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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.
True
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.
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Match the following criteria to their respective outcomes:
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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.
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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.
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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)?
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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.
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What is the minimum CRL measured on ultrasound for estimating gestational age?
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The biparietal diameter is measured in the _______ plane.
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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?
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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.
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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:
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Which condition typically shows a cauliflower-like appearance on ultrasound?
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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?
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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:
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What is the term used for the absence of the skull in anencephaly?
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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)?
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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:
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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).
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What is the typical prevalence of caudal defects in births?
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The _____ sign on ultrasound indicates downward displacement of the cerebellum.
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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?
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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?
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Fetal echo is typically performed between ______ and ______ weeks.
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Match the following conditions with their associated risks:
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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.
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What condition is associated with a severely short femur measurement?
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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.
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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.
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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?
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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?
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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:
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Which of the following indicates a missed abortion?
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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)?
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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).
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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.
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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.
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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).
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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.
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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
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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
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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.
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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.
