Late first trimester normal ultrasound survey Question of
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• A. 6-8 weeks
• B. 8-10 weeks
• C. 11-13+6 weeks
• D. 14-16 weeks
Answer: C. 11-13+6 weeks
Explanation:
The NT measurement is performed between 11 weeks and 13 weeks + 6 days. During this time, the fetal crown-rump length (CRL) is ideally between 45 mm and 84 mm, allowing for accurate measurement of the nuchal translucency. This measurement is crucial for assessing the risk of chromosomal abnormalities, such as Down syndrome (Trisomy 21).
• A. Biparietal diameter (BPD)
• B. Crown-rump length (CRL)
• C. Femur length (FL)
• D. Head circumference (HC)
Answer: B. Crown-rump length (CRL)
Explanation:
The CRL is the most accurate ultrasound parameter for estimating gestational age in the first trimester, especially between 7 and 13 weeks of gestation. After the first trimester, other parameters like BPD, HC, and FL become more reliable.
• A. 90-110 bpm
• B. 120-160 bpm
• C. 160-190 bpm
• D. 200-220 bpm
Answer: B. 120-160 bpm
Explanation:
The normal fetal heart rate in the late first trimester (10-13 weeks) is typically 120-160 beats per minute (bpm). Before 9 weeks, the heart rate is usually lower, but it increases rapidly and then stabilizes.
• A. Nasal bone
• B. Nuchal translucency
• C. Kidneys
• D. Yolk sac
Answer: C. Kidneys
Explanation:
The kidneys are not typically assessed in a standard first-trimester ultrasound. During the late first trimester, the focus is on measuring CRL, evaluating nuchal translucency, and identifying key structures such as the nasal bone, yolk sac, and fetal heart. Detailed anatomical surveys, including assessment of the kidneys, are usually performed during the mid-trimester anatomy scan (18-22 weeks).
• A. It is a normal finding and will resolve spontaneously.
• B. It is associated with chromosomal abnormalities.
• C. It indicates a congenital diaphragmatic hernia.
• D. It is indicative of intrauterine growth restriction.
Answer: B. It is associated with chromosomal abnormalities.
Explanation:
A cystic hygroma is a fluid-filled sac located in the fetal neck region, often identified during the first-trimester ultrasound. It is associated with chromosomal abnormalities such as Turner syndrome, Down syndrome, and trisomy 18, as well as congenital heart defects. Further evaluation through chorionic villus sampling (CVS) or amniocentesis may be indicated.
• A. To assess fetal cardiac function
• B. To screen for neural tube defects
• C. To assess for chromosomal abnormalities
• D. To evaluate amniotic fluid volume
Answer: C. To assess for chromosomal abnormalities
Explanation:
The nasal bone assessment is a key component of the first-trimester ultrasound. The absence or hypoplasia of the nasal bone, particularly between 11 and 13+6 weeks, is associated with an increased risk of chromosomal abnormalities, including Down syndrome (Trisomy 21).
• A. 6-7 weeks
• B. 8-9 weeks
• C. 10-12 weeks
• D. 13-14 weeks
Answer: C. 10-12 weeks
Explanation:
The fetal bladder can usually be visualized by 10-12 weeks of gestation. It appears as a small, fluid-filled structure in the lower abdomen. Its visualization is important to confirm the presence of functioning kidneys and urinary tract development.
• A. Inside the amniotic cavity
• B. Between the amnion and chorion
• C. Adjacent to the fetal spine
• D. Near the placenta
Answer:B. Between the amnion and chorion
Explanation:
The yolk sac is located in the extraembryonic coelom, between the amnion and chorion. It is typically visualized from around 5-6 weeks until 10-12 weeks, after which it gradually regresses. The yolk sac provides nutrients and assists in early blood formation.
• A. Less than 2 mm
• B. 2-3 mm
• C. 3.5 mm or more
• D. 5 mm or more
Answer: C. 3.5 mm or more
Explanation:
An NT measurement of 3.5 mm or greater is considered abnormal and is associated with an increased risk of chromosomal abnormalities (e.g., Down syndrome, trisomy 18, and Turner syndrome), as well as congenital heart defects. Further diagnostic testing, such as CVS or amniocentesis, is recommended in such cases.
• A. 4-5 weeks
• B. 5-6 weeks
• C. 7-8 weeks
• D. 9-10 weeks
Answer: B. 5-6 weeks
Explanation:
A fetal heartbeat can typically be detected by 5-6 weeks of gestation using a transvaginal ultrasound. At this stage, the heart rate is usually between 90-110 bpm and gradually increases to 120-160 bpm by 9-10 weeks.
• A. Yolk sac
• B. Embryo
• C. Amnion
• D. Placenta
Answer: A. Yolk sac
Explanation:
The yolk sac is the first structure visible within the gestational sac and can be seen as early as 5 weeks of gestation. It provides early nutrients to the embryo and serves as a marker for a viable intrauterine pregnancy.
• A. Dichorionic diamniotic (DCDA)
• B. Monochorionic diamniotic (MCDA)
• C. Monochorionic monoamniotic (MCMA)
• D. Conjoined twins
Answer: A. Dichorionic diamniotic (DCDA)
Explanation:
The most common type of twin gestation observed in the first trimester is dichorionic diamniotic (DCDA), where each twin has its own chorion and amnion. This occurs in both dizygotic (fraternal) and some monozygotic (identical) twins, depending on the timing of the zygote split.
• A. Echogenic with a central cystic area
• B. Anechoic with a central yolk sac
• C. Complex with multiple cystic areas
• D. Hyperechoic with a solid appearance
Answer: B. Anechoic with a central yolk sac
Explanation:
The chorionic cavity (also known as the extraembryonic coelom) appears as an anechoic space containing the yolk sac and embryo. It is surrounded by the chorion and will gradually decrease in size as the amniotic cavity expands.
• A. 10 mm
• B. 12 mm
• C. 15 mm
• D. 20 mm
Answer: B. 12 mm
Explanation:
A yolk sac should typically be visible when the mean gestational sac diameter (MSD) reaches 12 mm or greater. Absence of a yolk sac at this size may raise suspicion for a failed pregnancy or anembryonic gestation (blighted ovum).
• B. Nasal bone
• C. Amniotic membrane
• D. Fetal spine
Answer: D. Fetal spine
Explanation:
The fetal spine is a key anatomical landmark for determining fetal orientation and assessing the correct plane of the ultrasound image. It helps in establishing the cranial-caudal orientation and facilitates identification of other structures.
• A. It indicates inevitable miscarriage.
• B. It is a normal finding with no clinical implications.
• C. It may increase the risk of pregnancy loss.
• D. It is diagnostic of molar pregnancy.
Answer: C. It may increase the risk of pregnancy loss.
Explanation:
A subchorionic hematoma appears as a crescent-shaped hypoechoic or anechoic area adjacent to the gestational sac. While many resolve spontaneously, larger hematomas, especially those measuring more than 30% of the gestational sac size, may increase the risk of miscarriage, placental abruption, or preterm labor.
• A. Fetal macrosomia
• B. Incorrect dating of LMP
• C. Placental insufficiency
• D. Maternal obesity
Answer: B. Incorrect dating of LMP
Explanation:
In the first trimester, the most common reason for a discrepancy between LMP and ultrasound dating is incorrect dating of the LMP. CRL measurement provides the most accurate estimation of gestational age during this period, with a margin of error of approximately ±5-7 days.
• A. Crown-rump length (CRL)
• B. Biparietal diameter (BPD)
• C. Yolk sac diameter
• D. Gestational sac diameter
Answer: D. Gestational sac diameter
Explanation:
While the gestational sac diameter can provide an early estimate of gestational age, it is less accurate than CRL, especially after 7 weeks. CRL remains the gold standard for dating in the first trimester, as it correlates more precisely with the actual gestational age.
• A. A single, thick, hyperechoic line
• B. Two parallel, echogenic lines
• C. A thin, echogenic line surrounding the fetus
• D. A hypoechoic ring without a distinct border
Answer: C. A thin, echogenic line surrounding the fetus
Explanation:
The amniotic membrane is a thin, echogenic line that surrounds the fetus. It is clearly visible by 8-10 weeks and gradually fuses with the chorionic membrane by 16-18 weeks.
• A. Production of amniotic fluid
• B. Hematopoiesis and nutrient transfer
• C. Formation of the fetal kidneys
• D. Development of the fetal brain
Answer: B. Hematopoiesis and nutrient transfer
Explanation:
The yolk sac serves as the primary site of hematopoiesis (formation of blood cells) and nutrient transfer to the embryo until the placenta takes over at around 12 weeks. It also contributes to the formation of the gut and early circulatory system.
• A. 5-6 weeks
• B. 7-8 weeks
• C. 9-10 weeks
• D. 11-13 weeks
Answer: C. 9-10 weeks
Explanation:
The choroid plexus, a paired echogenic structure within the fetal brain, can typically be visualized by 9-10 weeks of gestation. It produces cerebrospinal fluid and is a key landmark in identifying the developing fetal brain.
• A. 20-30 mm
• B. 35-50 mm
• C. 50-60 mm
• D. 65-75 mm
Answer: C. 50-60 mm
Explanation:
At 12 weeks gestation, a normal CRL typically ranges from 50-60 mm. Accurate CRL measurement is crucial for determining gestational age and assessing fetal growth patterns in the first trimester.
• A. It is primarily composed of fetal urine.
• B. It is produced by the placenta and chorion.
• C. It appears echogenic on ultrasound.
• D. It is primarily produced by the amniotic membrane.
Answer: B. It is produced by the placenta and chorion.
Explanation:
In the first trimester, amniotic fluid is primarily derived from the placenta and chorion. Fetal urine production begins around 11-12 weeks, and by the second trimester, it becomes the main component of amniotic fluid.
• A. Dandy-Walker cyst
• B. Choroid plexus
• C. Enlarged ventricles
• D. Absent cavum septum pellucidum
Answer: B. Choroid plexus
Explanation:
The choroid plexus is a normal structure in the fetal brain that is visible as a paired echogenic area within the lateral ventricles. It is responsible for the production of cerebrospinal fluid and is commonly seen from 9-10 weeks onward.
• A. Crown-rump length (CRL)
• B. Gestational sac diameter
• C. Yolk sac diameter
• D. Biparietal diameter (BPD)
Answer: A. Crown-rump length (CRL)
Explanation:
The CRL is the most accurate parameter for confirming fetal viability and dating the pregnancy in the first trimester. A fetal heartbeat is usually detected when the CRL is ≥ 7 mm, and absence of cardiac activity at this size is diagnostic of pregnancy loss.
• A. 90 bpm
• B. 100 bpm
• C. 110 bpm
• D. 120 bpm
Answer: C. 110 bpm
Explanation:
A fetal heart rate of 110-160 bpm is considered normal in the late first trimester (10-12 weeks). A heart rate less than 110 bpm is considered bradycardia and may indicate an increased risk of miscarriage.
• B. T-sign at the intertwin membrane
• C. Lambda or twin-peak sign
• D. Single amniotic sac
Answer: C. Lambda or twin-peak sign
Explanation:
The lambda or twin-peak sign indicates the presence of a thick membrane between two gestational sacs and is characteristic of a dichorionic-diamniotic (DCDA) twin pregnancy. This sign is typically seen in the first trimester and suggests two separate placental origins.
• A. CRL of 60 mm at 12 weeks
• B. Nuchal translucency of 4 mm at 12 weeks
• C. Fetal heart rate of 150 bpm at 11 weeks
• D. Nasal bone visualization at 13 weeks
Answer: B. Nuchal translucency of 4 mm at 12 weeks
Explanation:
An NT measurement of 4 mm at 12 weeks is considered abnormal and significantly increases the risk of chromosomal abnormalities and congenital heart defects. Further evaluation with genetic testing and fetal echocardiography is recommended.
• A. 8-9 weeks
• B. 10-11 weeks
• C. 12-13 weeks
• D. 14-15 weeks
Answer: C. 12-13 weeks
Explanation:
Physiological midgut herniation is a normal finding in the first trimester and typically resolves by 12-13 weeks of gestation. Persistence beyond 13 weeks may indicate an omphalocele or other abdominal wall defect.
• A. It is a normal finding.
• B. It indicates a molar pregnancy.
• C. It is associated with increased risk of miscarriage.
• D. It suggests a multiple gestation.
Answer: C. It is associated with increased risk of miscarriage.
Explanation:
A yolk sac diameter greater than 6 mm is considered enlarged and is associated with a higher risk of first-trimester miscarriage. Follow-up ultrasound and monitoring of fetal viability are recommended.
• A. Nasal bone hypoplasia
• B. Short femur length
• C. Single umbilical artery
• D. Subchorionic hemorrhage
Answer: A. Nasal bone hypoplasia
Explanation:
Nasal bone hypoplasia or absence is a strong indicator of aneuploidy, particularly Down syndrome (Trisomy 21). It is usually assessed in conjunction with nuchal translucency measurement and other biochemical markers.
• A. Amniotic sac
• B. Gestational sac
• C. Yolk sac
• D. Umbilical cord
Answer: C. Yolk sac
Explanation:
The yolk sac appears as a hyperechoic ring surrounding a central anechoic area on ultrasound. It is the first structure visualized within the gestational sac and serves as a vital source of nutrients for the developing embryo.
• A. Repeat ultrasound in one week
• B. Consider intrauterine growth restriction (IUGR)
• C. Recalculate gestational age
• D. Perform amniocentesis
Answer: C. Recalculate gestational age
Explanation:
A CRL of 30 mm at 10 weeks is smaller than expected. Since CRL is the most accurate parameter for dating in the first trimester, the gestational age should be recalculated based on the CRL rather than the LMP.
• A. Single artery and single vein
• B. Two arteries and one vein
• C. Three arteries and one vein
• D. Two veins and one artery
Answer: B. Two arteries and one vein
Explanation:
The normal umbilical cord contains two arteries and one vein. The arteries.
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