Correlation Between Endometrial Thickness And The Incidence Of Hypertensive Disorders Of Pregnancy In Frozen-thawed Embryo Transfer

BackgroundWith the wide application of assisted reproductive technology ART,an increasing number of infertile couples get the opportunity to give birth a baby in this way.Compared with fresh embryo transfer,frozen-thawed embryo transfer(FET)can reduce the incidence of ovarian hyperstimulation syndrome(OHSS)and improve the cumulative pregnancy rate in clinical practice,Finally,FET has implemented a wide range of applications globally.Perinatal complications after FET are the focus of both reproductive clinicians and obstetricians.Hypertensive disorders of pregnancy(HDP),one set of the serious obstetric complications,play a significant role in perinatal maternal and fetal mortality.Several large sample and multicenter clinical trials have also manifested that FET is associated with an increased risk of preeclampsia,one type of pregnancy-induced hypertension.The endometrial thickness is one of important factors affecting endometrial receptivity(ER),which has been proved to be related to adverse obstetric complications.Endometrium thickness,one of relatively controllable factors in FET compared with fresh embryo transfer(ET).The study was designed to explore the relationship between EMT and the incidence of hypertensive disorders complicating pregnancy in frozen embryo transfer,and obtain a relatively safe endometrial thickness with a view to optimizing the pregnancy outcome by adjusting the endometrial thickness in FET.ObjectiveTo investigate whether endometrial thickness is associated with the risk of hypertensive disorders of pregnancy in frozen-thawed embryo transfer cycles.Study designThis respective cohort study enrolled patients who received vitrified embryo transfer and had a singleton delivery in the Reproductive Hospital affiliated to Shandong University from January 2015 to December 2019.All the patients were divided into 3 groups,consisting of 827 patients with an EMT<0.8 cm(thin endometrial thickness group),1069 patients with an EMT>1.2 cm(thick endometrial thickness group),and 11 562 patients with an EMT between 0.8 cm and 1.2 cm(reference group).Statistical methods were used to evaluate the relationship between endometrial thickness and the incidence of pregnancy-induced hypertension.ResultsThe incidences of hypertensive disorders complicating pregnancy in a thin endometrial thickness group(<0.8cm)and a deep endometrial thickness group(>1.2cm)were significantly greater than in a reference group(0.8 cm-1.2 cm)(7.98%vs 5.24%vs 4.59%,P<0.001).There was higher cesarean section rate(74.61%vs 69.15%vs 64.36%,P<0.001)and lower neonatal birth weight(3.38±0.56 kg vs 3.46±0.51 kg vs 3.45±0.50 kg,P<0.001)found in thin endometrial thickness compared with reference group and thick endometrial thickness group.Logistic regression analysis was used to investigate the relationship between endometrial thickness and the risk of hypertensive disorders of pregnancy.Stepwise Logistic regression suggested that both thin endometrium and thick endometrium are associated with higher HDP rate after adjusting for confounding variables.Subsequently,subgroup logistic regression analysis based on endometrial preparation regimens showed that thick endometria were still significantly associated with a higher morbidity rate in the natural cycle group,while in the artificial cycle group(OR=1.59,95%CI:1.11-2.21,P=0.008),thin endometria were closely associated with increased morbidity(OR=1.71,95%CI:1.22-2.33,P<0.001).ConclusionThe results of this study confirm that the endometrial thickness in FET cycles is an independent risk factor on the risk of pregnancy-induced hypertension.Reproductive clinicians should focus on adjusting endometrial thickness in different preparation regimens,when women with thin endometria(<0.8 cm)in natural cycles or excessively thicker endometria(>1.2 cm)in hormone programmed cycles achieve pregnancy through frozen-thawed embryo transfer.