Among pregnant women with polycystic ovary syndrome (PCOS), decreased endometrial thickness (EMT) was associated with increased risk for preterm birth (PTB), low birthweight (LBW), and small-for-gestational age (SGA) infants. These findings were published in Frontiers in Endocrinology.

Health records of women (N=1755) who had PCOS and a singleton livebirth after frozen-thawed embryo transfer (FET) between 2009 and 2019 at the Shanghai Ninth People’s Hospital in China were retrospectively reviewed for the study. Prior to pregnancy, the women underwent controlled ovarian stimulation using gonadotropin-releasing hormone (GnRH) agonist, GnRH antagonist, or progestin for pituitary suppression. All women underwent hormone therapy cycle or ovulation induction cycle for endometrial preparation.

Of the entire cohort of 1755 women with PCOS, 10.5% had EMT of £8 mm, 78.6% had EMT of >8-13 mm, and 10.9% had EMT of >13 mm EMT.  The 3 EMT categories were classified as “thin”, “intermediate” and “thick”, respectively, for this study. Patients in these 3 EMT cohorts were aged mean 29.9±3.3, 30.0±3.5, and 30.1±3.5 years; body mass index (BMI) was 23.44±3.70, 23.45±3.85, and 24.02±4.26 kg/m2; and 37.5%, 29.6%, and 25.0% had PCOS without any other fertility issues, respectively.

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The patients differed significantly for gravidity and endometrial preparation regimen (both P <.001) among the thin, intermediate, and thick EMT categories. No significant differences in pregnancy complications were found on the basis of maternal age, BMI, parity, or other factors.

For neonatal outcomes, thin EMT associated with increased PTB (13.6% vs 9.3% vs 3.6%; P =.003), lower birthweight (mean, 3260.1 g  vs 3314.6 g vs 3443.3 g; P =.004), LBW (9.2% vs 5.6% vs 2.1%; P =.010), lower birthweight Z-score (mean, 0.33 vs 0.39 vs 0.61; P =.006), and SGA (9.2% vs 4.3% vs 1.6%; P =.001) compared with the intermediate and thick EMT cohorts, respectively.

Using multiple logistic regression models for the same 3 groups, researchers discovered that a 1 mm decrease of EMT led to a 9% decrease ([adjusted odds ratio] 1.09, 95% CI, 1.00-1.19, P = .053), 14% ([aOR]1.14, 95% CI, 1.02-1.38, P=.002), and 22% ([aOR]1.22, 95% CI, 1.07-1.38] P= .003) led to a greater likelihood of developing PTB, LBW, and SGA, respectively.

Researchers acknowledged their study was limited by not adjusting for variants of PCOS or metabolic patterns before pregnancy. Only frozen-thawed embryo transfer (FET) cycles were included in the analysis, so generalization of the study findings should be done with caution.

“Our study demonstrated that decreased EMT was an independent risk factor for PTB, LBW, and SGA in PCOS,” the researchers concluded. “This novel finding suggests that EMT may be applied as a simple indicator of neonatal complications among women with PCOS.”


Huang J, Lin J, Xia L, et al. Decreased endometrial thickness is associated with higher risk of neonatal complications in women with polycystic ovary syndrome. Front. Endocrinol. 2021;12:766601. doi:10.3389/fendo.2021.766601