Effect of exogenous gonadotropins on endometrial maturation in oocyte donors

Effect of exogenous gonadotropins on endometrial maturation in oocyte donors

FERTILITY AND STERILITYt VOL. 71, NO. 1, JANUARY 1999 Copyright © 1998 American Society for Reproductive Medicine Published by Elsevier Science Inc. P...

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FERTILITY AND STERILITYt VOL. 71, NO. 1, JANUARY 1999 Copyright © 1998 American Society for Reproductive Medicine Published by Elsevier Science Inc. Printed on acid-free paper in U.S.A.

Effect of exogenous gonadotropins on endometrial maturation in oocyte donors William R. Meyer, M.D.,* Debra B. Novotny, M.D.,† Marc A. Fritz, M.D.,* Stan A. Beyler, Ph.D.,* Lynda J. Wolf, M.D.,* and Bruce A. Lessey, Ph.D., M.D.* University of North Carolina School of Medicine, Chapel Hill, North Carolina

Received May 26, 1998; revised and accepted July 31, 1998. Supported by National Institutes of Health grants HD 35041 and HD 34824 (B.L.) and CA 46866 (S.T.). These studies were funded in part by the National Cooperative Program on Markers of Uterine Receptivity for Blastocyst Implantation. Reprint requests and present address: William R. Meyer, M.D., Department of Obstetrics and Gynecology, University of North Carolina School of Medicine, CB 7570, Chapel Hill, North Carolina 27599 (FAX: 919-966-5244). Presented in part at the Society for Gynecologic Investigation, Philadelphia, Pennsylvania, March 1996. * Department of Obstetrics and Gynecology, University of North Carolina School of Medicine. † Department of Pathology and Laboratory Medicine, University of North Carolina School of Medicine. 0015-0282/98/$19.00 PII S0015-0282(98)00390-2

Objective: To determine the effects of controlled ovarian hyperstimulation (COH) on endometrial maturation. Design: Prospective, before and after evaluation of midluteal endometrial biopsies in oocyte donor’s spontaneous and subsequent COH cycles. Setting: Tertiary academic medical center assisted reproductive technologies clinic. Patient(s): Nineteen oocyte donors. Intervention(s): Exogenous gonadotropins, endometrial biopsies. Main Outcome Measure(s): Endometrial histology and an immunohistochemical marker of uterine receptivity, the avb3 vitronectin. Result(s): Glandular and stromal dyssynchrony was more common after COH in 16 (80%) of 20 cycles than 6 (30%) of 20 spontaneous cycles (P ,.05). Glandular lag was more frequent in COH cycles and unaffected by progesterone administration. The b3 subunit of the avb3 vitronectin receptor was present in 9 (45%) of 20 spontaneous and 2 (10%) of 20 COH cycles (P ,.05). Conclusion(s): Exogenous gonadotropin use in healthy reproductive age women did not result in endometrial evidence of a luteal phase defect. A greater incidence of glandular-stromal dyssynchrony resulted from the use of exogenous gonadotropins. The presence of avb3 was noted in most endometrial specimens demonstrating in phase glandular maturation. We conclude that endometrial dyssynchrony that results from delayed glandular development most likely represents a normal histologic variant. (Fertil Sterilt 1999;71:109 –14. ©1998 by American Society for Reproductive Medicine.) Key Words: Endometrial dyssynchrony, gonadotropins, avb3 vitronectin, oocyte donor

Refinements in ovarian stimulation protocols have improved ovarian follicular recruitment and oocyte quality in IVF programs, and intracytoplasmic sperm injection (ICSI) now provides the means to overcome even severe male factor infertility (1). Although these advances have improved results achieved with assisted reproductive technologies, success rates overall remain relatively modest, primarily because embryo implantation rates have failed to appreciably change. Assisted hatching techniques may improve implantation efficiency in certain subsets of women, but in broader application they have had little, if any, impact on IVF success (2). Endometrial “receptivity” thus remains the apparent rate-limiting step in IVF (3). Many believe receptivity is affected adversely by factors intrinsic to the IVF process; the prime

suspect is the grossly abnormal endocrine milieu that typically accompanies controlled ovarian hyperstimulation (COH) (4 – 6). Normal secretory endometrial development and maturation depend largely on the combined actions of estrogen and progesterone. The endometrium appears to tolerate relatively wide variations in the relative amounts of estrogen and progesterone, but if sufficiently profound, a deficiency or excess or a temporal imbalance of either hormone may alter endometrial morphology (7, 8). If the morphological and functional maturation of the endometrium are temporally linked, as accumulating evidence suggests, then the extreme elevations in ovarian steroid and peptide hormone levels that often are observed in IVF stimulation cycles may indeed have adverse effects on endometrial receptivity. 109

The higher implantation efficiencies observed in natural cycles of IVF and in recipients of donor oocytes who receive a programmed regimen of steroid hormone replacement, compared with conventional IVF patients, suggest that compromised endometrial function after COH may be a critical factor affecting conception rates (9, 10). Observations in infertile women suggest that dyssynchronous endometrial glandular and stromal maturation is a common feature of COH cycles and may be a direct consequence of such treatment, but the clinical significance of endometrial dyssynchrony remains unclear (5, 11, 12). Confident conclusions cannot be drawn from histologic analyses of tissue specimens obtained outside the putative “implantation window.” Moreover, it is possible that infertile patients who require COH or who exhibit endometrial dyssynchrony during such treatment may have an underlying predisposition to this and other forms of abnormal endometrial development. Direct within-subject comparisons between spontaneous and COH cycles in normal women would be most informative. Ethical constrains ordinarily would preclude such a study, but the unique circumstances of oocyte donation offer the opportunity to make this comparison. To more closely examine the effect of COH on endometrial development, we compared the histologic characteristics and patterns of glandular epithelial integrin expression in endometrial tissue specimens obtained from healthy young cycling women in both a spontaneous cycle and a COH cycle in which they served as an oocyte donor.

MATERIALS AND METHODS Oocyte Donors Nineteen oocyte donor candidates, mean (6SD) ages of 26 6 4 – 8 years, were recruited to participate in this study, which was approved by the Institutional Review Board of the University of North Carolina at Chapel Hill. Twelve of the 19 subjects had been pregnant; fertility was untested but presumed in the remaining seven donors. Paired endometrial tissue specimens were obtained from each subject via an endometrial pipelle 8 days after detection of the midcycle urinary LH surge (Ovuquick; Quidel, San Diego, CA) and after exogenous hCG, 10,000 IU; Profasi, Serono, Randolph, MA) administration in a spontaneous and a COH oocyte donation cycle, respectively. One subject was studied in each of 2 pairs of cycles (spontaneous and COH), yielding a total of 20 pairs of cycles for analysis. In the first 9 COH study cycles, subjects received no supplemental exogenous progesterone (typically administered to patients undergoing standard IVF). In the final 11 COH study cycles, progesterone in oil 50 mg/d was administered intramuscularly beginning immediately after oocyte retrieval and ending after biopsy was performed. Progesterone vials were returned and inspected to verify 110

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compliance with the prescribed regimen before biopsy in the COH cycle. Immediately after biopsy in spontaneous cycles, subjects began treatment with leuprolide acetate (1 mg/d subcutaneously, Lupron; Tap, Chicago, IL), reduced to 0.5 mg/d once effective down-regulation was confirmed (serum estradiol of ,40 pg/mL, no ovarian follicle or cyst of .10 mm in mean diameter). The serum E2 concentration was determined after exogenous gonadotropin (225 IU/d, Metrodin; Serono or Humegon, Organon, West Orange, NJ) was administered for 3 days, and the dosage was increased or decreased (75 IU) at concentrations of ,100 pg/mL or of .200 pg/mL, respectively. Leuprolide was discontinued, and exogenous hCG was administered once development of two or more preovulatory follicles of $18 mm in mean diameter was confirmed as observed with serial transvaginal ultrasound examinations (5 Mhz, Model 3200; General Electric) but never after ,8 or .11 days of gonadotropin stimulation. Ultrasound-guided oocyte retrieval was performed 34 to 36 hours thereafter, and mock ET was performed 2 days after oocyte retrieval in all COH study cycles. Tissue specimens were divided at collection; one portion was fixed in 10% formalin for histologic examination, and the remainder was snap frozen in liquid nitrogen and stored at 280°C for later immunohistochemical analysis of integrin expression. Histologic endometrial maturation in endometrial tissue specimens was assessed by an experienced gynecological pathologist (D.B.N.) who was unaware of treatment conditions. Glandular and stromal development were dated separately according to the criteria of Noyes et al. (13). Maturation in each compartment was classified as delayed (,luteal day 6), normal (luteal day 6 –10), or advanced (.luteal day 10). The same criteria were applied in judging endometrial development overall with use of the most advanced date exhibited by either most of the glands or stroma. Glandular-stromal dyssynchrony was defined as a discrepancy of 3 or more days between the dates corresponding to the most advanced elements in the two compartments. Methods of immunohistochemical staining and analysis of integrin expression have been described previously in detail. A monoclonal antibody specific for the b3 subunit of the avb3 vitronectin receptor (SSA6) was used in these studies (14). Staining intensity in tissue sections was evaluated and graded in a blinded fashion by two examiners (1, weak; 2, moderate; 3, strong) and assigned an HSCORE calculated according to the following equation: HSCORE 5 S Pi(i11), where i 5 staining intensity and Pi 5 the percentage (0%–100%) of stained epithelial cells at each level of intensity. As previously reported, intraassay (r 5 0.983; P 5 .00001) and interassay (r 5 0.994; P 5 .00001) coefficients of variation using this technique in evaluating immuVol. 71, No. 1, January 1999



Characterization of endometrial samples obtained 8 days after either a urinary LH surge or hCG administration in 20 spontaneous and COH cycles of oocyte donors. Natural (spontaneous cycle)

Histologic day

Histologic glandular maturation in endometrial specimens from spontaneous and COH cycles of oocyte donors. ■, spontaneous cycles; h, COH cycles.

Controlled ovarian hyperstimulation cycle


Histologic day


Cycle no.







1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

7–8 11–12 2–3 4–6 3–5 7–8 8–9 3–5 9–10 5–6 6–7 8 3–4 11–12 3–5 9–10 9–10 11–12 7–8 7–8

7–8 11–12 8–9 9–10 8–9 7–8 8–9 8–9 9–10 7–8 6–7 7–8 6–7 11–12 7–8 9–10 9–10 11–12 7–8 7–8

0 1 0 0 0 1 1 0 1 0 1 1 0 1 0 1 1 0 0 0

4–5 4–6 2–3 3–5 5–6 2–3 5–8 2–5 3–5 3–5 7–8 3–5 3–5 7–8 4–6 5–6 2–3 10–11 3–5 3–5

9–10 8–9 8–9 7–9 9–10 9–10 8–9 8–9 9–10 8–9 7–8 7–8 7–8 7–8 9–10 10–11 7–8 10–11 8–9 7–8

0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0

Note: Cycles 5 and 6 were in the same donor; cycles 10 –20 received progesterone support.

acteristics. Histologic dates assigned to the most advanced glandular and stromal elements in all tissue specimens obtained from oocyte donors are shown in Table 1. In spontaneous cycles, glandular maturation was delayed in 5 of 20 specimens (25%), normal in 12 of 20 (60%), and advanced in the remaining 3 tissues (15%); stromal maturation was never delayed, normal in 17 of 20 (85%), and advanced in 3 specimens (15%). In the 3 spontaneous cycles in which glandular maturation was advanced, stromal development also was advanced and to the same extent (Figs. 1 and 2). In COH cycles, glandular development was delayed in 12 of 20 tissues (60%), normal in 7 of 20 (35%), and advanced

nohistochemical staining in endometrium are low. An HSCORE of #0.7 was not clearly distinguishable from negative controls and was used to define a “negative” result. Photomicrographs were made with Kodak Tmax 100 ASA film.


FIGURE 2 Histologic stromal maturation in endometrial specimens from spontaneous and COH cycles of oocyte donors. ■, spontaneous cycles; h, COH cycles.

Ten of 20 recipients (50%) matched with our oocyte donor subjects became pregnant after IVF of oocytes derived from studied COH cycles; pregnancy did not correlate with donor parity. Serum E2 concentrations on the day of exogenous hCG administration in progesterone-supplemented cycles (2,982 6 749 pg/mL) and nonsupplemented COH cycles (2,617 6 960 pg/mL) were not different (P ..05), and serum progesterone levels on that same day were uniformly of ,1.0 ng/mL.

Endometrial Histologic Characteristics in Oocyte Donors All 40 endometrial tissue specimens collected during our study demonstrated classic secretory phase histologic charFERTILITY & STERILITYt


in 1 specimen (5%); stromal maturation was again never delayed, normal in 18 of 20 (90%), and advanced in 2 tissue specimens (10%) (Fig. 1). Glandular maturation was delayed significantly more often (P ,.05) in COH cycles (12 of 20 [60%]) than in spontaneous cycles (5 of 20 [25%]). The characteristics of stromal development in spontaneous and COH cycles were not different (Figs. 1 and 2). Progesterone supplementation had little or no effect on glandular or stromal maturation in COH cycles. In unsupplemented COH cycles, glandular development was delayed in 6 of 9 (67%) and normal in 3 of 9 cycles (33%); stromal maturation was normal in all. In progesterone-supplemented COH cycles, glandular maturation was delayed in 6 of 11 (55%), normal in 4 of 11 (36%), and advanced in 1 cycle (9%); stromal development was normal in 9 of 11 (82%) and advanced in 2 cycles (18%). These differences were not statistically significant. Overall, not one of the tissue specimens obtained in any spontaneous or COH cycle was classified as delayed because the histologic date of the most advanced elements observed in either glands or stroma in any one tissue specimen was never less than luteal day 6. Seventeen of 20 specimens obtained in spontaneous cycles (85%) were histologically normal overall (histologic date of 6 –10 in the most advanced elements in either compartment), and 3 of 20 (15%) were advanced (histologic date of .10). In COH cycles, 18 of 20 tissues (90%) were normal overall, and 2 of 20 (10%) were advanced; both of these were obtained in progesteronesupplemented cycles. Again, progesterone supplementation had no significant effect on overall endometrial maturation in COH cycles. Tissue dating was normal in all 9 unsupplemented cycles and in 9 of 11 (82%) supplemented cycles; dating was advanced in 2 of 11 (18%) progesterone-supplemented COH cycles. As defined, dyssynchronous glandular and stromal endometrial development was a common finding. Dyssynchrony was observed in 22 of 40 cycles (55%) overall but was identified significantly more often (P ,.05) in COH cycles (16 of 20 [80%]) than in spontaneous cycles (6 of 20 [30%]). The rather high incidence of dyssynchrony we observed was generally attributable to delayed glandular development. In 17 of 22 (77%) dyssynchronous specimens overall, 5 of 6 (83%) obtained in spontaneous cycles and 12 of 16 (75%) in COH cycles, glandular development was delayed by 3 or more days, and stromal maturation was appropriate. Of the remaining 5 (23%) dyssynchronous specimens, both glandular and stromal development were normal by definition (histologic date 6 –10) in 4 (1 spontaneous cycle and 3 COH cycles); glandular maturation was normal and stromal development advanced (histologic date of .10) in 1 (COH) cycle. In all six oocyte donors who had glandular-stromal dyssynchrony in a spontaneous cycle, endometrial development was again dyssynchronous in the COH cycle that immediately followed. In the one oocyte donor studied in two 112

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separate pairs of spontaneous and COH cycles, both the spontaneous and COH cycle specimens were dyssynchronous in her first cycle, whereas endometrial development was synchronous in the spontaneous cycle but dyssynchronous after COH in the second.

Endometrial Glandular Integrin Expression Results of immunohistochemical analysis of endometrial glandular avb3 integrin expression in spontaneous and COH cycles are shown in Table 1. Glandular expression of avb3 was detected in 9 of 20 specimens (45%) obtained in spontaneous cycles but in only 2 of 20 tissues (10%) derived from COH cycles (P ,.05). In spontaneous cycles, avb3 expression was demonstrable in 9 of 15 tissue specimens (60%) in which the most advanced glandular elements were assigned a histologic date of luteal day 6, the earliest histologic date corresponding to the interval during which b3 is normally expressed (14). Absent avb3 expression was not altogether surprising in 2 of the other 6 specimens that met these criteria, given that glandular development was not uniform and included elements that were significantly less histologically mature. Of the remaining 4 specimens meeting these criteria, however, the most immature glandular elements were consistent with luteal day 7 in 3 tissues and luteal day 11 in one other. In COH cycles, the most advanced glandular elements were consistent with luteal day $6 in only 8 of 20 tissue specimens (40%); in the remaining 12, no glands had matured to this extent or beyond.

DISCUSSION It seems clear that the two factors having the greatest influence on the results achieved with IVF are embryo quality and endometrial receptivity. Available data suggest that endometrial histology in COH cycles has some unusual features, but the clinical relevance of these observations is uncertain. We examined the effects of COH on the endometrium by directly comparing the histologic characteristics and patterns of integrin expression in tissue specimens obtained in paired spontaneous and COH cycles in a group of healthy young volunteer oocyte donors in whom the prevalence of intrinsic endometrial dysfunction should be negligible. Our study group is more homogeneous than are infertile patients and one that typically exhibits less variable patterns of response to COH than are seen in an infertile population. Given our interest in the effects of COH on preimplantation endometrial development, we obtained all tissue specimens 8 days after the LH surge or exogenous hCG administration in spontaneous and COH cycles, respectively (15). Consistent with traditional diagnostic criteria, we defined endometrial maturation as normal when the most advanced elements in either the glands or stroma were assigned a histologic date within 2 days of the known day of sampling Vol. 71, No. 1, January 1999

and considered delayed only those in which maturation was 3 or more days behind in both compartments (13). It is surprising that, in contrast with earlier reports (16, 17), none of the specimens we obtained in any spontaneous or COH cycle met these latter criteria. Others have described delayed but synchronous endometrial development in midluteal phase endometrial specimens obtained in COH cycles that could not be corrected with either exogenous progesterone supplementation or hCG stimulation (18). Although our contrasting results may reflect only the inherent subjectivity of endometrial dating or differences attributable to the day of sampling, it is possible that previous observations derived from treatment cycles in infertile patients may reflect the influence of the confounding variables we specifically sought to avoid in our study in normal young women (16, 19). In the absence of any established definition, we defined endometrial dyssynchrony as a discrepancy of 3 or more days between the histologic dates assigned to the most advanced elements of glandular and stromal development, criteria that are consistent with the principles traditionally applied in evaluating the extent of endometrial maturation (13). Given that our criteria for endometrial dyssynchrony were designed to detect only relatively gross differences in maturation between the two compartments, we were surprised to observe dyssynchronous endometrial development in more than half of the specimens we examined. As defined, dyssynchrony was an extremely common feature of endometrium obtained after COH, one we observed in 80% of oocyte donation cycles and almost uniformly resulted from delayed glandular development; stromal maturation progressed normally in all but a few specimens. Although our findings might suggest that COH directly or indirectly interferes with the normal progress of secretory endometrial development, the fact that endometrial dyssynchrony was also relatively common in spontaneous cycles (30%) suggests an alternative interpretation. It is possible that endometrial dyssynchrony may not reflect intrinsic or drug-induced pathology at all and that our observations provide evidence that the spectrum of normal variation in midsecretory phase endometrial histology may be broader than previously recognized. Separate evaluations of maturation in the endometrial glands and stroma, as though they were distinctly different tissues, are a relatively new practice and a by-product of the more intense scrutiny patterns of endometrial development have received since the advent of donor oocyte recipiency. Endometrial dyssynchrony may not, in fact, represent an abnormal pattern of maturation. Its prevalence in cycles of healthy young women has not been investigated previously. We, like other investigators, initially attributed the high frequency of endometrial dyssynchrony we observed in unsupplemented COH cycles to deficient steroid production FERTILITY & STERILITYt

resulting from our use of a long-acting GnRH agonist and residual effects of pituitary down-regulation (18). However, in contrast to earlier reports, addition of exogenous progesterone supplementation did not reduce or eliminate this presumed abnormal pattern of endometrial maturation (20). Our decision not to initiate progesterone treatment until after oocyte retrieval may explain this observation. Bourgain et al. (20) began treatment before oocyte retrieval, and DeZiegler et al. (21) reported that treatment with small doses of exogenous progesterone over the last few days of the follicular phase can synchronize glandular and stromal maturation in IVF stimulation cycles and in donor oocyte recipients receiving a programmed sequential regimen of exogenous estrogen and progesterone. Because of our observations in spontaneous cycles and the generally high success rates widely achieved in donor oocyte recipiency cycles (in which endometrial dyssynchrony is an extremely common if not characteristic feature), the clinical relevance of midsecretory phase endometrial dyssynchrony and the importance of “correcting” this pattern of development are unclear (22). Endometrial expression of the avb3 vitronectin receptor has emerged as a useful marker of endometrial receptivity. It correlates closely with endometrial histology and, with few exceptions, first appears in the glandular epithelium at some time within the putative implantation window, generally regarded as postovulatory days 6 –10 (14). Our analysis of avb3 expression was intended as a means to identify potential functional consequences of COH that might escape detection with histologic evaluation alone, but the unexpectedly high prevalence of delayed glandular maturation we observed in COH cycles limited our ability to address this possibility. In 16 of 20 specimens (80%) obtained in COH cycles, histologic maturation in the most advanced elements of the glandular epithelium did not exceed postovulatory day 6, the earliest point at which avb3 expression might be detected, and was sufficiently advanced to have clearly expected its expression in only one of the remaining four specimens (14). Consequently, we were unable to determine whether COH was associated with any functional uncoupling of histologic development and epithelial integrin expression. In spontaneous cycles, avb3 expression was detected in 9 of 15 specimens in which glandular development reached at least postovulatory day 6. Glandular histology reached or exceeded postovulatory day 10, the latest date by which avb3 expression would be expected, in only one of the remaining 6 specimens (14). These observations suggest that later sampling would be a more sensitive method for detecting any functionally important temporal shift in the implantation window resulting from COH or any other form of treatment. In summary, the results of our study demonstrate that 113

dyssynchronous glandular and stromal development is a common feature of the implantation phase endometrium in COH cycles, regardless of whether exogenous progesterone supplementation is provided. Although COH clearly appears to predispose to delayed glandular maturation and endometrial dyssynchrony, our observations that similar patterns of histologic development are observed frequently in spontaneous ovulatory cycles in healthy young women suggest that such patterns may reflect only a wider range of normal variation than previously recognized and question its functional significance. References 1. Van Steirteghem AC, Nagy Z, Joris H, Lie J, Staessen C, Smitz J, et al. High fertilization and implantation rates after intracytoplasmic sperm injection. Hum Reprod 1993;8:1061– 6. 2. Cohen J, Alikani M, Trowbridge J, Rosenwaks Z. Implantation enhancement by selective assisted hatching using zona drilling of human embryos with poor prognosis. Hum Reprod 1992;7:685–91. 3. Paulson RJ, Sauer MV, Lobo RA. Factors affecting embryo implantation after human in vitro fertilization—a hypothesis. Am J Obstet Gynecol 1990;163:2020 –3. 4. Sharma V, Whitehead M, Mason B, Physe-Davies J, Ryder T, Dorsett M, et al. Influence of superovulation on endometrial and embryonic development. Fertil Steril 1990;53:822–9. 5. Ben-Nun I, Jaffe R, Fergin MD, Beyth Y. Therapeutic maturation of endometrium in in vitro fertilization and embryo transfer. Fertil Steril 1992;57:953– 62. 6. Macrow PJ, Li TC, Seif MW, Buckley CH, Elstein M. Endometrial structure after superovulation: a prospective controlled study. Fertil Steril 1994;61:696 –9. 7. Good RG, Moyer DL. Estrogen-progesterone relationships in the development of secretory endometrium. Fertil Steril 1968;19:37– 49. 8. Toner JP, Hassiakos DK, Muasher SJ, Hsiu JG, Jones HW Jr. Endometrial receptivities after leuprolide suppression and gonadotropin stimulation: histology, steroid receptor concentrations, and implantation rates. Ann NY Acad Sci 1991;620:220 –9. 9. Navot D, Laufer N, Kopolovic J, Rabinowitz R, Birkenfeld A, Lewin A, et al. Artificially induced endometrial cycles and establishment of pregnancies in the absence of ovaries. N Engl J Med 1984;314:806 –11.


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10. Paulson RJ, Sauer MV, Francis MM, Macaso TM, Lobo RA. In vitro fertilization in unstimulated cycles: a clinical trial using hCG for timing of follicle aspiration. Obstet Gynecol 1990;76:788. 11. Benadiva CA, Metzger DA. Superovulation with human menopausal gonadotropins is associated with endometrial gland-stroma dyssynchrony. Fertil Steril 1994;61:700 – 4. 12. Garcia JE, Acosta AA, Hsiu J-C, Jones HWJ. Advanced endometrial maturation after ovulation induction with human menopausal gonadotropin/human chorionic gonadotropin for in vitro fertilization. Fertil Steril 1984;41:31–5. 13. Noyes RW, Hertig AI, Rock J. Dating the endometrial biopsy. Fertil Steril 1950;1:3–25. 14. Lessey BA, Damjanovich L, Coutifaris C, Castlebaum A, Albelda SM, Buck CA. Integrin adhesion molecules in the human endometrium: correlation with normal and abnormal menstrual cycle. J Clin Invest 1992;90:188 –95. 15. Li TC, Cooke ID. Evaluation of the luteal phase. Hum Reprod 1991; 6:484 –99. 16. Graf MJ, Reyniak JV, Battle-Mutter P, Laufer N. Histological evaluation of the luteal phase in women following follicle aspiration for oocyte retrieval. Fertil Steril 1988;49:616 –9. 17. Frydman R, Testart J, Giacomini P, Imbert MC, Martin E, Nahoul K. Hormonal and histological study of the luteal phase in women following aspiration of the preovulatory follicle. Fertil Steril 1982;38:312–7. 18. Van Steirteghem AC, Smitz J, Camus M, Van Waesberghe L, Deschacht J, Khan I, et al. The luteal phase after in vitro fertilization and related procedures. Hum Reprod 1988;3:161– 4. 19. Reshef E, Segavs JH, Hill GA, Pridham DD, Yussman MA, Wentz AC. Endometrial inadequacy after treatment with human menopausal gonadotropin/human chorionic gonadotropin. Fertil Steril 1990;54:1012– 6. 20. Bourgain C, Smitz J, Camus M, Erard P, Devroey P, Van Steirteghem AC, et al. Human endometrial maturation is markedly improved after luteal supplementation of gonadotropin-releasing hormone analogue/ human menopausal gonadotrophin stimulated cycles. Hum Reprod 1994;1:32– 40. 21. DeZiegler D, Fanchin R, Massonneau M, Bergeron C, Frydman R, Bouchard P. Hormonal control of endometrial receptivity: the egg donation model and controlled ovarian hyperstimulation. Ann NY Acad Sci 1994;734:209. 22. Navot D, Anderson TL, Droesch K, Scott RT, Kneiner D, Rosenwaks Z. Hormonal manipulation of endometrial maturation. J Clin Endocrinol Metab 1989;68:801–7.

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