Fetal Demise Ultrasound
The embryonic phase of development is complete by the end of the 10th menstrual or gestational week (this corresponds to 12 weeks 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 ultrasonography 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.
Fetal Demise Ultrasound is demonstrated in the images below.
Fetal Demise Ultrasound Presentation
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 that the rest 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 fetal 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 human choriogonadotropin (hCG) level to increase at the expected rate.
Fetal Demise Ultrasound 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 ultrasonographic examination. If clinical dating suggests a gestational age (GA) of 8 weeks or older, some sonographers begin the ultrasonographic 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 ultrasonographic 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.
Fetal Demise Ultrasound Limitations of Techniques
Transabdominal probes are limited, because they typically use 3.5-5 MHz transducers, compared with the 5-10MHz transducers used in transvaginal probes. Even if a 5-MHz transducer were 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 ultrasonographic 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.
The transvaginal approach, however, can be limited by the presence of a large pelvic mass, which can interfere with visualization of 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 ultrasonographic 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 is imaged but 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 aid in the detection of an ectopic pregnancy. Occasionally, serial ultrasonography and/or hCG determinations may be required to determine the etiology of the intrauterine sac.
A final, but important, admonition (that relates to all ultrasonographic 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.