Predicting factors for endometrial thickness during treatment with assisted reproductive technology.

OBJECTIVE: To discover the factors contributing to endometrial thickness, and to assess the impact of endometrial thickness on pregnancy rates (PRs) according to these factors.
DESIGN: Retrospective study.
SETTING: In vitro fertilization unit in a university hospital. PATIENT(S): All women with primary infertility and no previous pregnancies who underwent IVF treatment at the Chaim Sheba Medical Center, Tel Hashomer, Israel, between August 9, 2001-December 31, 2004. INTERVENTION: Measurement of endometrial thickness by the use of transvaginal ultrasound probe on the day that hCG was administered during an IVF cycle. MAIN OUTCOME MEASURE(S): Factors influencing endometrial thickness and the relationship between endometrial thickness and PRs. RESULT(S): The mean endometrial thickness decreased as a function of the patient's age. The thickest endometrium was found in patients <25 years of age (11.9 +/- 2.5 mm), and the thinnest endometrium was found in patients >40 years of age (9.6 +/- 2.3 mm). Other factors, such as E(2) levels, etiology of infertility, induction of ovulation protocol, and type of gonadotropin used, were also found to contribute to endometrial thickness. CONCLUSION(S): Our data support the case for an "aging" of the endometrium. The chances of achieving a thick endometrium for patients >40 years of age are lower than for younger patients. Furthermore, a thicker endometrium is correlated with a higher PR only for patients >35 years of age.