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Radiology > OBSTETRICS/GYNECOLOGY
Embryonic Demise
Article Last Updated: Aug 23, 2004
AUTHOR AND EDITOR INFORMATION
Section 1 of 6  
Author: Faye C Laing, MD, Professor of Radiology, Department of Radiology, Division of Ultrasound, Harvard Medical, Brigham and Womens Hospital
Faye C Laing is a member of the following medical societies: American College of Radiology, American Roentgen Ray Society, Radiological Society of North America, and Society of Radiologists in Ultrasound
Editors: Christopher L Sistrom, MD, Associate Chair for Research, Assistant Professor, Department of Radiology, University of Florida School of Medicine; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Karen L Reuter, MD, FACR, Professor, Department of Radiology, Lahey Clinic Medical Center; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Eugene C Lin, MD, Consulting Staff, Department of Radiology, Virginia Mason Medical Center
Author and Editor Disclosure
Synonyms and related keywords:
nonviable embryo, first trimester demise, early pregnancy failure
Background
The embryonic phase of development is complete by the end of the 10th menstrual or gestational week (this corresponds to 10 wk following the onset of the last normal menstrual period). During this critical period of development, a single fertilized cell undergoes dramatic transformation as the cell mass evolves into major organs and a recognizable human form. Because of the complex sequence of events that occurs during this short time period, it is not unusual for complications to develop. Currently, transvaginal ultrasound is the imaging examination of choice to evaluate the rapidly evolving intrauterine events that occur following implantation of the gestational sac and the development of a visible embryo. Although a variety of terms are used to describe early pregnancy failure, in the presence of clear-cut sonographic evidence that a nonliving embryo is present, the term embryonic demise should apply.
Pathophysiology
Some causes of first trimester demise are well understood; however, in most instances, the etiology is unknown (Moore, 1998). In general, significant embryologic malformations that result in demise can be the result of genetic or chromosomal, environmental, or combined factors. Chromosome abnormalities are the leading known cause of pregnancy loss. An estimated 6-7% of zygotes have chromosome aberrations (Moore, 1998), and more than 95% of chromosomally abnormal concepti die in utero. Although the precise incidence is unknown, cytogenic abnormalities are reported in 20% of concepti in women who undergo in vitro fertilization (Bateman, 1992) and in 70% of women with spontaneous abortion (Ohno, 1991). In addition, many chromosome aberrations increase with advancing maternal age (Hook, 1981). This is particularly true for Down syndrome (trisomy 21) but is also evident with other less common trisomies. Pathologic examination of chromosomally abnormal concepti confirms trisomy in approximately 50% of cases. The timing of exposure to environmental causes or teratogens is crucial to the outcome of pregnancy. Early exposure, typically before 5 weeks gestational age (GA), has an all-or-none result such that the embryo will either die or be unaffected (Moore, 1998). Not surprisingly, exposure during the period of organ formation (5-10 wk) usually affects organ development and results in either demise or severe congenital abnormalities. Environmental causes include immunologic factors, drugs, infectious agents, alcohol, smoking, environmental chemicals, and radiation. Once implantation has occurred, another cause of early pregnancy failure relates to an inability of the corpus luteum to adequately support the conceptus (Blumenfeld, 1992). This condition, which tends to occur with maternal obesity and/or advancing maternal age, can be treated successfully during the embryonic phase of development by administrating human choriogonadotropin (hCG). A developmental uterine anomaly such as a uterine septum or acquired uterine anomalies such as submucosal, large, or degenerating leiomyomas also can increase the incidence of embryonic demise.
Frequency
United States
Overall, an estimated 75% of pregnancies fail to result in a living offspring. Of course, most of these failures occur before implantation of the gestational sac. In these chemical or preclinical pregnancies, the only proof of pregnancy is a transiently positive pregnancy test and possibly a history of an atypical menstrual cycle. According to some investigators (Wilcox, 1988; Bateman, 1992), the incidence of loss following implantation ranges from 20-31%.
- Studies confirm that during embryonic development, the rate of pregnancy failure is inversely related to GA and that with onset of fetal development (beginning at 11 wk GA), demise becomes relatively unusual. Using vaginal ultrasound, one study (Goldstein, 1994) showed that if a gestational sac was visible, the embryonic loss rate was 11.5%; with a yolk sac it was 8.5%; with an embryo less than 5 mm in length, it was 7.2%; and with an embryonic length of 6-10 mm, it was 3.3%. In contrast, loss during the fetal phase of development was 2%.
Clinical Details
During the first trimester of pregnancy, approximately 25% of women experience mild vaginal bleeding and/or cramping. Pelvic examination usually reveals a closed and normal appearing cervix. This clinical presentation characterizes a threatened abortion. Analysis of women with these findings reveals that 50% of the pregnancies will fail, and 50% will have a normal outcome. If the cervix is dilated, the pregnancy will certainly fail, although based on clinical examination, it is not usually possible to determine whether there are retained products of conception. Some women with embryonic demise will be asymptomatic, and in these patients the diagnosis may be suggested based on subnormal uterine growth, inability to auscultate fetal cardiac activity, or failure of the hCG level to increase at the expected rate.
Preferred Examination
In most instances the clinical pelvic examination cannot determine the cause for the patient's symptoms. Thus, the patient should be referred for a real-time pelvic ultrasound examination. If clinical dating suggests a GA of 8 weeks or older, some sonographers begin the ultrasound study using a transabdominal approach. This is because in a normal pregnancy, when using a transabdominal approach, cardiac activity should be visible by 8 weeks GA. However, an increasing number of sonographers begin the ultrasound examination with a transvaginal approach. This is because a higher transducer frequency is used, which in a normal pregnancy can detect cardiac activity approximately 2 weeks earlier or by 6 weeks GA. Furthermore, in comparison to a transabdominal approach, vaginal transducers provide superior resolution with respect to examining the appearance and contents of the gestational sac as well as the ovaries and adnexa.
Limitations of Techniques
Transabdominal probes are limited because they typically use 3.5-5 MHz transducers compared to transvaginal probes, which use 5-10 MHz transducers. Even if a 5-MHz transducer is used for a transabdominal and transvaginal scan, the transabdominal images of an early intrauterine pregnancy (IUP) would be inferior to those obtained by the transvaginal probe. This is because the transvaginal probe is physically closer to the object being scanned, and the transvaginal ultrasound beam does not traverse the abdominal wall. This results in fewer near-field artifactual echoes. These comparative effects are most pronounced when scanning obese patients.
A limitation of the transvaginal approach is if a large pelvic mass is present that precludes visualizing the intrauterine contents. Most often, large or strategically placed calcified uterine fibroids cause this problem. Under these circumstances, an abdominal approach should be used in an effort to image the uterus and its contents.
Another limitation is if the ultrasound study is performed prior to the time a yolk sac can be detected. Using a vaginal approach, this structure should be observed by 5.5 weeks GA. If a small saclike structure b is imaged but it does not contain a yolk sac, it is often not possible to determine if the intrauterine finding is the result of an early IUP or a pseudosac associated with an ectopic pregnancy. In these instances, careful evaluation of the adnexa may be helpful to detect an ectopic pregnancy. Occasionally, serial ultrasound and/or hCG determinations may be required to determine the etiology for the intrauterine sac.
A final but important admonition (that relates to all ultrasound examinations) is to recognize the technical adequacy of the study, to know the limitation(s) of the equipment, and, importantly, to determine the experience of the person who performs and interprets the examination.
Other Problems to be Considered
Pseudosac from ectopic pregnancy
Missed abortion
Blighted ovum
Early IUP (before cardiac activity is visible)
Findings
Visualizing a dead embryo - If an embryo is identified on a transabdominal scan and cardiac activity is not visible, the prognosis is usually poor. It is important to realize that occasionally a very small embryo may be present in which cardiac activity cannot be confirmed. According to the experience of one group of investigators who used a transabdominal approach (Pennell, 1991), 21% of the time a normal IUP lacked visible embryonic heart motion when the embryonic crown rump length (CRL) was 9 mm or less. Based on their experience, these investigators recommended that when using a transabdominal approach, 9 mm should be considered the discriminatory embryonic length for detecting cardiac motion. Used in this manner, the discriminatory level denotes the numeric value when a certain finding should always be present.
- Given its superior resolution, it is not surprising that vaginal ultrasound scans can detect cardiac activity with a smaller embryonic CRL. According to the experience of a different group of investigators who used a transvaginal approach (Levi, 1990), 18% of the time a normal IUP lacked visible embryonic heart motion when the embryonic CRL was 4 mm or less. Based on their experience, these investigators recommended that when a transvaginal approach was used, 4 mm be considered the discriminatory embryonic length for detecting cardiac motion (see Image 1). Other investigators suggest 5 mm as the discriminatory embryonic size for detecting cardiac motion (Brown, 1990).
- If an embryo exceeds the discriminatory length and cardiac activity is absent, a nonviable gestation should be diagnosed. Because this observation has such important clinical ramifications, this observation should be made by two independent observers, and interpretive caution must be exercised in any questionable case. Documentation should be available by M mode imaging and/or by obtaining a videotape or video clip.
- If the length of the embryo is less than the discriminatory value, the patient should be managed expectantly, and a repeat ultrasound examination should be performed when the expected embryonic CRL exceeds the discriminatory value. Alternatively, or additionally, the level of serum hCG may be useful for determining whether a normal IUP is present.
Visualizing a living embryo
- Although seemingly a paradox, it is well known that detecting cardiac activity when using a vaginal transducer does not guarantee as favorable an outcome as detecting cardiac activity when using an abdominal transducer. With a transvaginal approach, mortality rates of 20-30% have been reported in women with threatened abortion in whom embryonic cardiac activity is documented at 6 weeks GA (Levi, 1990; Rosen, 1990).
- Several factors account for these less favorable statistics. First, the vaginal approach detects cardiac activity earlier when the incidence of pregnancy loss is relatively higher. In addition, a number of other important observations have been made, which, when observed with a living embryo, are predictive of a poor outcome (Falco 1996).
Predicting a poor outcome
- Bradycardia: At 5-6 weeks GA, the mean embryonic heart rate is 101 beats per minute (bpm) (see Image 2). This rate increases to 143 bpm by 8-9 weeks GA and subsequently plateaus at approximately 140 bpm (Doubilet, 1995). Therefore, it is not unusual for an initially detected embryonic heart rate to be somewhat slower than the fetal heart rate recorded later in pregnancy. An unusually slow heart rate is cause for concern. In one study, all embryos from 5+ to 8+ weeks GA in which the heart rate was less than 85 bpm resulted in spontaneous miscarriage (Benson, 1994).
- Small sac size: From 5.5-9 weeks GA, the mean gestational sac size (MSS) is normally at least 5 mm greater than the CRL. When this difference is less than 5 mm, the subsequent spontaneous abortion rate exceeds 90% (Bromley, 1991) (see Image 3). The etiology for first trimester oligohydramnios is unclear, but this observation suggests that with suboptimal first trimester gestational sac growth, a high likelihood of pregnancy loss exists.
- Subchorionic hemorrhage: As many as 18% of women with vaginal bleeding during the first half of pregnancy have sonographic evidence for a subchorionic hemorrhage as the etiology for their bleeding (Pederson, 1990) (see Image 4). The clinical significance of this type of hemorrhage is controversial, with some investigators reporting an increased incidence of spontaneous abortion (Abu-Yousef 1987; Bennett 1990), while others conclude this condition does not adversely affect pregnancy outcome (Pederson, 1990). Several authorities have suggested that the size of the blood clot can be used to predict the outcome (Abu-Yousef 1987); this has not been universally accepted (Dickey, 1992).
- Abnormal yolk sac/amnion
- The yolk sac normally forms by 28 menstrual days and is the first structure visible in the gestational sac. Normally, it should be seen on a transabdominal scan when the mean sac diameter (MSD) is 20 mm or larger (Nyberg, 1986). This corresponds to a GA of 7 weeks. Transvaginal transducers can uniformly detect the yolk sac when the MSD is 8 mm or larger (Levi 1988). This corresponds to a GA of 5.5 weeks (see Image 5). Failure to visualize a yolk sac when the GA has reached these discriminatory values signals the pregnancy is not progressing normally. An abnormal appearing yolk sac also can predict subsequent demise. Abnormal features include large size (diameter greater than 6 mm), calcification or echogenic material within the yolk sac, and a double appearance to the yolk sac (Harris, 1988; Barzilai, 1989) (see Image 6).
- The amnion develops somewhat earlier than the yolk sac, but because this membrane is so thin, it is more difficult to visualize than the yolk sac. Normally, the amnion is visible on transabdominal scans late in the embryonic period. If the amnion is easily seen, it is probably too thick and most likely is abnormal. Other features consistent with pregnancy failure include a visible amnion without a simultaneously visible yolk sac, embryo, or cardiac activity. An enlarged amniotic sac is another sonographic sign that predicts a failed pregnancy or embryonic death (Horrow, 1992).
- Doppler findings: To date, conflicting reports exist with regard to the usefulness of first trimester Doppler for predicting pregnancy outcome. Some reports suggest if the resistive index is measured at the subchorionic level and exceeds .55, a high likelihood of spontaneous abortion exists (Jaffe, 1995); however, others claim that Doppler analysis of these vessels are not predictive of outcome (Frates 1996).
Visualizing an "empty" gestational sac
- An "empty " gestational sac is the result of 1 of 3 entities: (1) a normal early IUP, (2) an abnormal IUP, or (3) a pseudogestational sac in a patient with an ectopic pregnancy. Based on careful ultrasound sac analysis, it may be possibly to distinguish among these entities. The earliest appearance for a normal sac is a small fluid collection surrounded by high-amplitude echoes embedded in the decidualized endometrium. This appearance has been termed the "intradecidual sac sign" (IDSS) (see Image 7). Not infrequently, because it may be difficult or impossible to distinguish these 3 conditions, a follow-up ultrasound examination should be considered if clinically feasible (Laing, 1997).
Abnormal sac criteria
- Size
- An early normal intrauterine gestational sac often can be identified transabdominally by 31 days GA and can consistently be identified by 35 days GA. To confidently diagnose an IUP, most sonographers rely on the double decidual sac (DDS) finding, which is not universally present until the MSD is 10 mm (40 d GA) (Nyberg, 1983).
- Specific size criteria can be used to distinguish normal from abnormal intrauterine gestational sacs. Using a transabdominal approach, size criteria that unequivocally suggest an abnormal sac include failure to detect a DDS when the MSD is equal to or greater than 10 mm, failure to detect a yolk sac when the MSD is equal to or greater than 20 mm, or failure to detect an embryo when the MSD is equal to or greater than 25 mm (Nyberg, 1986).
- Using vaginal ultrasound, a normal intrauterine gestational sac can be detected reliably at 4-5 weeks GA, at which time the MSD approaches 5 mm. Using vaginal transducers, criteria that suggest an abnormal sac include failure to detect a yolk sac when the MSD is 8 mm or greater, and failure to detect cardiac activity when the MSD exceeds 16 mm (Levi, 1988)
- Growth rate
- The term "blighted ovum" or "anembryonic pregnancy" is used to describe an abnormal IUP with developmental arrest occurring prior to formation of the embryo or at a stage when it is not detectable using currently available equipment (see Image 8). In normal gestation, mean sac growth is 1.13 mm/d; in comparison, mean sac growth in an abnormal intrauterine gestation is 0.70 mm/d (Nyberg, 1987). Based on these observations, abnormal sac growth can be diagnosed confidently if the gestational sac fails to grow by at least 0.6 mm/d.
- Choriodecidual appearance
- This refers to the sonographic appearance of the echoes that surround an early intrauterine gestational sac. An abnormal appearance includes a distorted sac shape; a thin (<2 mm), weakly echogenic, or irregular choriodecidual reaction; and absence of the double decidual sac sign when the MSD exceeds 10 mm (see Image 9).
Visualizing a central cavity complex
- If the uterus appears normal on sonography, or if the central echoes are prominent, most often the outcome will be unfavorable. This is because most patients with recognized pregnancy loss are approximately 11 weeks pregnant (GA) when the ultrasound examination normally reveals intrauterine products of conception.
- When the central cavity complex is abnormally thickened (and often irregularly echogenic), the differential diagnosis includes intrauterine blood, retained products following an incomplete spontaneous abortion, decidual changes secondary to an early but not yet visible intrauterine pregnancy, or a decidual reaction from an ectopic pregnancy. If the uterus has this appearance and the patient does not desire her pregnancy, uterine evacuation should be performed to detect the presence or absence of chorionic villi. If chorionic villi are absent, the patient remains at risk for an ectopic pregnancy. If the patient desires to continue her pregnancy, the clinical status should determine whether serial tests (pregnancy and/or ultrasound) should be performed or if laparoscopy or laparotomy is required.
Degree of Confidence
When performed by an experienced examiner, and with state of the art equipment, vaginal ultrasound can detect an early intrauterine pregnancy with a high degree of confidence. This is particularly true once a yolk sac is identified. Using the criteria outlined above for predicting a poor outcome, it is usually possible to determine which pregnancies will fail. However, it is important to note that these discriminatory criteria are guidelines. If certain findings are not observed at the appropriate time, if the ultrasound findings are equivocal, if the examination is technically difficult, or if the sonographer is inexperienced, caution is warranted. The embryo always should be given the benefit of the doubt, and a follow-up ultrasound examination should be performed to obviate any risk of terminating a normal intrauterine pregnancy.
False Positives/Negatives
Prior to visualizing the yolk sac, it is often not possible to be certain if a small intrauterine saclike structure is due to an early intrauterine pregnancy (normal or abnormal), or a pseudosac associated with an ectopic pregnancy. This is because it may not be possible to clearly identify the IDSS. Under these circumstances, a follow-up examination should be performed if clinically feasible.
Occasionally, a subchorionic hemorrhage may resemble a second intrauterine sac. However, since most of these women are bleeding, with careful scanning, the correct diagnosis usually can be made. Whenever uncertainty exists, perform a short interval follow-up examination at 5-7 days.
Later in the first trimester, several anatomic structures undergo developmental changes that can be misinterpreted as abnormal. One potential pitfall is misinterpreting the developing rhombencephalon for an abnormal intracranial cystic structure, such as hydrocephalus or a Dandy Walker cyst. Note that because these anomalies require second trimester imaging, these conditions should not be diagnosed during the first trimester.
Another potential source of confusion is misinterpreting physiologic herniation of the bowel within the umbilical cord for an abdominal wall defect such as an omphalocele. In normal patients, the diameter of the base of the cord (that contains herniated bowel) should be less than 7 mm; in addition, no appreciable herniation should be seen once the CRL is greater than 45 mm. In questionable cases, perform careful follow-up ultrasound imaging.
| Media file 1:
Embryonic demise. Vaginal scanning determined the embryonic crown rump length as 5.4 mm, corresponding to 6.4 weeks gestational age. Cardiac activity was present at 121 beats per minute. |
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| Media file 2:
At 5.5 weeks gestational age, the embryonic heart rate was 92 beats per minute. Follow-up scan revealed embryonic demise. |
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| Media file 3:
This embryo was 8 weeks gestational age. Lack of fluid surrounding the embryo results in a disproportionately small sac. A follow-up scan 1 week later revealed demise. |
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| Media file 4:
A large subchorionic hemorrhage is present superior to the gestational sac (white arrow). Follow-up scan revealed embryonic demise. |
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| Media file 5:
Embryonic demise. A normal appearing yolk sac (arrow) is seen on this transvaginal scan done at 5.5 weeks gestational age. Diameter is 3 mm. |
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| Media file 6:
Embryonic demise. An abnormally large yolk sac is present (arrow) within this gestational sac. Diameter measured 10 mm. Follow-up imaging confirmed a failed pregnancy. |
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Embryonic demise. This very small sac (arrow) is positioned within the anterior endometrium. Note the linear central cavity echo positioned just deep to the sac. This relationship characterizes a normal-appearing intradecidual sac sign. |
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| Media file 8:
Embryonic demise. Using a vaginal approach, the mean diameter of this sac exceeded 20 mm. Neither a yolk sac nor embryo was visible. These findings are consistent with a "blighted ovum." |
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| Media file 9:
Embryonic demise. Note the irregular shape to this sac. In addition, the choriodecidual reaction is somewhat thin. Not surprisingly, this pregnancy failed. |
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Embryonic Demise excerpt Article Last Updated: Aug 23, 2004
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