Sonography and high-risk pregnancy





Objectives


On completion of this chapter, you should be able to:




  • Define high-risk pregnancy



  • Describe the maternal and fetal factors for a pregnancy that is considered high risk



  • Discuss the role of sonography in the high-risk pregnancy





A high-risk obstetric patient is one who has the potential for or is at an increased risk for an adverse maternal or fetal pregnancy outcome. At its extreme, adverse would mean maternal or fetal injury or death. When identifying the high-risk pregnant patient, both the mother and the fetus must be considered. Therefore this chapter discusses both maternal and fetal high-risk factors.




A high-risk obstetric patient is one who has the potential for or is at an increased risk for an adverse maternal or fetal pregnancy outcome. At its extreme, adverse would mean maternal or fetal injury or death. When identifying the high-risk pregnant patient, both the mother and the fetus must be considered. Therefore this chapter discusses both maternal and fetal high-risk factors.




Screening tests


Screening tests, as opposed to diagnostic tests, are offered to low-risk populations to identify patients whose risk is high enough for them to be offered diagnostic testing.


There are a variety of tests that can be offered in either the first or second trimester. The first-trimester screen is performed by looking for the pattern of biochemical markers associated with plasma protein A (PAPP-A) and free beta–human chorionic gonadotropin (beta-hCG). These laboratory values are used in conjunction with an ultrasound (performed between 11 and 14 weeks) to measure the nuchal translucency and the presence of the nasal bone. Based on the patient’s PAPP-A and free beta-hCG laboratory values, age, nuchal translucency measurement, and the presence or absence of the nasal bone, a more accurate risk calculation can be made for having a child with a chromosomal abnormality, congenital heart defect, skeletal dysplasia, or other syndromes. To offer this screening, sonographers must become certified for first-trimester screening. This requires the sonographers performing the test to take an online course and pass a written test. Upon receiving a passing score, a minimum of three ultrasound evaluations of the nuchal translucency must be evaluated for compliance with the certifying organization before the sonographer is certified to perform the examination. This evaluation is repeated annually. Laboratories performing the first-trimester screen will only accept samples and data from certified sonographers. The advantage to parents with first-trimester screening is that they can evaluate their risk for having a child with a chromosomal or syndromatic abnormality much earlier in pregnancy. They may then choose to undergo additional testing, including noninvasive prenatal testing (NIPT) or invasive testing such as chorionic villus sampling (CVS) or amniocentesis to obtain tissue for chromosomal analysis. NIPT is an advanced screening test with a much higher detection rate for Down syndrome and trisomy 18 (99%), and trisomy 13 (91%), than the first-trimester screen or the quad screen, which is performed in the second trimester. NIPT testing can be offered as early as 10 weeks and, because it can also screen for abnormalities with the sex chromosomes, such as Klinefelter syndrome (XXY), triple X syndrome (XXX), and Turner’s syndrome (XO), it can identify the fetal gender. This test evaluates the chromosomes from small pieces of fetal DNA found within a maternal blood sample. NIPT is usually combined with ultrasound evaluation of the nuchal translucency for additional accuracy. Although this test is currently offered to populations of pregnant women with a high risk of abnormal findings only, it holds promise for the future as an alternative to current screening and invasive testing.


Second-trimester screening can be performed with the maternal serum quad screen laboratory value and/or a detailed fetal anatomic survey ultrasound examination. The maternal serum quad screen looks at four serum markers: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), unconjugated estriol (uE3), and inhibin-A. If a first-trimester screening was performed, it would not include the AFP testing so it may be recommended to be done as a single test to screen for neural tube defects in the second trimester.


The detailed fetal anatomic survey ultrasound is a detailed evaluation of specified fetal anatomy and biometry that can be seen at the time of examination. Most ultrasound departments prefer to perform the detailed fetal anatomic survey examination between 18 and 20 weeks of gestation. This time period is chosen because it often yields the best view of fetal anatomy based on size and the accuracy of the dating biometry is within 10 to 14 days of expected date of confinement/delivery (EDC). The detailed fetal anatomic survey ultrasound examination includes, but is not limited to, the evaluation of the anatomy shown in Table 54-1 .



Table 54-1

Components of a Basic and Detailed Fetal Ultrasound
















































































































Component Basic Detailed
Head and neck Lateral cerebral ventricles
Choroid plexus
Midline falx
Cavum septi pellucidi
Cerebellum
Cisterna magna
3rd ventricle
4th ventricle
Lateral ventricles
Cerebellar lobes, vermis, and cisterna magna
Corpus callosum
Integrity and shape of cranial vault
Brain parenchyma
Neck
Face Upper lip Profile
Coronal face (nose/lips/lens)
Palate, maxilla, mandible, and tongue
Ear position and size
Orbits
Chest Cardiac activity Aortic arch
Heart and thorax 4-chamber view
Left ventricular outflow tract
Right ventricular outflow tract
Superior and inferior venae cava
3-vessel view
3-vessel and trachea view
Lungs
Integrity of diaphragm
Ribs
Abdomen Stomach (presence, size, and situs)
Kidneys
Small and large bowel
Adrenal glands Urinary bladder
Cord insertion site into fetal abdomen Liver
Umbilical cord vessel number
Gallbladder
Renal arteries
Spleen
Integrity of abdominal wall
Spine Cervical
Thoracic
Lumbar
Sacral spine
Integrity of spine and overlying soft tissue
Shape and curvature
Extremities Legs Number: architecture and position
Arms Hands
Feet
Digits: number and position
Genitalia In multiple gestations Sex
When medically indicated
Placenta Location Masses
Relationship to internal os Placental cord insertion
Appearance Accessory/succenturiate lobe with location of
Placental cord insertion (when possible) connecting vascular supply to primary placenta
Standard evaluation Fetal number
Presentation
Qualitative or semiqualitative estimate of amniotic fluid
Maternal anatomy Cervix (transvaginal when indicated)
Uterus
Adnexa
Biometry Biparietal diameter Cerebellum
Head circumference Inner and outer orbital diameters
Femur length Nuchal thickness (16–20 wk)
Abdominal circumference Nasal bone measurement (15–22 wk)
Fetal weight estimate Humerus
Ulna/radius
Tibia/fibula

Performed when medically indicated.

Also included in the basic obstetric examination.

(From American Institute of Ultrasound in Medicine (AIUM), 76811 Task Force: Consensus report on the detailed fetal anatomic ultrasound examnination, J Ultrasound Med 33:189–195, 2014.)


Based on the results of the screening maternal serum quad screen and the detailed fetal anatomic survey ultrasound, patients’ risk for having a child with a chromosomal anomaly or neural tube defect can be reassessed. Parents are counseled with this information and can then choose to have NIPT or a diagnostic amniocentesis to obtain fluid for chromosomal analysis, if desired.




Maternal factors in high-risk pregnancy


Advanced maternal age


By definition, advanced maternal age (AMA) describes a patient who will be 35 or older at the time of delivery. AMA can be an indicator for high-risk pregnancy. For example, the incidence of Down syndrome increases with age. The risk of a 35-year-old woman conceiving a fetus with Down syndrome is 1 in 385, but the risk rises to 1 in 32 at age 45. Maternal age alone, however, fails to detect approximately 66% of fetuses with Down syndrome because these babies are being born to younger women without known risk factors for chromosomal abnormalities. In the United States it is now standard practice to offer AMA women genetic counseling, screening options, or invasive prenatal testing for karyotypic analysis. The American College of Obstetricians and Gynecologists (ACOG) guidelines recommend that maternal serum screening for neural tube defects and Down syndrome be offered to all women.


Immune and nonimmune hydrops


Hydrops fetalis is a condition in which excessive fluid accumulates within the fetal body cavities. This fluid accumulation may result in anasarca, ascites, pericardial effusion, pleural effusion, placental edema, and polyhydramnios. There are two classifications of fetal hydrops: immune hydrops and nonimmune hydrops. By ultrasound evaluation, both types are characterized by extensive accumulation of fluids in fetal tissues or body cavities. Nonimmune hydrops is unrelated to the presence of maternal serum immunoglobulin G (IgG) antibody against one of the fetal blood cell antigens.


Immune hydrops.


Blood group isoimmunization is diagnosed on routine antenatal laboratory evaluation, which tests for the presence of a variety antibodies. Any significant antibodies are evaluated for strength of antibody response, which is reported in a titer format (i.e., 1:4, 1:16). If an antibody titer is detected, the pregnancy should be monitored.


Immune hydrops is initiated by the presence of maternal serum IgG antibody against one of the fetal red blood cell (RBC) antigens in a process known as sensitization. An antigen is any substance that elicits an immunologic response such as production of an antibody to that substance. In pregnancy, this can occur anytime a mother is exposed to red blood cell antigens different from her own. For example, if a father and fetus are Rh+ and a mother is Rh−, and there is a maternal-fetal hemorrhage (mixing of blood), maternal antibodies can be produced against the Rh antigen. In subsequent pregnancies, these antibodies can pass through the placenta and destroy fetal blood cells, resulting in fetal anemia ( Figure 54-1 ). Today, this condition is rare and can be prevented if RhoGAM is given any time there is potential mixing of the maternal and fetal circulation.




FIGURE 54-1


Diagram illustrating the concept of Rh sensitization.


When a sensitized gravid uterus is not treated with RhoGAM, the mother develops an antibody called maternal IgG. This antibody is able to cross the maternal fetal barrier and enter fetal circulation. It attaches to the fetal RBCs and destroys them in a process called hemolysis. Hemolysis can result in fetal anemia, leading to congestive heart failure and hydrops ( Figure 54-2 ). The severity of fetal anemia can be determined by sonographic surveillance, amniocentesis, and cordocentesis.




FIGURE 54-2


Hydropic, Rh-sensitized fetal demise. Note the edema of the extremities and protuberant abdomen.


Sonographic surveillance.


Sonographic surveillance for an isoimmunized pregnancy should include (but not be limited to) assessment for signs of hydrops. Sonographic findings of hydrops are scalp edema ( Figure 54-3 ), pleural effusion ( Figure 54-4 ), pericardial effusion, ascites ( Figure 54-5 ), polyhydramnios ( Figure 54-6 ), pericardial effusion ( Figure 54-7 ), and thickened placenta. Hydrops can be due to fetal anemia. Another ultrasound tool available to predict fetal anemia is Doppler evaluation of the middle cerebral artery (MCA) ( Figure 54-8 , Figure 54-9 ). Because there are fewer RBCs with anemia, the viscosity of the blood is decreased. A decrease in viscosity results in a decrease in resistance to flow, which can be detected by an increase in velocity in the MCA.




FIGURE 54-3


Scalp edema.



FIGURE 54-4


Pleural effusion.



FIGURE 54-5


Coronal view of the fetal abdomen with ascites. BL, Bladder; ST, stomach.



FIGURE 54-6


Two-dimensional and M-mode image demonstrating a pericardial effusion.



FIGURE 54-7


Fetal profile and polyhydramnios.



FIGURE 54-8


Doppler of the middle cerebral artery.



FIGURE 54-9


Graph of middle cerebral blood flow velocity for gestational age. Note that this fetus is anemic and the velocity is marked by the yellow caliper denoting an elevated velocity for gestational age.


Cordocentesis.


Cordocentesis is a procedure in which a needle is placed into the fetal umbilical vein to obtain a blood sample. The laboratory evaluates this sample for fetal blood type, hematocrit, and hemoglobin. If indicated, a fetal blood transfusion may be performed. There are two methods of transfusing a fetus. The first, intraperitoneal transfusion, uses ultrasound guidance to place a needle in the peritoneal cavity of the fetus. Blood is transfused into the peritoneal space where it is slowly absorbed by the fetus. The second method is direct intravascular transfusion via the umbilical vein (cordocentesis). Using ultrasound guidance, a fine needle is directed through the maternal abdomen toward the umbilical vein where it enters the placenta ( Figures 54-10 and 54-11 ). RBCs are transfused directly into the umbilical vein. This method is preferred because a specimen of fetal blood can be obtained before transfusion to confirm that the fetus is truly anemic and isoimmunized. A specimen can be obtained after transfusion to document that the fetal hematocrit is adequate.




FIGURE 54-10


Cordocentesis. Note echogenic needle tip placed in umbilical vein.



FIGURE 54-11


Possible needle paths in cordocentesis depending on placental position.


Alloimmune thrombocytopenia.


​In a rare circumstance, a mother may develop an immune response to fetal platelets, much as one might develop an immune response to RBCs. When this occurs, she develops antibodies to the fetal platelets. The result can be a fetus with a dangerously low platelet count (thrombocytopenia). Infants born with this condition are at increased risk for intracerebral hemorrhage in utero and spontaneous bleeding. Cordocentesis is performed in these cases to document fetal platelet counts before vaginal delivery is attempted. Ultrasound can also be useful to look for evidence of in utero fetal intracerebral hemorrhage.


Nonimmune hydrops.


Nonimmune hydrops (NIH) describes a group of conditions in which hydrops is present in the fetus but is not a result of fetomaternal blood group incompatibility. Numerous fetal, maternal, and placental disorders are known to cause or be associated with NIH ( Box 54-1 ). The incidence of NIH is approximately 1 in 2500 to 1 in 3500 pregnancies, but NIH accounts for about 3% of fetal mortality. The exact mechanism for why it occurs is unclear, although the same processes described for the hydrops associated with Rh sensitization may apply to NIH.



BOX 54-1

Disorders Associated with Nonimmune Hydrops












Cardiovascular Problems Respiratory Problems
Tachyarrhythmia
Complex dysrhythmia
Congenital heart block
Anatomic defects
Cardiomyopathy
Myocarditis
Intracardiac tumors
Chromosomal Problems
Trisomy 21
Turner’s syndrome
Other trisomies
XX/XY mosaicism
Triploidy
Twin Pregnancy
Twin-to-twin transfusion syndrome

Hematologic Problems
α-Thalassemia
Arteriovenous shunts
In utero closed-space hemorrhage
Glucose-6-phosphate deficiency
Urinary Problems
Obstructive uropathies
Congenital nephrosis
Prune-belly syndrome
Ureterocele
Diaphragmatic hernia
Cystic adenomatoid malformation of the lung
Tumors of the lung
Gastrointestinal Problems
Jejunal atresia
Midgut volvulus
Meconium peritonitis

Liver Problems
Hepatic vascular malformations
Biliary atresia

Infectious Problems
Cytomegalovirus/parvovirus
Syphilis
Herpes simplex
Rubella
Toxoplasmosis congenital hepatitis parvovirus B19

Placenta/Umbilical Cord Problems
Chorioangioma
Fetomaternal transfusion
Placental and umbilical vein thrombosis
Umbilical cord anomalies



A variety of maternal, fetal, and placental problems are known to cause or have been found in association with NIH (see Box 54-1 ). Cardiovascular lesions are the most frequent causes of NIH. Congestive heart failure may result from functional cardiac problems, such as dysrhythmias, tachycardias, and myocarditis, as well as from structural anomalies, such as hypoplastic left heart and other types of congenital heart disease. Obstructive vascular problems occurring outside of the heart, such as umbilical vein thrombosis, and pulmonary diseases, such as diaphragmatic hernia and congenital cystic adenomatoid malformation, can cause NIH. Large vascular tumors functioning as arteriovenous shunts can also result in NIH.


Severe anemia of the fetus is another well-recognized etiology for NIH. Although anemia is not caused by isoimmunization, the result is the same. Severe anemia may occur in a donor twin of a twin-to-twin transfusion syndrome, thalassemia, or significant fetomaternal hemorrhage. To make the diagnosis of NIH, isoimmunization is ruled out with an antibody screen.


Sonographic findings.


The fetus may appear similar to a sensitized baby. In addition to ascites, scalp edema and pleural and pericardial effusions may be present. Other abnormal findings may also be present that would indicate the cause of the hydrops. If the hydrops is a result of a cardiac tachyarrhythmia, a heart rate in the range of 200 to 240 is common. If a diaphragmatic hernia is present, bowel will be visible in the chest cavity.


Many times an etiology for NIH cannot be determined. If an etiology is found, treatment is dependent on the cause. As an example, if hydrops results from a tachycardia, medicine can be given to the mother in an attempt to slow the fetal heart rate. Ultrasound can be useful in monitoring the progress of the fetus. Resolution of ascites and gross edema has been documented after the fetal heart was converted to a normal rhythm. If the fetus is anemic because of twin-to-twin transfusion, intrauterine transfusion will not solve the anemia problem because most of the fetal blood is being shunted to the recipient twin ( Figure 54-12 ). Ultrasound can help the clinician assess how sick the fetus is by indicating the severity of the hydrops, by biophysical profile, and by Doppler evaluation. The clinician can then make an informed choice about when to deliver the fetus.




FIGURE 54-12


Twin-to-twin transfusion syndrome showing hydropic twin with scalp edema.


A thorough examination of the fetus, along with fetal echocardiography, must be carried out because abnormalities of almost every organ system have been described with NIH. In addition to the ultrasound examination, genetic amniocentesis for karyotype is indicated, because chromosomal abnormalities have been described as etiologies for NIH. If left unresolved, fetal hydrops has a very poor fetal prognosis and a very high incidence of fetal demise.


Vaginal bleeding


Vaginal bleeding in the second and third trimesters can be associated with placental anomalies such as placenta previa and placental abruption. Placenta previa is the main cause of third-trimester bleeding. In this condition, the placenta covers the internal cervical os and prohibits the delivery of the fetus ( Figure 54-13 ). If the cervical os dilates with labor, there is a significant risk of the placenta detaching from the uterus, resulting in maternal hemorrhage as well as loss of oxygen and blood supply to the fetus. Transvaginal sonography is the best way to evaluate the relationship of the cervical os to the placental edge. Early in pregnancy, the placenta is often lying low but as the uterus grows, the placenta will appear to migrate away from the cervical os. If this distance is less than 2 cm, the condition may be classified as a low-lying placenta. Even though the placenta may not entirely cover the internal os, the risk for blood loss from the low-lying placental vessels remains. It is important to identify a placenta previa so that a cesarean section may be planned if the previa persists until delivery.


May 29, 2019 | Posted by in ULTRASONOGRAPHY | Comments Off on Sonography and high-risk pregnancy
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