Ultrasound in the first trimester of pregnancy

High-resolution sonography, including transvesical and endovaginal techniques, has resulted in enhanced visualization of embryonic and extraembryonic structures. With endovaginal sonography, the gestational sac may be seen within the decidua at about 4.5 weeks menstrual age. The yolk sac is the first structure to be seen within the gestational sac, and confirms the presence of a gestational sac rather than a decidual cast. The embryo is identified by endovaginal sonography early in the 6th week, and cardiac activity is routinely identified by a crown-rump length of 3 to 5 mm. On endovaginal sonography, absent cardiac activity in an embryo having a crown-rump length of greater than 3 to 5 mm indicates embryonic death. With endovaginal scanning, a gestational sac of greater than 8 mm without a yolk sac, or greater than 16 mm without an embryo, also indicates a nonviable pregnancy. Routine sonography primarily to assess the menstrual age should be performed in the second trimester, when added clinically relevant information may be obtained. Although it is possible to diagnose some anomalies in the first trimester, most remain second trimester sonographic diagnoses.     

Complicated first-trimester pregnancies: evaluation with endovaginal US versus transabdominal technique

Endovaginal ultrasound (US) was performed in 38 pregnant women at 5-12 menstrual weeks, when the initial transabdominal sonograms had been considered inconclusive or equivocal. Clinical follow-up disclosed 32 intrauterine pregnancies (12 living, 18 spontaneous incomplete abortions, and two embryonic demises) and six ectopic pregnancies. In the 32 intrauterine pregnancies (normal and abnormal), the correct diagnosis was made in all cases with endovaginal US. The endovaginal images demonstrated the intrauterine embryo, its heart motion, and the yolk sac more clearly and more often when these structures were not apparent on the transabdominal scans. Abnormal gestational sacs were better resolved. In the six cases of ectopic pregnancy, while an extrauterine ectopic sac was visualized in only three, absence of an intrauterine gestational sac was confirmed in all cases with endovaginal scanning. No endovaginal study yielded less information than its transabdominal counterpart. Endovaginal sonography is likely to be diagnostic when transabdominal images fail to yield a definitive diagnosis in early pregnancies.     

Endovaginal sonographic evaluation of ectopic pregnancy: a prospective study

To determine the value of endovaginal sonography for evaluating women with a suspected ectopic gestation, we prospectively studied a group of 84 pregnant women in whom conventional transabdominal sonograms failed to show a living embryo. Of 84 patients studied, 25 had an ectopic gestation, 32 had a normal intrauterine pregnancy, and 27 had an abnormal (nonviable) intrauterine pregnancy. Endovaginal sonography, compared with transabdominal sonography, provided additional information in 50 cases (60%) and less information in only three cases (4%). Of 25 ectopic gestations, endovaginal sonography provided new information in 15 cases (60%) including detection of an extrauterine gestational sac (10 cases), extrauterine embryo (two cases), or adnexal mass (three cases) not observed on transabdominal sonography. Of 32 normal intrauterine pregnancies, endovaginal sonography provided additional information in 26 cases (81%) including detection of a yolk sac (14 cases), living embryo (11 cases), or small gestational sac (one case) not seen on transabdominal sonography. Of 27 abnormal intrauterine pregnancies, endovaginal sonography showed additional information in nine cases (33%) including detection of embryonic demise (three cases), retained intrauterine products (four cases), or a yolk sac (two cases) not seen on transabdominal sonography. Patient acceptance of endovaginal sonography was excellent; 82% of the patients preferred this method to transabdominal sonography, 13% expressed no preference, and 5% preferred transabdominal sonography. We conclude that endovaginal sonography can provide significant additional information in the majority of women who are referred for sonography with a suspected ectopic gestation. We believe that this method should become a integral part of sonographic evaluation in women who are suspected of having an ectopic gestation when conventional transabdominal sonography fails to show a living embryo.     

Threatened abortion: sonographic distinction of normal and abnormal gestation sacs

In an attempt to determine whether sonographic evaluation alone can distinguish normal from abnormal gestation sacs, a retrospective analysis was performed of ultrasound (US) scans from 168 women with threatened abortion. Gestation sacs were judged to be abnormal on the basis of specific sonographic criteria including large size (greater than or equal to 25 mm mean sac diameter) without an embryo; distorted shape; thin (less than or equal to 2 mm), weakly echogenic, or irregular choriodecidual reaction; absence of a double decidual sac; and low position. Two criteria - large sac and distorted shape - had 100% specificity and were called major criteria. The remaining criteria were individually less specific, although 100% specificity was achieved when three or more of these minor criteria were demonstrated. When one major or three minor criteria were present, 53% of abnormal gestations were correctly identified without any false-positive diagnoses. The authors conclude that experienced sonographers can reliably identify many abnormal gestation sacs on a single examination.     

Ectopic pregnancy: evaluation with endovaginal color flow imaging.

Endovaginal sonography and endovaginal color flow imaging were compared in 155 patients with clinical suspicion of ectopic pregnancy. Sixty-five patients (42%) had surgically confirmed ectopic pregnancies. Thirty-six of the pregnancies were diagnosed with endovaginal sonography alone, the criteria being an extrauterine sac or ectopic fetus (sensitivity, 54%). Sixty-two ectopic pregnancies were diagnosed with endovaginal color flow imaging (sensitivity, 95%) when an ectopic fetus or sac was seen or placental flow was identified in an adnexal mass separate from the ovary and uterus. The diagnosis of ectopic pregnancy was excluded with endovaginal sonography (specificity, 98%) and endovaginal color flow imaging (specificity, 98%) by finding an intrauterine gestation, nonvisualization of an adnexal mass, and absence of placental flow. Three false-positive and three false-negative diagnoses were made with endovaginal color flow imaging (positive predictive value, 97%). The addition of color Doppler flow imaging to endovaginal sonography allows increased sensitivity in the detection of ectopic pregnancy.     

Sonography during early pregnancy: dependence of threshold and discriminatory values on transvaginal transducer frequency

OBJECTIVE: Our goal was to determine if normal and abnormal pregnancies could be distinguished at smaller sac sizes with a higher frequency transvaginal transducer than with a 5-MHz transducer. SUBJECTS AND MATERIALS: Thirty-nine patients with potentially abnormal pregnancies identified with a 5-MHz transvaginal transducer were immediately reimaged with a 9-5-MHz transducer. We compared our ability to visualize the yolk sac, embryo, and cardiac activity relative to mean sac diameter on imaging at both frequencies in women with normal and abnormal pregnancies. RESULTS: Of the 39 pregnancies, 22 (56%) were normal or probably normal. Using the 5-MHz transducer, a yolk sac was first seen in a 6.4-mm gestational sac but was not definitively seen in 12 gestational sacs measuring 5-13 mm. Using the 9-5-MHz transducer, yolk sacs were identified in all gestational sacs measuring 4.6-13 mm, and live embryos were seen in five of eight sacs measuring 8.1-13 mm. The largest normal gestational sac without a live embryo measured 11 mm. When we compared these pregnancies with 17 (44%) abnormal pregnancies, we found that all pregnancies that had no yolk sac by the time the gestational sac measured 5.0 mm or no live embryo by 13 mm had abnormal findings on higher frequency imaging. CONCLUSION: The ability to visualize the yolk sac and embryo in early pregnancy is critically dependent on transvaginal transducer frequency. Threshold values and discriminatory sizes used to distinguish normal and abnormal pregnancies are smaller on higher frequency than on lower frequency imaging and, therefore, should be redetermined for specific transducer frequencies.     

Comparison of transvaginal and transabdominal sonography in the detection of early pregnancy and its complications

Ninety women with a positive pregnancy test and signs and symptoms of threatened abortion or ectopic pregnancy had endovaginal and abdominal sonography in order to compare the value of the two techniques for the detection of gestational abnormalities. Either a normal delivery occurred or surgical and/or pathologic confirmation of the diagnosis was available in all cases. Fifty-five women had normal intrauterine pregnancies, 22 had ectopic pregnancies, seven had blighted ova, and six had missed abortions. All 55 normal intrauterine pregnancies were detected by endovaginal sonography, while only 11 (20%) were diagnosed by transabdominal sonography. The yolk sac, fetal pole, and fetal heart motion were seen as early as 34 days from the last menstrual period with endovaginal sonography, compared with 42 days with transabdominal sonography. Fetal heart motion was detected with endovaginal sonography in fetal poles with a crown-rump length of 3 mm or greater, whereas the fetal pole had to be at least 6 mm before fetal heart motion could be detected with the transabdominal technique. In the 22 ectopic pregnancies, a specific diagnosis of an extrauterine sac containing a fetal pole with heart motion or yolk sac was possible in three cases with the endovaginal technique, but it was not possible in any case with transabdominal sonography. Both techniques showed that each of the seven patients with final diagnosis of blighted ova had a gestational sac that was 1.7 cm or larger without visualization of the fetal pole or yolk sac. All six missed abortions were detected by endovaginal sonography, but only three were diagnosed on transabdominal sonograms. Our findings show that endovaginal sonography is more sensitive than transabdominal sonography in the detection of early pregnancy and its complications.     

Suspected ectopic pregnancy: endovaginal and transvesical US

Until the advent of endovaginal ultrasonography (US), transvesical US was the only US technique availab le for evaluation of patients with suspected ectopic gestation. A study was undertaken to assess the predictive ability of transvesical and endovaginal US and determine whether endovaginal US could be used alone. Fifty-three patients who had a positive pregnancy test finding and who were at risk for ectopic pregnancy were examined with both endovaginal and transvesical US. Twenty-nine were examined retrospectively and 24 were examined prospectively. Standard sonographic criteria were used to differentiate between intrauterine pregnancy and ectopic gestation. The clinical or pathologic diagnosis was ectopic pregnancy in 18 patients (34%), normal intrauterine pregnancy in 19 (36%), and abnormal intrauterine pregnancy in 16 (30%). Endovaginal US increased the sensitivity of detecting a live ectopic pregnancy (from 6% to 17%). Endovaginal US, by allowing early diagnosis of intrauterine pregnancy, significantly increased the diagnostic accuracy for ectopic pregnancy (from 60% to 83%). Endovaginal US provided significant additional information in women referred for sonography with a suspected ectopic gestation. On the basis of these findings it is concluded that endovaginal US can be used alone in the majority of women with suspected ectopic gestation.     

Yolk sac diameter and shape at endovaginal US: predictors of pregnancy outcome in the first trimester.

Four hundred eighty-six consecutive women who underwent endovaginal sonography when their fetuses were less than 10 weeks menstrual age (MA) were evaluated to establish the normal size and shape of the secondary yolk sac (YS) and to assess the value of YS measurement in predicting pregnancy outcome in the first trimester. A YS diameter more than two standard deviations (SDs) above the mean when compared with the mean gestational sac diameter allowed prediction of an abnormal pregnancy outcome with a sensitivity of 15.6%, a specificity of 97.4%, and a positive predictive value of 60.0%. A YS diameter more than two SDs below the mean allowed prediction of an abnormal outcome with a sensitivity of 15.6%, a specificity of 95.3%, and a positive predictive value of 44.4%. No pregnancy with a normal outcome had a YS diameter of greater than 5.6 mm at less than 10 weeks MA. In six patients, the YS diameter was greater than 5.6 mm. All six had an abnormal outcome. Of seven patients with abnormal YS shape at initial sonography, three had abnormal YS shape at follow-up examinations. All three had an abnormal outcome.     

Ultrasound of the empty gestation sac in threatened abortion

The major concern when an empty gestation sac is encountered during threatened abortion is whether or not the pregnancy is viable. Viable pregnancies are managed expectantly, whereas non-viable pregnancies are treated by evacuation of the uterus. Early evacuation of the non-viable pregnancy spares the patient considerable anxiety and discomfort. This study shows that a single ultrasound examination is useful in differentiating viable from non-viable empty gestation sacs. The size of the empty gestation sac was found to be the most useful criterion for determining non-viability. Empty gestation sacs with sizes greater than 26 mm were non-viable, a specificity of 100%, accounting for 43% (42 out of 102) of patients in our series. Other ultrasound criteria found to be useful were shape, position, wall and decidual reaction. The positive predictive value for a successful outcome to a pregnancy was low, being only 41% (9 out of 22).     

Transvaginal sonography in the evaluation of normal early pregnancy: correlation with HCG level

Transvaginal sonography (TVS) is the procedure of choice in evaluating the viability of embryos early in pregnancy. However, viability based on TVS can be assessed more accurately when the exact gestational age from the last menstrual period is known or when the findings are correlated with beta human chorionic gonadotropin (HCG) levels. No large series has been reported with correlative data between early pregnancy findings, HCG, and gestational age. We performed 75 transvaginal examinations in 53 patients with proved normal pregnancy in the fifth through seventh weeks of gestation. The presence and size of the gestational sac, presence of a yolk sac, and identification of embryonic heart activity were correlated with the level of HCG. Sac size was correlated with yolk sac and heart activity and the three parameters correlated with gestational age in days. When the level of HCG reached 1000 mIU/ml by using the first International Reference Preparation, a gestational sac was seen sonographically in each patient. When the HCG level reached 7200 mIU/ml, a yolk sac was seen in every patient. Ten of 22 patients with HCG between 1000 and 7200 mIU/ml had a visible yolk sac. Every patient with an HCG level greater than 10,800 mIU/ml had a visible embryo with a heartbeat. A discriminatory level of 32 days was found for the presence of a gestational sac. A yolk sac was first seen in every patient between 36 and 40 days. Every patient with accurate dates greater than 40 days had an embryo with a heartbeat identified. When correlating sac size with structures within the sac, a yolk sac was first seen in a gestational sac between 6 and 9 mm and a heartbeat seen in every patient with a 9-mm or greater gestational sac diameter. These data allow identification of normal intrauterine pregnancy and distinction of normal from ectopic gestation at least 1 week earlier than is possible with transabdominal techniques.     

Diagnostic efficacy of endovaginal color Doppler flow imaging in an ectopic pregnancy screening program.

The authors compared the diagnostic yield of endovaginal color and pulsed Doppler ultrasound (US) in conjunction with endovaginal sonography with that of endovaginal sonography alone in patients prescreened to be at increased risk for ectopic pregnancy. Pelvic structures were evaluated for overall vascularity and for the presence of characteristic pulsed Doppler US velocity waveforms. The diagnostic sensitivity of the initial endovaginal sonographic examination increased with the addition of color and pulsed Doppler US, from 71% to 87% for ectopic pregnancy, from 24% to 59% for failed intrauterine pregnancy, and from 90% to 99% for viable intrauterine pregnancy. Specificities for endovaginal sonography with color and pulsed Doppler US ranged from 99% to 100%. Use of endovaginal color and pulsed Doppler US increased the percentage of diagnostic initial sonographic examinations from 62% to 82%. The improved diagnostic sensitivity of endovaginal color Doppler US for ectopic pregnancy may ultimately result in earlier treatment, with reduced morbidity and mortality.     

Expectant treatment of ectopic pregnancies: clinical and sonographic predictors

OBJECTIVE. We identified the potential clinical and sonographic predictors of the spontaneous resolution of ectopic pregnancies. SUBJECTS AND METHODS. We performed a prospective study of 78 consecutive patients with a transvaginal sonographic diagnosis of ectopic pregnancy who had either two consecutive quantitative measurements of their beta subunit of human chorionic gonadotropin (beta-hCG) more than 24 hrs apart or an embryo with a heart beat. We evaluated the patient's age, time from the last menstrual period, beta-hCG level, size of ectopic pregnancy, presence of a gestational sac or embryonic elements, vascularity on color Doppler sonography, peak systolic velocity, and resistive index of ectopic pregnancy at the time of presentation as potential independent predictors of the final outcome. Logistic regression was performed to identify the independent predictors. RESULTS. Forty-six patients had declining beta-hCG levels, and 32 ectopic pregnancies showed an embryo with a heart beat or had steady or rising beta-hCG levels. Univariate analysis indicated that a longer time from the last menstrual period (older ectopic pregnancies), lower beta-hCG levels, and the absence of gestational sac are statistically more significantly seen in ectopic pregnancies with declining beta-hCG levels (p < 0.05). Resistive index of ectopic pregnancy reached borderline significance (p = 0.05). In a multiple logistic model, the same variables were independent predictors of outcome (p < 0.05). Resistive index was also a predictor (p = 0.09). CONCLUSION. Longer times from the last menstrual period, lower beta-hCG levels, absence of gestational sacs, and higher resistive indexes of ectopic pregnancy at the time of presentation appear to be independent predictors of the spontaneous resolution of ectopic pregnancy.     

Can detection of the yolk sac in the first trimester be used to predict the outcome of pregnancy? A prospective sonographic study.

Recent reports have indicated that identification of the yolk sac should precede the detection of the embryo in a normal first-trimester sonographic examination and that failure to visualize a yolk sac strongly suggests an abnormal intrauterine pregnancy. A first-trimester prospective study was performed in 163 normal and 49 abnormal consecutive singleton gestations. All women were examined both abdominally and transvaginally, with pregnancy outcome determined by delivery of a normal infant or a spontaneous abortion. The yolk sac was analyzed in all patients in whom an embryo was not identified (n = 76). When the yolk sac was identified, the following was found: by the abdominal approach with the mean sac diameter (MSD) less than 27 mm (n = 15), nine gestations were normal and six were abnormal, and by the transvaginal approach with the MSD less than 18 mm (n = 13), seven gestations were normal and six were abnormal. The presence of a yolk sac was not consistently predictive of a normal early pregnancy. When the yolk sac was also not identified, the following was found: abdominally with the MSD less than 27 mm (n = 41), 19 gestations were normal and 22 were abnormal, and transvaginally with the MSD less than 18 mm (n = 11), six gestations were normal and five were abnormal. Absence of the yolk sac was not consistently predictive of a spontaneous abortion. When using the MSD range (20-27 mm abdominally and 7-16 mm transvaginally), over which the yolk sac but not the embryo should be identified sonographically, the yolk sac was again not consistently visualized. On abdominal sonograms, the yolk sac was present and absent in three and 10 patients, respectively, for both normal and abnormal pregnancies. On transvaginal sonograms, the yolk sac was present and absent in seven and five normal gestations and in six and four abnormal gestations, respectively. The results of this study suggest that detection of the yolk sac in the first trimester is not an early predictor of pregnancy outcome.     

Diagnosis of ectopic pregnancy: endovaginal vs transabdominal sonography

During a 25-month period, 193 women with the clinical diagnosis of suspected ectopic pregnancy had transabdominal and endovaginal sonograms. Most had quantitative determinations of serum human chorionic gonadotropin (HCG). Endovaginal sonography was diagnostic of ectopic pregnancy in 23 (38%) of the 60 patients with surgically proved ectopic pregnancies: transabdominal sonography was diagnostic in 13 patients (22%). All 83 intrauterine pregnancies were identified with endovaginal sonography, compared with 34 identified with transabdominal sonography. Endovaginal sonography was somewhat more helpful in the diagnosis of missed abortion and blighted ovum. Eighty endovaginal sonograms were classified as indeterminate as compared with 141 transabdominal studies. This indeterminate group included patients with complete abortions, ectopic pregnancies without sonographic evidence of an extrauterine gestation, incomplete abortions, and patients with subsequent negative serum levels. As in prior reports, endovaginal sonography was superior to transabdominal sonography in the evaluation of suspected ectopic pregnancies. Overall, endovaginal sonography was diagnostic in 113 patients, whereas transabdominal sonography was diagnostic in 52 patients. The finding of an extrauterine fetal pole or embryo was diagnostic for an ectopic pregnancy. Pelvic fluid, the appearance of the endometrium, and a single positive serum HCG determination were not helpful in making the diagnosis of ectopic pregnancy.     

Small sac size in the first trimester: a predictor of poor fetal outcome

A nonbradycardiac fetal heart rate is associated with a low rate of spontaneous abortion (2%-4%). To determine criteria for predicting impending first-trimester loss when a normal fetal heart rate is identified sonographically, the authors studied 16 consecutively examined patients with pregnancies of 5.5-9 weeks gestation, a small sac size, and fetuses with normal cardiac activity. Mean sac size (MSS) was determined and a small sac was diagnosed when the difference between the MSS and crown-rump length (MSS--CR) was less than 5 mm. Fifty-two consecutively examined patients with pregnancies of 5.5-9 weeks gestation, normal sac size, and fetuses with normal heart rate formed the control group. An MSS--CR of 5 mm or greater was considered normal. Fifteen of the 16 patients (94%) with first-trimester small sacs had spontaneous abortions despite normal sonographic cardiac activity. Four of the 52 control patients (8%) with normal sac sizes had spontaneous abortions. The authors' data show that, despite the presence of fetal cardiac activity at the time of sonography, the usual reassurance provided to patients should be guarded when the sac size is small.     

Pseudogestational sacs: Doppler US differentiation from normal or abnormal intrauterine pregnancies

Doppler ultrasound (US) evaluation of 40 empty intrauterine sac-like structures was performed to evaluate the ability of this technique to permit distinction between intrauterine pregnancy and pseudogestational sac associated with ectopic pregnancy. Proof of the location of the pregnancy was available in all cases. There were 31 intrauterine pregnancies, of which 23 were missed or incomplete abortions and eight were early normal pregnancies. With an insonating frequency of 3 MHz, the average frequency shift detected from these intrauterine pregnancies was 1.7/1.0 kHz (peak systolic/end diastolic ratio). Nine pseudogestational sacs were evaluated, of which seven demonstrated no flow and two demonstrated minimal flow that averaged 0.4/0.1 kHz. Defining intrauterine peritrophoblastic flow as a peak systolic frequency shift of 0.8 kHz or greater (equivalent to 21 cm/sec with an angle of 0 degree) correctly classifies 26 of the 31 intrauterine pregnancies and all of the nine pseudosacs. The sensitivity of the Doppler technique for the detection of intrauterine pregnancies was 84%, and the specificity was 100%.     

Endovaginal color Doppler sonographic evaluation of ectopic pregnancy in women after in vitro fertilization and embryo transfer

The aim of this study was to evaluate the value of endovaginal color Doppler ultrasonography in the early diagnosis of ectopic pregnancy in women after in vitro fertilization and embryo transfer, and to correlate the sonographic findings with ?-hCG serum levels. Thirty-five patients had proven ectopic pregnancies and 4 other patients had heterotopic pregnancies. The diagnosis was disclosed correctly in all cases by endovaginal color Doppler US by identifying an adnexal mass with placental flow and a nongravid uterus called a “cold uterus”. An intrauterine sac with “double ring sign” was found in all normal intrauterine pregnancies when the hCG levels exceeded 1000 IU/l but in none of the patients with ectopic pregnancy (EP). These findings suggest the efficacy of the discriminatory hCG serum level of 1000 IU/l in the investigation of EP. In conclusion, this study describes the diagnostic importance of transvaginal color Doppler US in correlation with hCG serum levels in the early detection of EP avoiding life-threatening complications and improving patient outcome. Received: 4 May 1998; Revision received: 10 August 1998; Accepted: 10 September 1998     

Extrauterine findings of ectopic pregnancy of transvaginal US: importance of echogenic fluid

Transvaginal ultrasound (US) studies of 232 consecutive patients with positive serum pregnancy tests who were considered to be at risk for ectopic pregnancy were prospectively evaluated to determine the significance of various extrauterine findings, including echogenic fluid in the cul-de-sac. All patients were found to have a surgically proved ectopic gestation (group 1, 68 patients [29.3%]), reliable evidence of intrauterine pregnancy at initial transvaginal US (group 2, 83 patients [35.8%]), or no evidence of pregnancy at initial transvaginal US, but subsequent proof of an intrauterine pregnancy (group 3, 81 patients [34.9%]). Adnexal findings were demonstrated in 45 (66%) group 1 patients, including a living extrauterine embryo in 10 (15%), an extrauterine gestational sac in 21 (31%), and an adnexal mass in 14 (21%). Intraperitoneal fluid was detected in 43 (63%) group 1 patients and in 81 (31%) group 3 patients. Echogenic fluid was the only abnormal finding at US in 10 (15%) group 1 patients and added confidence to the diagnosis of ectopic pregnancy in many others. Echogenic fluid correlated with hemoperitoneum at the time of surgery. The presence of echogenic fluid indicates a high risk for ectopic pregnancy in women referred with this clinical indication.     

Abnormal pregnancy: early diagnosis by US and serum chorionic gonadotropin levels

Simultaneous sonography and quantitative serum human chorionic gonadotropin (HCG) levels from 126 women with threatened abortion were compared. Of 56 women with normal outcome, 39 (70%) had a gestation sac greater than or equal to 5 mm in mean sac diameter, and in each case the HCG level was 1,800 milli-international units (mIU/ml) or greater. The serum HCG levels strongly correlated with the gestation sac sizes to a mean sac diameter of 25 mm. Of 70 abnormal pregnancies, 31 demonstrated a gestation sac. Of these, 20 women (65%) had disproportionately low HCG levels relative to sac size, including 12 in whom the HCG level was less than 1,800 mIU/ml. One woman with an early molar pregnancy had a disproportionately elevated HCG level. Correlation of sonograms with a simultaneous measurement of serum HCG level is a useful method for evaluating threatened spontaneous abortion. A disproportionately low HCG level relative to gestation sac size is evidence for an abnormal pregnancy.