By the end of postgraduate training, using a patient-centred approach and appropriate selectivity, a resident, considering the patient’s cultural and gender contexts, will be able to...
Key Feature 1: In any woman with vaginal bleeding, rule out pregnancy.
Skill: Clinical Reasoning
Phase: Hypothesis generation, Diagnosis
Quite simply, history and physical examination are not able to rule out pregnancy with absolute certainty, and because the underlying pathology can be serious (ex: ectopic pregnancy), and because a urine dip for B-hCG is such a cheap, not at all uncomfortable, and swift test to do, there is little harm in doing one even if the pretest probability is low. Better safe than sorry. In a previous post I also mentioned the importance of doing a urine dip to rule out pregnancy in the setting of abdominal pain as well, and the same reasoning holds.
The woman who is found to be pregnant pretty much has a whole other differential diagnosis to consider for vaginal bleeding or for abdominal pain, along with the differential diagnosis one would consider in the patient who is not pregnant. Furthermore, knowing a woman is pregnant may affect management. Ruling out pregnancy is certainly important to do before hunting down a source of abdominal pain with imaging that has a high quantity of radiation such as a CT scan, and which could be teratogenic to a developing embryo or fetus. As well, in the setting of vaginal bleeding, considering the need to give Rh immunoglobulin could be life-saving, or in the setting of dehydration, knowing the patient is pregnant could change your choice of maintenance fluid from the default normal saline for everyone to 5% dextrose infused in half normal saline (ensuring the developing embryo/fetus continues to receive a steady supply of energy). There are lots of little things to consider when you're treating two people instead of the obvious one, so just dip the dang urine and call it day.