Obstetrics Marrow Pg 325-334 (Normal Pregnancy & ANC)

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.