Determining the viability of early pregnancies: two case reports

Journal of Family Practice, Oct, 1991 by Pamela M. Davis

First-trimester bleeding demands that an expedient diagnosis be made if an ectopic pregnancy is suspected. In addition, rapid determination of a failed pregnancy or blighted ovum is often sought to facilitate quick evacuation of the products of conception. Ultrasonography and quantitative measurement of the [beta]-subunit of human chorionic gonadatropin ([bega]-HCG) have raised the expectation that early determination of fetal viability is possible. These expectations may be unfounded. This report presents two cases in which undue reliance on laboratory interpretations could have led to adverse iatrogenic outcomes.

Case 1

A 28-year-old woman, gravida 6, para 1, with a history of 3 therapeutic abortions and 1 spontaneous abortion, presented to the office 6 5/7 weeks after her last menstrual period. She has a history of occasional irregular periods and was not using contraception. Her examination was unremarkable except for obesity. A qualitative serum [beta]-HCG pregnancy test was positive. Two weeks later the patient reported pain on the left side of her pelvis. The uterus felt soft and enlarged, and the adnexa were normal. A pelvic ultrasonogram showed an echogenic ring in the center of the uterus, consistent with an atypical gestational sac, and a 5-cm cyst on her right ovary. The radiologist reported this as most consistent with a blighted, ovum, but concluded that abnormal gestation or early normal gestation was possible. At the time of the test, the patient's [beta]-HCG level was 9100 mIU/mL, and 48 hours later it was 14,300 mIU/mL. The patient remembered some "red discharge" 1 month after her reported last menstrual period. The implications of the slow rise in the [beta]-HCG were discussed, and the patient wished the pregnancy terminated if the physicians believed it was abnormal. Two days later the [beta]-HCG was 17,900. After gynecological consultation, she was tentatively scheduled for a dilation and curettage (D&C).

On further consideration, surgery was postponed. A repeat ultrasound 6 days after the initial one revealed no change: a persistent empty gestational sac without a fetal pole (Figure 1). The evidence pointed to an inevitable abortion; however, the patient's stable condition and the clinician's skepticism about the available information prompted further waiting. Two days later, the [beta]-HCG level was 29,000, and a third ultrasound 13 days after the original one demonstrated a viable intrauterine pregnancy corresponding to a fetal age of 8 weeks. The patient subsequently gave birth to a normal male infant at term.

Case 2

A 35-year-old woman, with an obstetric history identical to the patient in case 1, was seen 6 1/2 weeks after her last menstrual period to confirm a possible pregnancy. She had a history of regular periods and was trying to conceive; therefore, she was not using contraception. The patient began spotting that day. Examination revealed a drop of blood on a closed cervix, a soft fundus, and normal adnexa. Continued spotting and fears arising from a recent miscarriage prompted the patient to request an ultrasound examination. At 7 2/7 weeks a pelvic ultrasound examination was obtained. It indicated a gestational sac of 22 mm mean diameter, which corresponded to an age of 7 weeks. No fetal pole was visualized, however, and the possibility of a blighted ovum or an incomplete abortion was raised (Figure 2). One week later the physical examination was unchanged. The patient's [beta]-HCG level that day (8 2/7 weeks) was 123,000 mIU/mL; 48 hours later the level was 50,840 mIU/mL. The patient was informed of the significance of the results and advised to repeat the tests in 1 week. The following week the patient's [beta]-HCG level was 710,000 mIU/mL, and a second ultrasound examination 2 1/2 weeks after the initial study demonstrated a viable 9 1/2-week fetus (Figure 3). The patient gave birth to a normal female infant at 42 weeks.

Discussion

Ultrasonic demonstration of cardiac activity by 9 weeks is an established test of fetal viability.[1] Earlier confirmation is now frequently possible with vaginal probe ultrasonography. Measurements of [beta]-HCG are most predictive before 6 weeks.[2,3] It is in the 6-to-9-weeks stage, when bleeding often occurs, that prognosis is difficult.

Single samples of [beta]-HCG are not reliable predictors of fetal viability[4,5]; therefore, serial measurements of [beta]-HCG are advocated.[2,6-12] The character of [beta]-HCG levels to rise in normal pregnancy has led to the use of the [beta]-HCG "doubling time" to establish viability. Measured doubling times vary from 1.4 to 5 days and increase with gestational age.[6,7] The need to translate these data into clinical practice has resulted in the establishment of 48 hours as the normal doubling time in early pregnancy.[8,13-15] The use of doubling time is often faulty, however, owing to its relationship to the gestational age, which may be in error.

One difficulty in establishing pregnancy viability early lies in differentiating the blighted ovum ("empty sac") from the similar appearing misdated early gestation. The pelvic ultrasound cannot distinguish between the two before 8 weeks' gestation.[16,17] Therefore, the diagnosis of a blighted ovum requires two or three serial ultrasound examinations. Certain sonographic findings are proposed as measures of nonviability. The only indicator universally agreed upon is that a sac 2.5 mL in size without a fetal pole is the threshold of nonviability.[15-21] The vaginal probe ultrasound, which is now available, offers earlier confirmation of viability. Additional experience is necessary to see if it eliminates the uncertainty in identifying a blighted ovum.