Endometrial Waves in Frozen Embryo Transfer Cycles
Endometrial waves (uterine contractions) are generally unfavorable during a frozen embryo transfer cycle, as persistent contractions during the implantation window can reduce pregnancy success and increase ectopic pregnancy risk.
Understanding Endometrial Contractility and Implantation
The uterus exhibits wavelike contractile activity that varies throughout the menstrual cycle, with different patterns associated with reproductive success 1. While these contractions serve beneficial functions during certain phases—such as assisting sperm transport around ovulation—their persistence into the receptive phase can be detrimental 1, 2.
Impact on Embryo Implantation
Uterine quiescence is essential for successful implantation, as embryo attachment to the predecidualized endometrium and subsequent invasion require a non-contractile environment 1.
Persistent endometrial contractions during the implantation window decrease the probability of successful uterine pregnancy in both natural and assisted reproduction cycles 2.
Excessive uterine contractility is directly associated with ectopic pregnancies in IVF treatment cycles, representing a significant clinical concern 1, 2.
Physiological Regulation
Progesterone is the primary determinant of uterine quiescence during the receptive phase, promoting local vasodilation and musculature relaxation by inducing nitric oxide synthesis in the decidua 1.
Adequate wave patterns appear related to successful reproduction, but these patterns must transition to quiescence during the actual implantation period 1.
Clinical Implications for FET Cycles
Timing Considerations
Endometrial contractions that persist beyond the periovulatory period interfere with embryo nidation, making their absence during the transfer window more favorable than their presence 1, 3.
The lack of uterine contractions during the receptive phase plays a role in successful pregnancy establishment, though the exact mechanisms continue to be investigated 3.
Assessment Limitations
Ultrasound imaging can visualize endometrial contractions through time-lapse video recordings, providing a noninvasive method to assess uterine contractility 2, 3.
While endometrial thickness alone is a poor prognostic marker for fertility outcomes (with low-to-moderate quality evidence), the presence or absence of contractions may provide additional information 4, 3.
Common Pitfalls and Clinical Approach
The key caveat is distinguishing between appropriate mid-cycle contractility (which aids conception) versus inappropriate late-cycle contractility (which impairs implantation). For an ongoing FET cycle specifically, you want minimal to absent endometrial waves at the time of transfer 1, 2.
Overstimulation protocols can exacerbate uterine contractility, suggesting that more physiologic hormone replacement protocols may be preferable for FET cycles 2.
Inadequate progesterone support may fail to suppress uterine contractions, as progesterone's induction of uterine quiescence is critical for embryo nidation 1.
Practical Management
If endometrial waves are detected on ultrasound during an FET cycle:
Consider delaying transfer if prominent contractions are visualized, as this suggests the endometrium may not yet be in an optimal receptive state 3, 2.
Ensure adequate progesterone supplementation, as this is the primary mechanism for achieving uterine quiescence 1.
Avoid excessive hormonal stimulation in future cycles, as minimal stimulation protocols that more closely mimic natural cycles may reduce problematic uterine contractility 2.