Reproductive Biology and Endocrinology

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Reproductive Biology and
BioMed Central
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The correlation between endometrial thickness and outcome of in
vitro fertilization and embryo transfer (IVF-ET) outcome
Ahlam Al-Ghamdi*, Serdar Coskun, Saad Al-Hassan, Rafat Al-Rejjal and
Khalid Awartani
Address: Reproductive Medicine, Department of Obstetrics and Gynecology, King Faisal Specialist Hospital and Research Centre Riyadh, Kingdom
of Saudi Arabia
Email: Ahlam Al-Ghamdi* - [email protected]; Serdar Coskun - [email protected]; Saad Al-Hassan - [email protected]; Rafat Al-
Rejjal - [email protected]; Khalid Awartani - [email protected]
* Corresponding author
Published: 2 September 2008
Received: 22 May 2008
Accepted: 2 September 2008
Reproductive Biology and Endocrinology 2008, 6:37
This article is available from:
© 2008 Al-Ghamdi et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background: To evaluate the relationship between endometrial thickness on day of human
chorionic gonadotrophin administration (hCG) and pregnancy outcome in a large number of
consecutive in vitro fertilization and embryo transfer (IVF-ET) cycles.
Methods: A retrospective cohort study including all patients who had IVF-ET from January 2003–
December 2005 conducted at a tertiary center.
Results: A total of 2464 cycles were analysed. Pregnancy rate (PR) was 35.8%. PR increased
linearly (r = 0.864) from 29.4% among patients with a lining of less than or equal to 6 mm, to 44.4%
among patients with a lining of greater than or equal to 17 mm. ROC showed that endometrial
thickness is not a good predictor of PR, so a definite cut-off value could not be established (AUC
= 0.55).
Conclusion: There is a positive linear relationship between the endometrial thickness measured
on the day of hCG injection and PR, and is independent of other variables. Hence aiming for a
thicker endometrium should be considered.
vaginal ultrasound, which is considered as both
Assisted reproductive technology (ART) has been com-
atraumatic and simple [1]. The effect of endometrial
monly used in infertility treatment over the last two dec-
thickness on pregnancy rates in ART patients has been
ades. The high cost and relatively low implantation and
evaluated by many authors [2-11], with controversial
pregnancy rates (PRs) in in-vitro fertilization (IVF) and
results. Some authors demonstrated a higher pregnancy
intracytoplasmic sperm injection (ICSI) treatment cycles
rate at certain endometrial thickness [3,4,10-12], while
has led to a need to evaluate the predictors of success in
others did not show a significant correlation between
these patients. One of the important factors is the
endometrial thickness and PRs in IVF/ICSI patients
endometrial receptivity. Endometrial thickness has been
[5,7,8]. Other authors reported a threshold of <7 mm
utilized as an indirect indicator for endometrial receptiv-
and/or >14 mm with a significant reduction in implanta-
ity and is measured in the midsaggital plane during trans-
tion rate and PR [2,6].
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Reproductive Biology and Endocrinology 2008, 6:37
With these controversies, no conclusive cut-off value of
of oocyte retrieved, length of stimulation, dose of hMG,
endometrial thickness has been established in order to
fertilization rate, number of cleaved embryos, number of
help clinicians in counseling the couple about the out-
transferred embryos.
come. The reason for such controversy could be probably
due to a relatively low number of cycles for patients with
Statistical analysis
both extremes of endometrial thicknessess.
Data were analyzed using SPSS version 14 software (Chi-
cago, Ilin, USA). All tests were two tailed, and p < 0.05 was
The aim of this study is to determine if there is any effect
considered statistically significant. Continuous variables
of endometrial thickness measured on the day of admin-
are presented as mean and SD and were tested by student's
istration of human Chorionic Gonadotrphin (hCG) on
t-test. Comparisons of proportions were made by the chi-
pregnancy rate while analyzing large number of cycles,
squared test. The effect of endometrial thickness on the
and if so, to identify a cut off value at which pregnancy
pregnancy outcome was studied using multivariate analy-
rate is too low, hence helping clinicians in counceling the
sis, where all other factors affecting the pregnancy out-
come were controlled for. To determine the correlation
between endometrial thickness, patient characteristics
and treatment characteristics a stepwise logistic regression
All fresh cycles of IVF or ICSI conducted at King Faisal Spe-
analysis was performed including (age of the patient,
cialist Hospital and Research Center IVF unit from January
body mass index (BMI), endometrial thickness on day 3
2003 to December 2005 were identified from our elec-
of the cycle, duration of stimulation, dose of hMG
tronic database and the charts were reviewed. The study
needed, number of oocytes retrieved, number of cleaved
was approved by the Ethics Committee of our hospital. All
embryos, and number of embryos transferred). The
fresh IVF or ICSI treatment cycles that reached oocyte pick
Receiver operating characteristic (ROC) analysis was used
up and embryo transfer within the study period were
to evaluate an endometrial thickness that can predict preg-
included, women with known intrauterine anomalies
nancy outcome.
were excluded from the study. Endometrial thickness was
not used as a criteria for cancellation. Endometrial thick-
ness was defined as the maximal distance between the
A total of 2464 cycles were included in the study. Clinical
echogenic interfaces of the myometrium and the
pregnancy rate (PR) was 35.8%. 79% of the patients had
endometrium and was measured in the midsagittal plane
undergone the long protocol. The pregnancy rate was
by two dimensional transvaginal ultrasound on the day of
39.4% in the long protocol group vs 22.4% in the short
hCG administration.
protocol group. Compared to group B, group A patients
were younger, required lower dose of hMG, had more
Two protocols for pituitary down regulation were used,
medium sized and mature follicles, higher number of
long or short protocol as previously described [1]. The
oocytes retrieved, higher number of oocytes fertilized, and
medication for stimulation used in all cases was human
higher number of cleaved embryos. Both groups had sim-
menopausal gonadotrophin (hMG, Menegon®, Ferring,
ilar BMI, duration of stimulation, baseline endometrial
Germany). When at least three follicles were ≥ 18 mm,
thickness (measured on day 3 of the cycle before the start
hCG 10,000 units was administered. The endometrial
of hMG), and number of transferred embryos (Table 1).
thickness was measured by the same sonographer and
There was no statistical difference between the two groups
documented in the chart. Oocyte retrieval was performed
in the primary infertility diagnosis (Table 2). Endometrial
36 hours later. Fertilization was achieved by IVF or ICSI
thickness measured on the day of hCG administration
according to the indication. Cleavage stage embryos were
ranged between 5 – 20 mm, and was higher in cycles
transferred on day 3. Maximum two embryos were trans-
where pregnancy was achieved, with statistical signifi-
ferred under transabdominal ultrasound guidance with a
cance (mean 11.6 vs. 11.3 mm, respectively, p < 0.0001).
full bladder. The patients were started on IM progesterone
Pregnancy rate increased from 29.4% among patients
injections (Gestone, Nordic Pharma, UK) on the same day
with an endometrial thickness of ≤6 mm, to 44.4%
of embryo transfer for luteal phase support and continued
among patients with an endometrial thickness of ≥17 mm
till pregnancy test on day 15. Clinical pregnancy was con-
(Table 3). (Figure 1) shows the positive linear correlation
firmed by ultrasound observation of fetal cardiac activity
(r = 0.864) and ROC with an area under the curve (AUC)
two weeks after positive hCG test.
= 0.55. From this ROC a cut-off value of ≥11 mm would
be suggested. When dividing the patients into two groups,
The patients were divided into two groups; those who got
group 1 with endometrial thickness of <11 mm, and
pregnant (group A) and those who did not (group B).
group 2 with endometrial thickness ≥11 mm, PRs were
Both groups were compared for the various parameters
30.9% and 38.7% respectively, p = 0.001, RR = 1.25
including age, body mass index (BMI), diagnosis, number
(95%CI 1.12–1.41) (Table 4). Multiple logistic regression
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Reproductive Biology and Endocrinology 2008, 6:37
Table 1: Demographic data
Group A
Group B
P value
mean ± SD
mean ± SD
Number of cycles (n)
Age (years)
30.27 ± 5.53
31.14 ± 5.38
BMI (weight kg/height m2)
28.44 ± 4.58
28.32 ± 4.42
Long protocol # (%)
765 (39.4%)
1177 (60.6%)
< 0.0001
Short protocol # (%)
117 (22.4%)
405 (77.6%)
Stimulation length (days)
10.92 ± 2.63
10.79 ± 2.46
Dose of hMG (ampoules)
37.67 ± 15.03
40.73 ± 16.54
< .0001
Endometrial thickness cycle day 3 (mm)
3.23 ± 1.22
3.21 ± 1.22
Endometrial thickness hCG day (mm)
11.64 ± 2.13
11.26 ± 2.17
< 0.0001
Number of medium sized follicles
8.08 ± 5.33
7.12 ± 5.31
< 0.0001
Number of mature follicles
7.92 ± 3.51
7.62 ± 3.69
Number of oocytes retrieved
10.51 ± 5.43
9.86 ± 5.73
Number of fertilized oocytes
5.79 ± 3.23
4.97 ± 3.35
< 0.0001
Number of embryos
5.3 ± 2.82
4.44 ± 2.81
< 0.0001
Number of embryos transferred
1.88 ± 0.37
1.98 ± 0.26
analysis indicated significant independent effects of age (P
line and that on hCG day [15]. Our results are with agree-
= 0.01), Type of protocol used (P = 0.0001), endometrial
ment to those that reported a positive correlation [3,4,10-
thickness on hCG day (P = 0.001), number of oocytes
21]. Endometrial thickness measured on the day of hCG
retrieved (P = 0.0001), number of cleaved embryos (P =
administration was higher in cycles where pregnancy was
0.0001), and number of embryos transferred (P = 0.0001)
achieved (mean 11.6 vs. 11.3 mm, respectively, p <
on pregnancy rates.
0.0001), but the difference is not of clinical significance,
because results fell within the range of measurement
error. When using a multiple logistic regression analysis to
This study is to our knowledge so far the largest in regards
control all other confounding variables, we found an
to sample size that addresses the effect of endometrial
independent effect of endometrial thickness on PR. The
thickness on PR. The day of the stimulation cycle on
uniqueness of this study is that it demonstrated a steady
which the endometrial thickness is measured to docu-
and gradual increase in PR as endometrial thickness
ment adequate endometrial development has varied
increases. Many previous studies reported significant dif-
between authors. The most often used is the measurement
ferences in PRs above and below a threshold thickness of
taken on the day of hCG administration, but some
8 – 10 mm, but didn't show a continuous relationship
authors have used the measurement that was taken on the
such as we found [3,4,11,12,19]. Although we found a
day of oocyte retrieval or the day of embryo transfer in
clear positive correlation between endometrial thickness
their studies, which makes it difficult to compare between
and PR, our PR was 29.4% among patients with ≤ 6 mm
studies. We have used the measurement taken on the day
endometrial thickness in contrast to Gonen et al 1990
of hCG administration in our data. The change in
who reported poor PR with endometrial thickness < 6 mm
endometrial thickness occurring during IVF stimulation
[14]. Furthermore, there were several reports of successful
has been evaluated by several authors [8,13,14]. Grant et
pregnancies resulting from cycles with endometrial thick-
al 2007, demonstrated a trend toward significance in the
ness of ≤ 4 mm [22] indicating that a thin endometrium
overall change in endometrial thickness between the base-
does not necessarily preclude the possibility of implanta-
tion. Hence cancellation of cycle based on a thin
Table 2: Diagnostic categories
endometrium is unwarranted.
Group A
Group B
Some authors suggested a detrimental effect of endome-
trial thickness of ≥ 14 mm on PR [6]. Our results on the
Male factor 1763 (71.6%)
623 (70.6%)
1140 (72.0%)
contrary, suggest that PRs are highest for patients with the
Tubal factor 338 (13.7%)
114 (13.0%)
224 (14.2%)
thickest lining, and are consistent with other recent stud-
Unexplained 213 (8.6%)
85 (9.6%)
128 (8.1%)
ies finding no reduction in PRs with very thick
Others 150 (6.1%)
60 (6.8%)
90 (5.7%)
endometrium [16,23-25]. In fact there was a case report of
a successful twin pregnancy after IVF with an endometrial
P = 0.319
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Reproductive Biology and Endocrinology 2008, 6:37
Table 3: Pregnancy rates at different endometrial thicknesses
Endometrial thickness on day of HCG
Group A (n)
Group B (n)
Pregnancy rate
≤6 mm
7 mm
8 mm
9 mm
10 mm
11 mm
12 mm
13 mm
14 mm
15 mm
16 mm
≥17 mm
Table 4: Pregnancy rates below and above 11 mm endometrial thickness
Endometrial thickness on day of HCG
Group A (n)
Group B (n)
Pregnancy rate
< 11 mm
≥ 11 mm
P = 0.001
RR = 1.25, (95% CI 1.12–1.41)
ROC Curve
R Sq Linear = 0.864
Sensitivity 0.00
1 - Specificity
Diagonal segments are produced by ties.
The ROC and linear
Figure 1
regression curves
The ROC and linear regression curves.
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Reproductive Biology and Endocrinology 2008, 6:37
thickness of 20 mm [26]. Limitations of our study, it is ret-
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