Detailed Explanation of the IVF Transfer Process in Thai Hospitals: Endometrial Preparation and Transfer Surgery Steps

Opening: Examination Report Perspective

▎An Endometrial Thickness Examination Report
Thickness 7.2mm, Grade B morphology, Grade II blood flow signal. This is the endometrial assessment result on day 12 of the transfer cycle. For women planning an embryo transfer in Thailand, this report directly determines whether the transfer window is open. Adequate endometrial preparation is the first hurdle to overcome in the transfer process.

I. Core Stages of the Transfer Process

The transfer process in Thai IVF hospitals is typically divided into four stages: Endometrial Preparation → Embryo Thawing → Transfer Surgery → Luteal Phase Support. Each stage has clear medical indications and operational standards, which are broken down below.

1. Endometrial Preparation Stage

Endometrial preparation is the starting point of the transfer cycle, aiming to make the endometrium suitable for embryo implantation. Three common clinical protocols are used:

• Natural Cycle: Suitable for patients with regular menstruation and normal ovulation. Follicle development and endometrial thickness are monitored via ultrasound, and transfer is scheduled after ovulation. Advantages include being close to the physiological state and requiring less medication; disadvantages are that ovulation timing is difficult to control and requires frequent monitoring.
• Artificial Cycle (Hormone Replacement Cycle): Uses exogenous estrogen (e.g., Progynova, Femoston) to promote endometrial growth. Once the endometrium reaches the target thickness, progesterone is added to transform the endometrium, and the transfer date is determined. Suitable for patients with ovulation disorders, irregular menstruation, or those needing flexible transfer scheduling.
• Ovulation Induction Cycle: Used for a small number of patients whose endometrium responds poorly to hormones. Low-dose ovulation induction medications are used to promote follicle development, utilizing the body's own estrogen to stimulate endometrial growth.

Endometrial Thickness Target: Most Thai reproductive centers require an endometrial thickness of 7–14 mm (measured on the day of endometrial transformation or ovulation). Regarding morphology, type A or B endometrium (clear trilaminar structure) has better receptivity. Blood flow assessment (uterine artery PI value < 3.0) is also becoming a reference indicator in some hospitals.

2. Embryo Thawing and Preparation

Thai IVF hospitals generally use vitrification technology, with embryo thawing survival rates exceeding 95%. Thawing is performed on the morning of the transfer day. After confirming good embryo recovery, laboratory technicians assess the embryo's expansion state and cell integrity, then place it in culture media for 2–4 hours of further culture before transfer.

• Blastocysts typically re-expand after thawing, indicating embryo viability.
• If the thawed embryo shows significant cell damage or degeneration, the lab will consult with the clinician to evaluate whether to proceed with the planned transfer.
• Some hospitals perform Assisted Hatching (AH) on embryos before transfer, creating an opening or thinning the zona pellucida to help the embryo hatch and improve implantation rates. Currently, most Thai reproductive centers routinely perform AH on frozen embryo transfers.

3. Transfer Surgery Procedure

The transfer surgery is performed under ultrasound guidance and takes about 5–10 minutes. The specific steps are as follows:

• The patient empties her bladder and assumes the lithotomy position. The doctor inserts a vaginal speculum and cleanses the cervix with saline.
• Under abdominal ultrasound monitoring, a transfer catheter containing the embryo is gently inserted through the cervix into the uterine cavity, reaching a position about 1–1.5 cm from the uterine fundus.
• The embryo is slowly expelled, and after a 30-second pause, the catheter is withdrawn. Laboratory personnel check the catheter under a microscope for any retained embryo.
• After the transfer, the patient rests supine for 15–30 minutes before being discharged. Strict bed rest is not required.

Most Thai reproductive centers use "soft catheter" transfer techniques (e.g., Cook or Kitazato catheters) to minimize cervical and endometrial irritation. Some hospitals use Atosiban (an oxytocin antagonist) before transfer to suppress uterine contractions, especially for patients who have experienced contractions after previous transfers.

4. Post-Operative Luteal Phase Support

Luteal phase support is crucial for maintaining pregnancy after transfer. Commonly used medications include:

• Oral Progesterone: Such as Dydrogesterone (Duphaston) or Micronized Progesterone (Utrogestan). Convenient but with lower bioavailability.
• Vaginal Progesterone: Such as Crinone gel or Progesterone vaginal sustained-release tablets (Endometrin). Acts directly on the uterus with low first-pass effect, making it the most common regimen in Thai hospitals.
• Intramuscular Progesterone: Such as Progesterone injection. Provides stable blood levels but can cause lumps and pain at the injection site.

Luteal phase support usually starts from the day of endometrial transformation and continues until 10–12 weeks after transfer (gradually tapered after placental formation). Some hospitals may add estrogen or hCG for additional support based on the patient's condition.

II. Differences in Processes Among Hospitals

Major Thai reproductive centers (such as Jetanin, BNH, Vittihavej, Bumrungrad, Siam Fertility Center, etc.) have some detailed differences in their transfer processes, mainly in the following aspects:

These differences are not about superiority or inferiority but represent operational preferences formed by different medical teams based on their clinical experience. When choosing a hospital, it is advisable to consider your own endometrial condition, previous transfer history, and preference for medication protocols.

III. Most Easily Overlooked Details

IV. Management of Special Situations

▎Thin Endometrium (< 7 mm)

For patients with recurrent thin endometrium, Thai hospitals may try the following approaches:

• Optimized Estrogen Dose: Combined oral + transdermal (patch) administration to increase blood concentration.
• Intrauterine Infusion: Autologous Platelet-Rich Plasma (PRP) or Granulocyte Colony-Stimulating Factor (G-CSF) infusion to promote endometrial regeneration.
• Endometrial Micro-stimulation: Gentle scratching of the endometrium during the menstrual or follicular phase to induce a local repair response.
• Adjust Transfer Strategy: If the endometrium persistently fails to meet the target, consider freezing the embryo and transferring it when conditions improve.

▎Repeated Implantation Failure

For patients who have had two or more failed transfers without implantation, Thai reproductive centers typically recommend:

• Hysteroscopy: To rule out chronic endometritis, small polyps, adhesions, or endometrial calcifications.
• ERA Testing (Endometrial Receptivity Analysis): To determine the individualized window of implantation; some patients may need to advance or delay the transfer time.
• Preimplantation Genetic Testing for Aneuploidy (PGT-A): To rule out implantation failure due to chromosomal aneuploidy.
• Immunological Factor Assessment: Including NK cell activity, T cell subsets, antiphospholipid antibodies, etc. However, immunological intervention remains controversial and should be approached with caution.

▎Uterine Fibroids or Adenomyosis

Submucosal fibroids or intramural fibroids compressing the uterine cavity require surgical treatment before transfer. Endometrial receptivity may be impaired in patients with adenomyosis. Thai doctors may use a longer endometrial preparation cycle (20–25 days) combined with GnRH-a pretreatment for 2–3 months to improve the uterine environment.

V. Timeline Planning

A complete Thai IVF transfer cycle (from starting endometrial preparation to pregnancy test) typically takes 20–30 days, depending on the chosen protocol and individual response:

Note: Patients on an artificial cycle need to start medication earlier, and the medication schedule is fixed and cannot be changed arbitrarily. Patients on a natural cycle require more frequent ultrasound monitoring but use less medication. The total duration of stay is similar for both protocols, approximately 14–18 days.

VI. Frequently Asked Questions

VII. Practitioner's Observation

In my years working at Thai reproductive centers, I have noticed a common phenomenon: many patients focus all their attention on the transfer surgery itself, while neglecting the quality of pre-transfer endometrial preparation and the standardization of post-transfer luteal phase support. In reality, the transfer surgery is just one procedural step; what truly determines the outcome is the coordination among endometrial receptivity, embryo quality, and luteal phase support.

Furthermore, the differences in transfer operation details among hospitals are far less significant than patients imagine. What truly affects the success rate is the laboratory's embryo culture proficiency, the doctor's ability to individualize endometrial preparation protocols, and the patient's own physical condition. Instead of obsessing over "which hospital has a better transfer technique," it is more productive to focus on optimizing pre-transfer evaluation and preparation.

Ending: Risk Reminder

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