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Questions and Answers
What is the suspected diagnosis if the gestational sac is ≥10mm and no yolk sac is visible?
What is the suspected diagnosis if the gestational sac is ≥10mm and no yolk sac is visible?
Cardiac activity can be observed via m-mode at 6 weeks of gestation.
Cardiac activity can be observed via m-mode at 6 weeks of gestation.
True
What is the cutoff value for mean sac diameter (MSD) to measure crown rump length (CRL) or visualize the fetal pole?
What is the cutoff value for mean sac diameter (MSD) to measure crown rump length (CRL) or visualize the fetal pole?
≥25mm
At 6 weeks of gestation, the fetal heart rate (FHR) ranges from _____ bpm.
At 6 weeks of gestation, the fetal heart rate (FHR) ranges from _____ bpm.
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Match the following criteria to their respective outcomes:
Match the following criteria to their respective outcomes:
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What does the double decidual sac sign indicate?
What does the double decidual sac sign indicate?
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The crown rump length is considered the best parameter to estimate gestational age in the second trimester.
The crown rump length is considered the best parameter to estimate gestational age in the second trimester.
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What is the first ultrasound sign of early pregnancy?
What is the first ultrasound sign of early pregnancy?
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The _____ sign consists of one bleb for the yolk sac and another for the amniotic sac.
The _____ sign consists of one bleb for the yolk sac and another for the amniotic sac.
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Match the trimester with its best parameter for estimating gestational age:
Match the trimester with its best parameter for estimating gestational age:
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What is the formula to estimate gestational age using the Mean Sac Diameter (MSD)?
What is the formula to estimate gestational age using the Mean Sac Diameter (MSD)?
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Crown Rump Length (CRL) is used for estimating gestational age until 13 weeks + 6 days and can be used when CRL is greater than or equal to 84mm.
Crown Rump Length (CRL) is used for estimating gestational age until 13 weeks + 6 days and can be used when CRL is greater than or equal to 84mm.
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What is the minimum CRL measured on ultrasound for estimating gestational age?
What is the minimum CRL measured on ultrasound for estimating gestational age?
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The biparietal diameter is measured in the _______ plane.
The biparietal diameter is measured in the _______ plane.
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Match the ultrasound recommendation with its indicated week range:
Match the ultrasound recommendation with its indicated week range:
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What is the best time frame for performing a TIFFA ultrasound to detect congenital malformations?
What is the best time frame for performing a TIFFA ultrasound to detect congenital malformations?
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Routine ultrasound (Level 1) is used primarily for detecting chromosomal anomalies.
Routine ultrasound (Level 1) is used primarily for detecting chromosomal anomalies.
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Name a condition that results from the failure of the cranial neuropore to close.
Name a condition that results from the failure of the cranial neuropore to close.
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A condition where brain tissue herniates out through a defect in the skull is called an __________.
A condition where brain tissue herniates out through a defect in the skull is called an __________.
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Match the following types of cranial defects to their descriptions:
Match the following types of cranial defects to their descriptions:
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Which condition typically shows a cauliflower-like appearance on ultrasound?
Which condition typically shows a cauliflower-like appearance on ultrasound?
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Karyotyping is required for the diagnosis of gastroschisis.
Karyotyping is required for the diagnosis of gastroschisis.
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At what gestational age is maximum alpha-feto protein level found in fetal serum?
At what gestational age is maximum alpha-feto protein level found in fetal serum?
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Elevated alpha-feto protein levels in the fetus are associated with __________ defects.
Elevated alpha-feto protein levels in the fetus are associated with __________ defects.
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Match the following fetal conditions with their associated alpha-feto protein levels:
Match the following fetal conditions with their associated alpha-feto protein levels:
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What is the term used for the absence of the skull in anencephaly?
What is the term used for the absence of the skull in anencephaly?
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Anencephaly is a viable condition.
Anencephaly is a viable condition.
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What is the recommended daily dose of folic acid supplementation to prevent recurrence of neural tube defects (NTD)?
What is the recommended daily dose of folic acid supplementation to prevent recurrence of neural tube defects (NTD)?
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The _____ sign on ultrasound is associated with the irregular contour of the fetal head in anencephaly.
The _____ sign on ultrasound is associated with the irregular contour of the fetal head in anencephaly.
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Match the ultrasound signs with their descriptions:
Match the ultrasound signs with their descriptions:
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Which of the following conditions is associated with caudal defects of the neural tube?
Which of the following conditions is associated with caudal defects of the neural tube?
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The best biochemical marker for detecting neural tube defects is alpha-fetoprotein (AFP).
The best biochemical marker for detecting neural tube defects is alpha-fetoprotein (AFP).
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What is the typical prevalence of caudal defects in births?
What is the typical prevalence of caudal defects in births?
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The _____ sign on ultrasound indicates downward displacement of the cerebellum.
The _____ sign on ultrasound indicates downward displacement of the cerebellum.
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Match the types of spina bifida with their descriptions:
Match the types of spina bifida with their descriptions:
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At what gestational age is the best time to localize the placenta using ultrasound?
At what gestational age is the best time to localize the placenta using ultrasound?
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Short femur measurements can indicate constitutional delay or Down syndrome.
Short femur measurements can indicate constitutional delay or Down syndrome.
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What is the purpose of performing serial ultrasounds in a suboptimally dated pregnancy?
What is the purpose of performing serial ultrasounds in a suboptimally dated pregnancy?
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Fetal echo is typically performed between ______ and ______ weeks.
Fetal echo is typically performed between ______ and ______ weeks.
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Match the following conditions with their associated risks:
Match the following conditions with their associated risks:
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What is an indication for performing a fetal echo?
What is an indication for performing a fetal echo?
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A single ultrasound before 22 weeks is sufficient for dating a pregnancy.
A single ultrasound before 22 weeks is sufficient for dating a pregnancy.
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What condition is associated with a severely short femur measurement?
What condition is associated with a severely short femur measurement?
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What is the key characteristic that differentiates gastroschisis from omphalocoele?
What is the key characteristic that differentiates gastroschisis from omphalocoele?
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Chiari 3 malformation involves the herniation of the cerebellum and meninges through a cranial defect.
Chiari 3 malformation involves the herniation of the cerebellum and meninges through a cranial defect.
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What is the medical term for the condition where both brain and meninges herniate through a cranial defect?
What is the medical term for the condition where both brain and meninges herniate through a cranial defect?
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The _____ sign on an ultrasound indicates a specific abnormality related to the fetal brain.
The _____ sign on an ultrasound indicates a specific abnormality related to the fetal brain.
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Match the following conditions with their descriptions:
Match the following conditions with their descriptions:
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What is the cut-off value for crown rump length (CRL) to visualize cardiac activity?
What is the cut-off value for crown rump length (CRL) to visualize cardiac activity?
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A pseudo gestational sac is characterized by the presence of a yolk sac.
A pseudo gestational sac is characterized by the presence of a yolk sac.
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What does an increase in β hCG but not doubling suggest about the pregnancy?
What does an increase in β hCG but not doubling suggest about the pregnancy?
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The minimum β hCG value at which the gestational sac is visible on transvaginal ultrasound (TVS) is _____ IU/L.
The minimum β hCG value at which the gestational sac is visible on transvaginal ultrasound (TVS) is _____ IU/L.
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Match the following conditions with their respective criteria:
Match the following conditions with their respective criteria:
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Which of the following indicates a missed abortion?
Which of the following indicates a missed abortion?
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The presence of double bleb sign indicates a true gestational sac.
The presence of double bleb sign indicates a true gestational sac.
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What is the critical titer for β hCG to visualize a gestational sac via transabdominal ultrasound (TAS)?
What is the critical titer for β hCG to visualize a gestational sac via transabdominal ultrasound (TAS)?
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Study Notes
Ultrasound In Pregnancy Part 1
- Missed Abortion: If gestational sac is ≥ 25mm and no fetal pole/CRL can be measured then it can be concluded as missed abortion.
- CRL measurement: In twin pregnancies, if there is a discrepancy in CRL measurements, the EDD is calculated based on the larger twin.
- Biparietal Diameter (BPD): Measured in the transthalamic plane (from the outer table on one side to the inner table on the opposite side).
-
Ultrasound Indications:
- Done to rule out ectopic pregnancy when a patient experiences abdominal pain.
- Done to determine viability when a patient has bleeding in the first trimester.
- Done to determine if the size of the uterus matches the length of gestation
- Done when a patient is unsure about their LMP.
-
USG Recommendations:
- 6-8 weeks: Viability scan.
- 18-22 weeks: Target/anomaly/booking scan (TIFFA).
- 11-13 weeks + 6 days: Nuchal translucency scan.
- 32-34 weeks: Growth scan.
Early Pregnancy on USG
- Intradecidual Sign: This is the first sign observed when a gestational sac is present, indicating the implantation of the blastocyst in the endometrium.
- Double Decidual Sac/Double Ring Sign: This is the second sign observed where the inner ring represents the decidua capsularis and outer ring the decidua parietalis.
- Double Bleb Sign: The third sign is the presence of two blebs. One bleb represents the yolk sac and the other bleb represents the amniotic sac.
- Gestational Age Estimation: The accuracy of gestational age relies on the time of ultrasound. The earlier the ultrasound, the more precise the gestational age estimation.
-
Estimating Gestational Age:
- Trimester 1: Crown rump length (CRL) is the best parameter to estimate gestational age.
- Trimester 2: BPD (biparietal diameter) is the best parameter.
- Trimester 3: A combination of parameters, with femur length being the best single parameter, are used to estimate gestational age.
Ultrasound In Pregnancy Part 2
- Level 2 USG (TIFFA): Best performed between 18-22 weeks. It detects gross congenital anomalies in the fetus and chromosomal anomalies need to be assessed with karyotyping.
- Level 1 USG: Useful for detecting some common congenital malformations like neural tube defects (NTDs).
- Neural Tube Defect (NTD): Occurs when there is a problem with the closure of the neuropore, or fusion of the neural tube.
Cranial Defect
- Acrania: Absence of skull, meninges, and muscles.
- Encephalocele: Herniation of brain tissue covered by meninges and scalp, mostly through the occipital bone.
- Anencephaly: Severe NTD where brain tissue degenerates and is destroyed.
Omphalocoele
- On USG: Appears with a smooth outline.
- Site: Located at the umbilicus.
- Associated with: Trisomy 18 > Trisomy 21.
- Karyotyping: Required.
Gastroschisis
- On USG: Appears with a cauliflower-like appearance.
- Site: Located to the left or right of the umbilicus.
- Karyotyping: Not required.
Alpha-Fetoprotein (AFP)
- Salient features: Fetal-specific globulin produced by the yolk sac, fetal GIT, and liver.
- Maximum level in fetal serum: At 13 weeks of pregnancy.
- Maternal serum AFP: Ideally tested between 16-18 weeks, but earliest detection can be done by 15 weeks.
Fetal conditions associated with raised AFP levels:
- Neural tube defects (NTD)
- Abdominal wall defect
- Pilonidal sinus
- Fetal death
Fetal conditions associated with decreased AFP levels (Mnemonic: Diabetic GOAT):
- Maternal Diabetes
- Gestational Trophoblastic Disease
- Overestimated Gestational Age
- Abortion
- Trisomy of fetus
Normal Pregnancy and Antenatal Care
- CRL cutoff to see cardiac activity: ≥ 7mm (Cardiac activity present), <7mm (Cardiac activity absent).
-
Missed Abortion on USG:
- Specific criteria: - If MSD ≥ 25mm and fetal pole not seen/CRL cannot be measured. - If CRL ≥ 7mm and cardiac activity absent. - If ≥ 14 days have passed after the first scan showing gestational sac: yolk sac/cardiac activity absent. - If ≥ 11 days passed after the first scan showing gestational sac + yolk sac: cardiac activity absent.
-
β hCG:
- Cut-off value to visualize gestational sac (Critical titer): 2000 IU/L for TVS and 6500 IU/L for TAS.
- If β hCG value ≥2000 IU/L and the gestational sac is not seen, then it is an ectopic pregnancy.
- Minimum β hCG value at which a gestational sac is visible on TVS: 1000 IU/L.
- β hCG repeat value (After 48hrs): - Doubled: Live intrauterine pregnancy. - Increased but not doubled: Ectopic pregnancy. - Decreased: Dying intrauterine pregnancy (Abortion).
Anencephaly
-
Salient features:
- Missing skull (Acrania)
- Absent or hypoplastic adrenal and pituitary gland
- Increased risk of post-term pregnancy
- Decreased fetal DHEAS and estrogen levels
- Associated swallowing defect (Polyhydramnios)
- Fetal presentation: Face (Face of the fetus is normal)
- Non-viable condition
-
On USG:
- First congenital anomaly to be recognized on USG, with the earliest detection at 10 weeks and best detection at 14 weeks.
- Shower cap sign (irregular contour of the fetal head)
- Mickey mouse sign (triangular face)
- Frog eye sign (large bulging eyes/deep eye sockets)
- Polyhydramnios (In the T2 or late 2nd trimester)
Management
- MTP: Irrespective of gestational age after a medical board decision.
Recurrent risk of NTD:
- 5% after one NTD
- 10% after two NTD
Prevention of NTD:
- Folic acid supplementation:
- Dose: 400mcg/day
- Dose to prevent recurrence: 4mg/day
Note:
- Hyperthermia/fever in the first trimester (temperature ↑ by ≥ 1.5°C) can cause teratogenic effects.
- NTD, microcephaly, learning disability, and seizures.
Diagnosis of NTD:
- Screening test:
- Current Level I USG
- Earlier maternal serum AFP levels (15-20 weeks)
- Diagnostic test:
- Level 2 USG/TIFFA
- Amniocentesis (AFP and acetylcholinesterase levels)
Caudal Defect of Neural Tube
- Prevalence: 1 in 2000 births
-
Caudal Defects: Non-closure of vertebral arches
- Spina bifida occulta: No herniation of meninges and spinal cord
- Meningocele: Herniation of meninges and no herniation of spinal cord.
- Meningomyelocele: Herniation of meninges and spinal cord.
-
On USG:
- Banana sign: Downward displacement of the cerebellum.
- Lemon sign: Bossing of the frontal bone.
- Associated ventriculomegaly.
- Polyhydramnios.
- These signs are also seen in Arnold Chiari malformation/Chiari II malformation
Craniorachischisis: Cranial + Caudal Neural Tube Defect.
-
Note:
- Cephalocele: Herniation of meninges through a cranial defect.
- Encephalocele: Herniation of brain and meninges through a cranial defect.
- Chiari 3 Malformation: Encephalocele with herniation of cerebellum and other posterior fossa structures.
Abdominal Wall Defect
- Omphalocoele: Herniation of abdominal contents that is enclosed in a sac.
- Gastroschisis: Herniation of abdominal content that is not enclosed in a sac.
Ultrasound In Pregnancy Part 1
- Uses of USG:*
- Cervical Length Measurement (in preterm labor): For all pregnant women with a history of preterm labor, a transvaginal ultrasound (TVS) should be performed between 16 and 24 weeks to measure cervical length.
- Placental Localization: Best performed at 32 and 36 weeks gestation.
- Chorionicity in Twins: Measured between 10 and 14 weeks.
- Short Femur Indicates:*
- Constitutional delay
- Down syndrome
- Severely Short Femur Indicates:*
- Skeletal dysplasia
- Early-onset IUGR
- Suboptimally Dated Pregnancy:*
- No USG before 22 weeks
- Single USG is not useful
- Serial USG (3-4 weeks apart) is useful to:
- Estimate gestational age
- Rule out Intrauterine Growth Restriction (IUGR)
- Fetal Echo:*
- Not routinely performed unless there is suspicion of fetal cardiac disease.
- Performed between 22 and 24 weeks.
- Indications for Fetal Echo:*
- Fetal heart rate (FHR) arrhythmia
- Maternal rubella infection (increased risk of patent ductus arteriosus)
- Fetal aneuploidy (e.g., Down syndrome, endocardial cushion defect)
- Nuchal translucency (NT) ≥ 3mm
- Monochorionic twin (TTTS): Increased risk of heart failure (HF) in the recipient twin
- Other Factors:*
- Lithium therapy: Ebstein anomaly
- History of fetus with heart block in the setting of maternal anti-Ro/La antibodies (SLE): Increased risk of VSD
- Gestational diabetes: Increased risk of VSD
- Phenylketonuria: Increased risk of microcephaly and central nervous system (CNS) abnormalities.
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Description
This quiz covers essential concepts related to prenatal ultrasound, including methods for assessing missed abortion, measuring crown-rump length (CRL) in twin pregnancies, and understanding various ultrasound indications and recommendations. It is a valuable resource for students and practitioners in obstetrics and gynecology, providing foundational knowledge for interpreting ultrasound results during pregnancy.
