To the Editor:
We have read with great interest the excellent study by Miwa et al. (1) and would like to comment on the potential relationship between endometrial thickness, a woman’s age and endometrial morphologic pattern.
Miwa et al. (1), in a population of 96 infertile women aged 23-44 years, reported a significantly impaired angiogenesis and lower uterine blood flow in patients with an endometrial thickness of <8 mm (thin) compared to those with ≥8 mm (normal). The number of blood vessels was significantly lower and uterine artery RI was significantly higher in the “thin” endometrium group (n=17) than that in the normal thickness endometrium group (n=57). The authors concluded that high blood flow impedance of uterine arteries could be a trigger resulting in an impaired growth of glandular epithelium, decreased endometrial VEGF levels and consequently poor vascular development which might further decrease endometrial blood flow, forming a vicious circle leading to “thin” endometrium. The authors at the end stated that the cause of high blood flow impedance of radial arteries in patients with a “thin” endometrium was unclear.
We want to make comment to the study by Miwa et al. (1) that although this study is not a clinical study and aimed at evaluating the pathophysiologic features of “thin” endometrium, the women’s age should also have been taken into consideration. The women’s age was observed to be significantly diffferent in two groups. It would be better if age-matched women in normal thickness group had been selected for comparison with those in “thin” endometrium group. It could be complementary if this point had been discussed by the authors, since the woman’s age may be the cause of high blood flow impedance of radial arteries in patients with a “thin” endometrium. We suggest that the age of the woman is an important factor in patients with a “thin” endometrium. In a recent study (2), we evaluated the outcome of ART in women with “thin” endometrium and we noted quite good results when the woman was <35 years old.
We further want to make a contribution regarding endometrial morphologic pattern in women with “thin” endometrium. In a recent study (3), no correlation was noted between endometrial thickness dynamics and pregnancy outcomes. However, a trilaminar endometrial morphologic pattern was positively related to pregnancy outcomes.
The question that arises at that point is whether endometrial thickness alone is enough during evaluation, or whether endometrial morphologic pattern and woman age should also be taken into consideration in a woman with “thin” endometrium. “Thin” endometrium might be strongly related to impared endometrial receptivity, however it is not enough by itself. Therefore, we suggest that future studies about “thin” endometrium should also incorporate data regarding the woman’s age and endometrial morphologic pattern.
Banu Kumbak, M.D.
Levent Sahin, M.D.
Department of Obstetrics and Gynecology
Yeditepe University Hospital
1. Miwa I, Tamura H, Takasaki A, Yamagata Y, Shimamura K, Sugino N. Pathophysiologic features of “thin” endometrium. Fertil Steril 2009; 91: 998-1004.
2. Kumbak B, Erden HF, Tosun S, Akbas H, Ulug U, Bahceci M. Outcome of assisted reproduction treatment in patients with endometrial thickness less than 7 mm. RBM Online 2009; 18: 79-84.
3. Detti L, Yelian FD, Kruger ML, Diamond MP, Puscheck EE. Endometrial thickness dynamics and morphologic characteristics during pituitary downregulation with antagonists in assisted reproductive technology cycles. J Ultrasound Med 2008; 27: 1591-6.
Published online in Fertility and Sterility doi:10.1016/j.fertnstert.2009.05.034
The Authors Respond:
We thank Drs. Kumbak and Sahin for their interest in our study on “thin” endometrium.
Our hypothesis on pathophysiology of thin endometrium is that high blood flow impedance of radial arteries is a possible cause of thin endometrium. Very recently, this hypothesis has been strengthened by our further study, in which thin endometrium was improved by increasing radial artery blood flow with vitamin E, l-arginine, or sildenafil citrate (1). However, the cause of high blood flow impedance of radial arteries in women with a thin endometrium is unclear. As Drs. Kumbak and Sahin point out, mean age was significantly higher in the thin endometrium group than in the normal-thickness endometrium group [34 (26-38) vs 31 (23-44), median (range)]. Therefore, aging may be involved in high blood flow impedance of radial arteries in women with a thin endometrium. However, there was no significant negative correlation between age and endometrial thickness in our unpublished data (n=125, y = -0.0167x + 10.553, R2 = 0.0013), suggesting that endometrial thickness is not always dependent on age.
Regarding endometrial morphologic pattern in ultrasonographic findings, there was no relation between endometrial thickness and endometrial morphologic pattern. Some women with a thin endometrium showed a trilaminar endometrial morphologic pattern, and some women with a normal-thickness endometrium did not.
I agree that it is important for evaluating pregnancy outcome to take not only endometrial thickness but also patients’ age and endometrial morphologic pattern into consideration.
1. Takasaki A, Tamura H, Miwa I, Taketani T, Shimamura K, Sugino N. Endometrial growth and uterine blood flow: a pilot study for improving endometrial thickness in the patients with a thin endometrium. Fertil Steril 2009, in press.
Norihiro Sugino, MD, PhD
Department of Obstetrics and Gynecology
Yamaguchi University Graduate School of Medicine
Published online in Fertility and Sterility doi:10.1016/j.fertnstert.2009.05.035