A prospective controlled study of luteal and endometrial abnormalities in an infertile population*+

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1 FERTILITY AND STERILITY Copyright '{' 1996 American Society for Reproductive Medicine Printed on acid-free paper in U. S. A. A prospective controlled study of luteal and endometrial abnormalities in an infertile population*+ Marcelo C. Batista, M.D.:j: Tannia P. Cartledge, R.N.II Ann W. Zellmer, R.N.II Maria J. Merino, M.D. ~ Lynnette K. Nieman, M.D.:j:** D. Lynn Loriaux, M.D., Ph.D.:j:tt George R. Merriam, M.D.:j: National Institute of Child Health and Human Development, Warren Grant Magnuson Clinical Center, and National Cancer Institute, National Institutes of Health, Bethesda, Maryland Objective: To investigate whether luteal and endometrial abnormalities occur more frequently in an infertile population and thus contribute to infertility. Design: Prospective controlled clinical study. Setting: Outpatient clinic in an academic research institution. Participants: Thirty-three fertile controls and 31 infertile women without ovulatory disorders, tubal disease, or male factors. Interventions: All women underwent an endometrial biopsy 9 days after the LH surge followed by an 1M injection of 5,000 IV hcg. Blood samples were drawn immediately before hcg administration for serum P and placental protein 14 (PP14) measurements, at 6 hours after hcg stimulation for serum P concentrations, and on day 5 after hcg administration for serum PP14 levels. Main Outcome Measures: Histologic dating of the endometrium and serum P and PP14 measurements. Results: Abnormal endometrial biopsies occurred more frequently in infertile (43%) than in fertile women (9%). Except for one case, these specimens were not associated with low hcgstimulated P levels. Serum PP14 measurements varied widely and did not discriminate subjects with abnormal endometrial development. Conclusions: Disruption of endometrial maturation without a concomitant defect of the corpus luteum occurs more frequently in an infertile population and thus may contribute to infertility. Fertil Steril 1996; 65: Key Words: Endometrial biopsy, progesterone, placental protein 14, human chorionic gonadotropin Progesterone is the major hormone secreted by the corpus luteum (el) throughout the second half of the menstrual cycle (1). Its main function is to induce the differentiation of the endometrium in preparation for nidation (1). If either P is not produced in sufficient amounts or the endometrium is not capa- Received May 13, 1994; revised and accepted August 4, * Supported in part by grant /88.4, Conselho Nacional de Desenvolvimento Cientifico e Tecnol6gico, Brasilia, Brazil and by a grant from Serono Laboratories, Norwell, Massachusetts. t Presented in part at the 74th Annual Meeting of The Endocrine Society, San Antonio, Texas, June 24 to 27, :j: Developmental Endocrinology Branch, National Institute of Child Health and Human Development. Present address: Department of Endocrinology, Hospital das Clinicas, University of Sao Paulo, Sao Paulo, Brazil. II Nursing Department, Warren Grant Magnuson Clinical Center. ~ Laboratory of Pathology, Division of Cancer Biology and Diagnostics, National Cancer Institute. ** Reprint requests: Lynnette K. Nieman, M.D., National Institutes of Health, Building 10, Room 10N262, Bethesda, Maryland (FAX: ). tt Present address: Division of Endocrinology and Metabolism, Oregon Health Sciences University, Portland, Oregon. Present address: Research and Development Service, American Lake Division, Seattle/American Lake VA Medical Center, and Division of Endocrinology, University of Washington School of Medicine, Seattle, Washington. Batista et al. Luteal and endometrial abnormalities 495

2 ' ble of a normal response to P stimulation, the development of the endometrium may not be adequate to sustain implantation of an embryo, leading perhaps to infertility or habitual abortion (1, 2). Abnormalities of the CL and endometrium have been proposed as possible causes of infertility (1, 2). If they contribute significantly to infertility, one would expect them to occur at a higher frequency in infertile than in fertile women. Unfortunately, previous studies addressing this question have yielded conflicting results, perhaps because of the different methodologies used (3-7). Whereas one group reported that abnormal development of the endometrium is more common in an infertile population (3, 4), suggesting that this condition may contribute to infertility, other investigators found no differences between infertile and normal subjects (5-7). Thus, the role of luteal and endometrial abnormalities in the pathogenesis of infertility remains unsettled. To investigate whether luteal and endometrial abnormalities occur more frequently in an infertile population and thus contribute to infertility, we examined endometrial histology, and also CL and endometrial secretory function, in similar groups offertile and infertile women. Endometrial maturation was evaluated by the traditional and most widely used method of histologic dating of an endometrial biopsy according to the criteria of Noyes et al. (8). The functional capacities of the CL and endometrium were assessed by performing an hcg stimulation test in the midluteal phase (9). This new approach consists of a single 1M injection ofhcg given on day 9 after the LH surge, followed by serum measurements ofp and placental protein 14 (PPI4), the main secretory products ofthe CL and endometrium, respectively (1, 10). Human chorionic gonadotropin is a potent luteotrophic factor that acts through the LH receptor to promote P secretion (11). Progesterone, in turn, is required for the differentiation of the endometrium and induction of PPI4, a major glycoprotein synthesized by the secretory endometrium and early gestational decidua (10). In spontaneous cycles, serum PP14 levels start to increase in the midluteal phase, when P concentrations are maximal, and peak just before the onset of next menses (10). Because LH and hcg receptors recently have been described in endometrial and decidual cells, it is possible that hcg also may exert direct effects on the endometrium to stimulate PP14 secretion (12). Subjects MATERIALS AND METHODS Thirty-three healthy fertile women were recruited for the control fertile group. All underwent a thor- ough history and physical examination before entering the study to exclude any disease that might impact on their fertility. Their ages ranged from 23 to 48 years (36.1 :::'::: 7.7 years; mean:::'::: SD); 18 subjects were 2:35 years. Their weight varied from 45 to 94 kg (65.2 :::'::: 11.2 kg) or from 85% to 111% of ideal value according to the 1983 Metropolitan height and weight tables (13). All had regular menstrual cycles,,0; 35 days and reported at least one spontaneous pregnancy in the past. None had a prior history of primary or secondary infertility or habitual abortion. Likewise, none had used steroid contraception or intrauterine devices during the previous 3 months. All subjects had completely normal hematologic, renal, and liver function tests. Whenever there was a clinical suspicion of hyperprolactinemia or thyroid dysfunction, PRL measurements and thyroid function tests were ordered to exclude these diseases. Thirty-one infertile women volunteered for this study. All underwent a thorough history and physical examination and a complete review of their past medical records before entering the study. This initial evaluation was carried out by the principal investigator (M.C.B.) and also by a board-certified reproductive endocrinologist. Most women had had an extensive infertility evaluation performed elsewhere and were referred to the National Institutes of Health (Bethesda, MD) primarily to participate in this protocol. Whenever the infertility evaluation was judged incomplete, additional tests were ordered in our clinic to clarify the diagnosis. In a few subjects, the infertility evaluation was done totally in our service. The age of the infertile group ranged from 23 to 43 years (36.4 :::'::: 4.5 years); 21 subjects were 2:35 years. The weight varied from 43 to 90 kg (63.6 :::'::: 11.2 kg) or from 87% to 120% of ideal value according to the 1983 Metropolitan height and weight tables (13). All had primary or secondary infertility of 2: 1 year duration; regular menstrual cycles,,0; 35 days, with ovulation confirmed by a luteal plasma P level> 5 ng/ml (16 nmolll); normal hematologic, renal, and liver function tests; normal PRL measurements and thyroid function tests (ordered in women with a clinical suspicion of hyper prolactinemia or thyroid dysfunction); normal semen analysis of the partner according to previously described criteria (14); and normal patent tubes without adhesions, as documented by normal hysterosalpingogram and laparoscopy. Thus, only women who did not have a major cause of infertility such as oligoovulation or anovulation, tubal disease, or male factors were selected so as to recruit a population at high risk for deficient luteal phases. Nine patients had mild endometriosis, eight subjects had abnormal postcoital tests, and four had positive antisperm 496 Batista et al. Luteal and endometrial abnormalities Fertility and Sterility

3 antibodies. They were not excluded from the study because these are minor and controversial causes of infertility and may be found in conjunction with luteal and endometrial abnormalities. The study was approved by the Clinical Research Subpanel of the National Institute of Child Health and Human Development. Informed consent was obtained from each subject. All women were urged strongly to use barrier methods or to abstain from sexual intercourse during the study. They were advised specifically that, should pregnancy occur during the study cycle, it would not be detected before the day ofthe biopsy and thus it could be terminated by this procedure. Pregnancy was excluded by a plasma,b-hcg concentration $ 2 ng/ml (the detection limit for pregnancy in this assay) at the beginning and end of the study cycle. Protocol The study was conducted over one menstrual cycle. Blood or urine were collected daily at 8:00 to 10:00 A.M. starting on cycle day 6 to 10 and continuing until the LH surge was detected, using a rapid plasma assay or a home urinary ovulation prediction kit (OvuQuick; Monoclonal Antibodies, Mountain View, CA). This kit shows an excellent correlation with blood LH determinations in defining the day of the LH surge (15). To confirm the day of the LH peak, women who used urinary kits also had blood drawn for rapid LH measurements on the day(s) of a rise in urinary LH excretion. Thus, whenever the kit turned positive on ~2 days, blood determinations helped define the day of the highest LH level. An endometrial biopsy and hcg stimulation test were scheduled prospectively and performed 9 days after the LH peak to coincide with the time of maximal P and PP14 responses to hcg stimulation in the luteal phase (9). On this day, women reported to the outpatient clinic at 8:00 to 10:00 A.M. and first underwent the biopsy. Mter this procedure, they received an IM injection of 5,000 IV hcg (LyphoMed, Inc., Melrose Park, IL), which results in supra physiologic levels ofthis hormone (11). Blood samples were drawn immediately before hcg administration for serum P and PP14 measurements, at 6 hours after hcg stimulation for serum P concentrations, and on day 5 after hcg administration for serum PP14 levels. Endometrial Biopsy An endometrial biopsy was obtained from the uterine fundus using the Pipelle (Prodimed, Neuilly-en TheIle, France), as described in detail elsewhere (16). At the end of the study, all slides were reviewed independently by two pathologists who were blinded to the group (i.e., fertile or infertile) and to the day ofthe cycle when the biopsy was obtained. Histologic dates were assigned according to the criteria of Noyes et al. (8), using a 2-day reading, e.g., secretory day 22 to 23 (16). An overall histologic date could not be assigned when the glandular and stromal parts of the specimen were at very different stages of endometrial maturation (dysynchronous pattern) or when the endometrium was infiltrated with inflammatory cells suggesting endometritis (inflammatory pattern). Chronological dating of the biopsy was done prospectively, by counting forward from the day of the LH surge (taken as cycle day 14) until the day ofthe biopsy (16). Endometrial maturation was evaluated by correlating the chronological date with the most advanced histologic date of the biopsy (i.e., day 23 if the histologic reading was day 22 to 23), in keeping with Noyes et al.'s (8) recommendation that dating should rely primarily on the morphology of the most advanced portion or feature of the endometrium. The development of the endometrium was considered abnormal when the histologic dating lagged > 2 days behind the chronological dating of the biopsy (delayed pattern) or when the endometrial pattern was dysynchronous or inflammatory (2). Hormone Measurements Plasma LH levels were measured by a commercial RIA kit (Diagnostic Products Corporation, Los Angeles, CA). Serum P concentrations were determined by RIA after extraction of the samples (16). Serum PP14 levels were measured by RIA following the method of Bolton et al. (17), with minor modifications (18). Radioiodination of PP14 (lot no. 120/ 135; Behringwerke AG, Marburg, Germany) was carried out with lactoperoxidase, followed by purification of the tracer over Sephadex and concanavalin A-Sepharose columns. The anti-pp14 antibody (lot no. 201ZA; Behringwerke AG) was used at a final dilution of 1:40,000. Bound and free radioactivity were separated by adding goat anti-rabbit y-globulin antiserum and polyethylene glycol. The detection limit was 0.1 to 0.2 ng/ml (0.3 to 0.6 nmolll) for P and 2.0 to 5.9 ng/ml for PP14. The intra-assay and interassay coefficients of variation (CV s) were $11% and $16% for P and $9% and $17% for PP14. Inconsistencies in the extraction of P samples and the presence of a variable serum effect in the PP14 assay prevented the achievement oflower CVs. Progesterone levels after hcg stimulation were considered abnormal when they failed to exceed 11 ng/ml (35 nmolll), which was the lowest value found in our previous study of normal, fertile women Batista et al. Luteal and endometrial abnormalities 497

4 Table 1 Duration of the Follicular and Luteal Phases and of the Entire Menstrual Cycle in Women Grouped According to Reproductive History or Endometrial Histology*t Group Follicular phase Fertile women (n = 33) 14.6 ± 2.8 Infertile women (n = 30) 14.5 ± 3.1 Normal biopsy (n = 47) 14.3 ± 2.6 Abnormal biopsy (n = 16) 15.4 ± 3.7 Luteal phase d 15.7 ± ± ± ± 1.2 Cycle length 30.4 ± ± ± ± 3.8 * Values are means ± SD; n = 63. There were no significant differences between groups by unpaired two-tailed t-tests. t All subjects underwent an endometrial biopsy followed by 1M administration of 5,000 IV hcg on day 9 after the LH surge. aged 23 to 38 years (9). Because those subjects exhibited inconsistent and highly variable PP14 concentrations after hcg administration, no similar cutoff limit for PP14 could be defined (9). Analysis The follicular phase was defined as the days elapsed from the onset of menses until (and including) the day of the LH peak. The luteal phase was defined as the days after the LH peak until the day before next menses. Results are presented as means ± SD. Comparison of means was carried out by paired or unpaired two-tailed t-tests. Differences in the frequency ofluteal and endometrial abnormalities in fertile and infertile women were evaluated by X 2 analysis. A P value < 0.05 was considered significant. RESULTS An infertile woman became pregnant during the study cycle and therefore was excluded from all data analysis. She had a normal P response (28.4 nglml [90 nmol/ld and a rising PP14 concentration (69.5 nglml) after hcg stimulation, as well as a normal endometrial biopsy (2-day lag between histologic and chronological dating). Cycle Length The durations of the follicular and luteal phases and of the entire menstrual cycle were similar in fertile and infertile women (Table 1). Likewise, no differences were seen in these parameters in subjects with normal endometrial specimens compared with those with abnormal biopsies (i.e., delayed, dysynchronous, and inflammatory patterns; Table 1). Endometrial Maturation All biopsies showed secretory endometrium in the fertile and infertile groups, confirming that ovulation occurred in every single study cycle. Histologic patterns of endometrial maturation (normal, delayed, dysynchronous, or inflammatory) were identical in 84% of women, as assigned by two pathologists. Because of the high agreement between the two pathologists, all data analyses presented below rely on the readings provided by only one pathologist (M.J.M.). Conclusions did not vary if the readings provided by the other pathologist were used instead. To analyze the frequency of endometrial abnormalities in the fertile and infertile groups, biopsies were classified as either normal or abnormal. The latter included all delayed, dysynchronous, and inflammatory specimens. Abnormal biopsies occurred at a significantly higher frequency in infertile than in fertile women (13 versus 3 cases or 43% versus 9%; P < 0.01; Fig. 1). These abnormalities were equally common in infertile subjects < or ~35 years (four versus nine cases or 44% versus 43%; P > 0.05). Human Chorionic Gonadotropin Stimulation Test In the fertile group, P levels were higher at 6 hours after hcg stimulation compared with basal determinations (Table 2). Placental protein 14 concentrations also were increased in these women on day 5 after hcg administration (Table 2). In the infertile group, P levels were higher (Le., not lower as expected) than in fertile women, both at baseline and at 6 hours after hcg (P < 0.01, Table 2). Deficient P responses to hcg stimulation (P :5 11 ng/ml [35 nmol/ld occurred at a similar low frequency in fertile and infertile women (three versus one case or 9% versus 3%; P > 0.05, power = 0.15; Fig. 2). In both populations, subnormal P responses were seen only in subjects ~ 35 years. There was a poor correlation between P responses to hcg stimulation and the results of the endometrial biopsy (Fig. 2). Only 1 of 15 subjects with delayed or dysynchronous patterns of endometrial maturation had reduced P concentrations after hcg (3.0 ng/ml [10 nmol/ld; she was a 48-year-old fertile woman who had a severe delay in endometrial development in the study cycle (6-day lag between histologic and chronological dating). A similar pattern was observed in an infertile woman who was excluded from this study because of tubal disease; she also had a subnormal P response to hcg stimulation (5.5 nglml [17 nmol/l]) in association with severely retarded endometrium (7-day lag). In contrast, in other women with significant delays in endometrial maturation (lag of 4 to 6 days), hcg-stimulated P 498 Batista et al. Luteal and endometrial abnormalities Fertility and Sterility

5 til 4 Q) "in 2 c. 0 "-m Q).c 12 E ::l Z Fertile o Oys Inf Infertile Oys Inf Histologic - Chronologie Dating (days) Table 2 Serum P and PP14 Levels in Fertile and Infertile Women Given an 1M Injection of 5,000 IU hcg on Day 9 Mter the LH Surge*t Group Before hcg Pi: 6 hours after hcg Before hcg PP14 5 days after hcg ng/ml ng/ml Fertile (n = 33) 9.5 :+: :+: :+: :+: 34.0 Infertile (n = 30) 15.9:+: :+: :+: 65.9~ * Values are means:+: SD. t Blood samples were drawn immediately before hcg administration for serum P and PP14 measurements, at 6 hours after hcg stimulation for serum P concentrations, and on day 5 after hcg administration for serum PP14 levels. i: Conversion factor to SI unit, Significantly different compared with basal determinations (P < 0.01 by paired two-tailed t tests). II Significantly different compared with fertile women (P < 0.01 by unpaired two-tailed t-tests). ~ Significantly different compared with fertile women (P < by unpaired two-tailed t-tests). The main controversy resides on whether these defects occur more frequently in infertile than in fertile women and as such contribute to infertility (3-7). Delayed maturation of the endometrium, perhaps resulting from a defective CL, has been reported to occur occasionally in as many as 20% to 31 % of cycles of fertile women (20, 21), raising concern as to the clinical significance of these findings. It is possible that in normal subjects these abnormalities only occur in sporadic cycles, whereas in infertile women they recur every month, thus leading to infertility. In this case, the probability of detecting these abnor- Figure 1 Frequency distribution of the difference between histologic and chronological dating of endometrial biopsies obtained 9 days after the LH surge in 33 fertile and 30 infertile women. Endometrial maturation was considered normal (.), delayed (!fjl), dysynchronous (D), or inflammatory (l1li) by criteria described in the text. levels were completely normal, ranging from 27.2 ng/ml (86 nmolll) to 34.7 ng/ml (110 nmolll). Placental protein 14 concentrations were higher in infertile than in fertile women at the end of the luteal phase, i.e., on day 5 after hcg administration (Table 2). However, PP14 levels varied widely in women with normal and abnormal endometrial maturation and did not distinguish clearly between these two groups (Fig. 3). DISCUSSION Corpus luteum and endometrial abnormalities are possible but unproven causes of infertility (2, 19) oo~oo i~~8 ~8g8 0 8~ Fertile Infertile Figure 2 Serum P levels in 33 fertile and 30 infertile women with normal (0) or abnormal (e) endometrial biopsies 6 hours after 1M administration of 5,000 IU hcg given on day 9 after the LH surge. The dashed line across the graph indicates the cutoff limit for normal P responses to hcg stimulation (11 ng/ml [35 nmolll]). Conversion factor to SI unit, Batista et al. Luteal and endometrial abnormalities 499

6 -..J e 250 en c 200 -~, cx:pcp ~ Fertile o o :4m Infertile Figure 3 Serum PP14 levels in 31 fertile and 30 infertile women with normal (0) or abnormal (.) endometrial biopsies 5 days after 1M administration of 5,000 IU heg given on day 9 after the LH surge. malities in a particular cycle most likely would be higher in an infertile population with persistent defects of this kind than in normal subjects with only occasional deficiencies of the luteal phase. Thus, one would expect a higher rate ofluteal and endometrial abnormalities in single cycles of infertile women compared with those of fertile women. To address this question, we compared the frequency of these defects in single cycles offertile and infertile women. To confirm the presence of persistent luteal phase defects in our subjects, an additional menstrual cycle would need to be evaluated, because this condition traditionally is diagnosed by examining endometrial histology in two consecutive menstrual cycles as opposed to only one study cycle in the present trial. Our two study groups, albeit not exactly matched, had very similar mean ages and weights. To maximize the chance of detecting a difference between these two populations, we only recruited infertile women who did not have a defined cause of infertility such as oligo-ovulation or anovulation, tubal disease, or male factors. The inclusion of patients with the latter conditions could obscure our results, because they are much more common than luteal and endometrial abnormalities (14). The development of the endometrium was evaluated by the traditional and widespread method of histologic dating of an endometrial biopsy according to the criteria of Noyes et al. (8). All specimens were obtained before hcg stimulation on day 9 after the LH surge to avoid any effect of this compound on endometrial maturation. In addition, this approach helped reduce imprecisions that could result from the histologic reading of biopsies performed on different days ofthe luteal phase. Although some inves- tigators prefer to perform an endometrial biopsy as late as possible in the luteal phase, others have reported that histologic dating is more precise and agrees more closely with chronological dating when specimens are obtained in the midluteal phase, as was done in this study (22, 23). The latter view is corroborated by the fact that our two pathologists agreed on the histologic pattern of endometrial maturation in a high percentage (84%) of biopsies. Another step taken to improve the accuracy of our dating method was to assign chronological dates prospectively from the day of the LH surge rather than retrospectively from the onset of next menses (16, 24). Use of the latter approach could introduce errors in the interpretation of our biopsy data, because hcg may prolong the luteal phase and thus artificially retard the onset of next menses (9), the reference point for retrospective dating (16,24). Histologic abnormalities of the endometrium occurred at a significantly higher frequency in infertile than in fertile women (43% versus 9%). These abnormalities most often were due to delayed or dysynchronous maturation of the endometrium, although chronic inflammation was the primary finding in one case. The proportion of abnormal biopsies (9%) seen in our fertile group was lower than the 20% or 31% figure previously reported in the literature (20, 21). These numbers, however, are not precisely comparable because of the different approaches used to obtain and interpret endometrial specimens. Our results suggest that disruption of endometrial maturation, as diagnosed by histologic dating of a midluteal phase endometrial biopsy according to the widespread criteria of Noyes et al. (8), occurs more frequently in an infertile population and thus may playa significant role in infertility. They validate the usefulness of this procedure to assess endometrial development in the course of an infertility evaluation. Our data are in agreement with those reported by Li et al. (3), who used morphometric analysis and found a higher proportion of endometrial abnormalities in single cycles of infertile women compared with those of fertile women. Our results and those of Li et al. (3) argue against the findings of Balasch et al. (5) and Peters et al. (7), who reported that abnormal biopsies, as diagnosed by Noyes et al.'s (8) criteria in single or multiple cycles, are equally common in fertile and infertile women. A new method, the hcg stimulation test, was used in the present study to evaluate the functional capacity of the CL and endometrium. Deficient P responses to hcg (P :s; 11 ng/ml [35 nmollld occurred at a similar low frequency in the fertile and infertile groups (9% versus 3%). This finding, associated with the fact that P levels measured before and after hcg 500 Batista et ai. Luteal and endometrial abnormalities Fertility and Sterility

7 were unexpectedly higher in infertile than in fertile women, suggests that functional defects of the CL do not commonly contribute to infertility. Progesterone responses to hcg stimulation correlated poorly with endometrial histology. This is not surprising considering that a midluteal phase endometrial biopsy does not correlate well even with the integrated P secretion (16), the gold standard for the evaluation ofluteal function (2). Only 1 of 15 subjects with delayed or dysynchronous biopsies (and an additional patient with retarded endometrium who was excluded from this study because of tubal disease) had reduced P concentrations after hcg administration. Both exhibited major delays in endometrial maturation and had perhaps more severe defects of the CL that could not be overcome by the supra physiologic stimulus provided by hcg. It is possible that in several of our other patients with abnormal biopsies the endometrium was resistant to P stimulation and thus developed at a slower rate even in the presence of high P levels. Alternatively, an additional factor besides P, which could be missing in women with abnormal endometrial maturation, may be necessary for the full development of the endometrium. Serum PP14 levels were higher in infertile than in fertile women after hcg administration, although this difference barely reached statistical significance (P = 0.049). Because PP14 is a glycoprotein produced by the secretory endometrium in response to P stimulation (10), increased PP14 concentrations may have been induced by the elevated P levels seen in the infertile group. Unfortunately, PP14 responses to hcg overlapped substantially in subjects with normal and abnormal endometrial biopsies, suggesting that this parameter does not reflect accurately histologic maturation of the endometrium. These results contrast with those reported by Joshi et al. (25), who found lower basal serum levels of progestagen-dependent endometrial protein, a glycoprotein immunologically identical to PP14 (10), in infertile women with delayed endometrial development. In summary, histologic abnormalities of the endometrium, as diagnosed by a midluteal phase endometrial biopsy dated according to the widespread criteria of Noyes et al. (8), occur at a higher frequency in infertile than in fertile women and thus may playa significant role in infertility. They usually are not associated with functional defects of the CL, as assessed by basal and hcg-stimulated P levels, suggesting that the latter do not commonly contribute to infertility. Acknowledgments. We are indebted to the nursing staff of the 9th Floor Clinic of the Warren Grant Magnuson Clinical Center of the National Institutes of Health (Bethesda, Maryland) for supporting this study. We are grateful to Michael J. 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