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RDMS OB/GYN practice questions

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Question 1First Trimester Obstetric Sonography (Normal and Abnormal)

On transvaginal sonography, an embryo should be visible when the mean sac diameter reaches which size?

  1. 15 mm
  2. 10 mm
  3. 25 mm Correct answer.
  4. 35 mm

Explanation

An empty gestational sac with a mean sac diameter of 25 mm or more is a definitive criterion for pregnancy failure. Below that threshold, an absent embryo may simply reflect a very early pregnancy and requires follow-up.

Question 2First Trimester Obstetric Sonography (Normal and Abnormal)

What is the double decidual sac sign used for?

  1. Measuring the crown-rump length accurately
  2. Diagnosing a subchorionic hematoma
  3. Confirming fetal cardiac activity at 6 weeks of amenorrhea
  4. Distinguishing a true sac from a pseudogestational sac Correct answer.

Explanation

The double decidual sac sign consists of two echogenic rings around a fluid collection, representing the decidua capsularis and parietalis. Its presence favors a genuine intrauterine gestational sac rather than a pseudogestational sac.

Question 3First Trimester Obstetric Sonography (Normal and Abnormal)

On transvaginal scanning, the secondary yolk sac is typically first visible at approximately what mean sac diameter?

  1. 35 mm
  2. 2 mm
  3. 20 mm
  4. 8 mm Correct answer.

Explanation

The secondary yolk sac becomes visible when the gestational sac reaches about 8 mm in mean diameter, usually preceding visualization of the embryo. It confirms that the sac is a true gestational sac.

Question 4First Trimester Obstetric Sonography (Normal and Abnormal)

What is the upper limit of normal for secondary yolk sac diameter?

  1. 6 mm Correct answer.
  2. 12 mm
  3. 2 mm
  4. 9 mm

Explanation

A normal secondary yolk sac measures up to about 6 mm in diameter when measured inner-to-inner. Enlargement beyond this is associated with an increased risk of pregnancy loss and aneuploidy.

Question 5First Trimester Obstetric Sonography (Normal and Abnormal)

The nuchal translucency measurement should be obtained between:

  1. 11 and 14 weeks of gestation Correct answer.
  2. 8 and 10 weeks of gestation
  3. 15 and 18 weeks of gestation
  4. 18 and 22 weeks of gestation

Explanation

Nuchal translucency is measured when the crown-rump length is between 45 and 84 mm, corresponding to roughly 11 to 14 weeks. Before and after this window the measurement is not valid for screening.

Question 6First Trimester Obstetric Sonography (Normal and Abnormal)

Which sonographic appearance is typical of a complete hydatidiform mole?

  1. Multiple cystic spaces within thickened endometrium Correct answer.
  2. An empty sac with a thin decidual rim
  3. A simple adnexal cyst with posterior acoustic enhancement
  4. A live fetus with severe oligohydramnios and a small sac

Explanation

A complete mole distends the cavity with vesicular, cystic tissue producing a heterogeneous mass, often described as a snowstorm pattern. No fetus is present because the pregnancy is entirely androgenetic.

Question 7First Trimester Obstetric Sonography (Normal and Abnormal)

Which adnexal finding is most consistent with a normal corpus luteum cyst in early pregnancy?

  1. An anechoic cyst with no detectable wall
  2. A thin-walled cyst smaller than 5 mm
  3. A thick-walled cyst with internal echoes Correct answer.
  4. A solid hypoechoic mass with coarse calcifications

Explanation

The corpus luteum typically appears as a thick-walled cystic structure with internal echoes or a cobblestone pattern and may show a peripheral ring of vascularity. It supports the pregnancy until the placenta assumes progesterone production.

Question 8First Trimester Obstetric Sonography (Normal and Abnormal)

Transvaginally, an intrauterine gestational sac is usually first visible at about:

  1. 3.0 weeks of gestation
  2. 7.5 weeks of gestation
  3. 4.5 weeks of gestation Correct answer.
  4. 6.5 weeks of gestation

Explanation

With a transvaginal probe the gestational sac can be identified at approximately 4.5 to 5 weeks, roughly one week earlier than with a transabdominal approach. This corresponds to a serum hCG of about 1000 to 2000 mIU/mL.

Question 9First Trimester Obstetric Sonography (Normal and Abnormal)

What is the correct method for determining mean sac diameter?

  1. Inner-to-inner calipers in three planes, averaged Correct answer.
  2. From the fundal endometrium to the internal cervical os
  3. Outer-to-outer calipers in a single plane
  4. Along the longest axis of the chorionic cavity

Explanation

Mean sac diameter is the average of three orthogonal measurements taken inner-to-inner across the anechoic sac fluid. Using consistent inner calipers in three planes minimizes over- and underestimation that could mislead threshold-based diagnosis.

Question 10First Trimester Obstetric Sonography (Normal and Abnormal)

How should crown-rump length be measured in the first trimester?

  1. Outer-to-outer across the fetal head and rump
  2. From the top of the head to the feet in a coronal plane
  3. Longest crown-to-rump length, neutral sagittal view Correct answer.
  4. Along the spine from the skull base to the sacrum

Explanation

Crown-rump length is measured in a true mid-sagittal plane with the fetus in neutral flexion and extension, using the longest crown-to-rump dimension. Limbs and yolk sac must be excluded from the calipers.

Question 11First Trimester Obstetric Sonography (Normal and Abnormal)

Which finding suggests an interstitial ectopic pregnancy?

  1. A gestational sac below the level of the internal cervical os
  2. A sac surrounded by a thick rim of myometrium within the fundus
  3. A sac over 1 cm from the cavity with thin myometrium Correct answer.
  4. An empty uterine cavity with fluid in the pouch of Douglas

Explanation

An interstitial ectopic implants in the proximal tubal segment within the uterine wall, so the sac lies eccentrically more than 1 cm from the endometrial cavity and is covered by a thin myometrial mantle. An echogenic interstitial line may be seen extending to the sac.

Question 12First Trimester Obstetric Sonography (Normal and Abnormal)

Which feature favors a pseudogestational sac over a true gestational sac?

  1. A sac surrounded by two decidual layers
  2. Central fluid in the cavity that tapers at the margins Correct answer.
  3. A sac with a visible yolk sac inside
  4. A sac located eccentrically within the endometrial cavity

Explanation

A pseudogestational sac is a fluid collection centered in the endometrial cavity, often with pointed or tapering margins, and contains no yolk sac or embryo. It reflects decidual reaction to an ectopic pregnancy rather than a true gestation.

Question 13First Trimester Obstetric Sonography (Normal and Abnormal)

A crescentic anechoic collection between the chorion and the endometrium in a 7-week pregnancy most likely represents:

  1. A subchorionic hematoma Correct answer.
  2. An anembryonic pregnancy
  3. A chorioamniotic separation
  4. A partial molar pregnancy

Explanation

Blood tracking between the chorionic membrane and the decidua produces a crescentic, usually anechoic collection, the classic subchorionic hematoma. Its size relative to the sac helps predict outcome.

Question 14First Trimester Obstetric Sonography (Normal and Abnormal)

A 6-week patient has a beta-hCG above the discriminatory zone, an empty uterus, and a 3 cm thick-walled adnexal ring containing an embryo with cardiac activity. What is the diagnosis?

  1. Interstitial ectopic pregnancy
  2. Ruptured corpus luteum cyst
  3. Tubal ectopic pregnancy Correct answer.
  4. Complete hydatidiform mole

Explanation

An extrauterine thick-walled ring with a yolk sac or embryo, together with an empty uterus and hCG above the discriminatory zone, is diagnostic of a tubal ectopic pregnancy. Cardiac activity in the adnexal sac confirms a live extrauterine gestation.

Question 15First Trimester Obstetric Sonography (Normal and Abnormal)

Which patient is at highest risk for a heterotopic pregnancy?

  1. A woman with a first-trimester subchorionic hematoma
  2. A woman with a spontaneous singleton pregnancy
  3. A woman who conceived with in vitro fertilization Correct answer.
  4. A woman with a prior cesarean delivery

Explanation

Heterotopic pregnancy is rare in spontaneous conceptions but rises substantially with assisted reproduction, where multiple embryos are transferred. Finding an intrauterine pregnancy therefore does not exclude a coexisting ectopic in these patients.

Question 16First Trimester Obstetric Sonography (Normal and Abnormal)

At 10 weeks of gestation, which finding is normal?

  1. An absent nasal bone at 10 weeks
  2. Midgut herniation into the umbilical cord Correct answer.
  3. An omphalocele containing liver and bowel
  4. A nuchal translucency of 4.0 mm measured at 10 weeks

Explanation

Physiologic midgut herniation occurs between roughly 8 and 12 weeks as the bowel rotates within the umbilical cord, and it resolves by about 12 weeks. Only bowel herniates; a sac containing liver indicates a true omphalocele.

Question 17First Trimester Obstetric Sonography (Normal and Abnormal)

What embryonic heart rate is considered normal at 7 weeks of gestation?

  1. 60 to 90 beats per minute
  2. Below 100 beats per minute
  3. 120 to 160 beats per minute Correct answer.
  4. 170 to 200 beats per minute

Explanation

Embryonic heart rate rises steadily in early pregnancy, reaching roughly 120 to 160 beats per minute by 7 weeks. Rates below 100 beats per minute at this stage are bradycardic and associated with pregnancy loss.

Question 18First Trimester Obstetric Sonography (Normal and Abnormal)

The amnion and chorion normally fuse by approximately:

  1. 14 to 16 weeks of gestation Correct answer.
  2. 8 weeks of gestation
  3. 20 to 22 weeks of gestation
  4. 11 to 12 weeks of gestation

Explanation

The amniotic cavity expands and the amnion fuses with the chorion by about 14 to 16 weeks. Persistence of a visible separation beyond this point warrants evaluation.

Question 19First Trimester Obstetric Sonography (Normal and Abnormal)

Which measurement is the most accurate for dating a pregnancy between 7 and 13 weeks?

  1. Last menstrual period
  2. Yolk sac diameter
  3. Mean sac diameter
  4. Crown-rump length Correct answer.

Explanation

Crown-rump length provides the most accurate gestational age estimate in the first trimester, with an accuracy of about plus or minus 5 to 7 days. Mean sac diameter is less precise and yolk sac size is not used for dating.

Question 20First Trimester Obstetric Sonography (Normal and Abnormal)

A scan at 9 weeks shows one viable fetus and a second empty gestational sac. This finding is best described as:

  1. A complete mole with a coexisting fetus
  2. A subchorionic hematoma
  3. A vanishing twin Correct answer.
  4. A missed abortion of a singleton pregnancy

Explanation

In a multiple gestation one sac may fail very early while the other continues normally, a phenomenon called the vanishing twin. The residual empty sac is resorbed over time and usually does not affect the surviving fetus.

Question 21First Trimester Obstetric Sonography (Normal and Abnormal)

A viable embryo with CRL 8 mm is seen in a gestational sac with MSD 10 mm. What does this discrepancy suggest?

  1. A small sac, associated with a poor outcome Correct answer.
  2. An impending molar degeneration of the placenta
  3. A miscalculated mean sac diameter only
  4. A normal pregnancy with no increased risk

Explanation

When the difference between mean sac diameter and crown-rump length is less than 5 mm, the sac is small for the embryo. A small gestational sac is associated with an increased risk of miscarriage and adverse pregnancy outcome.

Question 22First Trimester Obstetric Sonography (Normal and Abnormal)

At 7 weeks, an embryo with CRL 5 mm has a heart rate of 85 beats per minute. What is the most appropriate interpretation?

  1. Bradycardia with a poor prognosis, warranting follow-up Correct answer.
  2. A rate too fast to be measured accurately
  3. Artifact caused by transmitted maternal arterial pulsation
  4. A normal rate that requires no further follow-up

Explanation

An embryonic heart rate below 100 beats per minute at 6 to 7 weeks is bradycardic and carries a high rate of pregnancy loss. It does not by itself meet criteria for a failed pregnancy, so follow-up scanning is appropriate.

Question 23First Trimester Obstetric Sonography (Normal and Abnormal)

At an 11-week scan the fetal cranial vault is not visualized and the brain tissue appears exposed. Which is the most likely diagnosis?

  1. Occipital encephalocele
  2. Acrania Correct answer.
  3. Alobar holoprosencephaly
  4. Severe hydrocephalus

Explanation

Absence of the ossified calvarium with exposed brain tissue is acrania, which later degenerates into the anencephaly appearance. The cranial vault should be ossified and visible by 11 weeks, so its absence is abnormal.

Question 24First Trimester Obstetric Sonography (Normal and Abnormal)

Which finding favors a cervical ectopic pregnancy?

  1. A barrel-shaped cervix with a sac below the internal os Correct answer.
  2. A sac located in the fundus surrounded by myometrium
  3. A sac that slides freely with transducer pressure
  4. A sac within the interstitial segment of the fallopian tube

Explanation

A cervical ectopic implants within the cervical canal, expanding the cervix into a barrel shape with the sac below a closed internal os and an empty uterine body above. Lack of sliding with transducer pressure helps separate it from a miscarriage in progress.

Question 25First Trimester Obstetric Sonography (Normal and Abnormal)

A transvaginal scan at 7 weeks shows an embryo with CRL 4 mm and no cardiac activity. What is the most appropriate next step?

  1. Refer for immediate uterine evacuation
  2. Repeat the scan in about one week Correct answer.
  3. Diagnose an inevitable miscarriage now
  4. Perform chorionic villus sampling

Explanation

Absence of cardiac activity diagnoses pregnancy failure only when the crown-rump length is 7 mm or more. Below that threshold, a repeat scan in about a week is required to confirm whether the pregnancy is viable.

Question 26First Trimester Obstetric Sonography (Normal and Abnormal)

On transvaginal sonography, which structure is normally the first to become visible within a gestational sac?

  1. The embryonic pole
  2. The fetal heart
  3. The secondary yolk sac Correct answer.
  4. The amniotic membrane

Explanation

The secondary yolk sac appears at about 5 to 5.5 weeks, when the mean sac diameter is roughly 8 mm, and it precedes any visible embryonic structure. It serves as early confirmation that a sac is a true intrauterine gestation rather than a pseudogestational sac.

Question 27First Trimester Obstetric Sonography (Normal and Abnormal)

Most ectopic pregnancies implant in which portion of the fallopian tube?

  1. Fimbrial portion
  2. Ampullary portion Correct answer.
  3. Uterine cornu
  4. Isthmic portion

Explanation

The ampulla is the longest and most capacious segment of the tube and accounts for the majority of tubal ectopic gestations. Isthmic and fimbrial implantations are less common, and cornual implantation is a small minority.

Question 28First Trimester Obstetric Sonography (Normal and Abnormal)

Nuchal translucency measurement for first-trimester aneuploidy screening is performed within which gestational window?

  1. 10 weeks 0 days to 12 weeks 6 days
  2. 12 weeks 0 days to 14 weeks 6 days
  3. 11 weeks 0 days to 13 weeks 6 days Correct answer.
  4. 8 weeks 0 days to 10 weeks 6 days

Explanation

Nuchal translucency is validated only between 11 weeks 0 days and 13 weeks 6 days, corresponding to a crown-rump length of about 45 to 84 mm. Before 11 weeks the neck is not yet fully formed, and after 13 weeks 6 days physiologic fluid resolution alters the measurement.

Question 29First Trimester Obstetric Sonography (Normal and Abnormal)

A viable intrauterine gestation should be visible transvaginally once the serum beta-hCG exceeds approximately which level?

  1. 1,000 mIU/mL
  2. 500 mIU/mL
  3. 3,500 mIU/mL Correct answer.
  4. 10,000 mIU/mL

Explanation

The commonly cited discriminatory zone for transvaginal scanning is about 3,500 mIU/mL, above which an intrauterine sac should be identifiable. An empty uterus above this level raises concern for an ectopic pregnancy or an early failing gestation.

Question 30First Trimester Obstetric Sonography (Normal and Abnormal)

Which finding is diagnostic of an anembryonic pregnancy on transvaginal sonography?

  1. A yolk sac present with a mean sac diameter of 8 mm
  2. A mean sac diameter of 12 mm with no visible embryo
  3. A mean sac diameter of 25 mm or more with no visible embryo Correct answer.
  4. A mean sac diameter of 18 mm containing only a yolk sac

Explanation

A mean sac diameter of 25 mm or more on transvaginal scanning with no embryo is a definitive criterion for pregnancy failure. Smaller sacs without an embryo require follow-up scanning, because normal early gestations may not yet show an embryo.

Question 31First Trimester Obstetric Sonography (Normal and Abnormal)

Which placental finding favors a partial hydatidiform mole over a complete mole?

  1. Bilateral multilocular theca lutein cysts
  2. Fetal tissue accompanied by focal cystic placental changes Correct answer.
  3. Markedly enlarged cystic villi filling the cavity with no fetus
  4. A normal placenta with isolated echogenic foci

Explanation

Partial moles are usually triploid and therefore typically show some fetal tissue alongside focal, less severe cystic placental change. Complete moles are diploid and show diffuse vesicular change without any fetal parts.

Question 32First Trimester Obstetric Sonography (Normal and Abnormal)

Which technique is standard for documenting embryonic cardiac activity in the first trimester?

  1. Spectral Doppler of the fetal cardiac outflow
  2. Color Doppler interrogation of the umbilical cord
  3. M-mode tracing across the embryo Correct answer.
  4. Pulsed-wave Doppler sampling over the embryo

Explanation

M-mode is used to record and measure the embryonic heart rate because it provides a clear temporal display of cardiac wall motion. Spectral and color Doppler deliver higher energy to the early embryo and are avoided for routine heart-rate documentation.

Question 33First Trimester Obstetric Sonography (Normal and Abnormal)

The intradecidual sign refers to which sonographic finding?

  1. Two concentric echogenic rings surrounding a sac
  2. A fluid collection centered within the endometrial cavity
  3. An empty uterus with fluid in the posterior cul-de-sac
  4. An early sac eccentrically placed within one decidual layer Correct answer.

Explanation

The intradecidual sign is an early gestational sac that is embedded eccentrically within one thickened decidual layer, confirming an intrauterine location. It appears before the more familiar double decidual sac sign is evident.

Question 34First Trimester Obstetric Sonography (Normal and Abnormal)

Which describes correct caliper placement for a nuchal translucency measurement?

  1. Calipers placed after the fetal neck is flexed
  2. Calipers on inner borders in a coronal plane
  3. Calipers on outer borders in a mid-sagittal plane
  4. Calipers on inner borders in a mid-sagittal plane Correct answer.

Explanation

The nuchal space is measured in a true mid-sagittal plane with calipers placed on the inner borders of the widest portion of the collection. The fetal neck should be in a neutral position, since flexion or extension falsely alters the value.

Question 35First Trimester Obstetric Sonography (Normal and Abnormal)

At 8 weeks of gestation, which finding best establishes the chorionicity of a twin pregnancy?

  1. Discordance in crown-rump length
  2. Thickness of the inter-twin membrane
  3. Presence of a twin-peak sign
  4. Number of gestational sacs and yolk sacs Correct answer.

Explanation

Before about 10 weeks, chorionicity is determined by counting gestational sacs and yolk sacs, since the amnion and chorion have not yet fused. Membrane thickness and the lambda or twin-peak sign become reliable only after fusion occurs.

Question 36First Trimester Obstetric Sonography (Normal and Abnormal)

A yolk sac measuring 8 mm at 8 weeks is associated with which outcome?

  1. A reliably normal pregnancy outcome
  2. An error caused by caliper placement
  3. Maternal rather than fetal abnormality
  4. Increased risk of pregnancy loss Correct answer.

Explanation

A normal yolk sac measures roughly 3 to 6 mm; enlargement beyond about 7 mm is associated with an increased risk of miscarriage and aneuploidy. It is a marker for closer follow-up rather than a normal variant.

Question 37First Trimester Obstetric Sonography (Normal and Abnormal)

A bleeding patient at 10 weeks has a gestational sac in the lower uterine segment, an open internal cervical os, and no embryonic cardiac activity. Which term best describes this?

  1. Complete abortion
  2. Inevitable abortion Correct answer.
  3. Threatened abortion
  4. Missed abortion

Explanation

An inevitable abortion is characterized by cervical dilatation with the gestational sac still present in the uterus, typically accompanied by cramping and bleeding. Once the cervix opens, the pregnancy cannot continue.

Question 38First Trimester Obstetric Sonography (Normal and Abnormal)

Which combination of findings most supports a cesarean scar pregnancy?

  1. Empty uterus with a separate adnexal mass
  2. Fundal sac with normal anterior myometrial thickness
  3. Anterior lower uterine segment sac with a thin myometrial mantle Correct answer.
  4. Sac within the cervical canal with a closed internal os

Explanation

A cesarean scar pregnancy implants in the prior hysterotomy site, appearing anteriorly in the lower uterine segment with a very thin layer of myometrium between the sac and the bladder. The uterine cavity and cervical canal are typically empty.

Question 39First Trimester Obstetric Sonography (Normal and Abnormal)

At 12 weeks a fetus shows a single midline ventricle with fused thalami and absent midline cerebral structures. Which is the most likely diagnosis?

  1. Acrania
  2. Cystic hygroma
  3. Encephalocele
  4. Alobar holoprosencephaly Correct answer.

Explanation

Failure of the prosencephalon to cleave produces a single monoventricle with fused thalami, the hallmark of alobar holoprosencephaly. It is strongly associated with trisomy 13 and with midline facial defects.

Question 40First Trimester Obstetric Sonography (Normal and Abnormal)

A 12-week fetus has a large septated fluid collection posterior to the neck that extends along the fetal body. Which condition is most strongly associated with this finding?

  1. Neural tube defect
  2. Turner syndrome Correct answer.
  3. Gastrointestinal obstruction
  4. Skeletal dysplasia

Explanation

A septated nuchal fluid collection extending along the fetus is a cystic hygroma, which is most strongly associated with Turner syndrome and other aneuploidies. It also warrants assessment for structural cardiac defects.

Question 41Second and Third Trimester Obstetric Sonography: Fetal Anatomy, Biometry, and Anomalies

At which intracranial level is the biparietal diameter correctly measured?

  1. At the level of the lateral ventricle bodies and choroid plexus
  2. At the level of the thalami and cavum septum pellucidum Correct answer.
  3. At the level of the cerebellum and cisterna magna
  4. At the level of the orbits and nasal bridge

Explanation

The biparietal diameter is obtained on an axial plane at the level of the thalami, with the cavum septum pellucidum and the continuous midline echo visible, and calipers placed outer-to-outer across the skull. This reproducible landmark gives the most reliable width measurement.

Question 42Second and Third Trimester Obstetric Sonography: Fetal Anatomy, Biometry, and Anomalies

The abdominal circumference is correctly obtained on a plane that includes which structures?

  1. The umbilical cord insertion into the anterior wall
  2. The stomach bubble and the umbilical vein at the portal sinus Correct answer.
  3. Both renal pelves at the level of the kidneys
  4. The fetal heart and both ventricles

Explanation

The abdominal circumference is measured on a transverse plane at the level of the stomach and the portal sinus of the umbilical vein, with the spine, ribs, and skin line all visible. A circular section is required for accuracy.

Question 43Second and Third Trimester Obstetric Sonography: Fetal Anatomy, Biometry, and Anomalies

How should the femur length be measured?

  1. Including the distal femoral epiphysis in the measurement
  2. Along the ossified shaft, perpendicular to the beam Correct answer.
  3. Across the surrounding soft tissues and skin line
  4. Across the cartilaginous condyles only

Explanation

Femur length is measured along the ossified diaphysis from one end to the other, with the beam perpendicular to the bone so only the shaft is measured. Cartilage and epiphyses are excluded because they are not ossified.

Question 44Second and Third Trimester Obstetric Sonography: Fetal Anatomy, Biometry, and Anomalies

What is the normal depth range of the cisterna magna in the second and third trimester?

  1. 2 to 10 mm Correct answer.
  2. 4 to 6 mm
  3. 6 to 8 mm
  4. 1 to 3 mm

Explanation

The cisterna magna is measured from the posterior aspect of the cerebellar vermis to the inner border of the occipital bone, and a depth of 2 to 10 mm is normal. Values outside this range raise concern for Dandy-Walker spectrum or Chiari II malformation.

Question 45Second and Third Trimester Obstetric Sonography: Fetal Anatomy, Biometry, and Anomalies

Which statement describes correct technique for measuring the lateral ventricle?

  1. At the occipital horn, outer edge to outer edge, normal under 5 mm
  2. At the atrium, inner edge to inner edge, normal under 10 mm Correct answer.
  3. At the third ventricle, anterior to posterior, normal under 3 mm
  4. At the frontal horns, outer edge to outer edge, normal under 15 mm

Explanation

The lateral ventricle is measured at the atrium, just behind the choroid plexus glomus, with calipers placed inner edge to inner edge perpendicular to the ventricle long axis. A measurement of 10 mm or more defines ventriculomegaly.

Question 46Second and Third Trimester Obstetric Sonography: Fetal Anatomy, Biometry, and Anomalies

Which statement about the transcerebellar diameter is accurate?

  1. It is measured on the same plane used for the biparietal diameter
  2. It increases with gestational age and is smaller than expected in Chiari II malformation Correct answer.
  3. It is normally larger than the biparietal diameter in the third trimester
  4. It stays constant at about 10 mm throughout gestation

Explanation

The transcerebellar diameter grows steadily with gestational age and correlates closely with it, so it is useful for dating. In Chiari II malformation the cerebellum is abnormally small and the cisterna magna is obliterated.

Question 47Second and Third Trimester Obstetric Sonography: Fetal Anatomy, Biometry, and Anomalies

A fetus whose long axis lies perpendicular to the long axis of the uterus is in which lie?

  1. Longitudinal
  2. Oblique
  3. Cephalic
  4. Transverse Correct answer.

Explanation

Lie describes the relationship between the fetal long axis and the uterine long axis. A perpendicular relationship defines a transverse lie, whereas a parallel relationship defines a longitudinal lie.

Question 48Second and Third Trimester Obstetric Sonography: Fetal Anatomy, Biometry, and Anomalies

Which structures are assessed on the standard four-chamber cardiac view?

  1. The ductus arteriosus and its arch
  2. The pulmonary artery bifurcation
  3. The aortic arch in long axis
  4. The interventricular septum and AV valves Correct answer.

Explanation

The four-chamber view demonstrates both atria, both ventricles, the interventricular and interatrial septa, and both atrioventricular valves. It is the basic screening plane for major congenital heart disease.

Question 49Second and Third Trimester Obstetric Sonography: Fetal Anatomy, Biometry, and Anomalies

A fetal head has a cephalic index of 92. How is this shape described?

  1. Normocephaly
  2. Macrocephaly
  3. Brachycephaly Correct answer.
  4. Dolichocephaly

Explanation

The cephalic index is the biparietal diameter divided by the occipitofrontal diameter times 100, with 70 to 86 considered normal. Values above 86 indicate a rounded, shortened head, termed brachycephaly.

Question 50Second and Third Trimester Obstetric Sonography: Fetal Anatomy, Biometry, and Anomalies

The four-parameter Hadlock formula for estimated fetal weight uses which measurements?

  1. BPD, HC, AC, and FL Correct answer.
  2. AC and FL only
  3. BPD and FL only
  4. HC and TCD only

Explanation

The four-parameter Hadlock model combines biparietal diameter, head circumference, abdominal circumference, and femur length. The abdominal circumference carries the greatest weight because it reflects hepatic glycogen and fat deposition.