DIAGNOSTIC ACCURACY OF GESTATIONAL TROPHOBLASTIC DISEASE WITH A COMBINATION OF HCG ESTIMATION AND

ULTRASONOGRAPHY IN TYGERBERG HOSPITAL

BACKGROUND/RATIONALE

Gestational trophoblastic disease (GTD) encompasses a range of disorders from the pre-malignant disorders of complete (CHM) and partial (PHM) hydatidiform moles through to the malignant invasive mole, choriocarcinoma (CC) and very rare placental site trophoblastic tumour/epithelioid trophoblastic tumour (PSTT/ETT). The malignant disease forms are also collectively known as gestational trophoblastic tumours or neoplasia (GTN). Nine to twenty percent of patients with complete hydatidiform mole go on to have GTN.

GTD incidence has been reported to vary from 1/1200 to 1/2000 pregnancies in USA (1), 1/1347 to 1/3004 in Tunisia (2), 4.8/1000 to 2/10000 in Turkey (3) and 1/314 in Iran (4). Although GTD is most associated with advanced maternal age (>45 years), an increased risk is seen in the very young (<16 years) (5). According to FIGO’s 26th report, most women with GTN are between 25 and 29 years of age, and 82.7% are younger than 40 years (6)

Abnormal vaginal bleeding in the first trimester of pregnancy is the most common presentation of GTD. Anemia, uterine enlargement, pre-eclampsia, hyperemesis, hyperthyroidism and respiratory distress were previously reported but are now rare (7), as a result of the introduction of routine ultrasonic examination in early pregnancy.

The initial diagnosis of hydatidiform mole is often made by ultrasound. Characteristic sonographic findings of a heterogeneous mass (‘snowstorm’), without fetal development and with theca lutein ovarian cysts are typically seen in second trimester but not in first trimester pregnancies (8). The combination of ultrasound findings and an elevated serum human chorionic gonadotropin (hCG) level above that expected for gestational age is highly suggestive of GTD.

Suction curettage is the recommended initial treatment for all patients presenting with a possible diagnosis of GTD. Histological examination of the evacuated uterine contents/tissue is usually necessary for definitive diagnosis. Although a safe procedure, it is expensive. Furthermore, it adds little prognostic value in terms of progression to GTN. In addition, it is not essential as the management of both PHM and CHM remains the same. The inadequate infrastructure and capacity for histological examination in resource limited settings such as we have in many parts of Africa makes it imperative that we discern a highly sensitive and specific, cost effective strategy in the diagnosis of GTD.

This study aims to evaluate the diagnostic accuracy of a combination of ultrasonography and hCG estimation compared to histological examination in pregnant women presenting with abnormal vaginal bleeding at <20weeks gestational age, uterine enlargement greater than expected for gestational dates and other clinical features suggestive of GTD.

OBJECTIVE

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To assess the diagnostic accuracy of Gestational trophoblastic disease (GTD) using a combination of ultrasonography and hCG estimation compared to histological examination of evacuated uterine contents. The study population is pregnant women presenting with vaginal bleeding at <20weeks gestational age, uterine enlargement greater than expected for gestational dates, hyperemesis as well as other clinical signs suggestive of GTD at Tygerberg Hospital, Cape Town.

METHODS

Figure 1 shows the outline of the study.

Study design

The study design will be a prospective cohort diagnostic study. The laboratory performing the hCG estimation and the sonographer performing the ultrasonography will be blinded to the outcome of the reference standard. The gynecologic pathologists performing the histological examination of the evacuated uterine contents will be blinded to the outcome of the index test.

Participant recruitment

Consecutive pregnant women presenting to Obstetric and Gynecological outpatient clinic, Tygerberg Hospital, Cape Town in whom GTD is suspected by the physician based on clinical evaluation of abnormal vaginal bleeding or passing hydropic vesicles or grape-like pieces of tissue at < 20weeks gestational age, uterine enlargement greater than expected for gestational dates and hyperemesis will be identified and asked to participate in the study. Biodata, clinical, socio-demographic as well economic information will be collected from participants using a standardized questionnaire. Written informed consent will be obtained before the study begins.

Index test

Venous blood will be drawn from the participant and this sample will be sent to the laboratory where serum hCG level will be evaluated. Specimens will be coded to ensure blinding. An elevated hCG level above 80 000mlU/mL will define a positive result and below 80 000mlU/mL will define a negative result for GTD.

The participant will then have both trans-abdominal and endovaginal real time ultrasound examinations performed by a qualified sonographer using the combined American College of Radiology (ACR), the American Institute of Ultrasound in Medicine (AIUM), the American College of Obstetricians and Gynecologists (ACOG), and the Society of Radiologists in Ultrasound (SRU) Practice Guidelines for the Performance of Obstetrical Ultrasound (9). Positive result will include presence of solid and/or cystic molar tissue within the uterine cavity, presence of solid masses and/or cystic vascular spaces within the myometrium. When present,

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theca lutein cysts will also be evaluated. Negative result will be defined as absence of all of the aforementioned.

A positive index test result will be defined as positive hCG test and positive ultrasound test. A negative index test will be defined as positive hCG test and negative ultrasound test or negative hCG test and positive ultrasound test or negative hCG test and negative ultrasound test.

Reference Standard

A histological examination of the evacuated uterine contents, following suction curettage, will be the reference standard. This will be performed independently by two trained pathologists. The two pathologists will be blinded to each other’s results and also to the outcome of the index test. Both histological examinations will be carried out using the same histologic criteria by Szulman and Surti (10); the diagnosis of CHM will be made when there is a complete hydatidiform change from edema to central cistern formation, absence of an embryo, and conspicuous trophoblastic hyperplasia. The diagnosis of PHM will be made when there is partial villous involvement (normal and edematous villi), the presence of an embryo or fetus, mild to moderate focal trophoblastic hyperplasia, and ‘‘trophoblastic inclusion.’’ (10)

STATISTICAL ANALYSIS

Sample size estimation with the formulae provided in Jones (2003) yielded a sample size of 146 participants (11). This is for 95% sensitivity, 95% specificity, and 5% precision with an assumed prevalence of 50%. A 2 by 2 contingency table will be drawn up to present all the true positives, false positives, false negatives and true negatives. The sensitivity, specificity, positive and negative predictive values as well as likelihood ratios will be calculated with their 95% CIs. The primary outcome is diagnostic accuracy of the index test, compared to the reference test. The Kappa agreement (agreement beyond chance) between the two independent reference test results will be calculated and assessed as follows: k = 0 indicating poor agreement, k = 0 to 0.2 indicating slight agreement, k = 0.21 to 0.4 indicating fair agreement, k = 0.41 to 0.6 indicating moderate agreement, k = 0.61 to 0.8 indicating substantial agreement, and k = 0.81 to 1.0 indicating almost perfect agreement. We will also investigate the effect of gestational age on the accuracy of the index test by stratifying participants into 2 groups: gestational age <13weeks (1 st

trimester) and >13weeks (2nd trimester).

ETHICS

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This study protocol will be submitted to the research ethics committee of Stellenbosch University for approval prior to study commencement. Ethic approval will also be sought from the Western Cape Province Department of Health. Informed written consent will be sought from the management of Tygerberg Hospital. Written informed consent will be obtained from the participants before they are recruited into the study. Ascent forms will be provided for participants below the age of consent. Patient confidentiality will be maintained. Declaration of Helsinki Ethical Principles for Medical Research Involving Human Subjects and Good Clinical Practice will be adhered to.

STUDY LIMITATIONS

It may be difficult to get the sample size needed for this study given the incidence of GTD in South Africa as reported by Moodley et al is 1.2 per 1000 deliveries (12). A multi-centered approach would make up the numbers but this is not logistically feasible for this study given the limited funds available.

The variability in the interpretation of sonographic images is another limitation foreseen in this study. Establishing the reliability of the ultrasonography test will prove useful in future studies.

Given the low prevalence of GTD in South Africa, the use of 50% prevalence in the calculation of the sample size is for logistic reasons. The predictive values obtained in this study may differ significantly from that obtained in everyday clinical practice in South Africa.

Given the nature of the tests, the disease in question and for ethical reasons, the reference test may be carried out on only the index test positives and not on index test negatives. This introduces partial verification bias and may affect both sensitivity and specificity.

Figure 1 Study outline Illustrated by Flow diagram

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Bibliography

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Ethics approval and written informed consent

Study setting:

Tygerberg hospital, Cape Town

Index test:

Venous blood sample will be taken for hCG estimation

Ultrasound examination to be performed by a trained sonographer

Reference test:

Histological examination of uterine contents

2 trained gynecological pathologists will carry out the test independently and will be blinded to index test

result.

Participants are informed of the outcome of the tests

Physicians will inform potential participants

about the study and enroll participants

Participants will be followed up for 6 months

1. Gestational trophoblastic disease within an elective abortion population. Cohen BA, Burkman RT, Rosenshein NB, Atenza MF, King TM, Parmley TH. 135(4), s.l. : American Journal of Obstetrics and Gynaecology, 1979, American Journal of Obstetrics and Gynaecology. 452-454.

2. Gestational trophoblastic disease in Tunisia. Mourali M, Fkih C, Chikhaoui JE, Hassine ABH, Bino us N, Zineb NB, et al. 86(7), s.l. : Tunis Med, 2008. 665-669.

3. Can laboratory and clinical signs predict persistence in gestational trophoblastic disease? Kosus N, Celik C, Kosus A. 30(2), s.l. : Erciyes Tip Dergisi, 2008. 57-64.

4. Hydatidiform mole in southern Iran: A statistical survey of 113 cases. Javey H, Sajadi H. 15(5), s.l. : International Journal of Gynaecology and Obstetrics, 1978. 390-395.

5. Gestational trophoblastic disease. Seckl MJ, Sebire NJ, Berkowitz RS. 376: 717 - 729, s.l. : Lancet, 2010, Lancet.

6. Gestational trophoblastic neoplasia. FIGO 26th annual report on the results of treatment in gynaecological cancer. Ngan HY, Odicino F, Maisonneuve P et al. 95(Supplement1), s.l. : International Journal of Gynaecology and Obstetrics, 2006. S193-S203.

7. Changes of clinical features in hydatidiform mole: analysis of 113 cases. Hou JL, Wan XR, Xiang Y et al. 53, s.l. : Journal of Reproductiive Medicine , 2008. 629-633.

8. Histomorphometric features of hydatidiform moles in early pregnancy: relationship to detectability by ultrasound examination. Fowler DJ, Lindsay I, Seckl MJ, Sebire NJ. 29, s.l. : Ultrasound Obstet Gynaecol , 2007. 76-80.

9. ACR–ACOG–AIUM–SRU PRACTICE GUIDELINE FOR THE PERFORMANCE OF OBSTETRICAL ULTRASOUND. s.l. : http://www.acr.org/~/media/ACR/Documents/PGTS/guidelines/US_Obstetrical.pdf, 2013.

10. The syndromes of hydatidiform mole: II. Morphologic evolution of the complete and partial mole. Szulman, A E and Surti, U. 132, s.l. : American Journal of Obstetrics and Gynaecology, 1978. 20-27.

11. An introduction to power and sample size estimation. Jones, S R, Carley, S and Harrison, M. 20, s.l. : Emergency Medicine Journal, 2003. 453-8.

12. Gestational trophoblastic syndrome: an audit of 112 patients. A South African experience. Moodley, M, Tunkyi, K and Moodley, J. 13, s.l. : International Journal of Gynaecological Cancer, 2003. 234.

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