Pelvic Ultrasonography is used in obstetric patients to evaluate the pregnancy and the fetus. It is especially important in high-risk pregnancies. In nonpregnant women, it is used to evaluate the genital tract for disease and to monitor known pelvic disease (e.g., benign ovarian cysts).
In real-time diagnostic ultrasound, high-frequency sound waves are emitted from the transducer and penetrate the structure to be studied (e.g., uterus, ovaries, parametria, placenta, fetus). These sound waves are reflected back to a sensor within the transducer, and by electronic conversion are arranged into a pictorial image of the studied structure.
Pelvic ultrasonography can be performed with the transducer placed on the anterior abdomen, or in the vagina with a specially designed vaginal probe, which provides the best view of the pelvic organs in a nonpregnant woman. The images obtained with both transducers are complementary. Vaginal ultrasound provides significant accuracy in identifying paracervical, endometrial, and ovarian disease that may not be detected with the anterior abdominal probe. Occasionally abdominal organs fall into the pelvis and preclude good pelvic visualization with the anterior abdominal probe. Vaginal ultrasound provides better visualization under these circumstances. In the obese patient, the thick abdominal wall inhibits good transmission of ultrasonic waves, and vaginal ultrasound is preferred. The anterior abdominal probe, however, provides better visualization of the upper pelvis than does the vaginal probe, especially in pregnant women.
Pelvic ultrasonography may be useful in the obstetric patient in the following circumstances:
1. To make an early diagnosis of normal pregnancy or abnormal pregnancy (e.g., tubal pregnancy).
2. To identify multiple pregnancies.
3. To differentiate a tumor (e.g., hydatidiform mole) from a normal pregnancy
4. To determine the age of the fetus from the diameter of the head
5. To measure fetal growth rate.
6. To identify placental abnormalities such as abruptio placentae and placenta previa
7. To determine the position of the placenta (ultrasound localization of the placenta is done before amniocentesis).
8. To make differential diagnoses of various uterine and ovarian enlargements (e.g., polyhydramnios, neoplasms, cysts, abscesses).
9. To determine fetal position.
10. To diagnose ectopic pregnancy.
Ultrasound is quickly becoming a very accurate and easily performed screening test to recognize risks of fetal abnormalities. Fetal nuchal translucency (FNT) is an ultrasound measurement of subcutaneous edema in the neck region of the fetus. It is performed at 10 to 14 weeks of gestation. Major heart defects, trisomy 21, and other genetic defects are associated with increased edema in this location at this age of gestation. Screening for chromosomal defects by measurement of FNT identifies 80% of fetuses with trisomy 21 for a false-positive rate of 5%. This is especially helpful for older pregnant women. With FNT, these abnormalities can be identified earlier in the pregnancy when abortion is still possible. Although there may be advantages in early detection of fetal anomalies, there may be a disadvantage that should be considered. Many pregnancies complicated by fetal abnormality, both aneuploidy and other anomalies, will end in an early miscarriage. If these pregnancies are identified early, parents may be asked to make difficult decisions regarding termination of pregnancy. This imposed a potential burden and long-term consequence that may have been avoided had the pregnancy been lost spontaneously.
Pelvic Ultrasonography is useful in nonpregnant women to monitor the endometrium in patients who take tamoxifen and to aid in the diagnosis of:
1. Ovarian cyst
2. Ovarian tumor
3. Tubo-ovarian abscess
4. Uterine fibroids
5. Uterine cancer
6. Pelvic inflammatory disease (PID)
7. Uterine stripe (endometrium)
The procedure is performed in approximately 20 minutes. No discomfort is associated with the study, other than having a full bladder and the urge to void. Some patients may be uncomfortable lying on a hard table.
Pelvic Utlrasonography cannot be used with patients who have latex allergy because the vaginal ultrasound requires placement of the probe in a latex sac.
Causes of Pelvic Utlrasonography False Indications
- Patients who have recently undergone barium contrast studies, because barium creates severe distortion of reflective sound waves.
- Patients with air-filled bowels, because gas does not transmit sound waves well.
- Obesity or failure to fill the bladder, because the image may be uninterpretable.
How is Pelvic Ultrasonography Performed
- Drinking 2 to 4 glasses of water or other fluids before the test is helpful because a full bladder can be visualized better, which is used as a reference point in pelvic anatomy. The full bladder also displaces the bowel from the pelvis and pushes the uterus and ovaries away from the pubis. The fluid in the bladder acts as a window to the pelvis for transmission of sound waves.
- No water is required if ultrasonography is to be done vaginally only.
- If a transabdominal ultrasound is required urgently and there is no time to fill the bladder by ingestion or administration of fluids, the bladder can be filled by means of a bladder catheter.
- The patient is placed in supine position on the examining
- The ultrasonographer, usually a radiologist, applies a greasy, conductive paste to the abdomen to enhance sound wave transmission and reception.
- A transducer is passed vertically and horizontally over the skin.
- If a vaginal probe is used, it is inserted in the vagina and angled to identify the various parts of the pelvis.
- The sound waves are reflected back by the transducer, and an image appears on the cathode ray tube.
- During the examination, fetal structures are pointed out to the mother.
Findings of Pelvic Ultrasonography
By using Pelvic Ultrasonography , the following conditions can be easily Identified:
Abdominal or Tubal Pregnancy: Extrauterine pregnancy is evident when the placental complex is external to the uterus.
Hydatidiform Mole: Molar pregnancy can be diagnosed and monitored by ultrasound.
Compared to Biophysical Profile, fetal characteristics are easily evaluated with ultrasound which can easily help identifying:
- Intrauterine Growth Restriction.
- Fetal Hydrocephalus.
- Multiple Fetuses.
- Fetal Death.
- Abnormal Fetal Position including Breech and Transverse.
Abnormal Position of the Placenta (e.g., placenta previa, abruptio placentae): Placenta position and quality can be evaluated with ultrasonography. Doppler ultrasound can be used to evaluate placental blood flow.
Neoplasm of the Ovaries, Uterus, or Fallopian Tubes: Ultrasound is sensitive in detection of tumors of the female genital tract. The uterine stripe (endometrial lining of the uterus) is monitored in patients taking medications associated with hyperplasia or cancer (e.g., tamoxifen).
Cysts: Ultrasound is the most accurate method to differentiate an ovarian cyst from a solid ovarian tumor. Pure cysts (well-defined hypoechoic mass with clean walls) are more likely to be benign than are complex cysts (containing echogenic material).
Pelvic Inflammatory Disease and Abscesses: Abscesses (tubo-ovarian) appear similar to ovarian cysts but can be differentiated by means of their clinical features.
IUD localization: This test can locate an IUD.