Association Between Peri-Transfer Endometrial Peristalsis And Live Birth In Modified Natural Cycle Frozen Embryo Transfer: A Prospective Cohort Study (EPFE)

Effects Of Modified Natural Cycle Protocol Peristalsis And Live Birth In Frozen Embryo Transfer: A Prospective Cohort Study

The uterus is a dynamic muscular organ that undergoes rhythmic, wave-like contractions known as endometrial peristalsis or endometrial waves. This muscular activity, which is an essential component of natural fertility, presents a nuanced and sometimes contradictory role in the context of assisted reproductive treatments. Endometrial peristalsis refers to the frequency, amplitude, and pattern of myometrial contractions occurring in different reproductive phases. These peristalsis play vital roles in sperm transport, embryo migration, and implantation. Clinical and imaging studies suggest that abnormal patterns or excessive contractility at the time of embryo transfer may disrupt endometrial-embryo synchrony, impair implantation, and increase miscarriage risk. However, most evidence on endometrial peristalsis pertains to fresh embryo transfer cycles, natural conceptions, or pathological contexts, such as adenomyosis or fibroids, with limited insights regarding its effects on different endometrial preparation protocols in frozen embryo transfer (FET). Understanding the dynamics of endometrial peristalsis in this context is clinically important, as inappropriate contractile activity could physically expel the embryo or create a non-receptive environment, ultimately reducing the chances of live birth. Despite its theoretical significance, there is a paucity of robust, prospective data correlating endometrial peristalsis patterns measured around the time of FET with different endometrial preparation protocols with subsequent pregnancy outcomes.

Study Overview

• Status: Recruiting
• Conditions: Infertility; Uterine Contraction; Frozen Embryo Transfer (FET); Endometrial Peristalsis; Endometrial Waves; Uterine Peristalsis
• Intervention / Treatment: Other: Endometrial peristalsis and hormone measurements

Detailed Description

The uterus is a dynamic muscular organ that undergoes rhythmic, wave-like contractions known as endometrial peristalsis or endometrial waves. This muscular activity, which is an essential component of natural fertility, presents a nuanced and sometimes contradictory role in the context of assisted reproductive treatments. Endometrial peristalsis refers to the frequency, amplitude, and pattern of myometrial contractions occurring in different reproductive phases. These peristalsis play vital roles in sperm transport, embryo migration, and implantation.

Clinical and imaging studies suggest that abnormal patterns or excessive contractility at the time of embryo transfer may disrupt endometrial-embryo synchrony, impair implantation, and increase miscarriage risk. However, most evidence on uterine contractility pertains to fresh embryo transfer cycles, natural conceptions, or pathological contexts, such as adenomyosis or fibroids, with limited insights regarding its effects on different FET protocols. Several studies have demonstrated an inverse relationship between endometrial peristalsis and IVF success. Masroor et al. found that patients with lower endometrial peristaltic wave frequency (<4 waves/min) before embryo transfer had significantly higher chances of clinical pregnancy and live birth compared to those with more frequent peristalsis. Similarly, Chung et al. reported that increased endometrial peristalsis frequency immediately after embryo transfer was linked to reduced live birth rates, suggesting that excessive motility may physically expel the embryo or disturb its implantation. In the prospective cohort study of 292 infertile women, Zhu et al. found that lower uterine peristaltic wave frequency (<3.0 waves/min) before embryo transfer is associated with higher clinical pregnancy rates in both fresh and frozen-thawed embryo transfer cycles. In a study by Vuong et al. on patients with repeated implantation failure, they found that administering atosiban to patients with uterine peristalsis exceeding 16 waves per 4 minutes could improve pregnancy rates.

In recent years, there has been growing interest in performing FET in natural cycles. Natural-cycle FET protocols may better reproduce physiological endocrine and uterine environments than fully artificial, hormone-replacement cycles, potentially influencing uterine contractility patterns, implantation rates, and obstetric outcomes, while also reducing medication burden for ovulatory women. Building on this evidence, the present study will examine the relationship between peri-transfer uterine peristalsis in natural-cycle frozen embryo transfer and subsequent live birth, with the aim of identifying clinically relevant thresholds of contractile activity that could inform individualized embryo-transfer strategies.

• Study Type: Observational
• Enrollment (Estimated): 384

Contacts and Locations

• Study Contact: Name: Tuong M Ho, MD; Phone Number: +84903633377; Email: tuongho.ivfmd@gmail.com
• Study Contact Backup: Name: Xuyen Thi Ha Le, MD; Phone Number: +84945260494; Email: bsxuyen.lth@myduchospital.vn

Study Locations

• Vietnam
  • Ho Chi Minh City, Vietnam, 70000
    • Recruiting
    • My Duc Phu Nhuan Hospital
    • Contact: Xuyen TH Le, MD; Phone Number: +84945260494; Email: bsxuyen.lth@myduchospital.vn
  • Ho Chi Minh City, Vietnam
    • Not yet recruiting
    • IVFMD Phu Nhuan - My Duc Phu Nhuan Hospital

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

Women undergoing frozen embryo transfer during the study period.

Description

Inclusion Criteria:

• Women aged 18 - 42 years old
• Scheduled for frozen embryo transfer cycles using hormone replacement therapy protocol or natural cycle protocol (True natural cycles or modified natural cycles)
• Transferred no more than two cleavage embryos or one good-quality blastocyst or no more than two poor-quality blastocysts

Exclusion Criteria:

• Having an allergy and contraindications for exogenous hormone administration (e.g., breast cancer, thromboembolic disease)
• Cycles with preimplantation genetic testing, oocyte donation, or in vitro maturation
• Having untreated uterine or adnexal abnormalities (e.g., intrauterine adhesions, unicornuate/ bicornuate/ arcuate uterus, endometrial polyp, large leiomyoma ≥5 cm in diameter, hydrosalpinx, endometrial hyperplasia).
• Use of uterine relaxants or intralipid infusion during the embryo transfer process.
• Use of a GnRH-agonist for downregulation within one month.
• PCOS patients

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort

Intervention / Treatment

Modified natural cycle; On modified natural cycle, when the mean diameter of the dominant follicle is ≥16 mm, human chorionic gonadotropin (hCG, Ovitrelle® 250 µg; Merck, USA or IVF-C 5000IU, LG Chem, Korea) will be injected to trigger ovulation. Vaginal progesterone (Cyclogest, LD Collins, UK) at a dose of 800 mg per day was started 2 days after hCG injection. Embryo transfer will be scheduled by the time of hCG trigger and embryo stages. Vaginal progesterone administration will be maintained until the day of the pregnancy test. In the event of a positive test result, luteal phase support will be extended until 10 weeks of gestation.

Other: Endometrial peristalsis and hormone measurements; Time point for measurement Endometrial peristalsis will be assessed at three specific time points: On the second day to the fourth day of the menstrual cycle in the FET cycles.; The day of hCG trigger, (before progesterone exposure); On the day of embryo transfer, immediately prior to the procedure Hormone measurements Serum levels of estradiol (E2) and progesterone (P4) will be assessed three times, on the same days as the endometrial peristalsis measurements, using electrochemiluminescence immunoassays. (Elecsys® Estradiol III and Elecsys® Progesterone III, Cobas® e 411, Roche Diagnostics, Germany): On the second day to the fourth day of the menstrual cycle in the FET cycles; The day of hCG trigger; On the transfer day prior to the procedure.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
The association between live birth and uterine contraction frequency measured at different time points.	Live birth was defined as the complete expulsion or extraction from a woman of a product of fertilization, after 22 completed weeks of gestational age; which, after such separation, breathes or shows any other evidence of life, such as heartbeat, umbilical cord pulsation, or definite movement of voluntary muscles, irrespective of whether the umbilical cord has been cut or the placenta is attached. A birth weight of 500 grams or more can be used if gestational age is unknown. Live births refer to the individual newborn; for example, a twin delivery represents two live births.; Uterine contraction frequency is defined as the number of peristaltic waves per minute.	• On the second day to the fourth day of the menstrual cycle in the FET cycles. • The day of hCG trigger • On the day of embryo transfer, immediately prior to the procedure

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Preterm birth	Defined as delivery at <28, <32, <37 completed weeks. A birth that takes place after 22 weeks and before 37 completed weeks of gestational age.	At delivery
Gestational diabetes mellitus	A 75-g OGTT, with plasma glucose measurement when the patient is fasting and at 1 and 2 h, at 24-28 weeks of gestation in women not previously diagnosed with diabetes.	At 24-28 weeks of gestation
Direction of peristalsis.	Direction of peristalsis is categorized as cervix-to-fundus, fundus-to-cervix, indeterminate, or absent (no contractions observed)	• On the second day to the fourth day of the menstrual cycle in the FET cycles. • The day of progesterone initiation or LH surge/hCG trigger, (before progesterone exposure) • On the day of embryo transfer, immediately prior to the procedure
The correlation between endometrial peristalsis at different time points	The correlation between endometrial peristalsis at different time points.	• On the second day to the fourth day of the menstrual cycle in the FET cycles. • The day of progesterone initiation or LH surge/hCG trigger, (before progesterone exposure) • On the day of embryo transfer, immediately prior to the procedure
Live birth rates after the one embryo transfer.	Live birth was defined as the complete expulsion or extraction from a woman of a product of fertilization, after 22 completed weeks of gestational age; which, after such separation, breathes or shows any other evidence of life, such as heartbeat, umbilical cord pulsation, or definite movement of voluntary muscles, irrespective of whether the umbilical cord has been cut or the placenta is attached. A birth weight of 500 grams or more can be used if gestational age is unknown. Live births refer to the individual newborn; for example, a twin delivery represents two live births.	At delivery
Positive pregnancy test	Defined as serum human chorionic gonadotropin level ≥ 25 mIU/mL.	10-14 days after embryo transfer
Clinical pregnancy	A pregnancy diagnosed by ultrasonographic visualization of one or more gestational sacs or definitive clinical signs of pregnancy. In addition to intra-uterine pregnancy, it includes a clinically documented ectopic pregnancy.	4-6 weeks after embryo transfer
Ongoing pregnancy	A pregnancy diagnosed by ultrasonographic or clinical documentation of at least one fetus with a discernible heartbeat at 12 weeks gestation or beyond.	12 weeks of gestation or beyond
Implantation rate	The number of gestational sacs observed divided by the number of embryos transferred (usually expressed as a percentage).	At 4-6 weeks after embryo transfer
Ectopic pregnancy	A pregnancy outside the uterine cavity, diagnosed by ultrasound, surgical visualization, or histopathology.	Up to 12 weeks after embryo transfer
Miscarriage	Spontaneous loss of a clinical pregnancy before 22 completed weeks of gestational age, in which the embryo(s) or fetus(es) is/are nonviable and is/are not spontaneously absorbed or expelled from the uterus.	Up to 22 weeks of gestation
Multiple gestations	A pregnancy with more than one embryo or fetus.	At delivery
Multiple birth	The complete expulsion or extraction from a woman of more than one fetus, after 22 completed weeks of gestational age, irrespective of whether it is a live birth or stillbirth. Births refer to the individual newborn; for example, a twin delivery represents two births.	At delivery
Mode of delivery	Vaginal delivery, C-section (elective, suspected fetal distress, non-progressive labor).	At delivery
Birth weight	Weight of the newborn measured right after delivery.	At delivery
Gestational age at birth	Calculated by gestational age of all live births.	At delivery
Hypertensive disorders of pregnancy	Hypertensive disorders of pregnancy: Pregnancy-induced hypertension, pre-eclampsia (early and late), eclampsia, and HELLP syndrome are defined in the American College of Obstetricians and Gynecologists (ACOG) 2020 g	Up to delivery
Stillbirth	The death of a fetus before the complete expulsion or extraction from its mother after 28 completed weeks of gestational age. The death is determined by the fact that, after such separation, the fetus does not breathe or show any other evidence of life, such as heartbeat, umbilical cord pulsation, or definite movement of voluntary muscles. Note: It includes deaths occurring during labor.	Up to delivery
Very low birth weight	Birth weight less than 1.500 g.	Up to delivery
Low birth weight	Birth weight less than 2.500 g.	Up to delivery
High birth weight	Implies growth beyond an absolute birth weight, historically 4.000 g or 4.500 g, regardless of the gestational age.	Up to delivery
Very high birth weight	Birth weight over 4.500 g for women with diabetes, and a threshold of 5000 g for women without diabetes.	Up to delivery
Major congenital abnormalities	Structural, functional, and genetic anomalies that occur during pregnancy, and are identified antenatally, at birth, or later in life, and require surgical repair of a defect, or are visually evident, or life-threatening, or cause death. Any congenital anomaly will be included as follows definition of congenital abnormalities in Surveillance of Congenital Anomalies by Division of Birth Defects and Developmental Disabilities, NCBDDD, Centers for Disease Control and Prevention (2020).	Up to delivery
NICU admission	The admission of the newborn to the NICU.	Up to delivery
Neonatal mortality	Death of a live-born baby within 28 days of birth. This can be divided into early neonatal mortality, if death occurs in the first seven days after birth, and late neonatal if death occurs between 8 and 28 days after delivery.	Up to delivery
The frequency of endometrial peristalsis at different time points	The frequency of endometrial peristalsis at different time points	On the second day to the fourth day of the menstrual cycle in the FET cycles. The day of hCG trigger On the day of embryo transfer, immediately prior to the procedure

Collaborators and Investigators

• Sponsor: Mỹ Đức Hospital
• Collaborators: My Duc Phu Nhuan Hospital HCMC, Vietnam
• Investigators: Principal Investigator: Lan N Vuong, MD, PhD, IVFMD and HOPE Research Center, My Duc Hospital

Study record dates

Study Major Dates

• Study Start (Actual): February 22, 2026
• Primary Completion (Estimated): December 1, 2026
• Study Completion (Estimated): December 1, 2027

Study Registration Dates

• First Submitted: December 26, 2025
• First Submitted That Met QC Criteria: January 13, 2026
• First Posted (Actual): January 22, 2026

Study Record Updates

• Last Update Posted (Actual): August 19, 2026
• Last Update Submitted That Met QC Criteria: August 17, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Keywords: frozen embryo transfer; natural cycles; uterine contractions; artificial cycles; endometrial peristalsis; endometrial waves
• Additional Relevant MeSH Terms: Urogenital Diseases; Genital Diseases; Infertility
• Other Study ID Numbers: 18/25/DD-BVMD

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No