Invasive procedures, FGR, Twins & Alloimmunization

Amniocentesis · CVS · Fetal blood sampling · Fetal surgery · FGR definitions & diagnosis · Doppler · Biophysical profile · Twin pregnancy · TTTS · Red cell & platelet alloimmunization · Forfar & Arneil's Chapter 11
📌 Core principles: Invasive prenatal diagnosis (CVS, amniocentesis) for genetic/aneuploidy. FGR diagnosed by estimated fetal weight <10th centile + Doppler changes. Twin pregnancies require chorionicity determination. Alloimmunization (Rh, Kell) managed with MCA Doppler and intrauterine transfusion.

📖 Core summary: invasive procedures, FGR, multiple pregnancies & alloimmunization

🧪 Amniocentesis (≥15 wk)
Fetal cells from amniotic fluid. Indications: aneuploidy risk, infection (PCR), lung maturity. Miscarriage risk ~0.1-0.3%. Early amniocentesis (<15 wk) associated with higher complications.
🔬 Chorionic villus sampling (CVS; 11–14 wk)
Placental biopsy for karyotype, DNA. Faster results. Risk ~0.5-1%. Confined placental mosaicism possible → confirm with amniocentesis.
🩸 Fetal blood sampling (cordocentesis)
Umbilical vein puncture (≥18 wk). Indications: rapid karyotype, fetal anemia (MCA Doppler), platelet disorders, infection. Complications: bleeding, bradycardia, miscarriage (~1%).
📏 Fetal growth restriction (FGR)
EFW <10th centile + abnormal Doppler (UA PI >95th centile, AEDV/REDV). Early vs late FGR. Biophysical profile (BPP) assesses well-being. Manage with surveillance, delivery timing.
👶 Twin pregnancy & chorionicity
Monochorionic (MCMA, MCDA) – higher risk TTTS, TAPS, sFGR. Dichorionic – lower risk. TTTS staged I-V; laser photocoagulation for severe stages. Higher‑order multiples → multifetal reduction consideration.
💉 Alloimmunization (red cell & platelet)
Rh(D) prophylaxis prevents most cases. Kell, c, E also cause HDFN. MCA‑PSV for anemia. Intrauterine transfusion (IUT) for hydrops/severe anemia. Platelet alloimmunization (HPA‑1a) → intracranial hemorrhage risk; IVIG + fetal platelet transfusion.
📊 Key definitions: SGA (birth weight <10th centile) not same as FGR (growth restriction). Early FGR (<32 wk) often due to placental insufficiency. Late FGR (>32 wk) milder, lower perinatal morbidity.

🔍 Approach: invasive testing, FGR, twins, alloimmunization

1
High‑risk aneuploidy (combined test >1:250) or abnormal ultrasound marker – Offer CVS (11–14 wk) or amniocentesis (≥15 wk). Provide pre‑test counseling on risks/benefits. Rapid aneuploidy FISH available.
2
Suspected fetal anemia (MCA‑PSV >1.5 MoM) – Indication for cordocentesis (fetal blood sampling) to confirm hemoglobin and perform intrauterine transfusion. Causes: red cell alloimmunization, parvovirus B19, fetomaternal hemorrhage.
3
Fetal growth restriction (EFW <10th centile) – Doppler umbilical artery (UA), middle cerebral artery (MCA), ductus venosus. UA AEDV/REDV → severe placental insufficiency. Biophysical profile (BPP) score <6 → consider delivery.
4
Twin pregnancy: determine chorionicity first trimester – Lambda sign (dichorionic) vs T‑sign (monochorionic). Monochorionic twins require serial surveillance for TTTS (every 2 weeks from 16 weeks).
5
Rh(D)‑negative mother with positive indirect Coombs (antibody screen) – Monitor antibody titer. If anti‑D titer ≥1:16, refer to fetal center. MCA‑PSV surveillance. Hydrops or severe anemia → intrauterine transfusion.

📋 Stepwise management algorithms

1
Invasive procedure protocol – Ultrasound guidance, aseptic technique, post‑procedure anti‑D for Rh‑negative women (after CVS/amnio). Fetal blood sampling: prepare for emergency transfusion.
2
Early FGR (<32 wk) management – Twice weekly umbilical artery Doppler, weekly BPP. Deliver when: AEDV/REDV, BPP <6, or gestational age 34–37 wk with deteriorating status. Antenatal steroids (24–34 wk).
3
Late FGR (≥32 wk) management – Less aggressive; deliver at 37–38 wk if Doppler abnormal or growth plateau. Outpatient surveillance.
4
Twin–twin transfusion syndrome (TTTS) management – Stage I: observation ± amnioreduction. Stage II–IV: fetoscopic laser photocoagulation. Stage V: intrauterine demise of one twin → risk of neurological injury to survivor.
5
Red cell alloimmunization (Rh, Kell) – Serial MCA‑PSV. If ≥1.5 MoM → cordocentesis + intrauterine transfusion (IUT). IUT repeated every 2–4 weeks until delivery (34–37 wk). Administer IVIG for severe cases (Kell).
6
Fetal platelet alloimmunization (HPA‑1a) – Invasive procedures (fetal blood sampling) carry bleeding risk. Maternal IVIG (1 g/kg/week) with or without corticosteroids. Planned C‑section, avoid instrumental delivery.
⚡ Key reminder: Rh(D) alloimmunization is preventable with anti‑D at 28 weeks and after sensitizing events. Kell alloimmunization causes severe fetal anemia despite lower antibody titers.

🧠 Reflex prompts – high‑yield concepts

🤰 12 weeks: high risk on combined test. Which invasive test is appropriate?
Chorionic villus sampling (CVS) provides karyotype by 14 weeks. Risk of miscarriage ~0.5–1%.
🩸 28 weeks, Rh‑negative, antibody screen positive (anti‑D titer 1:32). Next step to assess fetal anemia?
MCA peak systolic velocity (MCA‑PSV) Doppler. >1.5 MoM indicates moderate‑severe anemia → cordocentesis + intrauterine transfusion.
👶 Monochorionic diamniotic twins, 20 weeks: polyhydramnios (recipient), oligohydramnios (donor), donor bladder visible. Quintero stage?
Stage I (donor bladder visible). Stage II: bladder not visible. Monitor closely for progression to higher stages.
📏 Biophysical profile (BPP) components
1) fetal breathing, 2) gross body movements, 3) tone, 4) amniotic fluid volume, 5) reactive NST. Score 8/8 – normal; ≤4/8 – abnormal, consider delivery.
🩺 Fetal growth restriction (FGR) vs SGA
FGR = EFW <10th centile + abnormal umbilical artery Doppler (PI >95th centile, AEDV). SGA = constitutional small without Doppler abnormality.
💉 Intrauterine transfusion (IUT) – most common indication?
Red cell alloimmunization (Rh, Kell, c). Also parvovirus B19‑induced aplastic anemia. Directly transfuse O‑negative blood into umbilical vein.