Ectopic Pregnancy Special Examinations

Several special procedures are helpful in diagnosing ectopic pregnancy.

1. Ultrasound - Ultrasound is useful in evaluating patients at risk for ectopic pregnancy, namely by documenting the presence or absence of an intrauterine pregnancy (IUP). β-hCG titers and ultrasound complement one another in detecting ectopic pregnancy, and have led to earlier detection with a subsequent decrease in adverse outcome. By correlating β-hCG titers with ultrasound findings, an ectopic pregnancy can often be differentiated from an IUP. Furthermore, ultrasound can help distinguish a normal intrauterine pregnancy from a blighted ovum, incomplete abortion, or complete abortion.

A normal intrauterine sac appears regular and well-defined on ultrasound. It has been described as a "double ring," which represents the decidual lining and the amniotic sac. In ectopic pregnancy, ultrasound may reveal only a thickened, decidualized endometrium. With more advanced ectopics, decidual sloughing with resultant intracavitary fluid or blood may create a so-called "pseudogestational sac." This sac is small and irregular as compared to a true gestational sac, but at times can be confused with a normal sac.

An intrauterine sac should be visible by transvaginal ultrasound when the β-hCG is approximately 1000 mIU/mL, and by transabdominal ultrasound approximately 1 week later, when the β-hCG is 1800-3600 mIU/mL. Thus, when an empty uterine cavity is seen with a β-hCG titer above this threshold, the patient is likely to have an ectopic pregnancy. An empty cavity is less of a concern when a β-hCG below the threshold is obtained, as this may be associated with an ectopic pregnancy, but may also be seen with an early IUP.

The presence of an adnexal mass with an empty uterus is also of concern. If the β-hCG is low, this may represent an early IUP with a corpus luteum cyst. However, if the β-hCG is above the discriminatory value, an ectopic is likely. A "tubal ring" seen on ultrasound may represent an unruptured ectopic, with a gestational sac and sometimes embryo surrounded by a distorted fallopian tube. This complex is seen adjacent to but separate from both the uterus and ovary. If rupture has occurred, ultrasound may reveal a dilated fallopian tube with fluid in the cul-de-sac.

2. Laparoscopy - The need for laparoscopy in the diagnosis of ectopic pregnancy has declined with the increasing use of ultrasound. It is still useful, however, in certain situations when a definitive diagnosis is difficult, especially in the case of a desired, potentially viable intrauterine pregnancy when a D&C is contraindicated. Laparoscopy may also be used as definitive management in early ectopic gestation.

3. D&C - D&C may confirm or exclude intrauterine pregnancy in the case of an undesired pregnancy. D&C may interrupt an intrauterine gestation and should not be performed if the pregnancy is desired, unless the β-hCG titers have plateaued or fallen and the pregnancy is definitely abnormal. When chorionic villi are recovered, the diagnosis of an intrauterine pregnancy is confirmed. On the other hand, if only decidua is obtained on D&C, ectopic pregnancy is highly likely.