Non-menstrual vaginal bleeding in a woman of reproductive age can be due to to a complication of pregnancy.
The first step in every evaluation of abnormal vaginal bleeding is evaluation of the vital signs (pulse rate, blood pressure, respiratory rate). If abnormal, evaluation in the emergency department is likely indicated.
If they are normal, then the next step is to check for abnormal orthostatic vital signs. The pulse and blood pressure are recorded with the patient supine and then both the pulse and blood pressure are recorded again with the patient standing. A lower blood pressure when standing or a faster pulse when standing can be an indication of significant blood loss and is again an indication that further evaluation should likely be in the emergency department.
If the orthostatic vital signs are normal, then the next step is evaluation of lab tests.
Next are two critical lab tests: a serum or urine pregnancy test and a complete blood count or hemoglobin level. If the hemoglobin level is below normal, then again evaluation in the emergency department may be indicated.
If the pregnancy test is positive, then the possible causes are threatened abortion, complete abortion, ectopic pregnancy, and molar pregnancy. And a positive pregnancy test needs to be followed up with a quantitative beta-HCG level and an abdominal ultrasound scan and/or a transvaginal ultrasound.
Vaginal bleeding in the first trimester of pregnancy is very common. Approximately 25% of pregnant women will have vaginal bleeding in the first trimester. If no cause is found the diagnosis is said to be threatened abortion. Of patients who have threatened abortion, about half will ultimately lose the pregnancy.
A threatened abortion means first trimester bleeding without passage of tissue and that is not due to the other causes of first trimester bleeding: Spontaneous abortion, ectopic pregnancy, or molar pregnancy.
Often, the ultrasound scan will be “normal” in a patient with first trimester bleeding. This means that the scan did not detect an intrauterine pregnancy, an ectopic pregnancy (a pregnancy outside the uterus), or any abnormal fluid in in the abdominal cavity (which can be sign of ectopic pregnancy).
“In this situation, the differential diagnosis includes the “triple rule out” of an early intrauterine
pregnancy <4.5 weeks, an early nonvisualized ectopic pregnancy or a spontaneous abortion. These patients may also be considered to have a “pregnancy of unknown
location” (PUL). In this situation, the American Society of Reproductive Medicine  advocates uterine curettage to rule out an ectopic pregnancy when the beta-hCG is >2,400 mIU/ML. However, this approach will result in the loss of some early intrauterine pregnancies.
Thus, if the patient is clinically stable, many authors recommend observation. A quantitative beta-hCG should be obtained and then followed. In a normal intrauterine pregnancy, the level should approximately double every 48 hours. If the initial level was low, when it reaches the
discriminatory zone a repeat pelvic sonogram may be obtained to confirm an intrauterine pregnancy. If the level drops appropriately, resolution of a nonvisualized PUL is assumed. If the level fails to decline and plateaus, an ectopic pregnancy is more likely. In such situations, follow-up US may be obtained and/or medical therapy for a presumptive ectopic pregnancy.”*
The reference below is an oustanding guide to the evaluation of first trimester bleeding disorders and is well worth review.
In keeping with the theme of January’s blogs, you can locate the reference easily by going to the National Guideline Clearing House home page at https://www.guideline.gov/index.aspx and typing ectopic pregnancy into the search box.
*American College of Radiology ACR Appropriateness Criteria: First Trimester Bleeding available for download from the list at https://acsearch.acr.org/list.