P-753 Pregnancy complications and placental histology following embryo transfer with a thinner endometrium
Authors: Ganer Herman H , Volodarsky-Perel A , Nhung Ton Nu T , Machado-Gedeon A , Cui Y , Shaul J , Dahan M. H 
Published: June 2022

Abstract

Study question
Our objective was to assess perinatal outcomes and placental findings following in vitro fertilization (IVF) with a thinner endometrium.

Summary answer
Live births following IVF with a thinner endometrium were associated with placental mediated obstetric complications and lower birthweight, yet with no differences in placental histology.

What is known already
A lower average birth weight and higher rate of small for gestational age infants have been demonstrated in both fresh transfer and frozen transfer cycles with thinner endometrial thicknesses. Additional adverse outcomes associated with thin endometrium included hypertensive disorders of pregnancy, placenta previa, cesarean section and overall obstetric complications. Yet, no study has explored placental histology in such cases.

Study design, size, duration
This was a retrospective cohort study of 1057 deliveries following IVF, between 2009 and 2017. All placentas were sent to pathology irrelevant of pregnancy complication status, per protocol at our institution.

Participants/materials, setting, methods
Data was from a university-affiliated tertiary hospital. Included were live singleton births after IVF, compared according to maximum endometrial thickness prior to transfer: thinner endometrium group, defined as &lt; 9-millimeters, as compared to controls, defined as ≥ 9-millimeters. Outcomes were placental findings, including anatomic, inflammatory, vascular malperfusion and villous maturation lesions and obstetric and perinatal outcomes. Continuous and categorial variables were compared as appropriate, and logistic and linear regression analyses employed.to control for confounders.

Main results and the role of chance
A total 292 deliveries in the thinner endometrium group, and 765 in the control (thicker) group were compared. Maternal demographics were similar between the groups, except for main treatment indication, which was more commonly diminished reserve in patients with a thinner endometrium – 17.8% vs. 9.4%, and less commonly male factor – 27.0% vs. 35.6%, p = 0.003. Live births following fresh transfer were more common in the control group, while the thinner endometrium group was notable for a higher rate of single blastocyst transfers. When controlling for confounding effects, thinner endometrium was associated with an increased rate of obstetric complications (preterm delivery, preeclampsia, low birth weight or placental abruption) - 26.0% vs. 17.5%, p = 0.001, while placental histological examination demonstrated no differences in anatomical, inflammatory or vascular lesions. In a linear regression analysis, after adjustment for confounders, thinner endometrium was associated with lower birthweights – β -101.3 grams, 95% CI (-185.0 to -17.6 grams), p = 0.01.

Limitations, reasons for caution
The study was limited by sample size. Missing historical information included obstetric complications in previous deliveries, which would increase the risk of reoccurrence in subsequent pregnancies and data regarding endometrial trauma (curettage for example).

Wider implications of the findings
Transfer with a thinner endometrium was associated with placental mediated complications and lower birthweights, despite similar placental histology. This may result from functional placental changes throughout implantation and placentation. Preventive measures for adverse obstetric outcomes, such as Micropirin, in cases in which endometrial thicknesses are suboptimal are to be determined.

Trial registration number
Not applicable