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SYMPOSIUM IOMC 2011
Year : 2011  |  Volume : 3  |  Issue : 3  |  Page : 329-338  

Transvaginal ultrasonography in first trimester of pregnancy and its comparison with transabdominal ultrasonography


Department of Radiology, Government Medical College and Rajindra Hospital, Punjab, India

Date of Submission05-May-2011
Date of Decision05-May-2011
Date of Acceptance05-May-2011
Date of Web Publication3-Sep-2011

Correspondence Address:
Aneet Kaur
Department of Radiology, Government Medical College and Rajindra Hospital, Punjab
India
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DOI: 10.4103/0975-7406.84432

PMID: 21966152

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   Abstract 

Objectives : Examination of pregnant women in the first trimester with transvaginal ultrasonography with the aim to study various fetal development markers, e.g., gestation sac, yolk sac, fetal heart motion, CRL length, and fetal anatomy in both normal and abnormal pregnancies. Comparative evaluation of transvaginal ultrasonography vis-ΰ-vis transabdominal scanning in the study of first trimester of pregnancy and its complications. To assess the relative merits and demerits of transvaginal ultrasonography in comparison with the transabdominal technique. Materials and Methods : The study will be conducted on 50 females patients during the first trimester of pregnancy. The study population will consist of both normal and abnormal pregnancies. These patients will be included on the basis of suspicion of or proven pregnancy of duration up to 12 weeks from LMP. The evaluation of the patients will include the following: Record of patients obstetrical history and clinical examination, record of pregnancy test and relevant investigations, ultrasonic examination of pregnancy. (a) Transabdominal ultrasound scanning will be done with moderately distended bladder by using real time scanners with low frequency probe (3/3.5 MHz); (b) transvaginal sonography will be done with the real-time sector scanner using high-frequency endovaginal probe (5/7.5 MHz), after the patient voids urine. Relevant images will be taken by using the multiformat automatic camera. Results and Conclusions : In the study of 46 normal intrauterine pregnancies, TVS showed additional information in 36 patients (78.3%) as compared to TAS, in detection of gestation sac, yolk sac, double bleb sign, or better visualization of embryonic anatomy. In the abnormal pregnancy (n=17), TVS provided more information in 11 cases (64.9%), which included detection of embryonic demise, yolk sac, double bleb sign, or subchorionic hemorrhage. Regarding ectopic gestations (n=7), TVS gave additional information in 5 cases (71.4%) which included detection of ectopic fetal pole, yolk sac, decidual cast, adnexal mass, and fluid in cul de sac. In two cases, both TAS and TVS gave equal information. However, in 2 cases TAS demonstrated the extent of intraabdominal fluid better than TVS. The other advantages of TVS over TAS are that there is no need for the patient to have uncomfortably full bladder and time is saved from having to wait for bladder to fill. Thus, the potential preoperative patient can be kept fasting. TVS is also superior in obese patients, in patients with retroverted uterus and it also bypasses obstacles such as bone, gas filled bowel, and extensive pelvic adhesions. The limitations encountered with TVS were limited manoveuribility of probe and because of the unorthodox position and angle of the transducer, correct orientation was difficult initially.

Keywords: Comparison, first trimester of pregnancy, transvaginal ultrasonography, various fetal development markers


How to cite this article:
Kaur A, Kaur A. Transvaginal ultrasonography in first trimester of pregnancy and its comparison with transabdominal ultrasonography. J Pharm Bioall Sci 2011;3:329-38

How to cite this URL:
Kaur A, Kaur A. Transvaginal ultrasonography in first trimester of pregnancy and its comparison with transabdominal ultrasonography. J Pharm Bioall Sci [serial online] 2011 [cited 2014 Oct 31];3:329-38. Available from: http://www.jpbsonline.org/text.asp?2011/3/3/329/84432

Ultrasonography is one of the most important and useful diagnostic tool in the field of modern medicine. Being noninvasive, safe and without hazards of radiation, it has gained wide acceptability, as an integral part of basic investigative procedures. The convenience, high portability, rapidity, and accuracy are few of the advantages of ultrasound over the other procedures. In the last two decades, ultrasound has become an essential diagnostic imaging modality in the field of obstetrics and is being extensively used for evaluation of pregnancy. Obstetrical ultrasound enables the clinician to evaluate the development, growth, and well being of the fetus. The ability to study the fetus in the intrauterine environment has been notably enhanced by dramatic improvement in imaging. Although static scan imaging may compliment ultrasound studies, obstetrical examination should always be accompanied by real time modalities.

In the standard transabodominal ultrasonography lower frequencies with poorer axial resolution (ability to distinguish two separate points in the direct line of the ultrasound beam) are being used to image structures deeper in the body such as pelvic organs. The recent development of higher frequency (5 and 7.5 MHz) transvaginal transducer probe has resulted in the increased resolution of the female pelvic organs as the endovaginal probe is placed close to the pelvic organs than the transabdominal probe.

Transabdominal scanning is used predominantly in second and third trimesters of gestation. Its use in first trimester is relatively limited and mostly diagnostic in nature. The introduction of the higher frequency transvaginal probe, with its higher resolution of images, opens new possibilities to study early gestation (Timor Tritsch). [1]

Acharya G, Morgan H [2] studied first-trimester, three-dimensional transvaginal ultrasound volumetry in normal pregnancies and spontaneous miscarriages. There was an exponential correlation between the mean gestational sac diameter and gestational sac volume and the crown-rump length and embryonic volume in cases of both normal and failed pregnancies.

Lazarus E [3] - what is new in first trimester ultrasound. He commented that there are several advantages to ultrasound examination in early pregnancy. Ultrasound performed during the first trimester confirms an intrauterine pregnancy, establishes accurate dating, and is crucial in diagnosing early pregnancy failure and ectopic pregnancy.

Hisaya Takeuchi [4] - Transvaginal ultrasound in the first trimester of pregnancy. He commented that recent improvements in transvaginal ultrasound permit the extremely detailed observation of the morphology of the early conceptus in utero.

Lucie Morin et al., [5] - ultrasound evaluation of first trimester pregnancy complications. They concluded that women presenting with first trimester bleeding may be incorrectly diagnosed with a missed abortion and (or) may be inappropriately reassured about viability. Transvaginal ultrasound provides improved resolution allowing description of early embryonic development characteristics.

Diane Ursu [6] - first trimester ultrasound: obstetric ultrasound for viability, age, and maternal health. He commented that first trimester abdominal and transvaginal ultrasound may be used. The uterus and ovaries, corpus luteum cyst, gestational sac, and embryo can be visualized/measured.

Timothy Jang et al., [7] in its bedside ultrasonography, first-trimester pregnancy: treatment and medication commented that ultrasonography maintains a high level of suspicion for ectopic pregnancy as a cause of symptoms during the first trimester.

Not many workers have compared various parameters of early pregnancy (normal as well as abnormal) by transvaginal and transbdominal sonography on the same patients. So, it was thought that it would be highly imperative to study both these techniques (TVS and TAS) on the same patients to rule out any subjectivity and examiner's bias for either of these two methods. Keeping these facts in mind, the present study was undertaken.


   Materials and Methods Top


The study was conducted on 70 female patients during the first trimester of pregnancy. These patients were included on the basis of suspicion or proven pregnancy of duration up to 12 weeks from last menstrual period (LMP). The patients were referred to for sonographic examination either for confirmation of pregnancy and fetal well-being or for various clinical indications such as bleeding per vaginum, pain abdomen, excessive vomiting, suspected ectopic pregnancy etc.

Patients obstetrical history, clinical examination, and relevant investigations including pregnancy test etc were recorded.

Transabdominal scanning was done with distended bladder by using real time scanners with the low frequency probe (3/3.5 MHz). After this patient was asked to void urine and transvaginal sonography was done with the real time sector scanner using high-frequency (5/7.5 MHz) endovaginal probe [Figure 1] and [Figure 2]. The scanning was done according to the technique described by Timor Tritsch et al.[1] The procedure was explained in detail to the patient and consent was taken. The endovaginal transducer was covered with a sterile condom lubricated with gel before insertion. The patient was placed in the lithotomy position with a slight reversed trendelenburg tilt. The transducer was inserted approximately 6-8 cm into the vagina. Scanning was done in both coronal and sagittal planes. The manipulations used for obtaining images in various planes and depth were tilting or angling the shaft by its handle. Push-pull rotation thus bringing a deeper or closer region organ into the focal zone and a rotating motion of the handle along the longitudinal axis of the probe thereby rotating the scanning plane to achieve sections along a full 360° of the pelvis.
Figure 1: Diagnosis-Normal early pregnancy. (a) (TVS)-Shows a single Intrauterine gestation sac. (b) (TAS)-Does not show any intrauterine gestation sac

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Figure 2: Diagnosis-Normal early pregnancy. (a) (TVS)-Shows a single Intrauterine gestation sac with a double decidual sac sign, embryo with FHM, yolk sac. (b) (TAS)-Shows a single Intrauterine gestation sac with a double decidual sac sign, no embryo visualised, yolk sac present

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A systematic approach was used for both TVS and TAS. First the uterus was scanned, then the adnexa, and finally the cul-de sac. The number, shape, and size of the gestation sac was assessed. The gestation sac was measured from inside the sac to inside decidual reaction. MSD was taken as average of two dimensions. The sac wall was evaluated for the double decidual reaction of early pregnancy and for decidual cast of ectopic pregnancy. The gestation sac was looked for the presence of yolk sac and its shape, size, and location was studied. Any abnormality of these were noted. In all the gestation sac, embryo with heart beat was sought.

In the early pregnancy between fifth to seventh week of menstrual age, the length of the demarcating line between the double bleb (echogenic line representing early embryo) was measured representing the crown rump length (CRL) of the embryo [Figure 3]. From eight to 12 th week, embryo appears as echogenic structure rather than echogenic line and maximum length of the embryo excluding yolk sac was measured [Figure 4],[Figure 5],[Figure 6],[Figure 7],[Figure 8],[Figure 9].
Figure 3: Diagnosis-Normal early pregnancy. (a) (TVS)-Shows a single Intrauterine gestation sac with a double decidual sac sign, single embryo with FHM, yolk sac, fetal head with single sonolucent ventricle, both upper/lower limb buds. (b) (TAS)-Shows a single Intrauterine gestation sac with a double decidual sac sign, single embryo with FHM seen

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Figure 4: Diagnosis-Normal pregnancy. (a) (TVS)-Shows a single Intrauterine gestation sac with a double decidual sac sign, single embryo with FHM, single undivided ventricle in fetal head, both upper/lower limb buds. (b) (TVS)-Shows a single Intrauterine gestation sac with a double decidual sac sign, fetal spine seen. (c) (TAS) - Shows a single Intrauterine gestation sac with a double decidual sac sign, single embryo with FHM, no other details seen except yolk sac in real time scanning

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Figure 5: Diagnosis-Twin pregnancy. (a) (TVS)-Shows a twin gestation sac with a double decidual sac sign, one gestation sac shows embryo with FHM, 2nd adjacent gestation sac shows neither a yolk sac nor an embryo. Thick wall separating the gestation sac suggest a dichorionic twin gestation. (b) (TAS)-Shows a single gestation sac with an embryo with FHM seen

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Figure 6: Diagnosis-Missed Abortion. (a) (TVS)-Shows a single Intrauterine gestation sac with irregular outline, a single embryo seen, no FHM seen, a solid looking yolk sac seen. (b) (TAS)-Shows a single Intrauterine gestation sac, no internal details seen in gestation sac

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Figure 7: Diagnosis-Blighted Ovum. (a) (TVS)-Shows a single Intrauterine gestation sac which shows a large amnion but no embryo seen. (b) (TAS)-Shows a single Intrauterine gestation sac, no internal details seen in gestation sac

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Figure 8: Diagnosis-Pregnancy with subchorionic hemorhage. (a) (TVS)-Shows a single Intrauterine gestation sac with subchorionic hemorrhage, a single embryo with FHM seen, fetal head showing echogenic choroid plexus with surrounding ventricles seen, both upper and lower limb buds seen. (b) (TAS)-Shows a single Intrauterine gestation sac, a single embryo with FHM seen, subchorionic hemorrhage and other sonoembryological details were not seen

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Figure 9: Diagnosis-Pregnancy with congenital abnormality omphalocele with anencephaly. (a) (TVS)-Shows a single Intrauterine gestation sac with a single fetus with FHM seen, a large omphalocele seen that appears to contain bowel liver and gall bladder. Absence of cranial vault and eviscerated brain matter seen. (b) (TAS) -Shows a single Intrauterine gestation sac with a single fetus with FHM seen, suspected omphalocele, suspected anencephaly

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The maximum details of embryonic anatomy wherever possible were sought and recorded. Also, maximum zoomed scanning was done for better visualization of the anatomic details of the embryo.

The diagnosis of blighted ovum was made with sonar in which the gestation sac could be defined but which could not be demonstrated to contain any fetus. [8] For TAS, a gestational sac diameter of 20 mm without a yolk sac or 25 mm without a fetus was taken as a criteria of blighted ovum.[9] For TVS the corresponding figures were 10 and 18 mm, respectively [Figure 7]. [10]

The diagnosis of missed abortion by either technique was made when a fetus could be clearly demonstrated and measured by Sonar within the gestation sac but no fetal heart movements could be detected. [11]

In case of ectopic pregnancy sonographic diagnosis of ectopic pregnancy was made either by demonstration of a yolk sac or fetal pole in the gestational sac located in the adnexa or by visualization of empty uterus, adnexal mass, adnexal ring (extra uterine gestation sac or a cyst with an echogenic ring in the adnexa), or haematosalphinx. In addition to these, the uterus was scanned for the decidual cast (fluid collection in the endometrial cavity with a thick echogenic border), for fluid in cul de sac and for the presence of intraabdominal fluid.

Relevant images in both techniques were recorded on a polyester base single coated 8 × 10" size film by using multiformat automatic camera.

The observations and results thus obtained were compiled and evaluated.


   Results and Discussion Top


This study has been undertaken to examine pregnant women in the first trimester with transvaginal ultrasonography to study various fetal developmental markers, e.g., gestation sac, yolk sac, fetal heart motion, CRL, and fetal anatomy in both normal and abnormal pregnancies and to compare it with transabdominal sonography and to evaluate the advantages and limitations of TVS as compared to TAS.

The study was conducted on 70 female patients during the first trimester of pregnancy. These patients were included on the basis of suspicion or proven pregnancy upto 12 weeks from LMP. All the patients were subjected to thorough clinical examination. The maximum number of patients were in the third decade (21-30 years age group) [Table 1].
Table 1: Distribution of cases according to age

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In this study, 40% of patients gave preference to TVS over TAS, whereas 51.4% of patients preferred TAS and 8.6% of patients gave no preference to either of the technique [Table 2].
Table 2: Preference of TVS versus TAS

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In this study the total number of patients (n=70) were divided into three groups according to the final outcome of pregnancy. These groups were normal pregnancies (n=46), abnormal pregnancies (n=17), and ectopic pregnancies (n=7). The abnormal pregnancies comprised of seven cases of missed abortion, six cases of blighted ovum, and four miscellaneous cases [Table 3].
Table 3: Distribution of cases according to final diagnosis of pregnancy

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While examining the cases for gestation sac in both normal and abnormal pregnancies (n=63) TVS showed single gestation sac in 62 patients and twin gestation sac in one case. Whereas in comparison TAS failed to detect a gestation sac with MSD of 3 mm and also the twin gestation sac [Table 4],[Figure 5].
Table 4: Number of gestation sac seen (n=63)

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Shape of the gestation sac

In the normal pregnancy (n=46) TVS showed regular gestation sac in all the patients (100%) whereas TAS showed regular shape in 43 cases (93.5%) and distorted shape of gestation sac in three patients (6.5%) due to overfilled urinary bladder. In the abnormal pregnancy, TVS showed abnormality in shape of gestation sac in five cases (29.4%) as compared to two cases (11.8%) by TAS. Thus, a conclusion can be drawn that abnormal shape of gestation sac is diagnostic of abnormal pregnancy and is 100% specific in the case of TVS, whereas this cannot be said about TAS, where over distended urinary bladder may distort even the normal gestation sac [Table 5],[Figure 4].
Table 5: Shape of the gestation sac

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Double decidual sac sign

An attempt was made to detect double decidual sac sign amongst the patients whose gestational age was between 5-10 weeks from LMP. In the normal pregnancy (n = 43), TVS detected DDSS in 32 patients (74.4%) and DDSS was not seen in 11 patients (25.6%), whereas with TAS DDSS was seen in 27 patients (62.8%), and was not seen in 16 patients (37.2%). In the abnormal pregnancy (n=17) TVS visualized DDSS in five cases (50%) and it was not seen in five cases (50%), whereas with TAS, the corresponding Figures were four cases (40%), and six cases (60%), respectively. The above results are comparable to the following studies [Table 6].
Table 6: Detection of the double decidual sac sign between 5-10 weeks

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Yolk sac

In the normal pregnancy yolk sac was seen in 38 patients (82.6%) by TVS, whereas with TAS yolk sac was seen in 17 cases (37%) only ( P < .01). In abnormal pregnancy, yolk sac was seen in seven cases (41.2%) and was not visualized in 10 cases (58.8%) by TVS. Whereas in comparison with TAS, YS was seen in one case (5.9%) and it was not seen in 16 cases (94.1%). While scanning for abnormalities of yolk sac (size, shape, location etc.), TVS was able to visualize abnormalities of YS in six cases (35.4%) as compared to one case (5.9%) by TAS. The various abnormalities of YS seen by TVS included distorted shape (one case), abnormal location (one case), abnormal size (one case), solid looking (two cases), and calcified YS (one case). In comparison, TAS visualized only one case of calcified YS. The above findings indicated that detection of any abnormality of YS by TVS was a strong indicator of abnormal outcome of pregnancy and conversely the absence of any abnormality in TVS examination almost always predicted normal outcome [Table 7] and [Table 8].
Table 7: Detection of the yolk sac (YS)

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Table 8: Abnormalities of yolk sac in abnormal pregnancies (n=17)

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Double bleb sign

In the present study in normal pregnancy group, the double bleb sign was seen in 15 cases (32.6%) with TVS, whereas in comparison it was seen in none of the cases by TAS (P < 0.01). In the abnormal pregnancy group, double bleb sign was seen in one patient by TVS, whereas it was not seen in any of the cases by TAS [Table 9].
Table 9: Detection of the double bleb sign

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Fetal pole/fetus and fetal heart motion (FHM)

While scanning with TVS in the normal pregnancy, fetal pole/fetus was seen in 43 cases (93.5%), whereas in comparison with TAS FP/fetus was seen in 33 cases (71.7%). In the abnormal pregnancy, FP/fetus was seen in 11 cases with TVS, as compared to six cases with TAS. In the normal pregnancy, fetal heart motion (FHM) was observed with TVS in all the 43 cases (91.3%) where FP/fetus was seen, whereas in comparison with TAS, FHM was seen in 32 cases (69.6%). Statistically this difference was found to be significant (P < 0.01) [Table 10].
Table 10: Detection of fetal pole/fetus

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Mean sac diameter

In the normal pregnancy minimal MSD measured by TVS was 3 mm at 4.5 weeks from LMP, whereas minimal MSD measured by TAS was 10 mm at 6.5 weeks from LMP. The mean values of MSD obtained by TVS and TAS, at various weeks from LMP were almost identical [Table 11].
Table 11: MSD distribution according to gestational age in normal pregnancy (n=44)

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Crown-rump length

The mean values of CRL obtained at various gestational weeks with TVS and TAS were nearly identical except during the fifth and sixth menstrual week. During these two weeks, the mean value of CRL by TVS was lower than that of TAS, as TVS could detect a minimal CRL of 3 mm whereas TAS failed to detect CRL below 7 mm. In the present study, while correlating early pregnancy structures to gestation age in normal pregnancy, it was observed that DDSS was seen earliest at gestation age of 37 days at MSD of 8 mm with TVS, whereas in comparison with TAS DDSS was seen earliest at gestation age of 43 days at corresponding MSD of 13 mm [Table 12].
Table 12: CRL distribution according to gestation age in normal pregnancy (n=44)*

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Yolk sac in this study was seen earliest at 41 days of gestation age by TVS and at 46 days by TAS in the normal pregnancy. The corresponding MSD at which yolk sac was seen earliest was 10 mm by TVS and 17 mm by TAS. In this study, the embryo with heartbeat was seen earliest at 41 days by TVS and at 47 days by TAS. Also FHM was seen earliest at MSD of 10 mm by TVS and at 18 mm by TAS. The minimum CRL length which showed FHM was 3 mm with TVS and 7 mm on TAS. These findings are consistent with those of following authors [Table 13].
Table 13: Relationship of gestation age to early pregnancy structures in normal pregnancy (n=44)

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Missed abortion

In this study, a diagnosis of missed abortion was made in all the seven cases by TVS, whereas with TAS, it was possible only in two cases. In the remaining five cases of missed abortion, TAS failed to detect embryonic demise, whereas in comparison, TVS showed embryonic demise in all the seven cases. The present study showed that TVS could diagnose all the six cases of blighted ovum, whereas with TAS the diagnosis of blighted ovum was made in 10 cases. These included five cases of missed abortion that were diagnosed as blighted ovum by TAS due to failure to detect embryonic demise in these cases. One case of normal pregnancy with MSD of 25 mm was misdiagnosed as Blighted ovum by TAS, as it did not show either a yolk sac or a viable embryo. TVS in this case correctly diagnosed it as normal pregnancy by demonstrating both a yolk sac and a viable embryo. Two cases where yolk sac or living embryo could not be seen with TVS at MSD of 1.7 and 1.5 cms, respectively, were diagnosed as blighted ovum by TVS (confirmed subsequently), whereas with TAS, diagnosis was not possible at this stage [Figure 6]. These results are comparable to those of other authors [Table 14].
Table 14: Detection of embryonic demise in missed abortion (n=7)

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Subchorionic hemorrhage

In this study pregnancy with subchorionic hemorrhage was seen in two patients with TVS, whereas with TAS it was detected only in one case [Figure 8].

Congenital abnormality

In this study, TVS could diagnose an encephalic fetus with omphalocele unequivocally, whereas with TAS though the diagnosis was suspected a confident diagnosis could not be given [Figure 3].

Ectopic pregnancy

The present study had seven surgically proven ectopic pregnancies. Transvaginal sonography identified adnexal ring containing a yolk sac and a nonviable fetus in one case, whereas TAS failed to see either the yolk sac or the fetus. Decidual cast was seen in two cases with endovaginal sonography, whereas with TAS, it was detected in one case only. Minimal amount of fluid was seen in the Cul de sac in one case, whereas this was not detected by TAS. However, TVS failed to detect the extent of haemoperitoneum in two cases, which was appreciated only with TAS. These findings are comparable to those of other authors [Table 15].
Table 15: Detailed diagnostic breakdown (n = 70)

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Overall evaluation of TVS

In this study of 46 normal intrauterine pregnancies, TVS showed additional information in 36 patients (78.3%) as compared to TAS, in detection of gestation sac, yolk sac, double bleb sign or better visualization of embryonic anatomy. In the abnormal pregnancy (n=17), TVS provided more information in 11 cases (64.9%), which included detection of embryonic demise, yolk sac, double bleb sign, or subchorionic hemorrhage. Regarding ectopic gestations (n=7), TVS gave additional information in five cases (71.4%) which included detection of ectopic fetal pole, yolk sac, decidual cast, adnexal mass, and fluid in the cul de sac. In two cases, both TAS and TVS gave equal information. However, in 2 cases TAS demonstrated the extent of intraabdominal fluid better than TVS.

The other advantages of TVS over TAS are that there is no need for the patient to have uncomfortably full bladder and time is saved from having to wait for bladder to fill. Thus, the potential preoperative patient can be kept fasting. TVS is also superior in obese patients, in patients with retroverted uterus and it also bypasses obstacles such as bone, gas filled bowel and extensive pelvic adhesions.

The limitations encountered with TVS were limited manoeuribility of probe and because of the unorthodox position and angle of the transducer, correct orientation was difficult initially.


   Conclusions Top


From last two decades, ultrasound has become an essential diagnostic modality in the field of obstetrics for evaluation of pregnancy and fetal well-being. However, the standard transabdominal scanning using lower frequencies with relatively poorer axial resolution is unsuitable for imaging first trimester conceptus. The introduction of higher frequency transvaginal probe that can be placed close to the pelvic organs and has better resolution has opened entirely new possibilities to study in detail the early gestation. Not many workers have compared various parameters of early pregnancy (normal as well as abnormal) by transvaginal and transbdominal sonography on the same patients. Therefore, it was thought that it would be highly imperative to study both these techniques on the same patients to rule out any subjectivity and examiner's bias.

To conclude TVS reliable identified normal and abnormal pregnancies and various developmental markers at an earlier stage than with TAS.


   Acknowledgement Top


This paper has been accepted and presented in the 4 th International Online Medical Conference (IOMC 2011).

 
   References Top

1.Timor-Tritsch IE, Farine D, Rosen MG. A close look at early embryonic development with the high frequency transvaginal transducer. Am J Obstet Gynecol 1988;159:679-81.  Back to cited text no. 1
    
2.Acharya G, Morgan H. First-trimester, three-dimensional transvaginal ultrasound volumetry in normal pregnancies and spontaneous miscarriages. Ultrasound Obstet Gynecol 2002;19:575-9.  Back to cited text no. 2
[PUBMED]  [FULLTEXT]  
3.Lazarus E. What's new in first trimester ultrasound. Radiol Clin North Am 2003;41:663-79.  Back to cited text no. 3
[PUBMED]    
4.Takeuchi H. Transvaginal ultrasound in the first trimester of pregnancy.(uptodate) [Last accessed on 2004 Mar 2].  Back to cited text no. 4
    
5.Morin L, Van den Hof MC; Diagnostic Imaging Committee, Society of Obstetricians and Gynaecologists of Canada. Ultrasound Evaluation of First Trimester Pregnancy Complications. J Obstet Gynaecol Can 2005;27:581-91.  Back to cited text no. 5
[PUBMED]    
6.Diane U. First Trimester Ultrasound: Obstetric Ultrasound for Viability, Age, and Maternal Health. From Ultrasound in Obstetrics And Gynecology: Textbook and Atlas, Volume 2-Gynecology Aug 22, 2009.  Back to cited text no. 6
    
7.Timothy Jang, Chen JC. Bedside Ultrasonography, First-Trimester Pregnancy: Treatment and Medication. (uptodate).Updated: May 29, 2009.  Back to cited text no. 7
    
8.Robinson HP. "Gestational sac" volumes determined by sonar in the first trimester of pregnancy. Br J Obstet Gynecol 1975;82:100-7.  Back to cited text no. 8
    
9.Nyberg DA, Laing FC, Filly RA. Threatened abortion: Sonographic distinction of normal and abnormal gestation sacs. Radiology 1986;158:397-400.  Back to cited text no. 9
[PUBMED]  [FULLTEXT]  
10.Nyberg, DA, Hill, LM. Normal early intrauterine pregnancy: Sonographic development and hCG correlation. In Transvaginal Ultrasound, Nyberg, DA, Hill, LM, Bohm-Velez, M, Mendelson, EB (Eds), Mosby-Year Book, St. Louis 1992. p.65.  Back to cited text no. 10
    
11.Robinson HP. Diagnosis of early pregnancy failure by sonar. Br J Obstet Gynecol 1975;82:849-56.  Back to cited text no. 11
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10], [Table 11], [Table 12], [Table 13], [Table 14], [Table 15]



 

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