Chapter 14. Second and Third Trimester Fetus
Patient Preparation
• No voiding immediately before the examination; some fluid in the bladder is needed to visualize the urinary bladder and may aid in visualization of the cervix and LUS.
Equipment and Technical Factors
• A curved linear transducer is commonly used. An EV transducer may be used to visualize the cervix and LUS, or the presence of a pathologic condition must be more clearly documented; ensure that the department protocols are followed. EV imaging may be contraindicated in the presence of vaginal bleeding, leakage of fluid, or cervical dilation.
• Fetal, uterine, or ovarian Doppler imaging may be performed as requested; Doppler imaging may be used in the evaluation of pathologic conditions found during the study.
• MI and TI settings must comply with the ALARA principle.
Imaging Protocol
• Determine the location of the placenta and the fetal lie; assess the presence of pathologic conditions or anatomical variants. The presence and location of fibroid(s) should be documented. The ovaries and adnexal areas should be evaluated.
• Braxton-Hicks contractions may occur throughout pregnancy. This type of contraction usually lasts 20 to 30 minutes and can occur in any area of the uterus (may mimic fibroid, placenta previa, or mass).
Minimum documentation images
• Placenta: sagittal plane images through the medial, mid, and lateral aspects of the uterus; transverse plane images through the cervix, body, and fundus.
• Length and diameter of the cervix (perform immediately after patient lies on scan table; use TA, transperineal, or EV imaging to clearly demonstrate cervix (follow department protocols in using EV imaging).
Fetal anatomy to include:
Posterior fossa for cisterna magna and nuchal thickness
Lateral ventricles and cerebral hemispheres
Profile for forehead shape, nose, mouth, and chin
Nose and mouth using a coronal plane
Spine: cervical, thoracic, and lumbar
Thorax to include the heart: apical long axis, parasternal long axis, short axis and outflow tracts: heart rate documented with M mode
Abdomen to include the stomach, liver, intrahepatic portal vein, kidneys, urinary bladder, bowel, and fetal umbilical cord insertion
Extremities; confirm two complete upper and lower
Sex (check department protocols)
• Biophysical profile 30 minutes; scoring: 2 = meets all criteria or 0 = did not meet criteria:
Fetal breathing: one episode lasting 30 seconds
Gross body movements: three trunk or limb movements
Fetal tone: one extension and flexion of limb or trunk
Amniotic fluid volume: single pocket of 2.0 cm in AP dimension
Measurements
• The uterus is generally not measured during pregnancy; however, fibroid size should be documented.
Fetal biometry (BPD, HC, AC, FL)
• Compare measurements obtained (recommend average of three of each required measurement) with patient’s estimated due date and standardized charts or use the equipment software.
Other
• Thorax/abdomen: 1:1 ratio
• Occipital-frontal diameter/BPD × 100: CI to correlate with BPD
• Ventricular atrium: <1 cm
• Cisterna magna: 5.0–10.0 mm
• Nuchal translucency at 9–13 weeks: <3.0 mm
• Nuchal thickness at 16–22 weeks: <6.0 mm
• Amniotic fluid: Amniotic fluid index (AP dimension of four quadrants = 5.0–24.0 cm)
• Single pocket (AP dimension = 2.0–8.0 cm)
• Ocular diameter
• All long bones
| Second and Third Trimester Fetus | |||
|---|---|---|---|
| Sonographic Finding(s) | Clinical Presentation | Differential Diagnosis | Next Step |
Two or more of the following are noted: Ascites Pleural effusion Pericardial effusion Edema Placentomegaly Polyhydramnios | Uterus is large for dates Rh sensitized (immune hydrops/fetal anemia) | Hydrops fetalis Isolated ascites, pleural effusion, pericardial effusion | Nonimmune causes include maternal infection, chromosomal abnormalities (especially Turner’s syndrome, trisomies 13, 18, and 21), and heart failure Associated with fetal tachycardia Elevated PSV from the MCA associated with immune hydrops |
Fetal biometry: all measurements (including weight) are below 10th percentile for gestational age Fetal soft tissues may appear thin Placenta may appear thin and small Oligohydramnios (especially in late pregnancy) may be present | Uterus measures small for dates Previous sonogram demonstrated below normal or normal fetal gestational age | Symmetric IUGR Wrong dates SGA fetus | Associated with both chromosomal and nonchromosomal abnormalities BPP score, umbilical artery Doppler, or S/D ratio may be abnormal if this is true symmetric IUGR Symmetric IUGR requires at least two sets of biometry to confirm finding |
| Fetal abdomen measures below 10th percentile for gestational age but head and femur measurements are within normal limits for gestational age | Uterus measures appropriately or small for dates Previous sonogram demonstrated normal fetal measurements for gestational age | Asymmetric IUGR | Placental insufficiency may be documented by Doppler interrogation of umbilical artery MCA S/D ratio < umbilical artery S/D ratio Pulsatile flow in umbilical vein |
Placenta may demonstrate aging (grade 3 or 4) early in pregnancy Oligohydramnios Echogenic bowel may be noted | Maternal diabetes or hypertension before pregnancy | ||
Fetal biometry reveals fetal abdominal measurement above 90th percentile for gestational age Evidence of skin thickening around fetal head and trunk; prominent fetal cheeks | Uterus measures large for dates Commonly seen in cases of maternal diabetes, obesity, advanced maternal age, and multiparity | Macrosomia | In suspected macrosomia, carefully scan the anatomy to document size of fetal liver and to search for anomalies such as GI tract, cardiovascular system (thickening of the cardiac IVS), CNS, and VACTERL |
| Possible mild polyhydramnios may be present | Increased size of facial cheeks is due to fat deposits Placenta usually demonstrates increased thickness | ||
| Second and Third Trimester Fetal Head and Neck | |||
|---|---|---|---|
| Sonographic Finding(s) | Clinical Presentation | Differential Diagnosis | Next Step |
Unable to obtain BPD/no skull is visible Fetal face has “mask” or “frog-face” appearance Polyhydramnios | Uterus may measure large for dates | Anencephaly | Associated with CNS and other anomalies, hydronephrosis, diaphragmatic hernia, cleft lip, and cardiac anomalies; may also be caused by amniotic band |
Cerebellar hemispheres lack rounded appearance; unable to visualize cerebellum Asymmetrical ventriculomegaly (third and lateral ventricles) with splaying of lateral ventricles; small cranial size Skull demonstrates depression of frontal bones | Asymptomatic | Chiari type II | Associated with spina bifida and agenesis of the corpus callosum Normal frontal bones may demonstrate slight depression |
Third ventricle is seen more superior in midline of brain Lateral ventricles are seen more lateral and parallel to midline Mild ventriculomegaly A communicating cyst may be seen superior to the third ventricle Gyri are more vertically aligned and appear to radiate from lateral ventricles Possible polyhydramnios | Asymptomatic | Agenesis of corpus callosum | Associated with several anomalies: Dandy-Walker syndrome, holoprosencephaly, medial facial clefts, encephalocele, or meningomyelocele, trisomy 8, 13, and 18, diaphragmatic hernia, cardiac malformations, missing or small lung(s), and renal agenesis or dysplasia |
Lateral ventricle(s) appear prominent BPD and HC within normal limits for gestational age Ventricular atrium measures >10.0 mm in AP diameter Choroid plexus may appear to “dangle” within dilated ventricular atrium | Asymptomatic | Ventriculomegaly | Associated with aqueductal stenosis Normal choroids should fill ventricular atrium or there should be no more than a 3-mm gap between choroid plexus and ventricle wall |
Ventricles (lateral and third, possibly fourth) and fetal head size are enlarged Brain mantle may appear thin Falx is intact Abnormal orbits, face, feet, and hands Polyhydramnios | Uterus may measure large for dates | Hydrocephalus | Indicates presence of obstruction (noncommunicating) in ventricular system or may be related to aqueductal stenosis, meningomyelocele, spina bifida, encephalocele, or Dandy-Walker malformation, trisomy 13 or 18 Document level or point of obstruction if possible |
Ventriculomegaly (lateral and third; fourth ventricle is normal) with intact falx and preservation of brain mantle Cerebellum and cisterna magna appear normal | Exposure to teratogens or cytomegalovirus Maternal history of toxoplasmosis or syphilis | Aqueductal stenosis | Causes 35.7% of hydrocephalus and is more common in males (X linked) In utero infections or intracranial tumor may be underlying cause Mild ventriculomegaly has been associated with trisomy 21 |
Large cyst in posterior fossa with normal fourth ventricle not seen Posterior fossa is enlarged Vermis of cerebellum is not seen and hemispheres may appear splayed and flattened Possible ventriculomegaly or hydrocephalus and agenesis of corpus callosum Possible polyhydramnios | Uterus may measure large for dates | Dandy-Walker malformation Enlarged cisterna magna | Associated with both intracranial and extracranial abnormalities: agenesis of corpus callosum, facial clefts, CNS, and cardiac ventricular septal defect, trisomy 13, 18, or 21 May be seen in Meckel-Gruber syndrome |
| Irregular cystic structure(s) noted adjacent to lateral ventricle(s); may show connection to lateral ventricle | Maternal thrombocytopenia, anticoagulation therapy, drug use such as cocaine; trauma | Porencephalic cyst | Rare: This finding is a result of resolved hemorrhage in parenchyma Associated with TTTS and death of a cotwin |
Fetal skull is enlarged and demonstrates bulge from top of head Polyhydramnios | Uterus may measure large for dates | Cloverleaf skull | Associated with thanatophoric dysplasia, Apert syndrome, or amniotic band |
Sac/mass protrudes from occipital portion of fetal skull If the sac/mass is large, microcephaly may be present Hydrocephalus may be seen Microcephaly or depressed frontal bones of the skull may be noted | Asymptomatic Labs: MSAFP may be elevated | Encephalocele | Associated with Meckel-Gruber syndrome, polydactyly, polycystic kidneys, liver cysts, cleft palate, and cardiac anomalies An encephalocele found on the lateral aspect of the head may be caused by amniotic band Large encephaloceles can cause microcephaly or depressed frontal cranial bones |
| Unable to identify normal fetal orbits | Maternal history of toxoplasmosis or rubella | Microphthalmia Anophthalmia | May be a sporadic anomaly, a result of in utero infection, trisomy 18, or Meckel-Gruber syndrome |
| Eyes are widely spaced | Asymptomatic | Hypertelorism | May represent familial trait or may be related to presence of frontal encephalocele, Noonan or Crouzon syndrome |
| Eyes are closely spaced | Asymptomatic | Hypotelorism | May represent familial trait or may be related to presence of holoprosencephaly, trisomy 13 or 18, or Meckel-Gruber syndrome |
| Single orbit is seen | Asymptomatic | Cyclopia | Strongly associated with holoprosencephaly |
Fetal chin is absent or difficult to see Possible polyhydramnios | Uterus may measure large for dates | Micrognathia | Associated with trisomy 18 and less commonly with trisomy 13 Also may be seen in other syndromes and skeletal dysplasias/dystoses |
Large midline fluid-filled space with thin rim of brain tissue Falx may or may not be present Thalamus appears fused May demonstrate univentricle (horseshoe-shaped ventricle); hydrocephalus | Uterus may measure large for dates | Holoprosencephaly Alobar Semilobar Lobar | Difficult to differentiate semilobar from alobar Associated findings: clubfoot, omphalocele, IUGR, and features of trisomy 13, 18, Meckel-Gruber syndrome |
Agenesis of the corpus callosum, cleft lip/palate may be noted Hypotelorism or cyclopia and proboscis may be seen | May mimic hydranencephaly | ||
Large, fluid-filled cranium with cerebellum and midbrain seen No brain mantle seen Polyhdramnios | Uterus may measure large for dates | Hydranencephaly Massive hydrocephalus | Falx may or may not be intact May mimic alobar holoprosencephaly |
A gap in soft tissue between the upper lip and nose (unilateral and bilateral) Sweeping coronal scan plane posteriorly through fetal mouth may reveal gap in bones of upper palate Polyhydramnios May be unilateral or bilateral | Uterus may measure large for dates | Cleft lip with/without cleft palate | Isolated or may be associated with midline cranial defects such as holoprosencephaly (midline clefts) or anencephaly Cleft lip and palate are seen in fetuses with chromosomal defects More commonly seen in male fetuses |
Fetal tongue protrudes from mouth at all times Polyhydramnios | Uterus may measure large for dates Maternal diabetes | Macroglossia | Associated with Beckwith-Wiedemann syndrome, trisomy 21, omphalocele, organomegaly Oral mass that is displacing tongue may be present |
A cyst or cystic structures seen on the posterior aspect or surrounding fetal neck Placenta may be large and edematous Hydrops | Uterus may measure large for dates Labs: MSAFP may be lower or higher than normal | Cystic hygroma Teratoma Neural tube defect Hemangioma | Associated with Turner syndrome (45,X) and trisomy 13, 18, or 21 Note: Cystic hygromas are most commonly found in the neck but can occur in the axilla, groin, or mediastinum |
| Second and Third Trimester Fetal Thorax and Heart | |||
|---|---|---|---|
| Sonographic Finding(s) | Clinical Presentation | Differential Diagnosis | Next Step |
Fetal thorax appears narrow Thorax to abdomen ratio is below 1:1 Polyhydramnios (skeletal disorders) or Oligohydramnios (renal agenesis) | Uterus measures small or large for dates | Lethal dwarfism Pulmonary hypoplasia | Associated with many skeletal dysplasias and dystoses: thanatophoric dysplasia, achondrogenesis, and osteogenesis imperfecta type II Also related to lack of lung development related to renal agenesis |
Cystic structure in thorax, possibly displacing the heart Polyhydramnios | Uterus may measure large for dates | Bronchogenic cyst | Document stomach inferior to diaphragm; if stomach is not seen in the normal location, the “cyst” may be the stomach: diaphragmatic hernia |
Fluid is seen to surround one or both lungs Fluid around left lung may displace heart to right side
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