day-7 embryos, though Day-5 remains the most commonly transferred because of its track record. This approach avoids dogma and keeps decisions case-specific, while still recognizing the statistical differences between developmental stages.
The Role of Time-Lapse EmbryoScope and IVFID Witness System
One reason blastocysts are favored is the ability to monitor them continuously in the lab without disturbing them. Time-lapse incubators such as EmbryoScope record the timing of each cell division and the quality of expansion. This gives embryologists a silent film of the embryo’s journey from fertilization to freeze. Subtle timing differences often correlate with chromosomal status or implantation potential.
This is also why SILK Medical invests in technology used by a smaller fraction of clinics worldwide, including the AI-supported EmbryoScope and the IVFID Witness system, which electronically tracks all biological materials in the lab. The lab’s job is not only to grow embryos but to choose the ones that give the surrogate the best possible chance at a healthy pregnancy.
How Many Embryos Do Surrogacy Programs Actually Need?
When people ask how many embryos a surrogacy program “should” start with, the honest answer depends on the biological ingredients. A couple using young donor eggs, tested embryos, and a proven sperm sample may succeed from the very first transfer. Someone using their own embryos created at an older reproductive age or without PGT-A may need several attempts.
The SILK Medical team uses this information to structure its programs. The Effective program exists for patients who already have embryos and want one transfer. The Classic allows up to three attempts when shipped embryos are used. The Successful and Guaranteed programs for donor-egg IVF build in either three attempts or unlimited attempts until childbirth, because donor eggs consistently produce strong blastocysts. The structure is flexible, but the biology is consistent: the better the embryos, the fewer transfers needed.
Why Strategy Matters More Than “Luck” in Surrogacy
Surrogacy might feel like a treatment of its own, but it is really the second half of the IVF process. A surrogate’s uterus can offer a stable environment, but it cannot turn a weak embryo into a strong one. Success depends on strategy: the stimulation protocol that produced the eggs, the embryology workflow, the use of PGT-A, the decision between Day-3 and Day-5 embryos, and the selection tools available in the lab. When those elements come together, surrogacy becomes predictable rather than uncertain. The surrogate takes on the physical work, but the embryo is still the one setting the rules.
English