282 Obstetrics and Gynecology Board Review •••
❍ What is the normal rate of rise of hCG in the first trimester?
Ninety-nine percent of normal intrauterine pregnancies have an increase in hCG levels of at least 53% in 2 days.
Newer hCG curves suggest using a cutoff of a rise of 35% to avoid misclassification of a normal intrauterine
pregnancy as an ectopic pregnancy.
❍ What is the normal fall of hCG in spontaneous abortions?
A minimal 2-day decline in hCG of 36% to 47% is present in 90% of spontaneous abortions.
❍ How do the hCG changes in ectopic pregnancies compare with those of viable intrauterine pregnancies or
spontaneous abortions?
Approximately 21% of ectopic pregnancies have a rise in hCG similar to an intrauterine pregnancy and 8% have a
fall similar to a spontaneous abortion.
❍ Is culdocentesis helpful in the diagnosis of ectopic pregnancy?
Historically, a culdocentesis was performed to evaluate for intraperitoneal blood. The presence of nonclotting
blood (especially with a hematocrit >15%) was used to confirm ruptured ectopic pregnancy but may also be
present with a bleeding corpus luteal cyst. The development of accurate ultrasounds has essentially replaced the
need for this test.
❍ What progesterone level predicts a normal intrauterine pregnancy?
A progesterone value >25 ng/mL suggests a normal pregnancy. There is no single level that will definitely confirm a
normal pregnancy or rule out an ectopic.
❍ What progesterone level predicts an abnormal pregnancy?
A progesterone level <5 ng/mL suggests an abnormal pregnancy; this does not distinguish between a spontaneous
abortion and an ectopic pregnancy.
❍ At what hCG level, would an intrauterine pregnancy be seen by transabdominal pelvic ultrasound?
An hCG level >6500 mIU/mL should show a gestational sac; the yolk sac and fetal pole may not be seen at
this level.
❍ At what hCG level, would an intrauterine pregnancy be seen by transvaginal ultrasound?
The discriminatory zone for detecting an intrauterine pregnancy by transvaginal ultrasound is an hCG level > 1500
to 2000 mIU/mL. A higher discriminatory zone may be used for patients who are considered to be at high risk of
multiple gestations, such as those patients undergoing assisted reproductive technology.
❍ List the significant ultrasound findings present in a normally developing intrauterine pregnancy according
to gestational age.
5.3 weeks: Gestational sac.
5.5 weeks: Yolk sac.
6 weeks: Fetal pole.
6.5 weeks: Cardiac activity.
In addition, an abnormal pregnancy is likely if there is absence of a fetal pole with a gestational sac of 2 cm and if
no cardiac activity is seen with crown-rump length of >0.5 cm.