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Ultrasound Assessment of Diabetes in Pregnancy

OB GYN residents, FM residents, EM residents, Radiology residents, Pediatrics residents

Learning objectives:

  1. List the indications for first trimester ultrasound
  2. Know the difference between threatened and missed abortion
  3. List fetal anomalies associated with diabetes in pregnancy
  4. List the most common US findings associated with gestational diabetes (e.g. polyhydramnios, macrosomia and intrauterine growth restriction)
  5. Know how to perform Amniotic Fluid Index (AFI) and fetal biometry

1. Early diagnosis of fetal acrania using 2D or 3D ultrasound is first possible during which of the following time frames?

  1. 5-6 weeks’ gestation
  2. 6-7 weeks’ gestation
  3. 11-14 weeks’ gestation
  4. 14-17 weeks’ gestation

Correct answer: c

Acrania is a uniformly lethal entity that is characterized by a partial or complete absence of the calvarium with complete, but abnormal development of brain tissue. The fetal cranium is not fully calcified before 10–11 weeks; therefore, a first-trimester diagnosis must be made with caution. Therefore, the most accurate answer is b (11-14 weeks’ gestation).

2. Which of the following ultrasound findings is consistent with a diagnosis of hypertrophic cardiomyopathy in-utero?

a.Bicuspid aortic valve

b.Aortic valve calcification with enlarged ventricles

c.Thickened interventricular septum with small fetal heart chambers

d.Tricuspid mitral valve with regurgitation

Correct answer: c

Infants of diabetic mothers have long been recognized to be at risk of having hypertrophic cardiomyopathy, a condition that is characterized by thickening of the interventricular septum and ventricular walls, and by systolic and diastolic dysfunction of the neonatal heart. This condition is normally asymptomatic in utero and may only result in congestive heart failure in the immediate postnatal period, although this is uncommon and transient. Other options (a, c and d) are not associated with diabetes in pregnancy.

3. Polyhydramnios is believed to affect between 1-3% of all pregnancies, with uncontrolled blood sugars being one of several causes. Polyhydramnios may be diagnosed by utilizing ultrasound to obtain the measurements needed for calculating the Amniotic Fluid Index (AFI). All of the following correctly describe the AFI except:

  1. The gravid abdomen should be divided into four quadrants with measurements obtained in each quadrant.
  2. Measurements of the three deepest pockets are summed to give the final AFI.
  3. A normal AFI is 8cm and 18cm, with an AFI greater than 25 cm diagnostic of polyhydramnios.
  4. The depth of the maximum vertical pocket of amniotic fluid containing no fetal parts is found in each quadrant and a straight line, vertical measurement is taken of this deepest pocket.

Correct answer: b

AFI is calculated by summing the depth in centimeters of 4 different pockets of fluid not containing cord or fetal extremities in 4 abdominal quadrants using the umbilicus as a reference point and with the transducer perpendicular to the floor. Single deepest pocket (SDP) is the criterion used in the biophysical profile to document adequacy of AFV. The most commonly used U/S diagnostic criteria for amniotic luid volume (AFV) abnormalities are polyhydramnios: SDP >8 cm or AFI >25 cm, and oligohydramnios: SDP <2 cm or AFI <5 cm. Maximum vertical pocket or single deepest pocket refers to the vertical dimension of the largest pocket of amniotic fluid (with a horizontal measure of at least 1 cm) not containing umbilical cord or fetal extremities and measured at a right angle to the uterine contour and perpendicular to the floor. The only option that is incorrect is b (measurements of the three deepest pockets are summed to give the final AFI).

4. Upon ultrasound exam of a 30 year-old G5P4004 diabetic mother, you diagnose an omphalocele. Which of the following do you most likely see on ultrasound?

a. Protrusion of the viscera through a paraumbilical defect with no membranous covering

b. Midline defect with abdominal contents herniating through the base of the umbilicus, covered with translucent membrane

c. Herniation of the urinary bladder through an anterior abdominal wall defect

d. Lower abdominal wall defect associated with epispadia

Correct answer: b

Option b is correct answer: Omphalocele is a midline defect with abdominal contents herniating through the base of the umbilicus, covered with translucent membrane. Gastroshisis is a protrusion of the viscera with no membranous covering through a paraumbilical defect (option a). Bladder extrophy is herniation of the urinary bladder through an anterior abdominal wall defect (option c). Cloacal extrophy is arare and complex anomaly of the urogenital and intestinal tracts resulting in extrophy of the bladder and bowel with or without epispadia (option d).

5. Which of the following is the correct finding on ultrasound of a missed abortion?

a. Empty gestational sac, closed internal os

b. Open internal os, gestational products present with fetal heart action present

c. Gestational products present, absent fetal heart action, presence of intervillous blood flow

d. Snow storm appearance

Correct answer: c

On ultrasound, a missed abortion is visualized as presence of gestational products, absent fetal heart action and presence of intervillous flow (option c). Blighted ovum or anembryonic pregnancy is visualized as empty gestational sac with closed internal os (option a). Ultrasound features of threatened abortion include open internal os with gestational products and present heart action. Snow storm appearance is typical sonographic representation of molar pregnancy.

Nursing students/Sonographers:

Learning objectives for nursing students in ultrasound station:

  1. List the indications for first trimester ultrasound
  2. Know the difference between limited and comprehensive (fetal anatomy) OB ultrasound exam
  3. Know the difference between threatened and missed abortion
  4. List fetal anomalies associated with diabetes in pregnancy
  5. List the most common US findings associated with gestational diabetes (e.g. polyhydramnios, macrosomia and intrauterine growth restriction)
  1. Obstetrical ultrasound…
  1. Is completely safe non-ionizing imaging modality that can be used repeatedly in early pregnancy without any restrictions
  2. Is a non-ionizing imaging modality that can be used safely multiple times as clinically indicated during the pregnancy
  3. Is an uncomfortable, costly and time-consuming diagnostic modality
  4. Should be used cautiously in pregnancy because the thermal effects and cavitation confer high risk for fetal brain injury

Correct answer: b

Ultrasound is a non-ionizing imaging modality that can be used safely multiple times as clinically indicated during the pregnancy (option b). There is not a recommended number of ultrasounds that should be performedduring routine prenatal care. Because ultrasound should only be usedwhen medically indicated, many healthy pregnancies will requireonly one or two ultrasound exams. The first ultrasound is, ideally performed in the first trimester to confirm the due date, and the second is at 18 to 22 weeks to evaluate fetal anatomy, placenta and amount of amniotic fluid.

  1. Your 18 weeks’ pregnant patient is getting prepared for an ultrasound exam. How should she prepare?
  1. She should drink at least 2 dl of water/fluid 1 hour before the exam
  2. She should drink at least 1 l of water/fluid 1 hour before the exam
  3. She should wear a loose-fitting one piece outfit for the examination
  4. She should wear a loose-fitting two piece outfit for the examination

Correct answer: d

There is no need to drink water before the second trimester ultrasound exam. This is usually required for the abdominal portion of the first trimester ultrasound exam. The patient should be advised to wear a loose-fitting two peace outfit for the examination. This will expedite patient preparation, because only lower abdominal area will be exposed during the exam. Sonographer will apply gel on exposed belly and will move the transducer over the abdomen to assess fetal structures from lots of different angles. A detailed fetal anatomy scan will last between 30 and 45 minutes, and the images will be reviewed by perinatologist and/or referring physician.

  1. In the first trimester ultrasound is used to:
  1. Detect a gestational sac
  2. Detect fetal heart activity
  3. Rule out missed abortion
  4. All of the above

Correct answer: d

The role of first trimester ultrasound is to confirm an intrauterine pregnancy (detect a gestational sac), detect fetal heart activity, and rule out missed abortion. The most complete option is d (all of the above).

  1. Ultrasound is used to study:
  1. Pre-embryonic stage of fetal development
  2. Embryonic (5 - 8 weeks) and fetal period (9th week - birth)
  3. Embryonic (5-10 weeks) and fetal period (11th week - birth)
  4. Embryonic (2 - 12 weeks) and fetal period (13th week - birth)

Correct answer: b

Between 5 and 8 days after fertilization, the blastocyst attaches to the lining of the uterus, usually near the fundus. This process, called implantation, is completed by day 9 or 10. This stage is called pre-embryonic stage and could not be assessed by ultrasound. During this period mother is usually unaware of pregnancy. Ultrasound can assess the embryonic (from 5 to 8 weeks) and fetal period (9th week to birth) (item b). Embryonic period is characterized by the formation of most internal organs and external body structures. Most organs form begin to form about 3 weeks after fertilization, which equals 5 weeks of pregnancy. At this time, the embryo elongates, first suggesting a human shape. Shortly thereafter, the area that will become the brain and spinal cord (neural tube) begins to develop. The heart and major blood vessels begin to develop earlier—by about day 16. The heart begins to pump fluid through blood vessels by day 20, and the first red blood cells appear the next day. Blood vessels continue to develop in the embryo and placenta. During fetal period, which begins from the 9th week the fetal structures that have already formed grow and develop.

  1. Ultrasound in second trimester is performed to:
  1. Measure biparietal diameter (BPD)
  2. Assess the amount of amniotic fluid
  3. Evaluate the placenta
  4. All of the above

Correct answer: d

Second trimester ultrasound is performed between 18 and 22 weeks’ gestation. Second trimester ultrasound should screen for the number of fetuses and fetal anomalies. Fetal biometry is routinely performed and includes the measurements of biparietal diameter, head circumference, abdominal circumference and femur length. The gestational age is confirmed and compared with any previous obstetrical ultrasounds and/or expected measurements. The amount of amniotic fluid and placenta are evaluated. Fetal anatomy survey includes the assessment of fetal brain and face, the heart (four chamber view and outflow tracts), lungs, fetal abdomen (stomach, bowel, bladder, kidneys, cord insertion), fetal spine, fetal genitalia and limbs. Therefore, the most accurate option is d (all of the above).

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