Pinpointing extrauterine pregnancy

Key Points

Ectopic pregnancy (EP) is one of the most challenging medical conditions. When a patient presents with biochemical evidence of an early pregnancy, the possible diagnoses derived sonographically at that time include a definite intrauterine pregnancy (IUP), a definite EP, and a pregnancy of unknown location (PUL). Consider the following cases:

CASE 1

Patient 1 presents with vaginal spotting and 5-1/7th weeks of amenorrhea. She has a history of pelvic inflammatory disease. Three weeks ago, the patient underwent in vitro fertilization (IVF) with the transfer of 2 blastocysts into her uterus. The IVF specialist noted what was believed to be an appropriate elevation in her serum human chorionic gonadotropin (hCG) level. Based on dating criteria, she is at 5 postmenstrual weeks and 1 day of pregnancy. The day prior to presentation, her hCG level was 2,500 IU/L.Transvaginal ultrasound (TVS) reveals a retroverted uterus with a 16-mm endometrium and 2 small intramural myomas, but no IUP. Both ovaries contain several cystic structures of varying sizes (between 15 mm and 26 mm), some with peripheral flow. Some pelvic fluid is observed as well.

CASE 2

2. The patient's diagnosis is:
a. Early pregnancy failure
b. Suspected right tubal pregnancy
c. PUL
d. Chemical pregnancy

3. The management you select for this patient is:
a. Dilation and curettage (D&C) to verify the presence or absence of villi
b. Laparoscopy to rule out/in an EP
c. Quantitative serum hCG now and again in 48 hours
d. TVS in 1 week

The correct answers are 1. b; 2. c; 3. c.

The category of PUL has been expanding because earlier biochemical detection of pregnancy leaves a wide group of clinical situations in which the location of the pregnancy cannot be established. PUL is a descriptive term rather than a pathologic entity and can apply to an IUP too early to visualize, a failed IUP without definitive sonographic confirmation, or a failed or continuing EP.

Before discussing the sonographic and laboratory diagnosis of PUL with a patient, it is useful to distinguish threshold levels of hCG from discriminatory levels of hCG. A threshold level is the lowest level at which a gestational sac or a yolk sac can be detected; a discriminatory level refers to the level at which all normal structures must be visualized.

One also can establish threshold and discriminatory levels for sonographic detection of structures by different ultrasound transducer probes at various operating frequencies. This will be discussed later.