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Keywords:

  • corpus luteum;
  • medical termination of pregnancy;
  • mifepristone;
  • progesterone;
  • three-dimensional ultrasound

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. REFERENCES
  8. Supporting Information

Objective

The antiprogestin mifepristone is widely used for medical termination of pregnancy (TOP). Previous studies have suggested that the mechanism of mifepristone is based on its action in the endometrium and myometrium. The aim of this study was to evaluate the possible effects of mifepristone on corpus luteum activity.

Methods

This was a prospective, longitudinal controlled study to which 20 patients undergoing medical TOP (study group) and 20 patients with normal ongoing pregnancy (control group) were recruited. Medical TOP was induced with 200 mg of mifepristone followed by 0.8 mg of misoprostol 2 days later. Three-dimensional ultrasound examinations and hormone assays (progesterone, human chorionic gonadotropin, and 17-hydroxyprogesterone) were performed in both groups on the day of, and 2 days after, administration of mifepristone. Total volume (vascularized + non-vascularized) of the dominant (containing corpus luteum) and non-dominant ovary and serum hormone levels were measured.

Results

After administration of mifepristone, a decrease in serum progesterone levels was observed with a simultaneous decrease in the non-vascularized volume of the dominant ovary in the study group. No such changes were observed in the control group.

Conclusions

The observations indicate that, in addition to trophoblastic tissue, the corpus luteum is also the target of mifepristone. Copyright © 2009 ISUOG. Published by John Wiley & Sons, Ltd.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. REFERENCES
  8. Supporting Information

Mifepristone (RU486) is a synthetic steroid with a high affinity for progesterone and glucocorticoid receptors. Owing to the antiprogestin properties of mifepristone, it has been used in clinical practice with the prostaglandin analog misoprostol for medical termination of pregnancy (TOP). The combination of these two drugs generally results in a success rate of more than 90%1. The biological mechanism of action of mifepristone is not fully understood, but earlier studies have shown that mifepristone has an effect on the uterine myometrium and endometrium2, 3. Mifepristone sensitizes the myometrium to subsequent prostaglandin application and ripens the cervix2, and is thought to have an effect on the endometrial hemostatic potential, causing endometrial hemorrhage and extracellular matrix degeneration3.

The corpus luteum, formed from a regressing ovarian follicle, is an active endocrine gland, the primary function of which is the secretion of progesterone, which is required for the maintenance of a normal pregnancy. In the corpus luteum progesterone is produced by the luteinized theca and granulosa cells, which form about 30% of the total cell count of the corpus luteum. In addition to these steroidogenic cells, the corpus luteum contains endothelial cells, fibroblasts, pericytes and immune cells. Approximately 50% of the total cell count of the corpus luteum consists of endothelial cells, which form an extensive vascular network to supply the steroidogenic cells4–6.

During the menstrual cycle, serum progesterone levels rise sharply after the luteinizing hormone surge and ovulation as a result of the formation of the corpus luteum. If fertilization and implantation occur, regression of the corpus luteum is delayed and luteal function is maintained until progesterone secretion is taken over by the developing placenta7. This change in progesterone synthesis and secretion is called the luteoplacental shift and, in humans, it seems to take place at 7–8 weeks of pregnancy. After the luteoplacental shift, the corpus luteum is no longer essential for the maintenance of the pregnancy8.

The most important factor in maintaining the human corpus luteum during early pregnancy is human chorionic gonadotropin (hCG)9, which is secreted by trophoblastic tissue. In addition to stimulating progesterone synthesis, hCG induces angiogenesis and blood vessel stabilization in the corpus luteum10. 17-hydroxyprogesterone (17-OHP) is a steroid hormone produced during the synthesis of glucocorticoids and sex steroids. Serum 17-OHP levels are thought to reflect the function of the corpus luteum, as the placenta does not secrete this steroid owing to a lack of 17-hydroxylase activity. The peak levels of 17-OHP are reached in the 5th week of pregnancy, after which levels decline until the lowest levels, in the 13th week of gestation11.

It has been hypothesized that progesterone might have an autocrine or paracrine role in regulating corpus luteum function7, 12, and therefore blockage of progesterone using mifepristone might affect corpus luteum function. Previous studies focusing on the corpus luteum as a target of mifepristone have not been performed in vivo but in vitro using cell-culture techniques13, 14. We aimed to evaluate the effect of mifepristone administration first by assessing the levels of circulating steroids and second, by measuring the changes in the volume and vascularization of the corpus luteum using three-dimensional (3D) power Doppler ultrasonography. The analyses were made in relation to gestational age (GA), as the luteoplacental shift occurs during the first trimester of pregnancy.

Patients and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. REFERENCES
  8. Supporting Information

This prospective, longitudinal and controlled study was carried out in the Department of Obstetrics and Gynecology, Oulu University Hospital, in 2004 and 2005, with the approval of the ethics committee of the Northern Ostrobothnia Hospital District. Twenty female volunteers undergoing medical TOP for social reasons and 20 women with matching GA and ongoing pregnancy participated in the study. The upper GA limit for inclusion was 63 days. In both groups GA was determined from the last menstrual bleeding and was confirmed by measuring fetal crown–rump length. Only viable singleton pregnancies were included. Written informed consent was obtained from all patients.

The medical TOP group had baseline hormonal assays and transvaginal sonography (TVS) performed during the first visit (day 0). After blood sampling and TVS, the women in the medical TOP group were given 200 mg of mifepristone orally under the supervision of the nurse. The next visit with blood sampling and TVS was 2 days later (day 2), when 0.8 mg (4 tablets) of prostaglandin E1 misoprostol was applied vaginally to complete the TOP. The observation time in the outpatient clinic after the administration of misoprostol was a minimum of 4 h. The control group with normal ongoing pregnancies had comparable visits with blood sampling and TVS 2 days apart.

The complete TOP was confirmed by TVS a week after misoprostol administration and/or by a urine hCG test 5–6 weeks later in all patients. In the normal pregnancy group, the course of pregnancy was assessed by patient records. All patients in this group gave birth at the Oulu University Hospital at between 37 and 43 weeks of pregnancy.

Serum concentrations of progesterone and total hCG were measured by an automated chemiluminescence system (Advia Centaur, Bayer Corporation, NY, USA) and 17-OHP by radioimmunoassay (Diagnostic Products Corporation, Los Angeles, CA, USA). The intra- and interassay coefficients of variation were 3.7 and 5.4% for progesterone, 2.0 and 3.5% for total hCG, and 5.0 and 5.4% for 17-OHP, respectively.

One operator (I.Y.J.) performed all the ultrasound measurements in the study. The ovaries were examined during each visit using 3D sonography with a machine equipped with a transvaginal probe (Voluson Expert 730®, GE Healthcare, Zipf, Austria). This equipment enables the determination of ovarian volume, including possible changes in the intraovarian vascular network. We measured the whole ovarian volume instead of the corpus luteum volume, because we believe that determination of the outlines of the ovary is easier and possibly more accurate than determining the outlines of the corpus luteum only. In addition, measuring the volume of the whole ovary enabled us to compare the dominant and non-dominant ovaries. Once the ovaries had been located and the quality of the two-dimensional gray-scale image maximized, 3D volume acquisition, including power Doppler, was performed. Only volumes of good quality and without artifacts were accepted for subsequent analysis for each of the 40 participants. Identical pre-installed settings were used to acquire the power Doppler information from the ovaries. The setting conditions for this study were as follows: frequency, mid; dynamic set, 2; balance, G > 170; smooth, 5/5; ensemble, 16; line density, 7; and power Doppler map, 5. The setting conditions for the power Doppler mode were as follows: gain, −5.6; quality, normal; wall motion filter, low 1; and PRF, 0.9 kHz.

Analysis of the volumes obtained was carried out using the built-in virtual organ computer-aided analysis (VOCAL; Voluson Expert 730®, GE Healthcare) imaging program for 3D power Doppler histogram analysis. The manual mode of the VOCAL contour editor was used to cover the whole 3D volume of the ovary, with 30°-rotation steps. Hence, six contour planes were drawn for each ovary to cover 360°. After obtaining the total ovarian volume, the program calculated the ratio of color voxels to all voxels; this ratio (%) was expressed as the vascularization index (VI). Vascularized volume in the ovary was calculated by multiplying the total ovarian volume by the VI. The volume without the power Doppler signal (non-vascularized volume) was calculated by deducting the vascularized volume from the total volume. The reproducibility of the volume and VI measurements using transvaginal 3D power Doppler sonography has been previously assessed15. The intraobserver correlation coefficient was 1.0 for the volume measurements and 0.89 for VI.

Statistical analysis

SPSS for Windows 12.0.1 (SPSS Inc., Chicago, IL, USA) was used to perform the statistical analyses. Departure from a normal distribution was assessed using the Kolmogorov–Smirnov test. Paired t-tests were used for normally distributed data, and the Mann–Whitney U-test was used for skewed data. Correlation was estimated using the Pearson correlation coefficient and proportions were compared by χ2 test; P < 0.05 was considered statistically significant. All values given are the mean ± SD.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. REFERENCES
  8. Supporting Information

The groups did not differ significantly by age (mean 24.8 ± 1.0 (range, 18–35) years in the normal pregnancy group vs. 28.6 ± 2.0 (range, 18–43) years in the medical TOP group). A greater proportion of patients in the normal pregnancy group were nulliparous than the patients in the medical TOP group (12 vs. 9), but the groups did not differ significantly in terms of previous pregnancies or deliveries. GA ranged from 47 to 62 days in the study group and from 46 to 63 days in the control group. Half of the patients (10 patients) in both groups had a GA of less than 56 days and the other half 56 to 63 days. Thus they were divided into subgroups of those with a GA of less than 56 days and those with a GA of 56 days or more. All the participants had TVS examinations on day 0 and day 2 and had ultrasound measurements available for analysis. In the medical TOP group the results of the blood tests were available for statistical analysis in 19 subjects (one sample missing for day 0), and in the control group the results were available for 17 subjects (three samples missing for day 2). The missing blood tests were caused by problems in blood sampling for technical reasons or by a lack of cooperation.

The correlations between the serum hormone levels and the total, vascularized and non-vascularized volumes of the dominant ovary on day 0 (before mifepristone administration) were assessed in the two subgroups: GA less than 56 days and GA 56–63 days (the study and the control groups combined) (Table 1, Figure S1). Serum progesterone levels in patients with a GA of less than 56 days correlated with the total, vascularized, and non-vascularized volumes of the ovary containing the corpus luteum (dominant ovary). In addition, the vascularized volume correlated with the level of 17-OHP, but no correlation was observed between hCG level and vascularized volume. In pregnancies with a GA between 56 and 63 days, the serum progesterone and hCG levels correlated with the vascularized volume. The total and the non-vascularized volume of the dominant ovary correlated with the level of 17-OHP, but not with the vascularized volume.

Table 1. Correlation between hormone levels and total, vascularized and non-vascularized volumes of the dominant ovary on day 0 before any medication; patients from the termination and ongoing pregnancy groups combined
HormoneTotal volume*Vascularized volumeNon-vascularized volume
r P r P r P
  • *

    Total volume = vascularized volume + non-vascularized volume. hCG, human chorionic gonadotropin; NS, not significant.

< 56 days' gestation (n = 19)
 hCG0.307NS0.330NS0.118NS
 Progesterone0.556< 0.050.740< 0.0010.470< 0.05
 17-hydroxyprogesterone0.400NS0.5930.0070.368NS
≥ 56 days' gestation (n = 20)
 hCG0.373NS0.554< 0.050.356NS
 Progesterone0.182NS0.662< 0.0050.136NS
 17-hydroxyprogesterone0.678< 0.0050.232NS0.672< 0.005

The findings before and after the administration of mifepristone are shown in Table 2. No differences were detected either in the hormone levels or in the ovarian volumes between the study and the control group on day 0 or 2 (data not shown here). After both groups had been divided into the two GA subgroups, there was still no difference in the basal hormone levels or in the ovarian volumes between the study and the control groups (data not shown). In the medical TOP group with GA less than 56 days, the hCG levels increased (P = 0.006) and the progesterone levels decreased (P = 0.019) 2 days after the administration of mifepristone. There was a statistically significant decrease in the total (P = 0.004) and in the non-vascularized volume (P = 0.005) of the dominant ovary. In the medical TOP group with pregnancy between 56 and 63 days, the administration of mifepristone induced a decrease in the progesterone levels (P = 0.011). The total volume of the dominant ovary did not change significantly, while the non-vascularized volume decreased (P = 0.047). No changes were observed in the non-dominant ovary in either of the groups. In the control group with GA less than 56 days, the serum hCG levels increased significantly (P = 0.003) in 2 days, whereas no change in the hCG levels was observed in pregnancies between 56 and 63 days. No changes in the serum progesterone or 17-OHP levels were detected in the control group. The total ovarian volume decreased significantly in the pregnancies between 56 and 63 days (P = 0.047).

Table 2. Hormone levels and three-dimensional Doppler measurements before (day 0) and 2 days after (day 2) mifepristone administration in the medical termination of pregnancy (TOP) and control groups, divided into subgroups according to gestational age
ParameterMedical TOPNormal pregnancy
Day 0Day 2 PDay 0Day 2 P
  1. Data are expressed as mean (SD). hCG, human chorionic gonadotropin; 17-OHP, 17-hydroxyprogesterone; total volume, vascularized volume + non-vascularized volume.

< 56 days' gestation
 hCG (IU/L)50 173 (35 578)57 817 (40 329)0.00659 740 (37 364)69 642 (37 463)0.003
 Progesterone (nmol/L)64.4 (20.4)60.3 (21.7)0.01962.0 (20.7)64.9 (27.8)NS
 17-OHP (nmol/L)15.7 (6.7)16.8 (6.4)NS14.7 (4.7)14.1 (5.7)NS
 Dominant ovary 
   Total volume (mL)11.0 (2.5)10.0 (2.5)0.00416.0 (10.2)16.2 (10.0)NS
   Vascularized volume (mL)2.7 (0.7)2.5 (0.9)NS3.0 (1.9)3.2 (2.3)NS
   Non-vascularized volume (mL)8.3 (2.3)7.5 (2.2)0.00513.0 (9.4)13.0 (9.0)NS
 Non-dominant ovary 
   Total volume (mL)5.9 (3.2)5.1 (2.4)NS4.4 (1.5)4.8 (1.6)NS
   Vascularized volume (mL)0.3 (0.26)0.2 (0.13)NS0.1 (0.1)0.2 (0.2)NS
≥ 56 days' gestation
 hCG (IU/L)93 351 (22 651)89 578 (22 883)NS137 399 (67 837)132 402 (56 119)NS
 Progesterone (nmol/L)66.2 (10.3)57.5 (10.1)0.01181.9 (36.5)84.3 (36.3)NS
 17-OHP (nmol/L)11.8 (5.3)13.0 (7.1)NS14.3 (3.7)13.4 (3.2)NS
 Dominant ovary 
   Total volume (mL)14.1 (8.4)12.4 (6.0)NS12.3 (2.3)12.0 (2.2)0.047
   Vascularized volume (mL)2.2 (0.5)2.4 (0.7)NS2.5 (0.7)2.4 (0.7)NS
   Non-vascularized volume (mL)11.9 (8.3)10.0 (5.8)0.0479.9 (1.9)9.6 (1.7)NS
 Non-dominant ovary 
   Total volume (mL)5.5 (2.6)6.1 (4.3)NS4.7 (1.8)4.4 (2.2)NS
   Vascularized volume (mL)0.1 (0.1)0.2 (0.2)NS0.1 (0.1)0.1 (0.2)NS

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. REFERENCES
  8. Supporting Information

The main findings of the present study are the decrease in serum progesterone levels regardless of GA, the decreased total volume of the dominant ovary (when GA is less than 56 days) and the decreased non-vascularized volume of the dominant ovary after administration of mifepristone. Moreover, the vascularized volume of the dominant ovary correlated with serum progesterone level across both GA subgroups and with 17-OHP when the GA was less than 56 days.

Serum levels of hCG increased significantly both in the study group and the control group when GA was less than 56 days, but with advanced GA no significant change was observed in either of the groups. Similarly, in previous studies serum hCG levels have been found to be increased16, 17 or unchanged18 after administration of mifepristone in pregnancies with a GA of less than 63 days.

Serum progesterone levels declined in both GA groups after mifepristone administration. Previous reports concerning the effect of mifepristone on progesterone secretion have not been entirely congruent16, 17. In a study using 200 mg of mifepristone, no statistically significant changes in the progesterone levels were observed in the 2-day follow-up16. In another study, with 600 mg mifepristone, progesterone and 17-OHP levels increased on day 1 and then decreased significantly17. The paradoxical effects (mifepristone both raises and lowers progesterone levels) have also been explained by the hypothesis that mifepristone can act either by preventing the progesterone effect or in a way that is similar to that of progesterone, which always stimulates its own secretion by autoregulation. It is possible that these effects are different depending on the duration of pregnancy19. We used the control group (ongoing pregnancies) with matching GA as well as the subgroups according to GA to rule out this effect.

Serum 17-OHP levels were measured in order to reflect corpus luteum activity. In the present study 17-OHP levels did not show significant changes in any of the groups, possibly owing to serum levels being physiologically low in this phase of pregnancy11.

After administration of mifepristone no changes occurred in the non-dominant ovaries, whereas there was a decline in the total and non-vascularized volume of the ovary carrying the corpus luteum in pregnancies of < 56 days. We speculate that the decrease in the dominant ovarian volume was related to the decline in progesterone levels observed here. Previously, it has been proposed that progesterone acts directly in the luteal cells to maintain their structural integrity and steroidogenic capacity20. Earlier studies have suggested that blockage of progesterone action using mifepristone could enhance apoptosis in the corpus luteum21, 22.

The total volume of the dominant ovary also decreased in the control group with a GA of more than 56 days. At this stage of pregnancy, the placenta has already become the main source of progesterone production8. Therefore, the decrease in the dominant ovarian volume observed in advanced pregnancy (> 56 days) may be due to a natural decline in corpus luteum activity23.

The vascularized volume of the dominant ovary correlated with serum progesterone and 17-OHP levels before mifepristone administration. This finding is well in line with previous studies showing that circulating progesterone concentrations depend on the amount of steroidogenic tissue and blood flow in the corpus luteum23, 24. Vascularization in the corpus luteum remained unchanged after mifepristone administration, which suggests that the mechanism by which mifepristone affects progesterone production is not associated with the changes in ovarian vasculature. It seems that the target of mifepristone in the corpus luteum is the non-vascular part, which consists mostly of steroidogenic cells. It is possible, however, that after a longer follow-up period changes in the vascularization of the corpus luteum could also take place. The volume of vascularization in the non-dominant ovary was minimal compared to that in the dominant ovary, suggesting that the most important function of the vascular network in the dominant ovary is to supply the corpus luteum.

This was a preliminary study to assess functional and morphological changes in the human corpus luteum during medical TOP. Previous studies have shown that GA has an inverse correlation with successful medical TOP, especially when mifepristone alone is used2, 25, 26. Our study offers a physiological explanation for that clinical finding. We believe that the corpus luteum is a target organ of mifepristone, and that the effect that mifepristone has on the corpus luteum decreases with advanced GA owing to the luteoplacental shift. This study gives novel information about the mechanism of action of mifepristone in medical TOP and strengthens our knowledge of the function of the corpus luteum in pregnancy.

SUPPORTING INFORMATION ON THE INTERNET

The following supporting information may be found in the online version of this article:

Figure S1 Scatterplots with linear regression lines showing correlations between hormone levels and the total, vascularized and non-vascularized volumes of the dominant ovary on day 0 before any medication; patients from both groups combined.

REFERENCES

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. REFERENCES
  8. Supporting Information

Supporting Information

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. REFERENCES
  8. Supporting Information
FilenameFormatSizeDescription
uog_6418_sm_suppinfofig.doc262KSupporting Information: Figure S1 Scatterplots with linear regression lines showing correlations between hormone levels and the total, vascularized and non-vascularized volumes of the dominant ovary on day 0 before any medication; patients from both groups combined.

Please note: Wiley Blackwell is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.