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.

4. Laparotomy - Laparotomy is indicated when the presumptive diagnosis of ectopic pregnancy in an unstable patient necessitates immediate surgery, or when definitive therapy is not possible by medical management or laparoscopy.

5. Culdocentesis - Culdocentesis is the transvaginal passage of a needle into the posterior cul-de-sac in order to determine whether free blood is present in the abdomen (

Fig 14-8). The procedure is simple and safe and may be useful in the diagnosis of intraperitoneal bleeding. It is generally accomplished with the unanesthetized patient in the dorsal lithotomy position. A speculum is placed in the vagina and the posterior lip of the cervix grasped with a tenaculum. The vagina is cleansed. An 18-gauge spinal needle is attached to a 10-mL syringe, and with gentle traction on the cervix, the needle is passed into the cul-de-sac.

This procedure will reveal nonclotting blood if intra-abdominal bleeding has occurred. If the blood clots, it is likely from a punctured vessel in the vaginal wall. Usually, the cul-de-sac will contain some straw-colored fluid, and this may be used to determine if the needle has been properly placed when there is no bleeding. If culdocentesis is positive, laparoscopy or laparotomy should be performed immediately. Indeed, some argue that the main purpose of culdocentesis is to better prioritize patients so that those with positive culdocenteses are taken immediately to the operating room.

Although nonclotting blood is assumed to be from a ruptured ectopic, similar results can also be obtained under other circumstances (eg, a hemorrhagic corpus luteum), and thus a positive result is not diagnostic of a ruptured ectopic pregnancy. Furthermore, a negative result may rule out a ruptured or leaking ectopic but not an intact one.