Third Trimester Bleeding

Like first trimester bleeding, bleeding in the third trimester has a broad range of etiologies. Obstetric etiologies cover the spectrum from benign "bloody show", to more concerning placenta previa or placental abruption, to life threatening uterine rupture. Because of the potentially serious causes of third trimester bleeding, two principles must be followed. First, evaluate the patient in a center that can manage maternal hemorrhage and a potentially compromised newborn, and second, do not perform a vaginal exam until placenta previa has been ruled out. Placenta accreta may be associated with placenta previa due to the placenta's implantation in the lower uterine segment. This is a placental abnormality that can result in significant maternal hemorrhage leading to maternal mortality. All three of these abnormalities: placenta previa, placental abruption, and placenta accreta can often be diagnosed with ultrasound during the antepartum period. Early diagnosis enables development of a plan of care that reduces maternal and fetal risk.

Placenta Previa and Placenta Accreta In patients with placenta previa, the placenta implants in the lower uterine segment. The placenta can completely occlude the cervical os or be considered a marginal placenta previa if the placenta is within 2 cm of the cervical os. Multiparity, advancing age, and previous cesarean section increase the risk of placenta previa. The risk is also slightly increased by multiple gestation.

Patients with placenta previa may have spotting in the first two trimesters of pregnancy, or they may have an uncomplicated pregnancy prior to 28 weeks. At this point, patients are much more likely to have their first episode of hemorrhage which is characteristically described as sudden, painless, and may be profuse. The amount of bleeding may soak clothes or bedding with bright red, clotted blood. However, despite the appearance of such profuse bleeding, blood loss is not usually extensive, seldom leads to shock, and is rarely fatal.

Patients with placenta previa have more placental implantation than usual in the lower uterine segment, as mentioned above. As a result, they may have associated placenta accreta due to the poorly developed decidua in the lower uterine segment. Placenta accreta is a term for abnormally firm adherence of the placenta to the uterine wall, typically leading to postpartum hemorrhage, unlike placenta previa which leads to third trimester bleeding. Uterine inversion is another potential complication of placenta accreta. Risk factors for placenta accreta include anything that disrupts the basement membrane of the endometrium including prior cesarean delivery, prior uterine curettage, advanced maternal age, and grand multiparity. The incidence of placenta accreta is rising along with the increased rate of cesarean sections. Keep these risk factors in mind as patients are often completely asymptomatic.

Ultrasound correlation 95% of placenta previas can be identified using bedside transabdominal ultrasonography. Nearly every case of placenta previa can be diagnosed using transvaginal or transperineal ultrasound. Translabial or transvaginal studies are helpful and safe for diagnosis of patients with an unclear transabdominal scan. Color flow Doppler used along with real-time ultrasound increases the sensitivity.

For patients with placenta accreta, ultrasonography alone will only detect the pathology less than half the time. However, the addition of color Doppler dramatically increases the sensitivity of a scan. Typical findings include a distance between the uterine serosal bladder interface and the retroplacental vessels of less than 1 mm, the presence of increased Doppler flow in the underlying area, and the presence of irregular hypoechoic spaces in the placenta.

Complete Placenta Previa

Marginal Placenta Previa

Placenta Accreta - Irregular Lacunae

Placenta Accreta - Bladder Wall/Serosal Space

Placenta Accreta - Color Flow

Placental Abruption In patients with placental abruption, part or all of the placenta abruptly separates from the lining of the uterus. Often some of the resulting bleeding occurs between the placenta and the uterine lining. At this point, the blood either drains through the cervix causing visible hemorrhage, or remains trapped between the uterus and the placenta forming a concealed hemorrhage. If there is concealed hemorrhage, a consumptive coagulopathy may develop. Risk factors for placental abruption include hypertension, cocaine use, trauma, cigarette smoking, advanced maternal age, grand multiparity, African-American or Caucasian race, and PPROM, among others. Bleeding and abdominal pain are the most common findings in patients with placental abruption.

Ultrasound correlation Placental abruption is inconsistently diagnosed with ultrasound. Because of this, it is important to remember that a negative ultrasound does not rule out abruption. Findings to look for when abruption is suspected include a hyperechoic area within the first 48 hours, or a hypoechoic area after the first 48 hours in the first two weeks. After two weeks, the clot may contain anechoic regions. If the patient has an acute abruption, an ill-defined region may appear retroplacentally. Because placental abruption is often not seen with ultrasound, this diagnosis is typically made based on a patient's clinical presentation with bleeding and contractions.

Extra-Ovular Clot - View 1

Extra-Ovular Clot - View 2

Extra-Ovular Clot - Click for Video