Imaging in Pregnancy

Diagnostic Approach

Transabdominal ultrasound should be performed to evaluate for free fluid in the abdomen, as it better assesses for intraperitoneal fluid, according to the American College of Radiology 1
Absence of intrauterine gestational sac with positive pregnancy test indicates pregnancy of unknown location (PUL), as stated by the American College of Radiology 1
Evaluation of the adnexal area should include checking for free fluid in cul-de-sac or abdomen, as recommended by the American College of Radiology 1
Endometrial assessment should include evaluation of endometrial thickness and appearance, and looking for subchorionic hemorrhage, which may explain bleeding, according to the American College of Radiology 1
Definitive intrauterine pregnancy is confirmed by the presence of a gestational sac with yolk sac or fetal pole in the uterus, while definitive ectopic pregnancy is confirmed by the presence of an extrauterine gestational sac with yolk sac or embryo 2

The following conditions can be identified using ultrasound:

Condition	Description
Placenta previa	A condition where the placenta covers the cervix
Low-lying placenta	A condition where the placenta is located near the cervix
Vasa previa	A condition where the umbilical cord is located near the cervix
Ectopic pregnancy	A condition where the pregnancy is located outside the uterus
Threatened abortion	A condition where the pregnancy is at risk of miscarriage

Transabdominal ultrasound is the preferred initial procedure for evaluation of vaginal bleeding in pregnancy, with transvaginal ultrasound frequently necessary if transabdominal views are inadequate or inconclusive 3
Transvaginal ultrasound is more accurate for assessing placental relationship to the cervix, provides better visualization of the cervix, and is more sensitive for detecting placental abruption 3
Color Doppler ultrasound is essential for diagnosis of vasa previa, helpful in distinguishing placental tissue from blood clot in suspected abruption, and can identify vessels overlying the internal cervical os 3
Immediate ultrasound evaluation is essential to determine the cause of bleeding and guide management, regardless of symptoms or pregnancy-related values, and should include evaluation of placental location and relationship to the cervix, assessment of fetal viability, and check for evidence of placental abruption 3

Placenta previa is the most common diagnosis, affecting approximately 1 in 200 pregnancies, and management includes pelvic rest, hospitalization for significant bleeding, serial ultrasound monitoring, and preparation for possible cesarean delivery 3
Low-lying placenta management is similar to placenta previa but less restrictive if minimal bleeding, with follow-up ultrasound to assess placental migration 3
Vasa previa is rare, affecting approximately 1 in 2,500-5,000 deliveries, but potentially fatal to the fetus, and requires hospitalization, close monitoring, and planned cesarean delivery 3
Placental abruption affects approximately 1% of pregnancies, with ultrasound sensitivity limited to detecting at most 50% of cases, and management includes continuous fetal monitoring, preparation for emergency delivery, and assessment of maternal hemodynamic status and coagulation 3
Significant bleeding, placenta previa with active bleeding, placental abruption, signs of preterm labor, and hemodynamic instability require prompt hospitalization and intervention 3

If no definitive intrauterine pregnancy or ectopic pregnancy is visualized, serial β-hCG measurements (48-72 hours apart) and repeat ultrasound when β-hCG reaches discriminatory zone should be considered, as suggested by the American College of Radiology 1
The American College of Emergency Physicians recommends that the initial emergency department workup for a female with amenorrhea and episodic pelvic pain must include a pregnancy test and pelvic ultrasound (transvaginal and transabdominal) regardless of β-hCG level, to rule out ectopic pregnancy due to its life-threatening potential 2
Hospital admission is necessary for significant bleeding, placenta previa, placental abruption, or signs of preterm labor, with management including continuous fetal monitoring, preparation for possible emergency delivery, and administration of Rh immunoglobulin to Rh-negative women, as recommended by the American College of Radiology and the Society for Maternal-Fetal Medicine 3, 4
Patients with normal intrauterine pregnancy and spotting can be managed as outpatients if no abdominal pain/contractions, normal fetal movement, and no signs of infection, as recommended by the Society for Maternal-Fetal Medicine 3, 4
Immediate obstetrical consultation is recommended, and preparation for possible surgical intervention or medical management is necessary, with patient education including pelvic rest, monitoring for increased bleeding, and return precautions for heavy bleeding or pain 2, 1

Potential pitfalls in management include performing digital pelvic examination before ruling out placenta previa, underestimating the significance of bleeding, failing to use transvaginal ultrasound when transabdominal views are inadequate, discharging patients without a definitive diagnosis of bleeding source, and neglecting to administer Rh immunoglobulin to Rh-negative women with bleeding 3
Relying solely on β-hCG levels without ultrasound in symptomatic patients, underestimating the significance of abdominal pain without bleeding, and discharging patients without confirming location of pregnancy are also potential pitfalls, as recommended by the American College of Radiology and the American College of Emergency Physicians 3, 2, 5