What Is Cycling in Surrogacy? The Process Explained

If you’ve started researching gestational surrogacy, you’ve probably come across the word “cycling” and wondered exactly what it means and what it involves.

Cycling refers to the hormonal preparation phase that coordinates the surrogate’s body with the fertility clinic’s timeline — getting the uterine lining ready to receive an embryo at precisely the right moment.

It’s one of the most medically specific parts of the surrogacy process. Understanding what’s happening at each step helps surrogates feel prepared rather than overwhelmed.

At Physician’s Surrogacy, our in-house Obstetrician/Gynecologists (OB/GYNs) oversee this phase directly — not just the matching and legal stages, but the full clinical process from the first medication through the embryo transfer.

This guide covers what cycling involves, what each medication does, how the surrogate and egg donor’s roles differ, and what the experience actually feels like from the surrogate’s perspective.

Key Takeaways

• “Cycling” in surrogacy refers to the hormonal preparation phase that gets the surrogate’s uterine lining ready for embryo transfer.
• Surrogates do not undergo egg retrieval — their role in cycling is to prepare the uterus, not to produce eggs.
• The surrogate’s protocol involves cycle suppression, estrogen to build the lining, and progesterone to stabilize it before transfer.
• When a fresh egg donor cycle is used, the surrogate’s cycle is synchronized with the donor’s to ensure the embryo is ready at the right time.
• Most surrogacy cycles today use frozen embryo transfers, which removes the need for real-time cycle synchronization.

This article is for informational purposes only and does not constitute medical advice. Consult with a qualified medical professional for guidance specific to your situation.

What “Cycling” Actually Means in Surrogacy

The term “cycling” comes from the process of synchronizing or controlling hormonal cycles in preparation for an embryo transfer. It doesn’t refer to the surrogate going through an IVF stimulation cycle — that’s a common misconception. The surrogate’s ovaries are not stimulated, and no eggs are retrieved from the surrogate.

What cycling does involve is a carefully timed sequence of medications that mimic, then replace, the surrogate’s natural menstrual cycle. The goal is to bring the uterine lining — the endometrium — to exactly the right thickness and receptivity on the day the embryo is transferred.

This matters because implantation only succeeds within a narrow biological window. The endometrium needs to be at a specific developmental stage, and the medications in the cycling protocol are designed to control when that window opens.

Two Types of Embryo Transfer: Fresh vs. Frozen

The specific cycling protocol your fertility clinic uses depends on whether the embryo transfer will involve a fresh egg donor cycle or a frozen embryo transfer.

Fresh Donor Cycles

In a fresh donor cycle, an egg donor undergoes ovarian stimulation. Her eggs are retrieved, fertilized with sperm from the intended father (or a sperm donor), and the resulting embryos are transferred to the surrogate within a few days.

This requires real-time coordination between the donor’s stimulation cycle and the surrogate’s uterine preparation — which is what people mean when they talk about “cycle synchronization.”

Fresh donor cycles are less common today than they were previously, largely because vitrification (flash-freezing) technology has improved to the point where frozen embryo transfers achieve equivalent or better outcomes. But they still occur, and the synchronization protocol is worth understanding.

Frozen Embryo Transfers (FET)

In the majority of modern surrogacy cases, the intended parents have already created and frozen embryos through IVF before the surrogate is even matched. The surrogate’s cycling protocol is then used to prepare her uterine lining at a time that suits the clinic’s schedule — without any need to synchronize with a live egg donor cycle.

A 2020 Cochrane systematic review covering 31 randomized controlled trials found that endometrial preparation using controlled hormonal protocols in frozen embryo transfer cycles is effective at achieving successful implantation.

For practical purposes, the shift to frozen embryo transfer has made surrogacy cycling simpler and more predictable for both surrogates and fertility clinics.

The Surrogate’s Cycling Protocol: Step by Step

Here is what the cycling process looks like from the surrogate’s perspective, in order.

Step 1: Suppression — Taking Control of the Cycle

Most protocols begin with cycle suppression: a period of medications designed to quiet the surrogate’s natural hormonal fluctuations so the fertility clinic can control the cycle on a precise schedule.

• Oral contraceptive pills (birth control) are the most common suppression method. The surrogate takes them for 2–4 weeks before estrogen begins. This suppresses ovulation and gives the clinic a predictable hormonal baseline to work from.
• Lupron (leuprolide acetate) is a Gonadotropin-Releasing Hormone (GnRH) agonist sometimes used instead of — or alongside — birth control for suppression.

Lupron works by initially triggering a brief surge of Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH). As the GnRH receptors become saturated, it then blocks further hormone release. This “downregulation” suppresses the pituitary gland’s control over the ovaries — preventing spontaneous ovulation and giving the clinic full control over timing.

Lupron is given as a daily subcutaneous injection — a short, fine needle into the skin of the abdomen or thigh.

Side effects during the suppression phase can include hot flashes, mood changes, and mild headaches. These reflect the temporary drop in estrogen and typically ease once estrogen replacement begins.

A 2024 systematic review and meta-analysis in MDPI Biomedicines covering 41 studies and 43,021 participants found that GnRH agonist pretreatment for frozen embryo transfer cycles generally improved clinical pregnancy rates, implantation rates, and live birth rates.

The benefit was most pronounced in patients with polycystic ovary syndrome (PCOS) and when depot (longer-lasting) formulations were used.

Not every protocol includes a full suppression phase. Some clinics use a natural cycle FET without suppression medications. Your fertility clinic will determine which approach is appropriate for your situation.

Step 2: Estrogen — Building the Uterine Lining

Once suppression is confirmed (usually via a blood test and ultrasound), estrogen begins. Estrogen drives the growth of the endometrium — the uterine lining — to the thickness needed for an embryo to implant successfully. Most clinics look for a lining of at least 7–8mm before proceeding.

Estrogen can be delivered in several ways:

• Oral tablets, taken 2–3 times daily
• Transdermal patches, changed every few days for a steady dose
• Intramuscular injections of estradiol valerate, every few days
• Vaginal suppositories in some protocols

The estrogen phase typically runs 2–3 weeks. During this time, the clinic monitors the surrogate with one or two transvaginal ultrasounds to confirm the lining is developing appropriately.

Common side effects during the estrogen phase are generally mild: bloating, breast tenderness, headaches, light nausea, and some mood changes. Most surrogates tolerate this phase well.

Step 3: Progesterone — Stabilizing the Lining for Transfer

Once the lining reaches the target thickness, progesterone is added.

Progesterone shifts the endometrium from a growth phase to a receptive phase — the biological window during which implantation can occur. Timing this precisely is critical: the embryo needs to arrive into a lining at exactly the right stage of development.

Progesterone is typically started 5–7 days before the scheduled embryo transfer, mirroring the natural post-ovulation progesterone rise.

The most common delivery method is progesterone in oil (PIO) injections — intramuscular injections into the upper outer quadrant of the buttocks, given daily. The oil base is thicker than a typical subcutaneous injection, which means a longer needle and more injection site soreness and bruising over time.

A few things that help:

• Warm the oil before injecting — hold the syringe in your hands or run it under warm water for a minute
• Alternate sides each day to prevent buildup at the injection site
• Massage the site firmly for 1–2 minutes after each injection
• Apply a heating pad to the area afterward

Alternatives include vaginal progesterone suppositories (Endometrin or Crinone gel), which avoid injection site discomfort but need to be used 2–3 times daily. Some protocols combine both methods.

Progesterone continues for several weeks after a positive pregnancy test — typically until 10–12 weeks, when the placenta takes over hormone production.

Step 4: The Lining Check and Transfer

Before the embryo transfer, the clinic performs a final ultrasound to confirm the lining has reached the right thickness and texture. If it looks good, the transfer proceeds as scheduled.

The embryo transfer itself is a brief outpatient procedure — typically 15–20 minutes. A thin catheter is guided through the cervix into the uterine cavity, and the embryo is placed under ultrasound guidance.

No anesthesia is needed. Most surrogates describe it as similar in discomfort to a pap smear. Our post on what embryo transfer is like for surrogates covers what to expect in full detail.

How Cycling Differs When a Fresh Egg Donor Is Involved

When the surrogacy uses a fresh (not frozen) egg donor cycle, the surrogate and egg donor must be synchronized so the embryo is ready to transfer at exactly the right moment in the surrogate’s uterine preparation.

Here’s how that coordination works:

The surrogate is typically placed 7+ days ahead of the egg donor in the suppression protocol. That way, when the embryo is ready — 3–5 days after the donor’s eggs are retrieved and fertilized — the surrogate’s lining is already in the optimal receptive phase.

The fertility clinic manages this coordination. The surrogate attends monitoring appointments (blood tests and ultrasounds) during the final phase, and the clinic adjusts timing as needed.

What the Surrogate Is Not Doing During Cycling

This point is worth stating clearly because it’s frequently misunderstood:

The surrogate does not undergo ovarian stimulation. To be clear about what that means:

• No FSH injections are given to stimulate the surrogate’s ovaries
• No eggs are retrieved from the surrogate
• The surrogate has no genetic connection to the embryo
• In gestational surrogacy, the embryo is created entirely from the intended parents’ genetic material (or from donors they selected)

The cycling protocol for the surrogate is entirely focused on the uterus. The goal is one thing: a well-prepared endometrium at exactly the right moment for the embryo to arrive.

What Cycling Feels Like: The Honest Version

Most surrogates find the cycling phase manageable — though there are real adjustments along the way. Here is what women consistently report across each stage:

• Suppression phase: The Lupron injections require daily self-administration, which takes some adjustment. Side effects — hot flashes, mood changes, headaches — are temporary and typically ease once estrogen begins.
• Estrogen phase: Generally well-tolerated. Bloating and breast tenderness are the most common complaints.
• Progesterone phase: The PIO injections are the most consistently discussed aspect. Injection site soreness is real and ongoing until the early weeks of pregnancy. Most surrogates develop a manageable routine within the first week.
• Overall timeline: From the start of suppression to the embryo transfer typically takes 6–8 weeks. The medications stop being a major feature of daily life once the pregnancy is established around 10–12 weeks.

For a detailed breakdown of what the medications involve and practical tips for managing progesterone injections, see our full guide on hormones surrogates take before transfer.

How Physician Oversight Shapes the Cycling Experience

At most surrogacy agencies, the cycling process is coordinated entirely by the fertility clinic — and the surrogacy agency has no physician involvement at all. Questions about medications, side effects, or monitoring results are handled by coordinators passing messages to outside physicians.

Our in-house OB/GYN team stays directly involved throughout the cycling phase. We review your monitoring results and communicate directly with the fertility clinic’s reproductive endocrinologist.

If something in your labs or ultrasound readings warrants attention, a physician on our team responds — not a coordinator.

That direct clinical involvement is part of what produces our preterm delivery rate 50% below the national average. It starts well before the pregnancy does.

Starting the Process

If you’re considering becoming a surrogate and want to understand what cycling involves before you apply, this guide is a starting point.

The specific protocol you’ll follow depends on your health profile, the fertility clinic the intended parents are working with, and whether the transfer uses a frozen or fresh embryo.

Our physician team reviews every surrogate’s medical history individually. Review our surrogate requirements to see if you qualify, and apply to become a surrogate when you’re ready. If you have medical questions about the cycling process or your specific health history, our OB/GYN team is the right place to ask.

Frequently Asked Questions

What is cycling in the surrogacy process?

Cycling refers to the hormonal preparation phase that gets a surrogate’s uterine lining ready to receive an embryo. It involves a sequence of medications — typically including suppression drugs, estrogen, and progesterone — administered over 6–8 weeks before the embryo transfer.

Does the surrogate take fertility drugs during cycling?

Surrogates take hormonal medications to prepare the uterine lining — not to stimulate egg production. The drugs involved are estrogen and progesterone, not the FSH medications used for ovarian stimulation in egg donors.

Why does the surrogate start cycling before the egg donor?

In fresh donor cycles, the surrogate needs to be several days further along in her uterine preparation so that her lining is in the optimal receptive phase exactly when the embryo is ready — typically 3–5 days after the donor’s eggs are retrieved and fertilized.

How long does the cycling phase last?

From the start of suppression to the embryo transfer, the cycling phase typically takes 6–8 weeks. Medications continue for several weeks after a positive pregnancy test, until approximately 10–12 weeks of pregnancy.

Is cycling the same as IVF?

No. IVF (In Vitro Fertilization) is the process of fertilizing eggs outside the body. Cycling refers specifically to the uterine preparation protocol that surrogates follow. Surrogates do not undergo IVF — that process happens for the intended mother or egg donor who provides the eggs.