Approach to first trimester bleeding: Clinical sciences

First trimester bleeding includes is any vaginal or uterine bleeding that occurs from the first day of a patient’s last menstrual period through 13 weeks and 6 days gestation. Pregnant patients who present with vaginal bleeding in the first trimester require a timely evaluation to rule out any life-threatening conditions. The most concerning cause is an ectopic pregnancy because it can progress to tubal rupture and intraperitoneal hemorrhage. Other common etiologies include genital tract pathology, implantation bleeding, spontaneous abortion, pregnancy of unknown location, and molar pregnancy

Your first step in evaluating a patient with first trimester bleeding is to perform a CABCDE assessment to determine if they are stable or unstable. If your patient is unstable, think about ruptured ectopic pregnancy and incomplete abortion. Regardless of the cause, your next step is to start acute management. Stabilize airway, breathing, and circulation; consider intubation as clinically indicated; obtain IV access and a type and cross for possible packed red blood cell transfusion; and continuously monitor vital signs.

Alright, now that unstable patients are covered, let’s talk about stable ones. First, obtain a focused history and physical examination. On history, determine the first day of your patient's last menstrual period, whether an intrauterine pregnancy, or IUP, has already been documented by ultrasound, and any previously assigned estimated due date. Next, assess if the patient has any risk factors for ectopic pregnancy or pregnancy loss, such as a history of either one of these. Also, characterize their vaginal bleeding, taking note of onset, frequency, quantity, and associated abdominal or pelvic pain. Additionally, ask if they have passed any large blood clots or tissue prior to your evaluation.

On physical exam, evaluate for any abdominal tenderness to palpation or peritoneal signs, like rebound pain and guarding. Next, perform a speculum exam to assess the quantity and source of bleeding and evaluate if any products of conception are present in the vagina or cervix. Also, check for any vaginal or cervical source of bleeding. On bimanual exam, evaluate uterine size and tenderness; and check for dilation of the internal cervical os. Finally, examine any tissue that may have already passed and see if you can visualize a clear gestational sac or placental villi.

Then, obtain labs, including a quantitative hCG, type and screen, and Rh status; as well as a CBC to evaluate for anemia and establish a baseline hemoglobin. Lastly, perform a transvaginal ultrasound to evaluate the location and viability of the pregnancy, making note of whether fetal cardiac activity is present or absent.

Now, if you see an intrauterine pregnancy on ultrasound, specifically a gestational sac with a yolk sac or an embryo, you should assess for fetal cardiac activity. When cardiac activity is present and your exam reveals a closed cervix with no visualized products of conception, consider either genital tract pathology or threatened abortion. Genital tract lesions are diagnosed by visual inspection and include vaginal lacerations, vaginitis, cervicitis, cervical polyps, fibroids, and rarely, neoplasm. So, if on a sterile speculum exam, you observe a clear source of vaginal or cervical bleeding, that’s genital tract pathology.

On the flip side, if a vaginal or cervical lesion is absent, you will instead diagnose a threatened abortion or implantation bleeding. A threatened abortion can present with bleeding anytime throughout the first trimester whereas implantation bleeding is generally characterized by light bleeding or spotting that occurs about 10 to 14 days after fertilization, or around the time of a missed menstrual period.

Here’s a clinical pearl! A common cause of a threatened abortion is a subchorionic hemorrhage or hematoma, which is when the chorion partially detaches from the uterine wall. On ultrasound, subchorionic hemorrhage appears as a hypoechoic crescent-shaped area adjacent to the gestational sac in the subchorionic space.

Going back a step, if cardiac activity is present, but your exam reveals an open cervix, with ongoing bleeding and no products of conception, you can diagnose an inevitable abortion.

Okay, time to see what to do if the cardiac activity is absent. In this situation, you will again rely on the findings of your physical exam to determine the bleeding etiology.

If the cervix is closed and no products of conception are visualized, refer to your ultrasound and assess the mean gestational sac diameter; or, if an embryo is present, the crown-rump length. If the mean gestational sac diameter is at least 25 mm OR if the crown-rump length of the embryo is 7 mm or greater, you will diagnose a missed abortion. However, if the mean gestational sac diameter is less than 25 mm OR if the crown-rump length is less than 7 mm, diagnose a pregnancy of uncertain viability.