Perils in the differentiation of a viable intra-uterine pregnancy (IUP) from an ectopic eccyesis

While the mainstay for differentiation of a viable intra-uterine pregnancy (IUP) from nonviable or ectopic gestations is serial measurement of β-hCG titres, strict adherence to 'normal' doubling time guidelines potentially may cause unnecessary intervention in a normal intra-uterine pregnancy, or inappopriately delay intervention in a patient with an ectopic pregnancy. To examine the frequency with which each of these events occurs, we reviewed the record of all pregnant patients with an initial titre less than 6500 mIU/ml and serial titres at 2 to 5 days from 5/88 to 7/90. Among women with an intra-uterine pregnancy, a 'normal' doubling time was observed in 77 of 87 women (88.5%) with an evaluated IUP. Among women with tubal ectopic pregnancies, 35 of 46 (76.1%) had falling or abnormally slow β-hCG rises. However, in 11 women with an ectopic pregnancy (23.9%), the titers initially rose appropriately with a normal doubling time. We conclude that, while serial serum β-hCG measurements in combination with appropriately timed ultrasound examinations can successfully differentiate most viable IUPs from ectopic gestations, strict regimented adherence to previously accepted guidelines may lead to incorrect diagnosis.