Predictive Value of Endometrial Thickness in Doubt

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Predictive value of endometrial thickness in doubt

Endometrial thickness is not predictive for live birth after embryo transfer, even without a cutoff

A retrospective study was performed to evaluate the predictive value of endometrial thickness (EMT) for live birth following embryo transfer, without a minimum thickness requirement in place for transfer.

Women who underwent a fresh or frozen-thawed embryo transfer (ET), at the Koç University Hospital Assisted Reproduction Unit, between October 2016 and August 2019 were reviewed for study inclusion.

All women had a hysterosalpingogram and a 3-dimensional transvaginal ultrasound scan (TVUS) to rule out subfertility. Uterine factors known to cause infertility or impair ART success were corrected prior to ART treatment.

In fresh ET cycles, GnRH agonist and antagonist protocols was used for ovarian stimulation dependent on patient characteristics. Ovarian response during stimulation was monitored by TVUS and hormone levels. Once 2 or more follicles reached 17 or 18µm in diameter (GnRH-agonist/antagonist respectively), a trigger shot was administered to induce ovulation.

Endometrium thickness was measured along the midsagittal plane and noted as per Grunfeld’s criteria. Oocyte retrieval was performed 36 hours later with luteal support (progesterone) given to commence that evening.

Following standard IVF protocols, embryo transfer was carried out on day 5 after oocyte retrieval or at the blastocyst stage using TVUS. Luteal support continued until a negative pregnancy test or the 8th week of gestation.

In frozen ET cycles, 2-mg of estradiol valerate (x 3 daily), was administered on the second or third day of menstruation. Ten days later a second TVUS was carried out and luteal support (progesterone) begun. On the 6th day of progesterone administration, the frozen embryo was then warmed and transferred under TVUS guidance.

Only one embryo transfer per woman was included in this study, specifically the first transfer (either fresh or frozen ET) in women with multiple transfers. Live birth was defined as the delivery of a live newborn after 24 weeks gestation, with miscarriage as the loss of a clinical pregnancy before gestation week 20.

Overall 560 embryo transfers (273 = fresh, 287 = frozen-thawed) met the inclusion / exclusion criteria for this study.

Initial patient characteristics according to outcomes (live birth vs no live birth) following fresh ET showed that endometrial thickness was statistically similar between the two groups (10.5mm vs 9mm, P=0.11). However women in the live birth group were significantly younger compared to the no live birth group (35 vs 37 years, P<0.01). Interestingly, in the no live birth group, levels of serum estradiol (1229 vs 1600pg/mL) on trigger day, along with the no of metaphase-2 oocytes (6 vs 7) and usable blastocysts (1 vs 2) was slightly lower than the live birth group.

In the frozen embryo transfer analysis, endometrial thickness was also similar between the women who had a live birth and does that did not (8.4 vs 9.0mm). Not surprisingly women who had a live birth were significantly younger on average compared to women who did not (32 vs 34 years). The proportion of women undergoing a single embryo transfer was similar for the 2 groups (Live Birth vs No Live Birth) with the majority of transfers performed within a year of oocyte retrieval.

Following this initial analysis, live birth and miscarriage rates per embryo transfer was then expanded according to fresh and frozen-thawed ET, for each millimeter of endometrial thickness (4 to 18mm). Statistical analysis of this data found no linear relationship between endometrial thickness and the rate of live birth or miscarriage.

Area under the curve analysis showed the predictive value of endometrial thickness on live birth rate to be overall poor. Specifically area under the curve = 0.56 (fresh ET), 0.47 (frozen-thawed ET) and 0.52 (all ET).

These results suggest that women with thinner endometrial thickness during ET have comparable outcomes to those with thicker endometrial thickness and therefore endometrial thickness should not be the main factor when considering cancellation of embryo transfer.


SUMMARY: IDEAL ENDOMETRIAL THICKNESS FOR PREGNANCY

According to this study, the ideal endometrial thickness for pregnancy is not a valid predictor of live birth rate (LBR) or miscarriage rate (P>0.09) following IVF embryo transfer (ET). Endometrial thickness between 6-6.9mm achieved a 38.1% LBR (frozen ET, n=21) and 27.8% LBR (fresh ET, n=18).


Limitations

  1. Retrospective study
  2. Smaller study size compared to similar studies


Similar studies

Simeonov M, et al. (2020). The entire range of trigger-day endometrial thickness in fresh IVF cycles is independently correlated with live birth rate. https://doi.org/10.1016/j.rbmo.2020.04.008

Groenewoud E R, et al. (2018). Influence of endometrial thickness on pregnancy rates in modified natural cycle frozen‐thawed embryo transfer. https://doi.org/10.1111/aogs.13349

Liu K E, et al. (2018). The impact of a thin endometrial lining on fresh and frozen–thaw IVF outcomes: an analysis of over 40 000 embryo transfers. https://doi.org/10.1093/humrep/dey281

Vaegter K K, et al. (2017). Which factors are most predictive for live birth after in vitro fertilization and intracytoplasmic sperm injection (IVF/ICSI) treatments? Analysis of 100 prospectively recorded variables in 8,400 IVF/ICSI single-embryo transfers. https://doi.org/10.1016/j.fertnstert.2016.12.005

Gingold J A, et al. (2015). Endometrial pattern, but not endometrial thickness, affects implantation rates in euploid embryo transfers. https://doi.org/10.1016/j.fertnstert.2015.05.036


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