INIYAN SCANS

ANTENATAL ULTRASOUND REPORT - Second Trimester

OBSERVATIONS

• Fetus A - Towards maternal right
• Fetus B - Towards maternal left
• Separating membrane seen.

• Uterine cervix measures 37 mm in length (Transvaginal approach)
• Single placenta - Location: Anterior. Retroplacental space: Normal. No clots.
• Liquor: Adequate
• Umbilical cord: 3 vessels

FETAL BIOMETRY - FETUS A

• Fetal cardiac activity: Present - FHR: 159 bpm
• Approximate fetal weight: 339 +/- 49 gms

FETAL BIOMETRY - FETUS B

• Fetal cardiac activity: Present - FHR: 149 bpm
• Approximate fetal weight: 373 +/- 54 gms

DETAILED ORGAN SURVEY (Fetus A & B)

• BPD plane: Interrupted falx seen. Cavum septum pellucidum visualised.
• LV plane: Lateral ventricles measures within normal limits. Normal choroid plexus.
• Posterior fossa: Both cerebellar hemispheres and Vermis seen. Cisterna magna measures within normal limits.

• Sagittal view: Contour appears normal. Sacral tapering seen normally.
• Transverse view: No demonstrable spinal defects.

• Both lungs appear echogenic. No evidence of cystic areas.

• 4-chamber view: Cardiac axis and situs appear normal. Chamber symmetry maintained.
• RVOT/LVOT: Appears normal and crosses at root.
• 3-vessel view: Size, number and alignment appear normal.

• Upper abdomen: Stomach visualised on left side. Abdominal situs appear normal.
• Mid abdomen: Both kidneys appear normal. No calyceal dilatation. Small bowel appear normal echogenic.
• Lower abdomen: Urinary bladder filled well. No abdominal wall defects.

• Humerus, Femur, Tibia, Fibula, Radius, Ulna visualised and appear normal echogenic.

• Both orbits seen. Nasal bone - partially ossified

UTERINE ARTERY DOPPLER

IMPRESSION

1. TWIN live intrauterine pregnancy of ~20 weeks gestation
2. Adequate liquor.
3. Fetus A - weight: 339 +/- 49 gms | Fetus B - weight: 373 +/- 54 gms
4. Fetus A & B - Nasal bone partially ossified
5. Single placenta - Anterior
6. Doppler study - Bilateral uterine arteries show no significant abnormality
7. Suggested NIPT

Note: This report is only a professional opinion based on imaging findings and not a diagnosis by itself. It has to be correlated clinically and interpreted along with other investigations.

Fetal Nasal Bone Ossification - Clinical Information

1. Definition

• Creasy & Resnik's Maternal-Fetal Medicine, p. 638

2. Incidence in Aneuploid Fetuses

• Creasy & Resnik's Maternal-Fetal Medicine, p. 638

3. Absent NB as a Screening Marker

• Sensitivity for Down syndrome: 65% (NB alone), rising to 85-93% when combined with NT + serum biochemistry
• False-positive rate: 0.8% with NB alone
• If NB is absent, likelihood of trisomy 21 is increased 87-fold
• Adding NB evaluation to NT + serum screening reduces the false-positive rate from 5.0% to 2.5% while maintaining a 90% detection rate
• Creasy & Resnik's Maternal-Fetal Medicine, p. 649

4. Ultrasound Appearances

• Midsagittal view of fetal profile
• Transducer at 45° angle to line from forehead to chin
• Image magnified so each caliper movement = 0.1 mm change
• When NB is present: three echogenic lines visible (skin line, NB, nasal tip)

5. Factors Affecting NB Ossification (Confounders)

• Gestational age - NB ossification is incomplete at earlier gestations; at CRL 45-54 mm, absent NB seen in 4.7% of euploid fetuses
• Ethnicity - South Asians have higher background rates of hypoplastic/absent NB in euploid fetuses (5%)
• Suboptimal fetal position - incorrect insonation angle can mimic absence
• High maternal BMI or fibroids - poor acoustic windows
• Enlarged nuchal translucency - NB absence more frequent as NT increases

6. Second-Trimester Significance (Relevant to This Report)

7. Clinical Outcome Data (Recent Evidence)

• Incidence of absent/hypoplastic NB: 1.16% of all pregnancies scanned
• Of those with absent/hypoplastic NB: 12.7% had aneuploidy, 8.5% had Down syndrome specifically
• Of those with isolated absent/hypoplastic NB (no other anomalies): lower risk, but still significant
• Conclusion: Isolated AHNB should prompt a comprehensive anomaly scan first, rather than immediate invasive testing. Invasive testing reserved for AHNB + other markers/anomalies.
• Chromosomal microarray (CMA) is recommended over standard karyotype as it detects more chromosomal aberrations.

8. Management Summary for This Case

1. NIPT (cfDNA) is the most appropriate first step - as recommended by Dr. Visagan. This is a highly sensitive non-invasive blood test.
2. If NIPT is negative: no further aneuploidy workup needed for this marker alone (SMFM Grade 1B).
3. If NIPT is positive or inconclusive: genetic counseling and discussion of amniocentesis.
4. The presence of this finding in both twins from a single placenta (monochorionic) or different placentas (dichorionic) may affect interpretation - a genetic counselor should advise.
5. The overall scan is otherwise entirely reassuring (normal cardiac, renal, brain, spine, extremities, Doppler).

Note: A partially ossified NB at 20 weeks is a softer marker than a completely absent NB. Combined with the normal detailed anatomy survey and normal Doppler, the baseline risk for aneuploidy remains relatively low - but NIPT provides definitive non-invasive reassurance.