1. Indications for Obstetrical Ultrasound Examinations
Focus on Third Trimester Bleeding

2. Indications: Confirm presence of an intrauterine pregnancy
Suspected ectopic pregnancy
Estimation of gestational age
Vaginal bleeding
Significant uterine size and dates discrepancy
Suspected multiple gestation
Evaluation of a pelvic mass or pelvic pain
Evaluation of fetal growth
Adjunct to amniocentesis, chorionic villus biopsy, fetal blood sampling
Suspected hydatidiform mole
Evaluation of incompetent cervix and/or risk of preterm delivery
Adjunct to cervical cerclage placement
Adjunct to special diagnostic or therapeutic procedures on the fetus
Confirm fetal viability or fetal death

3. Indications (cont): Suspected uterine abnormality
Adjunct to localization and removal of an intrauterine contraceptive device
Biophysical fetal evaluation
Suspected oligohydramnios or polyhydramnios
Suspected abruptio placentae
Adjunct to external cephalic version
Estimation of fetal weight
Determination of fetal presentation
Abnormal maternal serum analytes
Follow-up of observed fetal anomaly
Identification and follow-up of placental previa
History of previous congenital anomaly
Serial evaluation of fetal growth in multiple gestation
Evaluation of fetal condition in late registrants for prenatal care

4. Indications – 3rd Trimester:
Confirm presence of an intrauterine pregnancy
Suspected ectopic pregnancy
Estimation of gestational age
Vaginal bleeding
Significant uterine size and dates discrepancy
Suspected multiple gestation
Evaluation of a pelvic mass or pelvic pain
Evaluation of fetal growth
Adjunct to amniocentesis, chorionic villus biopsy, fetal blood sampling
Suspected hydatidiform mole
Evaluation of incompetent cervix and/or risk of preterm delivery
Adjunct to cervical cerclage placement
Adjunct to special diagnostic or therapeutic procedures on the fetus
Confirm fetal viability or fetal death

5. Indications – 3rd Trimester (cont):
Suspected uterine abnormality
Adjunct to localization and removal of an intrauterine contraceptive device
Biophysical fetal evaluation
Suspected oligohydramnios or polyhydramnios
Suspected abruptio placentae
Adjunct to external cephalic version
Estimation of fetal weight
Determination of fetal presentation
Abnormal maternal serum analytes
Follow-up of observed fetal anomaly
Identification and follow-up of placental previa
History of previous congenital anomaly
Serial evaluation of fetal growth in multiple gestation
Evaluation of fetal condition in late registrants for prenatal care

6. Third Trimester Vaginal Bleeding (may sometimes occur during second trimester)
Placental Abruption
Placenta Previa
Vasa Previa
Uterine Rupture
Cervical Change (assoc. w/ cervical insufficiency)
Rupture of Membranes
Labor
Cervico-vaginal Neoplasm
Placenta Accreta (can lead to massive hemorrhage at birth)
We will focus on placental abruption vs. placenta previa.

7. Placental Abruption

8. Placental Abruption
Definition: Placental abruption (aka abruptio placentae) is the premature separation of the normally implanted placenta from the uterine wall. The result is hemorrhage between the uterine wall and the placenta.
Breakdown: Abruptions before labor, after 30th wk (50%)
Abruptions during labor (15%)
Asymptomatic abruptions, seen on placental inspection after delivery (30%)
There are different types of abruption based on where the separation is located and whether or not there is vaginal bleeding.
Concealed bleeding (20%) – bleeding is confined w/in the uterine cavity
Apparent bleeding (80%) – bleeding is apparent due to dissection of blood downward toward the cervix

9. Placental Abruption
The underlying cause of placental abruption is not completely understood.
The immediate cause is thought to be separation of defective maternal vessels in the decidua basalis from the placental anchoring villi.
Rarely, bleeding can also originate from fetal placental vessels.
The separation of the maternal vessels causes an accumulation of blood, which can further separate the placenta from the uterus.
The degree of separation determines the type of abruption as mentioned above.
Partial abruptions (concealed bleeding) are smaller and self-contained.
Total abruptions (apparent bleeding) are complete or near complete placental separation.

10. Placental Abruption Predisposing Factors Precipitating Factors
Hypertension
Previous abruption
Advanced maternal age
Multiparity
Uterine distension
Multiple gestation
Hydramnios
Vascular deficiency
Diabetes mellitus
Collagen vascular disease
Cocaine use
Cigarette smoking
Alcohol use (>14 drinks/wk)
Circumvallate placenta
Short umbilical cord
Precipitating Factors
Trauma
External/Internal version
Motor vehicle accident
Abdominal trauma
Sudden uterine volume loss
Delivery of first twin
Rupture of membranes (with polyhydramnios)
Preterm premature rupture of membranes

11. Placental Abruption Epidemiology
Occurs in 0.5% to 1.5% of all pregnancies.
Is responsible for 30% of all cases of third trimester bleeding.
Incidence of abruption peaks at 24 to 26 weeks of gestation.
Is responsible for 15% of all cases of perinatal mortality.
In patients with a prior episode of abruption the risk in future pregnancies is 10%.
In patients with two prior episodes of abruption the risk in future pregnancies increases to 25%.

12. Placental Abruption Signs and Symptoms Presentation
The classic triad of symptoms is third trimester vaginal bleeding with severe abdominal pain and/or frequent strong contractions. However, this triad is not present in every patient.
Presentation
Symptom
Occurrence (%)
Vaginal Bleeding
80%
Uterine Tenderness / Abdominal or Back Pain
67%
Abnormal Contractions / Increased Uterine Tone
34%
Fetal Distress
50%
Fetal Demise
15%

13. Placental Abruption Diagnosis This is primarily a clinical diagnosis.
Only about 2% of abruptions are picked up by U/S (seen as a retroplacental clot). However, placenta previas are reliably diagnosed by U/S and therefore if not seen can likely be ruled out. This increases the likelihood of the diagnosis of abruption.
Coagulopathy (especially hypofibrinogenemia) on laboratory testing supports a diagnosis of severe abruption.
Gross examination of the placenta at birth often confirms diagnosis of abruption.

14. Example of Abruption on U/S
Placental Abruption
Example of Abruption on U/S
Courtesy of Charles Lockwood, MD.

15. Example of Abruption on U/S
Placental Abruption
Example of Abruption on U/S
Courtesy of Charles Lockwood, MD.

16. Placenta Previa

17. Placenta Previa
Definition: Placenta previa is the abnormal presence of placental tissue overlying or next to the internal cervical os. Bleeding may result from this abnormal implantation. This bleeding may range from spotting to hemorrhage.
There are different types of placenta previa based upon the actual location of the placenta in relation to the interval cervical os.
Complete previa – the placenta completely covers the internal cervical os.
Partial previa – the placenta covers a portion of the internal cervical os (which must be partially dilated for this to be possible).
Marginal previa – the placenta is adjacent to the internal cervical os, but does not cover the os.
Low-lying placenta – the placenta is implanted in the lower uterine segment, but does not reach the border of the internal cervical os.
*Marginal and low-lying placentas are interpreted in different ways by different
people and for clarification should always be described in terms of centimeters
between the edge of the placenta and the internal cervical os.

18. Placenta Previa
The cause of bleeding in placenta previa is small disruptions in the placenta attachment during normal development, as well as thinning of the lower uterine segment during the third trimester.
As the uterus grows and thins the placenta is stretched (when implanted in the lower uterine segment near or over the internal cervical os). This leads to separations in the placental attachment, which causes bleeding ranging from minor to severe.
There are multiple reasons for the implantation of the placenta in the lower uterine segment.
- Endometrial scarring of the upper segment of the uterus may promote implantation, growth, or both in the lower uterine segment.
- The need for increased placental surface area (to compensate for reduced uteroplacental oxygenation or decreased nutrient delivery) is thought to be another cause of placenta previa.
Placenta previa may also be complicated by an associated placenta accreta. Placenta accreta is abnormal invasion of the placenta into the uterine wall.

19. Placenta Previa Predisposing Factors Previous cesarean section(s)
Previous uterine surgery (such
as myomectomy or curettage)
Multiparity
Increasing maternal age
Multiple gestation
Residence at higher altitude
Maternal smoking
Erythroblastosis
History of placenta previa

20. Placenta Previa Epidemiology Occurs in about 0.5% of pregnancies.
Is responsible for 20% of all cases of third trimester bleeding.
Incidence increases to about 1-4% of women with prior cesarean sections.
Is responsible for perinatal mortality because of the high association with preterm delivery.
Is associated with placenta accreta in about 5% of cases. The risk of accreta is increased in women with previa who have had a prior cesarean section. (One prior section = 25-30% risk of accreta. Two prior sections = 33-50% risk of accreta. Three or more prior sections = 50-65% risk of accreta.)

21. Placenta Previa Signs and Symptoms
The classic presentation of placenta previa is sudden onset of profuse painless vaginal bleeding, usually occurring after 28 weeks of gestation.
This presentation is different from that of placental abruption in that there is usually no pain and no contractions. However, sometimes the presentations are similar and this can make it difficult to determine the cause of the vaginal bleeding from history alone.

22. Placenta Previa Diagnosis
This diagnosis is made primarily by ultrasound.
Vaginal examination should be deferred in cases of placenta previa as the digital exam may cause further separation of the placenta, leading to possible life-threatening hemorrhage. Therefore, vaginal exam should always be deferred until after ultrasound in cases of third trimester vaginal bleeding.
Placenta previa can be diagnosed with ultrasonography with a sensitivity of about 95%.
Traditionally transvaginal ultrasound has been avoided in patients with suspected placenta previa. Transabdominal ultrasound should be used for initial placental identification and localization. However, if the findings are unclear transvaginal ultrasound should be used to better define placental position. This procedure can be safely performed as the optimal position of the vaginal probe for best visualization of the internal cervical os is 2-3 cm away from the cervix and therefore minimizes the risk of causing further separation of the placenta.
The bladder should always be emptied prior to ultrasound, as an over-distended bladder can compress the lower uterine segment giving the appearance of a placenta previa.

23. Example of Complete Previa on U/S
Placenta Previa
Example of Complete Previa on U/S
Transabdominal U/S shows placenta completely covering internal cervical os.
Courtesy of Deborah Levine, MD.

24. Example of Marginal Previa on U/S
Placenta Previa
Example of Marginal Previa on U/S
Transvaginal U/S shows placenta next to the internal os, but not covering it.
Courtesy of Deborah Levine, MD.

25. Example of Normal Placenta (Full Bladder)
Placenta Previa
Example of Normal Placenta (Full Bladder)
Transabdominal U/S shows an over-distended bladder giving the appearance of a placenta previa.
Courtesy of Deborah Levine, MD.

26. Placental Abruption vs. Placenta Previa
By combining a thorough history with transabdominal and/or transvaginal ultrasonography the correct diagnosis is made in the majority of cases (about 95% of the time).

27. References
Callahan, Tamara L. and Caughey, Aaron B. Blueprints Obstetrics and Gynecology, 4th ed.
Lippincott Williams and Wilkins; 2007:
Oyelese, Y, Ananth, CV. Placental Abruption. Obstetrics and Gynecology 2006;
108:1005.
Thurmond, A, Mendelson E, Bohm-Velez, et al. Role of Imaging in Second and Third
Trimester Bleeding. American College of Radiology: ACR Appropriateness
Criteria. Radiology 2000; 215: 895.
Timor-Tritsch, IE, Yunis, RA. Confirming the Safety of Transvaginal Sonography in
Patients Suspected of Placenta Previa. Obstetrics and Gynecology 1993;
81: 742.
Clinical Features and Diagnosis of Abruptio Placentae. Jonathan
Gillen-Goldstein, MD. Last updated April 4, 2007.
Clinical Manifestations and Diagnosis of Placenta Previa. Karen
Russo-Stieglitz, MD and Charles J Lockwood, MD. Last updated February
12, 2007.
Indications for Diagnostic Obstetrical Ultrasound Examination. Jeffrey
L Ecker, MD and Michael F Greene, MD. Last updated December 29, 2006.