Susan E. Rowling, MD #{149}Beverly C. Coleman, MD #{149}Jill E. Langer, MDPeter H. Arger, MD #{149}Harvey L. Nisenbaum, MD #{149}Steven C. Horii, MD

First-Trimester US Parametersof Failed Pregnancy’

Index terms: Fetus, death, 856.825 #{149}Pregnancy, abnormalities, 856.825, 856.8266, 856.86 #{149}Preg-

nancy, US, 856.1298, 856.12989

Abbreviation: SD = standard deviation.

Radiology 1997; 203:211-217

I From the Department of Radiology, Hospital of the University of Pennsylvania, 3400 Spruce St,Philadelphia, PA 19104. From the 1994 RSNA scientific assembly. Received July 2, 1996; revision re-

quested July 31; revision received October 21; accepted November 18. Address reprint requests toS.E.R.

i RSNA, 1997

211

Obstetrical Ultrasound

PURPOSE: To test the reliability ofestablished ultrasound (US) param-eters in predicting the outcome offirst-trimester pregnancy.

MATERIALS AND METHODS: Theauthors retrospectively reviewed2,655 first-trimester US scans in 2,285patients. Parameters tested againstoutcome were (a) a yolk sac andmean gestational sac diameter of 8mm on transvaginal US scans, (b) anembryo and mean sac diameter of 16mm on transvaginal US scans, and (c)a difference between the mean sacdiameter and crown-rump length ofless than 5 mm (oligohydramnios) at5.5-9.0 weeks gestation.

RESULTS: Thirty (22%) of 135 pa-tients without yolk sacs and with an8-mm mean sac diameter developedlive embryos: 24 had normal fol-low-up or delivery; six were lost tofollow-up. Five (8%) of 59 patientswith no depiction of embryos andwith a 16-mm mean sac diameter de-veloped live embryos: Two delivered,one spontaneously aborted, one haddeath of one twin embryo before be-ing lost to follow-up, and one waslost to follow-up. Seventeen (0.74%)of 2,285 patients had early oligohy-dramnios: Six (35%) had normal fol-low-up scans or delivery, two (12%)spontaneously aborted, and nine(53%) were lost to follow-up.

CONCLUSION: Established param-eters predictive of early pregnancyfailure potentially result in misdiag-nosis of nonviability or poor progno-sis when applied to a large, unse-lected patient population. Closefollow-up is necessary in cases withborderline abnormal findings.

O NE of the major roles of ultraso-nography (US) during the first

trimester of pregnancy is in diffenenti-ating nonviable early gestation frompotentially normal gestation (1). SinceNybeng and colleagues (2) first pub-

tished the major and minor criteria forthe diagnosis with transabdominal USof abnormal gestational sacs in patientsat risk for spontaneous abortion in 1986,numerous investigators have devised

similar criteria for tnansvaginat US that

allow even earlier diagnosis of preg-nancy failure (3-6). The purpose of de-vetoping such criteria is to reliably diag-nose an abnormal early pregnancy andobviate serial US examinations (1).

The diagnosis of abnormal earlypregnancy has been based on a vari-ety of US findings, which include thefailure to depict a yolk sac, an em-bnyo, or both at a designated gesta-tionat sac size (2-7) and the discon-

dance between the mean sac diameterand crown-rump length (8-11). Wehave noted early gestations in our USlaboratory that have demonstrated

poor prognostic signs yet have pro-gressed to normal pregnancies.

This study was designed to test the

sensitivity and specificity of currentlypublished US parameters predictive ofpoor outcome of early intrauterine ges-tation in a large unselected population.

MATERIALS AND METHODS

A retrospective review of computerizedreports on consecutive pelvic US examina-

tions performed in our laboratory fromJanuary 1, 1991, through June 30, 1994, in

patients who demonstrated intrauterine

gestations of at most 13 weeks menstrual

age was undertaken. Menstrual age wasdetermined by means of the crown-rumplength when an embryo was present or bymeans of the gestational sac diameter

when an embryo was not present. Thecrown-rump length was calculated by av-eraging three separate measurements of

the longest embryonic or fetal length, ex-cluding the limbs, as first described byRobinson (12), and the mean sac diameter

was calculated by averaging the longitudi-

nat, anteroposterior, and transverse sacdimensions measured from the chorionic-fluid interface (1).

In the study period, 2,655 consecutivepelvic US examinations were performed in

2,285 patients. Patients were aged 13-42

years and were commonly referred from

the emergency department or clinic withpositive results of a pregnancy test, either

urine or serum, and symptoms of pelvicdiscomfort or vaginal bleeding. The statedindication for pelvic US was exclusion ofectopic pregnancy in 2,256 examinations

(85%). However, because presentations

are similar, this population inherently in-

cluded patients with ectopic pregnancyand patients at risk for spontaneous abor-

tion. A specific request for assessment of

viability in patients with symptoms indica-

tive of risk for spontaneous abortion ac-

counted for 292 (11%) of the examinations.

Three percent of patients were asymptom-atic and were referred for accurate deter-

mination of menstrual age, and 1% hadelevated human chorionic gonadotropinlevels and were referred to exclude molar

pregnancy or multiple gestations.

Transabdominal US was initially per-

a.

b.

!�#{227}�a*� �I�.

� ��. .::i:

...‘*‘_

C.

212 #{149}Radiology April 1997

Figure 1. Absent yolk sac at a mean gestational sac diameter of 8 mm with development of a live embryo. (a) Sagittal (left) and coronal(middle) transvagina! US scans show a gestational sac with a mean diameter of 11 mm without a yolk sac. The transabdominal US scan ob-

tamed after 45 days of follow-up (right) shows a normal fetus. (b) Sagittal (left) and coronal (middle) transvaginal US scans show an empty ges-

tational sac with a mean diameter of 11 mm. The transvaginal US scan obtained after 7 days of follow-up (right) reveals a normal embryo andyolk sac. (c) Sagittal (left) and corona! (middle) transvaginal US scans show an empty gestational sac with a mean diameter of 13 mm. The

transabdominal US scan obtained after 8 days of follow-up (right) demonstrates development of a normal embryo and yolk sac.

formed in patients with distended urinary

bladders by using either 4-2-MHz or 5-MHz

curved array transducers (Ultramark 9HDI system; Advanced Technology Labo-ratonies, Bothell, Wash) or 3.0-MHz or

3.75-MHz transducers (GE Medical Sys-

tems, Milwaukee, Wis). Transabdominal

US alone was performed in 1,380 examina-tions (52%). When transabdominal US

failed to reveal an embryo or yolk sacwithin the gestational sac, transvaginal US

was performed by using 5-MHz endocavi-

tary transducers (Advanced TechnologyLaboratories [Ultramark 9 HDI system] or

GE Medical Systems). Transvaginal US

alone was used in 425 examinations (16%)in patients with empty urinary bladders.

Both the transabdominal and the trans-vaginal US techniques were used in 850

examinations (32%). US examinations dur-ing routine hours were performed by ex-penienced technologists in the presence of

an attending US staff member or abdomi-nat imaging fellow (S.E.R., B.G.C., J.E.L.,P.H.A., H.L.N., S.C.H.). Studies after hourswere conducted by radiology residents orabdominal imaging fellows on call withvarying levels of training. However, allhad received a minimum of I month offormal training in the US department withhands-on experience before going on call.

The transcribed reports of the pelvic USscans were retrospectively reviewed, and

the following data were recorded: (a) mdi-cation for the examination, (b) scanning

technique (transabdominal US, transvagi-nat US, or both), (c) presence of a yolk sac

or live embryo within the gestational sac,

i � ����11F1� R � [1�

�

MSD (mm)

Figure 2. Bar graph compares the initial

mean sac diameters (MSD) in the 30 patients

without a yolk sac at a mean sac diameter of

8 mm on transvaginal US scans but with sub-sequent development of live embryos (black

bars) and the initial mean sac diameters in

the 55 patients without a yolk sac and withproved blighted ova (white bars). # = num-ber.

b.

Figure 3. Absent embryos at a mean sac diameter of 16 mm with subsequent normal deliveries. (a) Sagittal (left) and corona! (middle) trans-vagina! US scans show an empty gestational sac with a mean diameter of 18 mm. The transabdomina! US scan (right) obtained after 14 days of

follow-up shows a live embryo. (b) Sagittal (left) and coronal (middle) images show an empty gestational sac with a mean diameter of 18 mm.

The transvaginal US scan obtained after 8 days of follow-up (right) reveals a living embryo against the wall of the gestational sac, but the yolk

sac is not definitely seen.

a. b. c.

Volume 203 #{149}Number I Radiology #{149}213

Figure 4. Absent embryo at a mean sac diameter of 16 mm with subsequent development of a live embryo but no further follow-up. (a) Sagit-tal and (b) coronal transvaginal US images reveal a 19-mm empty gestational sac. (c) Transvaginal US scan obtained after 8 days of follow-up

reveals a yolk sac and living embryo, as well as perigestational hemorrhage.

(d) mean gestational sac diameter, and(e) crown-rump length when an embryo

was measured. The difference between

the mean sac diameter and the crown-rump length was calculated in all patients

who had a measured embryo.The hard-copy images were reviewed in

all cases in which reports suggested ab-

normal parameters. Because this is a retro-

spective study, with examinations per-

formed by individuals of varying levels of

expertise, it is impossible to determine

whether a yolk sac or embryo may havebeen present during the initial study, wasnot appreciated, and was therefore re-

ported as absent. The outcome of preg-

nancy was determined by means of fol-low-up US examination, review of pathology

or delivery records, and telephone calls tophysicians’ offices or to the obstetrics and

gynecology clinic.

RESULTS

A total of 154 patients with early

gestations with abnormal parameterswere identified. Of 137 patients inwhom blighted ovum was suspectedowing to the lack of visualization of ayolk sac, an embryo, or both at a des-ignated mean sac diameter, 32 wenton to develop live embryos. Of 17 pa-tients with a small gestationat sac, atleast six had a documented normal

outcome. These data are described indetail below.

Absence of a Yolk Sac at an 8-mmSac Diameter on Transvaginal USScans

The yolk sac and embryo were me-ported as absent on initial tnansvagi-nat US scans in 135 patients with in-trautenine gestationat sacs with amean diameter of at least 8 mm.Thirty (22%) subsequently developedviable gestations (Fig 1) that weredocumented at delivery or follow-upUS as follows: Nine delivered live

newborns at our institution with de-

Table 1Absent Embryo, per a Mean Sac Diameter �16 mm, with Subsequent Developmentof a Living Embryo

Mean Sac YolkExamination Diameter (mm) Sac Findings Outcome

Patient 1Initial 16 Yes Absent embryo

7-d follow-up 24 Yes Monochorionic twins UnknownCrown-rump length = 11

mm (and heartbeat)Crown-rump length = 11

mm (no heartbeat)Patient 2

Initial 17 Yes Absent embryo

6-d follow-up 22 Yes Crown-rump length = 5mm (and heartbeat)

Spontaneous abortionin 9 d

Patient3Initial 18 No Absent embryo14-d follow-up 30 Yes Crown-rump length = 12

mm (and heartbeat) Normal deliveryPatient4Initial 19 No Absent embryo

8-d follow-up 29 Yes Crown-rump length = 10mm (and heartbeat)

Perigestational bleeding

Unknown

Patient 5Initial 18 No Absent embryo

8-d follow-up 19 No Crown-rump length = 13mm (and heartbeat)

Normal delivery

22-d follow-up 35 Yes Crown-rump length = 21mm (and heartbeat)

Figure 5. Absent embryo at a mean sac diameter of 16 mm with subsequent development of

monochorionic twin gestation but unknown outcome. (a) Sagittal transvagina! US image ofa gestational sac with a mean diameter of 16 mm shows a single yolk sac but no embryo.

(b) Coronal transvaginal US scan obtained after 7 days of follow-up shows monochorionic

twin gestation. Embryo B measures I I mm with positive cardiac activity. Embryo A can be

faintly seen anteriorly and also measures 11 mm but does not show cardiac activity.

214 #{149}Radiology April 1997

livery dates and follow-up US scansthat were in concordance with agedetermination on the basis of the mi-tiat US scans; 21 patients had at leastone subsequent US scan that docu-mented the development of a normal,live embryo on fetus at 6-15 weeksmenstrual age but received subse-quent care elsewhere.

Fifty-five patients (41%) had blightedova proved at US on pathologic follow-up. In 47 patients (35%) with a US diag-nosis of probable blighted ova, nofollow-up data at our institution wereavailable; subsequent cane was mostlikely obtained elsewhere. In threepatients (2%), nonviable 6-7-weekembryos were found at the time of USfollow-up; these were not includedin the normal subgroup.

The initial mean sac diameter in the30 patients with favorable outcomeswas 8-19 mm, with a mean of 11.1

mm and a median of 10 mm. Themean sac diameter of proved blightedova was 9-44 mm, with a mean of19.8 mm and a median of 19 mm. At-though the anembryonic gestationalsacs were typically larger than those

with normal outcomes, theme was asubstantial overlap in the two groups

between mean sac diameters of 9 and19 mm (Fig 2). In this study popula-tion, including the 30 patients withnormal subsequent outcome and the55 with proved blighted ova, the ac-cepted discriminatory mean sac diam-eten of 8 mm was 100% sensitive foranembryonic gestation but had a 0%specificity and only a 65% positive

predictive value.

Absence of an Embryo at a 16-mmSac Diameter on Transvaginal USScans

An embryo was reported as absentin 59 patients with gestational sacs16 mm on larger on tnansvaginat USscans. In 57 patients, the yolk sac wasalso absent; these patients represent asubset of the 135 patients determinednot to have a yolk sac at a mean gesta-tional sac diameter of 8 mm. The me-maining two patients had yolk sacs atthe time of initial US.

Of these 59 patients, five (8%) wereidentified who subsequently devel-oped live embryos (Table 1) with out-comes as follows: Two delivered liveneonates at our institution at an ap-propriate menstrual age determinedon the basis of the first mean sac di-ameten (Fig 3); one developed a living10-mm embryo seen at US after 8 daysof follow-up but with uncertain out-come (Fig 4); one developed mono-chonionic twins, with one living and

one nonviable 11-mm embryo, anddid not undergo subsequent fol-tow-up at our institution (Fig 5); andone developed a living 5-mm embryoseen at US after 5 days of follow-up,but the pregnancy was spontaneouslylost shortly thereafter (Fig 6). The lat-

ten two patients, with poorer out-comes, had yolk sacs at the time ofinitial US, white the former three pa-tients did not.

In 34 patients (58%), US follow-up,uterine evacuation, or both confirmedthe suspected diagnosis of blightedovum or early embryonic death; in 20

(34%), no US on pathologic follow-up

data were obtained at our institution.In the five patients who developed

live embryos, the initial average meansac diameter was 16-19 mm, with a

mean of 17.6 mm and median of 18

mm. The mean sac diameter of proved

blighted ova was 16-48 mm, with amean of 24 mm and median of 23 mm.

First-Trimester Small Sac Size

First-trimester oligohydnamnios,with a difference of 1-4 mm betweenthe mean sac diameter and the crown-

Figure 6. Absent embryo at a mean sac diameter of 16 mm with development of a living embryo but subsequent spontaneous abortion at 8-9weeks menstrual age. (a) Sagittal and (b) coronal transvaginal US images show a well-formed gestational sac, with a mean diameter of 17 mm,

that contains a yolk sac. (c) Sagittal transvagina! US scan obtained after 6 days of follow-up shows an indistinct but living 5-mm embryo.

Volume 203 #{149}Number 1 Radiology #{149}215

Table 2

� Outcome of Gestations with First-Trimester Small Sac

PatientNo/Mean Sac

Diameter (mm)Crown-RumpLength (mm)

Difference between MeanSac Diameter and

Crown-Rump Length (mm) Follow-up

1/8 4 4 None2/8 4 4 Norma! US findings, 19 wk3/9 7 2 None4/11 7 4 None5/9 8 1 None6/10 8 2 Norma! delivery7/10 8 2 None8/139/14

1111

23

Spontaneous abortion, 10 wkNormal US findings, 22 wk

10/13 12 1 None11/17 13 4 None12/21 18 3 None13/19 18 1 Normal delivery14/22 19 3 Normal delivery15/24 20 4 Normal delivery16/23 20 3 None17/24 20 4 Spontaneous abortion, 11 wk

were not included in the initial reporton if follow-up was not available.

The average, normal difference be-tween the mean sac diameter andcrown-rump length plus or minus 2standard deviations (SD) was calcu-tated and plotted against the men-struat age in weeks and comparedwith data in cases with small gesta-tionat sacs and normal outcomes (Fig8). A large range of normal gestational

sac sizes exists. The peak average dif-

fenence between the mean sac diam-eten and the crown-rump length was14.4 mm at 8 weeks menstrual age,which progressively diminished toless than 1 mm by 12 weeks menstrual

age. In normal gestations at 6-9 weeksmenstrual age, 2 SD below the meanwas 4.1-5.7 mm. Gestations with early

- . oligohydramnios were just below 2SD of the mean.

rump length, was identified in 17 pa-tients (Table 2). Three patients, with

crown-rump lengths of 8, 11, and 18mm, were examined by means of

transabdominal US only. The remain-ing 14 patients, with mean sac diam-etens of 4-20 mm, were examined by

means of tnansvaginal US on bothtransabdominat and transvaginat US,

with the measurement recorded fromthe tnansvaginal study. In the eightpatients with available follow-up,pregnancy was subsequently normal

in six patients (35%), of whom fourdelivered live singletons (Fig 7) andtwo had normal second-trimester USscans obtained at our institution and

underwent delivery elsewhere. Two(12%) of the 17 patients spontane-

ously aborted at 10-11 weeks men-

struat age. The remaining nine pa-tients (53%), in most cases referred

from the emergency department,were unfortunately lost to follow-up,and outcome is uncertain. However,considering that at least six of 17 pa-tients had a normal delivery or sec-ond-trimestem US scan obtained at ourinstitution, there was no greater thana 65% early pregnancy toss.

The difference between the meansac diameter and the crown-rump

length was also determined in 595normal pregnancies at 5-12 weeksmenstrual age that were identifiedduring the initial review of the 2,655pelvic US reports. Normal outcomewas determined by means of either anormal second- or third-trimester US

scan or documentation of delivery atour institution on a date predicted atthe initial US examination. Examina-tions were excluded if both the meansac diameter and crown-rump length

DISCUSSION

US, especially the tmansvaginattechnique, has become invaluable inthe evaluation of early pregnancy.Multiple parameters have been de-vised to help identify an abnormalgestational sac or embryo. However, areview of the literature continues toreveal conflicting data on absoluteparameters that can be reliably usedto diagnose abnormal gestation at asingle examination. For example, thereported discriminatory sac size for

documentation of a yolk sac in non-mat gestation is 6-10 mm on trans-vaginal US scans (3-6,13,14). The mostwidely accepted data were reportedby Levi and colleagues (3), who foundthat a pregnancy was always abnom-mat when the mean sac diameter wasat least 8 mm without a yolk sac.

We determined that 30 patients had

25

E 15E-J 10

C.)

05)�

.10

Figure 7. Coronal transvagina! US image

shows a small sac at 8.3 weeks gestation withsubsequent normal delivery. The gestational

sac is 19 mm, and the live embryo is 18 mm.

The difference between the mean sac diam-eter and the crown-rump length was 1 mm.

216 #{149}Radiology April 1997

normal outcomes despite nonvisual-ization of the yolk sac at an 8-19-mmmean sac diameter. On the basis ofthese data, a yolk sac was always seenin normal gestation at a sac diameterof 20 mm; therefore, only a discrimi-natony value of 20 mm was associatedwith a 100% specificity and a 100%positive predictive value (Table 3).

Kurtz and colleagues (15) reportedthat a yolk sac may not always be vi-suatized before the embryo in gesta-tional sacs that are smatter than 18mm. We found that the yolk sac, at-though not initially seen, was eventu-ally detected in 26 of the 30 patientswho went on to develop live em-bryos. The remaining four patientswere not examined until after 15weeks, by which time the yolk sac isusually not seen at US.

Identifying a yolk sac is importantin excluding ectopic and anembryonicgestations; however, documentation

of a live embryo is necessary to diag-nose a potentially viable pregnancy(7,13,15). By using variable transvagi-

nat equipment and patient poputa-tions, a range of discriminatory vat-ues, 9-18 mm, has been reported fordocumentation of a live embryo.

We tested the most widely accepteddiscriminatory value of 16 mm, alsoreported by Levi and colleagues (3),against pregnancy outcome. Five pa-tients without embryos at an initial

mean sac diameter of 16-19 mm wereidentified who subsequently devet-oped live embryos seen at follow-upUS, at least two of whom went on tonormal delivery at our institution. It isinteresting that both patients whothen underwent normal deliverylacked both yolk sac and embryo mi-tiatly, white the patients who sponta-

neousty aborted and who had a non-

viable twin embryo had yolk sacspresent at the initial examination. Al-though this finding may be coinciden-tat, nondepiction of both the yolk sacand the embryo is more apt to be dueto technical limitations than is nonde-piction of the embryo with a yolk sacthat can be cleanly discerned. Docu-mentation of the yolk sac would makeerror related to transducer frequency,uterine position, on embryo locationless likely. It is possible for an embryo

not to be recognized because of theperipheral location within the sac andthe limited scanning planes inherentin transvaginat US. However, becausethe yolk sac and embryo are in prox-imity, one would expect both struc-

tunes to be either seen on missed inthis situation.

The question then arises, why areour data discrepant from those of a

number of previous studies? One im-portant factor is endocavitamy trans-ducen frequency. Investigators thatadvocated smaller discriminatorymean sac diameters for yolk sac andembryo depiction often used trans-ducems with frequencies of greatenthan 5 MHz. Specifically, Levi andcolleagues (3) used a 6.5-MHz endo-vaginal probe and Bree and cot-leagues (5), who reported a discnimi-natory gestational sac size of 6-9 mmfor the yolk sac and 9 mm for the liveembryo, used a 7-MHz transducer.

Diminished resolution related totransducer frequency may be a factorin nondepiction of gestationat saclandmarks, but the favorable outcome

in patients with initial large (15-19-mm) empty gestationat sacs likely

cannot be explained on the basis oftow transducer frequency. Althoughthese cases may represent examplesof first-trimester potyhydmamnios orabnormal early monochonionic twin-ning, inadvertent nondepiction ofa yolk sac on embryo that abuts the

watt of the gestationat sac cannotbe excluded.

The skill of the operating sonotogistis an important consideration in the

assessment of tnansvaginat US exami-nation quality. Although eight (25%)of the patients without an initial yolksac or embryo but normal outcome

were studied emergently after-hoursby a resident on fellow with variable

levels of training, the remaining 24

(75%) were examined during routine

hours in the presence of a US attend-ing physician or fellow and an experi-enced technologist.

Once a live embryo is documentedultrasonographically, there is a lowreported incidence of subsequentpregnancy toss (16,17). However,theme are US findings that are associ-ated with a higher risk of pregnancy

U #{149}

20 #{149} #{149} �

� i� :� � : �

� . ! � �

Menstrual Ag (ws#{149}ka)

Figure 8. Plot of the difference between the

mean sac diameter (MSD) and the crown-

rump length (CRL) ± 2 SD versus the men-

strual age (range, 5-12 weeks). Five hundred

ninety-five pregnancies with normal param-

eters and outcomes are compared with those

with oligohydramnios and normal follow-up

findings. U = normal + 2 SD, El = normal

mean difference between the mean sac diam-eter and the crown-rump length, #{149}= normal- 2 SD, � = 1-mm difference between mean

sac diameter and crown-rump length with

normal follow-up, A = 2-mm difference be-

tween mean sac diameter and crown-rump

length with normal follow-up, � = 3-mm

difference between mean sac diameter and

crown-rump length with normal follow-up,. = 4-mm difference between mean sac di-

ameter and crown-rump length with normal

follow-up.

failure, which include the discrepancybetween the sizes of the gestationalsac and the embryo (8-11). First-tn-

mesten oligohydnamnios, defined as a

difference of less than 5 mm betweenthe mean sac diameter and the crown-rump length in a pregnancy with alive embryo at 5.5-9.0 weeks men-struat age, has been reported as pre-dictive of miscarriage in 94% of cases

(8). The term “otigohydramnios” is

probably inappropriate when descnib-ing small first-trimester gestationatsacs, because, as conveyed by Gia-

cometlo (9), the amnion and embryoare normally in close apposition be-fore 9 weeks menstrual age, and theabnormality detected in cases withsmall gestationat sacs most tikety me-flects the diminished size of the choni-

onic, rather than the amnionic, cavity.The overall survival mate in gesta-

tions with early small gestationat sacsin our study was at least 35%. Thisfigure may be an underestimation,owing to the uncertain outcome in53% of the patients. Therefore, al-though small sac size is a poor prog-nostic sign, it may not be as grave asoriginally predicted.

We also found that gestationat sacsare often large relative to the crown-rump length in pregnancies withdocumented normal outcome. Thereis currently no reported difference

between the mean sac diameter andthe crown-rump length that is predic-tive of poor outcome in gestations

Table 3

Comparison of Discriminatory Sac Sizes for(n=30)versusBlightedOvum(n=55)

Yolk Sac Detection: Normal�

Outcome

Discriminatory Sac Size*

Parameter 8 mm 10 mm 12 mm 20 mm

True-positive findings�False-positive findings�True-negative findings�False-negative findingst

5530

00

521317

3

491020

6

270

3028

Sensitivity(%) 100 95 89 49Specificity (%) 0 57 67 100Positive predictive value (%) 65 80 83 100

* Discriminatory sac size is the mean sac diameter after which a pregnancy is always abnormal if a

yolk sac is not seen at transvagina! US.t Actual diagnosis is blighted ovum.* Actual diagnosis is normal.

actenize gestational sacs as normal onabnormal should be as conservative as

possible. We currently use the above

parameters only as a guideline. It me-mains imperative in desired pregnan-

cies to obtain serial US scans, to deter-

mine quantitative human chorionicgonadotropin levels, on both to defini-

tivety document abnormal progres-

sion before recommendation of uter-me evacuation. #{149}

with large sacs. It can be difficult to

distinguish an enlarged gestational

sac from a growth-retarded embryo,

the latter of which may be associatedwith triploidy or poor outcome (1,10,11).Further studies are needed to determine

the importance of an enlarged gesta-tional sac (polyhydramnios). As dis-cussed above, this phenomenon may

help to explain the unusual examplesin our study in which empty sacs thatmeasured up to 19 mm on transvagi-nat US scans resulted in favorableoutcomes.

In conclusion, established panam-eters suggestive of abnormal early

pregnancy are correctly predictive ofpoor outcome in the majority of cases.However, a substantial number of

patients were retrospectively found to

have normal follow-up findings de-spite abnormal parameters. The large

number of false-positive cases in ourstudy strongly suggests that the dis-

cniminatory values used to help char-

Volume 203 #{149}Number 1 Radiology #{149}217

- � 6. Cacciatore B, Titinen A, Stenman UH, Ylos-� tab P. Normal early pregnancy: serum

hCG levels and vagina! ultrasonographyfindings. Br I Obstet Gynaecol 1990; 97:

� 889-903.

� 7. Goldstein RB. Endovaginal sonography� in very early pregnancy: new observations.

� Radiology 1990; 176:7-8.� 8. Bromley B, Harlow BL, Laboda LA, Benac-

erraf BR. Small sac size in the first trimes-ter: a predictor of poor fetal outcome. Radi-

ology 1991; 178:375-377.9. Giacomello F. Small sac size as predictor

of poor fetal outcome (letter). Radiology1992; 184:578.

10. Benacerraf BR. Intrauterine growth retar-dation in the first trimester associated with

tnp!oidy.J Ultrasound Med 1988; 7:153-154.11. Crade M. First trimester growth retarda-

tion (letter). J Ultrasound Med 1989; 8:56.� 12. Robinson HP. Sonar measurement of fe-

ta! crown-rump length as a means of as-sessing maturity in the first trimester of

pregnancy. Br Med J 1973; 4:28-31.13. Filly RA. Ultrasound evaluation during

the first trimester. In: Calkn PW. Ultra-

sound in obstetrics and gynecology. 3rd ed.Philadelphia, Pa: Saunders, 1994; 63-85.

14. Jam KA, Hamper UM, Sanders RC. Corn-

parison of transvaginal and transabdorni-na! sonography in detection of early preg-nancy and its complications. AJR 1988; 151:

1139-1 143.15. Kurtz AB, Needleman L, Pennell RG, et a!.

Can detection of the yolk sac in the firsttrimester be used to predict the outcome ofpregnancy? A prospective sonographic

study. AIR 1992; 158:843-847.

16. Wilson RD, Kendrick V. Wittnan BK, Mc-

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