NT ANOMALY SCAN normal now IUD at 30 weeks how to send fetid for chromosomal analysis and what tests to be done
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Here is a comprehensive clinical guide for managing IUD (intrauterine death) at 30 weeks with a previously normal NT and anomaly scan, focusing on how to send the fetus for chromosomal analysis and the full investigative workup.
IUD at 30 Weeks — Chromosomal Analysis & Complete Workup
Context
A normal NT scan and normal anomaly scan do NOT exclude chromosomal abnormalities — they screen primarily for structural defects and common aneuploidies. Chromosomal causes (including submicroscopic deletions/duplications) still account for ~6–13% of stillbirths. A systematic workup is essential for determining cause and counselling for future pregnancies.
1. How to Send the Fetus for Chromosomal Analysis
A. Best Sample: Placental / Fetal Tissue
After delivery (or at the time of delivery), collect tissue under sterile conditions:
| Sample Type | How to Collect | Container |
|---|---|---|
| Placental tissue (preferred) | 1–2 cm² from the fetal side of placenta (not maternal side), away from infarcts | Sterile normal saline (NOT formalin) in a sterile container |
| Umbilical cord segment | ~2–3 cm segment | Sterile saline |
| Fetal skin biopsy | From inner thigh or axilla (less exposed) — if fetus already macerated | Sterile saline or cytogenetics transport medium |
| Amniotic fluid | If still in utero (pre-delivery) — amniocentesis | Standard cytogenetics container |
| Cord blood | If fresh and not macerated | EDTA tube (for rapid karyotype) |
Critical: Send to cytogenetics lab within 24–48 hours at room temperature (NOT refrigerated, NOT frozen). Refrigeration kills dividing cells needed for culture.
B. Tests to Request on the Sample
| Test | What it Detects | Notes |
|---|---|---|
| Conventional Karyotype (G-banding) | Numerical anomalies (trisomies, monosomies) + large structural rearrangements | Takes 2–4 weeks; needs viable cells |
| Chromosomal Microarray (CMA) / Array CGH | Submicroscopic deletions & duplications (CNVs) not visible on karyotype | Preferred over karyotype alone — works even on macerated/non-viable tissue (DNA-based) |
| FISH (Fluorescence In Situ Hybridization) | Rapid detection of trisomies 13, 18, 21, X, Y | Result in 24–48 hrs; useful when maceration is present |
| Whole Exome Sequencing (WES) | Monogenic disorders, if structural anomalies suspected | Second-line if CMA normal |
If macerated fetus: Karyotype culture will likely fail. CMA and FISH (on fetal tissue/DNA) are the tests of choice as they do not require live cells.
C. Labelling & Requisition Form
- Mark clearly: "Stillbirth/IUD tissue — chromosomal analysis requested"
- Include: gestational age, clinical history, previous scan reports, reason for referral
- Send simultaneously to pathology (for fetal autopsy) and cytogenetics
2. Complete Investigative Workup After IUD
A. Fetal Investigations
| Investigation | Purpose |
|---|---|
| Chromosomal analysis (as above) | Genetic cause |
| Fetal autopsy | Structural/pathological cause; done by perinatal pathologist |
| Placental histopathology | Placental abruption, infarction, villitis, TTTS changes, hydrops |
| Umbilical cord examination | Cord accidents (true knot, velamentous insertion, cord prolapse) |
| MRI fetal brain (if autopsy declined) | Alternative to autopsy |
| Fetal swab / culture | Rule out infection (Group B Strep, Listeria, CMV) |
| Fetal blood (if available) | Cord blood gas, FBC |
B. Maternal Investigations
Thrombophilia & Coagulopathy Screen
- Antiphospholipid antibody syndrome (APS) — most important in stillbirth:
- Lupus anticoagulant
- Anticardiolipin antibodies (IgG & IgM)
- Anti-β2 glycoprotein I antibodies
- Factor V Leiden mutation
- Prothrombin gene mutation (G20210A)
- Protein C, Protein S, Antithrombin III
Infections
- TORCH screen: Toxoplasma, Rubella IgG/IgM, CMV, HSV
- Parvovirus B19 IgG/IgM
- Syphilis (VDRL/RPR + TPHA)
- Malaria (if endemic area)
- Listeria cultures
Feto-Maternal Hemorrhage
- Kleihauer-Betke test (or flow cytometry) — rule out massive feto-maternal hemorrhage
Diabetes & Metabolic
- HbA1c (undiagnosed/poorly controlled diabetes is a major cause at 30 weeks)
- Random/fasting blood glucose
- Thyroid function tests (TSH, fT4)
Pre-eclampsia / Hypertension Related
- CBC with platelets
- Urine protein/creatinine ratio
- LFTs, RFTs
- Serum uric acid
- LDH
Autoimmune
- ANA, Anti-dsDNA (if APS suspected or autoimmune history)
- Anti-Ro/La antibodies (fetal heart block association)
Others
- Urine drug screen (cocaine, methamphetamine — vasospasm)
- Bile acids (obstetric cholestasis — especially in 3rd trimester)
- Indirect Coombs test (alloimmunisation / Rh disease)
- Blood group and antibody screen
C. Summary Table: Priority Tests
| Priority | Test | Timing |
|---|---|---|
| Immediate | Fetal tissue for CMA/FISH | At delivery — sterile, saline, room temp |
| Immediate | Placenta for histopathology | At delivery — fresh, separate pot, formalin |
| Immediate | Maternal blood: APS screen, Kleihauer-Betke, HbA1c, CBC | At delivery |
| Immediate | Fetal autopsy consent | Before delivery/soon after |
| Within 24h | TORCH, parvovirus, syphilis serology | Maternal blood |
| Within 24h | Thrombophilia screen | Maternal blood |
| Within 24h | TFTs, LFTs, bile acids | Maternal blood |
| 6 weeks later | Repeat APS antibodies | (Must be positive on 2 occasions ≥12 weeks apart to diagnose APS) |
3. Key Points for This Case
- Normal NT + normal anomaly scan does NOT exclude chromosomal microarray-detectable CNVs or late-onset causes (APS, diabetes, cholestasis, cord accident)
- CMA is preferred over conventional karyotype in stillbirth — it works on degraded DNA and has higher diagnostic yield
- If the fetus is macerated, prioritize CMA and FISH over culture-based karyotype
- Autopsy + placental histopathology together identify a cause in ~40–50% of stillbirths
- Even after full workup, ~25–35% of stillbirths remain unexplained ("unexplained stillbirth")
- Counsel parents: results take 2–6 weeks; offer bereavement support and follow-up consultation
For future pregnancy counselling: Once results are available, offer genetic counselling if a chromosomal/genetic cause is found. If workup is negative, recurrence risk counselling should still address modifiable risk factors (obesity, diabetes, APS prophylaxis with aspirin + LMWH if diagnosed).
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