PREDICTION OF THE TIME OF OVULATION*

Transcription

1 FERTILITY AND STERILITY Copyright c 1981 The American Fertility Society Vol. 36, No.3, September 1981 Printed in U.SA. PREDICTION OF THE TIME OF OVULATION* JAIRO E. GARCIA, M.D.t GEORGEANNA SEEGAR JONES, M.D. GEORGE L. WRIGHT, JR., PH.D.t Department of Obstetrics and Gynecology and Department of Microbiology and Immunology, Eastern Virginia Medical School, Norfolk, Virginia Prediction of ovulation was established by correlation of clinical parameters, follicular development by ultrasound, and estradiol, progesterone, and luteinizing hormone (LH) determination in 71 menstrual cycles. Laparoscopic follicular aspiration was accomplished in 41 of those cycles. A 28-hour interval from the ascending limb of the LH seems to be the "ideal time" for retrieval of a preovulatory oocyte. The variability in the amount of LH to which the follicle is exposed during the LH surge seems to indicate that there is a relatively low specific value necessary for ovulation. Ovulation occurs approximately 10 ± 5 hours from the LH peak. Progesterone occurs in relation to the LH surge and is helpful for the retrospective analysis of the menstrual cycle.. Fertil Steril 36:308, 1981 In vitro fertilization is the only procedure available for the treatment of infertile patients, due to the absence of fallopian tubes, failure oftuboplasty, or when tubal anastomosis is not possible. At the present time, the success rate has been very low because of several factors involved in such a procedure.! One of the most critical is the timely retrieval of an oocyte. For successful fertilization a mature oocyte should be obtained within minutes before spontaneous ovulation. This procedure has been attempted through ovulation induction with Pergonal and human chorionic gonadotropin (hcg), or clomid plus hcg, while the menstrual cycle is monitored with urinary es- Received March 19, 1981; revised and accepted May 20, *Presented at the 37th Annual Meeting of the American Fertility Society, Atlanta, Georgia, March 14 to 18, treprint requests: Jairo E. Garcia, M.D., Department of Obstetrics and Gynecology, Eastern Virginia Medical School, Norfolk, Virginia tcurrent address: George L. Wright, Jr., Ph.D., Department of Microbiology and Immunology, Eastern Virginia Medical School, Norfolk, Virginia trogen determinations and urinary luteinizing hormone (LH) assays determined every 3 hours by the Hi-Gonavis test. 2-4 The development of the dominant follicle has been followed by ultrasound. 5-7 With some of these protocols, when it was estimated that the follicle was suitable, hcg was injected intramuscularly, and laparoscopy was carried out after 32 to 36 hours. It was the experience of Steptoe and Edwards 8 and of the group in Melbourne, Australia,9 that only spontaneous cycles were successful. Therefore, the precise prediction of the time of ovulation in spontaneous cycles became of great importance. At the present time, there is no single completely reliable parameter for ovulation prediction. Variations from the mean among hormonal and clinical parameters during a specific menstrual cycle are troublesome, and there is considerable variation from cycle to cycle, even in the same patient. In the protocol adopted at the Eastern Virginia Medical School, serum steroid and gonadotropin assays were used to determine whether the values obtained were more precise

2 Vol. 36, No.3 PREDICTION OF OVULATION 309 than urinary values, which by necessity give an average reading spanning the interval of collection. The main purpose of this paper is to record our experience in predicting ovulation by the correlation of clinical parameters and steroid hormone values with estimates of follicle size by ultrasound. Serum estradiol (E2), the initial rise of serum progesterone (P), and particularly the rise of serum luteinizing hormone (LH) were measured daily and every 4 hours during the immediate preovulatory and ovulatory period. MATERIALS AND METHODS Thirty-two generally healthy menstruating patients were admitted into a program of Vital Initiation of Pregnancy (VIP), through December Of these 32 patients, 29 had one or two controlled, monitored cycles prior to a laparoscopy for an oocyte retrieval attempt. Oocyte aspiration was attemped in 41 cycles, making a total of 85 monitored cycles. Most of the patients were seen by one of the authors on a daily basis. Monitoring of parameters indicative of follicle growth and impending ovulation was begun on the 8th day of the menstrual cycle. Clinical estimation of the estrogen milieu was made by karyopyknotic index of cells from the lateral vaginal wall and by observation of the cervical os and analysis of cervical mucus for spinnbarkeit and fern formation. On "ideal day 10" daily real-time ultrasound by linear (ADR, model 2130) or sector scan (ADR, model 2140) measurements were done to assess the size of the developing follicle. Ultrasound was performed more frequently when ovulation was thought to be imminent, or to detect the presence of an early corpus luteum. A specimen of 10 ml of blood was obtained daily beginning on the 8th day of the cycle (defined as above) for rapid radioimmunoassay (RIA). When the clinical monitoring indicated that ovulation might occur within the next 48 hours, blood samples were taken every 4 hours, but in most patients the 4 A.M. sample was omitted. Estradiol determinations were made also in 10 of the control cycles only. The E2-RIA used has been described previously.lo Luteinizing hormone (LH) in the serum was assessed daily at 8 A.M. with the use of a radioimmunoassay kit (Amersham, Arlington Heights, Illinois). We modified the RIA kit protocol by changing the incubation period from between 16 and 24 hours to 3 hours. This change allowed the shortening of the assay time to 5 hours and permitted serum specimens to be processed and LH concentrations calculated on a daily basis. Although lower zero binding occurred, as expected, with the faster modification (approximately 65% of that observed in the overnight assay), the two protocols nevertheless maintained a close correlation (r = 0.97). Progesterone was assayed with a RIA kit from Wien Laboratories, Inc. (Succasunna, N. J.). The unknown sera, control sera, and reagent blanks were all extracted with glass-distilled petroleum ether. An appropriate aliquot was taken from the top ether layer and evaporated to dryness in a 45 to 50 C waterbath with the aid of a nitrogen airstream. The unextracted progesterone standards were also evaporated to dryness. All samples, including the standards, were run in duplicate. The RIA portion of the procedure was run by adding 3H-progesterone, phosphate buffer, and working progesterone antibody solution consecutively. All tubes were then incubated in a 6 to 10 C ice bath for 60 minutes. At the end of that time, cold dextran-coated charcoal was added to all tubes to absorb the unbound progesterone. The charcoal was then precipitated by centrifugation and the supernatant transferred to counting vials with scintillation cocktail. After standing in the dark at room temperature for at least one hour, the samples were counted in a Beckman model LS-250 scintillation counter. We constructed a standard curve for each assay by plotting the progesterone standards, picograms per tube, against a ratio of counts per minute (cpm) of the zero to each unknown. Each progesterone concentration minus the value of the blank was converted from picograms per tube to nanograms per milliliter. Daily basal body temperatures were kept on all the patients. Ovulation was estimated in the monitoring cycles, on the basis of the clinical parameters, shift of the temperatures, disappearance of the dominant follicle at ultrasound, and serum progesterone values higher than 1.25 ± 29 ng/ml, together with a pathologic report on an endometrial biopsy of secretory endometrium. In those patients where the laparoscopy was performed and aspiration of a dominant follicle was carried out, correlations were made with the progesterone values at aspiration time, and with the

3 310 GARCIA ET AL. characteristics of the oocyte. Whenever there was failure of aspiration of the oocyte, or an early corpus luteum was found, the ovulation times were correlated with the progesterone values. Laparoscopy was carried out under general anesthesia with the use of double puncture technique in most of the cases, and a third puncture when indicated. The aspiration of the oocyte was made through the offset scope with the use of a 12-gauge needle. Statistical Analysis Statistical analysis of all data was made with comparison of the means. Significance was determined with the one-way analysis of variance, using the Duncan Multiple Range Test. Significant differences were P values of < The Il-LH values were calculated according to Simpson's approximation discrete. RESULTS Seventy-one of the 85 menstrual cycles were satisfactorily completed and analyzed. These were from 32 women whose mean age was 30.5 ± 3.0 years. Thirty monitored cycles were designated as control, and 41 as treatment or aspiration cycles. Table 1 shows the relationship between clinical parameters and the LH peak in 71 cycles from 32 normal women. The basal body temperature (BBT) chart showed the lowest dip in 46 cycles on the day of the LH peak (day 0), in 5 the day after, and in 10 cycles on the day prior to the LH peak. However, in one cycle the lowest point was observed as early as 3 days prior to the LH peak. The cervical mucus displayed a 4 + ferning in 21 cycles at the time of the LH peak, but it was also TABLE 1. Relationship Among Clinical Parameters and Luteinizing Hormone (LH) Peak in 71 Cycles from 32 Normal Women Days related to LH peak Clinical parameters in number of cycles BBT" dip Fern: 4+ Cervical mucus Spinnbarkeit <10 em o (LH peak) Not available abasal body temperature. Z 1&1 i I&. o 1&1 CJ Z 1&1 () 1&1 Do September 1981 o m 00 ro PERCENTAGE OF PYKNOTIC CELLS FIG. 1. Histogram showing the percentage of pyknotic cells of the lateral wall of the vagina in 71 cycles from 28 normal women at the time of luteinizing hormone (LH) peak. Daily serum luteinizing hormone (LH) values in 50 menstruating cycles from 28 normal women. observed to be optimum in some cycles as early as day - 5. The spinnbarkeit, > 10 cm, usually appeared around day - 3, although in a few patients it was seen as early as 7 days prior to the LH peak. The karyopyknotic index at the time of the LH peak is shown in Figure 1. A wide range of percentage of pyknotic cells of the wall of the vagina was found, the highest being 40% in 21 % ofthe 71 cycles. Although not shown in this Figure, a tendency to an individualized repetitive pattern in each patient was observed. Serum estradiol determination carried out in 10 of the control cycles showed in most of them a double peak that might occur from day - 3 until the day of the LH peak. These data are not shown in the present paper. The LH radioimmunoassay (RIA) profile from 50 menstrual cycles, 21 being from cycles in which preovulatory oocytes (designated as 00- cytes surrounded by a good corona radiata, good cumulus, and a mucus coat) were obtained, is shown in Figure 2. As above, the time of the highest LH values was denoted as day 0, and all blood samples were normalized to this point, with all the samples drawn before that point designated as - 4 to - 8 hours, to day - 8. Samples drawn afterwards were designated as + 4 hours, + 8 hours, and to day + 8. The mean and standard deviation of the 29 control cycles is shown. The broken line designates the mean of the LH values in the 21 cycles in which a preovulatory oocyte was successfully aspirated.

4 Vol. 36, No.3 PREDICTION OF OVULATION ::>... E I, Break-/I I J \I. I Preovulatory Oocyte Cycles Monitored Cycles (Controls) 40!\td.jJ I] J l----l-i-...r 1 r--1---i o --(h-rs-.)'-96-8r4-7t r6_2t4'6lr22t4'48(ih-rsri.)----'---r I 0 I DAYS FIG. 2. Daily and every 4 hours serum LH levels from day - 8 to day + 8 in 50 menstrual cycles normalized to the day of the LH peak. Solid bar, controls (mean ± SO); broken line, preovulatory oocyte group. Laparoscopy was carried out in 41 cycles. Twenty-one preovulatory oocytes were obtained. Nine fresh corpora lutea were encountered, there were nine failures (aspiration of a secondary follicle with recovery of an immature oocyte was included in this group). Two patients had ovarian cysts mistaken for the dominant follicle in the prelaparoscopic sonograms. Table 2 shows the interval between the beginning of the serum LH surge (60 miu/ml), and laparoscopy, the mean being 27:20 ± 6:24 hours for the preovulatory oocyte group; 34:54 ± 8:00 hours for the corpus luteum group; and 28:24 ± 2:54 hours for the aspiration failure group. In three cases of failure, the aspiration occurred before 20 hours from the LH surge, as seen in Figure 3. The interval from LH peak and laparoscopy was 10:00 and 11:40 hours in the preovulatory oocyte and aspiration failure groups, respectively, and 17:30 hours in the corpus luteum group. There were significant differences between these groups (P < 0.05) (Table 3). Serum progesterone levels were determined at the time oflaparoscopy in 20 of 21 cycles in which a preovulatory oocyte was recovered; the mean was 1.36 ± 0.35 ng/ml, and no statistical significance was observed with relation to the aspiration failure group (Table 4). Progesterone values were found within the same range, and the mean was also not significantly different at the "ideal time of the laparoscopy," 28 hours, in 28 monitored cycles,' as shown in Table 5. The amount of LH to which the follicle was exposed (A-LH) was calculated from the beginning of the LH surge (60 miu/ml) and the time of laparoscopy, or at the estimated "ideal" time of laparoscopy, as shown in Table 6. The mean was ± in the control cycles, ± 1350 in the preovulatory oocyte group, and ± and ± in the corpus luteum and aspiration failure groups, respectively. There was no statistically significant difference within any of the groups. Figure 4 shows the relationship between the ultrasound diameter of the 41 aspirated follicles and the laparoscopic findings. Although in a few instances ultrasonography was done 18 to 20 hours prior to the laparoscopy, usually it was performed 1 hour prior to the procedure. TABLE 2. Interval Between Beginning Serum Luteinizing Hormone (LH) Surge" and Laparoscopy Cycle Number Hours Mean SD Range Preovulatory 21 27:20 6:24 26:30-31:00 oocyte Corpus luteum 9 34:54 8:00 28:00-52:00 Aspiration failure 6 28:24 2:54 26:30-34:00 "LH surge: > 60 miulml.

5 312 GARCIA ET AL. September 1981 Preovulatory Oocyte, 17 I Corpus Luteum, 9 Corpus Luteum & Preovulatory Oocyte ' 4 Oocyte Retrieval Failure, 8 o Immature Oocyte, 1 (2) Cyst, 2 O (2) (2) <''------}{--} l >36 HOURS FIG. 3. Interval of time, hours, from the onset ofluteinizing hormone.(lh) surge, 60 miu/ml, to laparoscopy; Correlation between mterval and laparoscopic findings in 41 aspiration cycles. Preovulatory oocytes were recovered from and fresh corpora lutea were formed in follicles with diameters of 18 and 19 mm. In one case, ovulation had occurred from a follicle 21 mm in diameter and the oocyte was recovered from the cul-de-sac fluid aspiration. It was also recovered in this manner in a patient in whom the results of ultrasonography were, not reliable. In two women with follicles measuring 22 and 23 mm, ovulation was observed in progress, and follicular fluid was dripping from the stoma. The preovulatory oocyte was recovered from the fluid remaining inside the follicle. DISCUSSION In the present study, the prediction of ovulation was based on three main parameters: (1) clinical evaluation ofbbt, cervical mucus,and karyopyknotic index; (2) follicular development as determined by ultrasound; and (3) serum LH and estradiol determinations. These parameters were TABLE 3. Interval Between Luteinizing Hormone (LH) Peak and Laparoscopy Cycle Number Hours Mean SD Range Preovulatory 21 10:00a 5:05 4:00-20:00 oocyte Corpus luteum 9 17:30 b 6:20 8:00-28:00 Aspiration failure 6 11:40a 5:40 8:00-20:00 ano statistical significance. bp < TABLE 4. Serum Progesterone Level at the Time of Laparoscopy Laparoscopic finding Progesterone No. cycles Mean SD Range nglml Preovulatory a oocyte Corpus luteum 8 l,4w Aspiration failure 6 1. loa ano statistical significance. correlated with the laparoscopic findings in treatment cycles or with the estimated "ideal laparoscopy time" in the monitoring cycles. Usually, the BBT has been helpful in retrospective analysis once the shift has occurred, indicating ovulationy Nevertheless, in our prospective study it was found that the lowest point corresponded to the day of the LH peak, but if this occurred prior to the LH' peak, the temperature remained low until the LH surge occurred and ovulation took place. At this time the temperature rose, although not necessarily to the 98 range. The changes in the cervical mucus are shown in Table 1. It was found that these must be evaluated in toto, with the use of volume, quality, and dilatation of the external os. There was a tendency for individuals to repeat a characteristic pattern, making it much easier to monitor the patient in a second or a'third cycle. The karyopyknotic index showed a wide variation, but it was also repetitive in individual cycles. Follicular development can be assessed by ultrasound 5-7 in most patients, although this process was sometimes difficult; It was especially helpful to know in advance from which ovary ovulation might occur, in those patients who had only one ovary available for oocyte retrieval at laparoscopy. However, ultrasound could not be used as a single unique parameter for prediction of ovulation, especially in patients who had adhesions and sometimes hydrosalpinx. Figure 4 is an TABLE 5. Serum Progesterone Level at the Estimated Ideal Time of Laparoscopy or at Laparoscopy Cycle Number Progesterone Mean SD Range nglml Monitored a 0; Preovulatory a oocyte Corpus luteum 8 l,4w 0, Aspiration failure a ano statistical significance.

6 Vol. 36, No.3 PREDICTION OF OVULATION. 313 TABLE 6..1 Luteinizing HorTTWne (LHr Between the Beginning LH Surgeband the Estimated Ideal Time of Laparoscopy or at Laparoscopy Cycles Number Mean Monitored c Preov:ulatory c oocytes Corpus. luteum < Aspiration 6 3,528.8c failure a.1_lh: Simpson's approximation. blh surge: > 60 miu/ml. <No statistical significance. SD Range "-l) example of the wide range of follicular diameter at which ovulation can occur. As with other clinical parameters, it seems that each patient has her own follicular development pattern. Serum estradiol was determined in our first 10 monitoring cycles. The results showed that the peak could occur from 72 to 24 hours prior to the LH peak. Korenman and Sherman found similar variations, and Pauerstein et al. reported an estradiol peak occurring within 48 to 28 hours of the estimated time of ovulation in 65% of their monitored cycles, although the mean interval in their series was 24 ± 3 hours.12, 13 Several patients in our series showed a second estradiol peak, and one occurred on the day of the LH peak. As a result of this fluctuation, the serum estradiol did not seem to be useful as an early indicator for prediction of ovulation, and was discontinued. The LH profile is shown in Figure 2. When the serum LH is determined every 4 hours, LH pulses may be detected, giving a profile of multiple pulses that in some cases are approximately of the same height. In some cycles, this created a biphasic LH surge, making it difficult or impossible to interpret which peak should be correlated with the LH-ovulation interval. We therefore decided to:use the beginning of the LH surge, rather than the peak, as the time to' calculate oocyte retrieval. In our assay this beginning surge was identified' as 60 miu/ml. Several papers in the literature indicate that the LH levels rise 12 to 24 hours prior to ovulation and that the peak occurs 4 to 16 hours prior. to ovulation.14, 15 Pauerstein and Croxatto estimated time of ovulation to be approximately 9 ± 2 hours from the LH peak.13 In the multicenter collaborative study from the World Helth Organization, the statistical model for LH indicated that ovulation could occur' in 90% of women between 16 and 48 hours after the first significant rise in the concentration of the hormone, and between -3.and 36 hours after the LH peak.16 Our study, using 4-hour serum LH samples.correlated with follicular diameter at laparoscopy, together with the characteristics of the. oqayte and the granulosa cells of the follicle, indicated that ovulation occurred at a mean of 27:20 hours from the onset of the LH surge and at a 10:00-hour interval from the LH peak. The cut-off for the: ascending limb of the LH surge was determined to be at the 60 miu/mlvalue in our assay system, from observations of previous monitored cycles. In some patients a small peak oflh proceeded the definitive LH surge. Unless' sufficiently frequent sampling was made to detect the spuriousness of this rise, it could lead to premature aspiration of the follicle. The statistical similarity among the control, the preovulatory oocyte, and the aspiration failure groups led to the conclusion that the aspiration failures might be related to technical problems or failures of proper oocyte maturation in some follicles rather than improper timing of the laparoscopic oocyte retrieval. When laparoscopic retrieval is plimned at. the latest possible moment, however; some ovulations. must be expected to have occurred. A recent ovulation occurred in four of our aspiration cycles. In two, the oocyte was recovered from the cul-de-sac fluid. In the other two ovulation was observed in progress, and the oocytes were recovered from the fluid remaining inside the follide. Five of the nine corpora lutea found at laparoscopy occurred in the aug- Preovulatory Oocyte' 17 l Corpus Luteum, 9 Corpus Luteum & Preovulatory Oocyte' 4 Oocyte Retrieval Failure, 8 o Immature Oocyte' 1 (!) Cyst, 2 0 (!) Not Reliable. MILLIMETERS l l l N.R: FIG. 4. Follicle diameter by ultrasound and laparoscopic findings in 41 aspiration cycles.

7 314 GARCIA ET AL. mented diagnostic laparoscopic group. These patients did not have the advantage of a previous monitored cycle. As has always been clinically suspected, stress may interfere with the normal function of the hypothalamic-pituitary-ovarian axis. Many of the patients showed some degree of menstrual irregularity during their first aspiration cycle, making their monitored cycles appear different from the aspiration cycle. One of the most intriguing findings was the enormous difference in the range of the LH surge between cycles, and even between cycles of the same individuals. In spite of these extreme variations in individual cycles, no statistically significant difference was found among the three aspiration groups. The correlation with the laparoscopic findings was also not statistically different. This correlation is being further investigated by comparison of individual cycles, and it is thought that the finding may indicate that there is a relatively low specific value necessary for ovulation, and the excess LH is not physiologically significant. It was observed that serum progesterone began to rise from a follicular phase level at the time of the LH surge, to reach the 1.36 ± 0.35 ng/ml range at the time of oocyte aspiration. The value at aspiration time does not seem critical. As the beginning rise is similar to LH, it does not offer an improveent in monitoring. There is not a definite rise until 24 hours from ovulation, as shown elsewherep These findings are in agreement with previous reports in the literature.16, Due to the length of the radioimmunoassay, it is our opinion that it is not a suitable parameter for the prediction of ovulation. It was helpful for the retrospective analysis of results of oocyte retrieval. In summary, prediction of ovulation is feasible. Clinical parameters are still important and are helpful in monitoring patients for oocyte aspiration. Ultrasound is an indispensable complementary tool for following the development of the follicle and for determining the side upon which ovulation will occur. The combination of these findings allow one to predict when the 4-hour blood samples for LH determination should be started. We have found that serum estradiol is too variable to be of clinical value in predicting accurately the time of ovulation surge or indicating when to begin 4-hour blood sampling. A 28-hour interval from the beginning of the LH surge seems to be the "ideal time for oocyte aspiration." September 1981 However, this interval does not allow ovulation to occur in the occasional patient. Ovulation occurs approximately 10 hours after the LH peak, but there is a variation of ± 5 hours that makes this period too great to be used as a clinical parameter. The amount of LH under the curve (.l-lh value) prior to ovulation needs further evaluation. Finally, serum progesterone shows a small rise with the LH surge; but because of the time involved, the assay does not help in the prediction of ovulation. Nevertheless, it has been helpful for retrospective evaluation of aspiration failures in some cases. Acknowledgments. The authors would like to express their thanks to Connie Holforty, Becky Spear, and Diane Brassil, Dr. George Wright's technicians, for their technical assistance in LH and progesterone determinations; to all of the nursing personnel in Labor and Delivery at the Norfolk General Hospital for their unselfish cooperation, and to Mrs. Linda Lynch for her constant help in all aspects of the program, and particularly for typing the manuscript. REFERENCES 1. Lopata A: Successes and failures in human in vitro fertilization. Nature 288:18, Steptoe PC, Edwards RG: Laparoscopic recovery of preovulatory human oocytes after priming of ovaries with gonadotrophins. Lancet 1:683, Brown J: Timing of ovulation. Med J Aust 2:780, Edwards RG, Steptoe PC: The induction of follicular growth, ovulation, and luteinization in human ovary. J Reprod Fertil [Suppl] 22:121, Hackeloer BJ, Fleming R, Robinson HP, Adam AH, Coutts JRT: Correlation of ultrasonic and endocrinologic assessment of human follicular development. Am J Obstet Gynecol 135:122, Renaud RL, Macler J, Dervain I, Ehret MF, Aron C, Spira A: Echographic study of follicular maturation and ovulation during the normal menstrual cycle. Fertil Steril 33:272, De Crespigny L, O'Herlihy C, Hoult I, Robinson H: Ultrasound in an in vitro fertilization program. Fertil Steril 35:25, Edwards RG, Steptoe PC, Purday JM: Establishing fullterm human pregnancies using cleaving embryos grown in vitro. Br J Obstet Gynaecol 87 (9):737, Lopata A, Johnston I, Hoult I, Speirs A: Pregnancy following intrauterine implantation of an embryo obtained by in vitro fertilization of a preovulatory egg. Fertil Steril 33:117, Albrecht E, Haskins A, Pepe G: The influence of fetectomy at midgestation upon the serum concentrations of progesterone, estrone, and estradiol in baboons. Endocrinol 107:766, Moghissi K: Accuracy of basal body temperature for ovulation detection. Fertil Steril 27:1415, Korenman SG, Sherman BM: Further studies of gonadotrophin and estradiol secretion during the preovulatory phase of the human menstrual cycle. J Clin Endocrinol Metab 36:1205, 1973

8 Vol. 36, No.3 PREDICTION OF OVULATION Pauerstein CJ, Eddy CA, Hess R, Siler-Khodr TM, Croxatto HB: Temporal relationships of estrogen, progesterone and luteinizing hormone levels to ovulation in women and infrahuman primates. Am J Obstet GynecoI130:876, Yussman MA, Taymor M: Serum levels of follicle stimulating and luteinizing hormone and of plasma progesterone related to ovulation by corpus luteum biopsy. J Clin Endocrinol Metab 30:396, Schmidt-Golwitzer K, Schmidt-Golwitzer M, Sackman V, Eiletz J: Ovulation timing by a radioreceptor assay for human luteinizing hormone. Int J Fertil 22(4):232, World Health Organization Task Force Investigators: Temporal relationships between ovulation and defined changes in the concentration of plasma estradiol-17, luteinizing hormone, follicle-stimulating hormone and progesterone. Am J Obstet Gynecol 138:383, Garcia JE, Jones GS, Acosta A, Wright G: Corpus luteum function after follicle aspiration for oocyte retrieval. Fertil Steril. In press (Nov. 1981) 18. Croxatto HD, Ortiz ME, Croxatto HB: Correlation between histologic dating of human corpus luteum and the luteinizing hormone peak-biopsy interval. Am J Obstet Gynecol 136:667, Landgren BM, Unden AL, Diczfalusy E: Hormonal profile of the cycle in 68 normally menstruating women. Acta Endocrinol (Copenh) 94:98, Thorneycroft I, Sribyatta-Boonlaw TW, Nakamura M, Mishell D: Measurement of serum LH, FSH, progesterone, 17 -OH progesterone and estradiol 17 levels at 4 hour intervals during the preovulatory phase of the menstrual cycle. J Clin Endocrinol Metab 39:754, Landgren BM, Aedo AR, Nunez M, Eckan SZ, Diczfalusy E: Studies on the pattern of circulating steroids in the normal menstrual cycle. Acta Endocrinol (Copenh) 84:620, 1977