Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (276 page)

Sperling RS, Newton E, Gibbs RS. Intraamniotic infection in low-birth-weight infants.
J Infect Dis.
1988;157:113–117.

ECTOPIC (TUBAL) PREGNANCY

   Definition

Ectopic pregnancy is the implantation of the conceptus outside of the endometrial cavity, in the Fallopian tube or cornu of the uterus.

   Clinical Presentation

Tubal pregnancy has increased in frequency and constitutes up to 2% of all pregnancies now
¹
. Patients present with abdominal pain, amenorrhea, and vaginal bleeding. With rupture, there is rapid onset of hypotension from intraperitoneal bleeding and if not immediately treated may result in death. Diagnosis is made by ultrasound and hCG in the serum or urine (see eBook Figure 8-14).

   Laboratory Findings

   
Human chorionic gonadotropin
(hCG): Tests for hCG should recognize the following three important forms. Intact hCG, H-hCG (hyperglycosylated hCG produced by invasive cytotrophoblasts; key component in early pregnancy), and free β-hCG that many kits and point-of-care (POC) tests do not recognize.

   hCG titer doubles about every 1.4–2.1 days during first 40 days of normal pregnancy (at least two measurements 48–72 hours apart are needed to calculate this); an abnormally slow increase in hCG (<66% in 48 hours during first 40 days of pregnancy) indicates ectopic pregnancy (S/S = 80%/91%) or abnormal intrauterine pregnancy in approximately 75% of cases
²
.

   The discrimination zone for normal versus ectopic pregnancy is reached when hCG reaches 6,500 mIU/mL (equivalent to approximately 6 weeks of gestation) without an intrauterine gestational sac seen by transabdominal US or at 1,500–2,000 mIU/mL hCG when visualizing by transvaginal ultrasound
³
. There is no proven discriminatory level for multiple gestations.

   The lack of visualization of a gestational sac may also occur with spontaneous abortion.

   Decrease of hCG of ≥15% 12 hours after curettage is diagnostic of completed abortion, but hCG that rises or remains the same indicates ectopic pregnancy.

   hCG level >50,000 mIU/mL in ectopic pregnancy is rare.

   Serum hCG is used to monitor methotrexate treatment of ectopic pregnancy (performed weekly until undetectable).

   Urine pregnancy test is more variable.

   
Progesterone
: Serum progesterone may be used to help identify ectopic pregnancy in patients with bleeding and abdominal pain with an hCG lower than expected for gestational age. A level of ≥25 ng/mL is said to indicate normal intrauterine pregnancy (sensitivity = 98%) and ≤5 ng/mL confirms nonviable fetus (100% sensitivity)
^4,5
.