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SLCOG Guideline No. 01 — Summary: Investigation & Management of SGA Fetus & Fetal Growth Restriction (March 2023)
1. Definitions
- SGA (Small for Gestational Age): Estimated fetal weight (EFW) or abdominal circumference (AC) below the 10th percentile for gestational age
- FGR (Fetal Growth Restriction): Diagnosed using a combination of fetal size measurements AND Doppler abnormalities (Delphi consensus criteria)
- Early-onset FGR (<32 weeks): EFW/AC <3rd centile, OR umbilical artery absent/reversed end-diastolic velocity (AREDV), OR EFW/AC <10th centile + abnormal UA PI or UtA PI
- Late-onset FGR (≥32 weeks): EFW/AC <3rd centile, OR ≥2 of: EFW/AC <10th centile, centile crossing >2 quartiles, CPR <5th centile or UA PI >95th centile
- 70% of SGA fetuses are constitutionally small; 30% are truly growth restricted
- Placental causes account for 70% of FGR
2. Risk Factors & Early Prediction
Major risk factors (warrant serial ultrasound from 26–28 weeks):
- Age >40, previous SGA/stillbirth, maternal/paternal SGA, chronic hypertension, diabetes with vascular disease, renal impairment, antiphospholipid syndrome, PAPP-A <0.4 MoM, cocaine use, heavy smoking (≥11 cigarettes/day)
Minor risk factors (≥3 = offer uterine artery Doppler at 20–24 weeks):
- Age ≥35, nulliparity, BMI <20 or 25–34.9, IVF, previous pre-eclampsia, short/long pregnancy intervals, low fruit intake
Key screening tools:
- Symphysis-fundal height (SFH): Primary screening in low-risk pregnancies (sensitivity ~58%)
- Routine 3rd-trimester ultrasound at 32–36 weeks recommended — detects SGA at 3× higher rate than clinically indicated scans
- Routine biochemical marker screening is not recommended; PAPP-A <0.415 MoM is a major risk factor
- Use Hadlock 3/4 equation (BPD, HC, AC, FL) in the absence of a validated Sri Lankan formula
- Use Intergrowth-21st charts in the absence of local charts
3. Prevention
| Intervention | Recommendation |
|---|---|
| Smoking/alcohol/drug cessation | Strongly advised |
| Optimal gestational weight gain | Counsel on targets |
| Aspirin 100–150 mg (evening) from <16 weeks | Recommended for high-risk (pre-eclampsia risk or history of placenta-mediated FGR) — reduces FGR risk by ~50% |
| Progesterone / Calcium | Not effective for FGR prevention |
| LMWH | Not recommended for prevention |
4. Further Investigation Once FGR/SGA Diagnosed
- Detailed history (including infection exposure, dating confirmation)
- Detailed anatomy scan — look for structural anomalies, soft markers, signs of fetal infection
- Doppler studies — at minimum umbilical artery (UA); add uterine artery (UtA) and middle cerebral artery (MCA) when available
- Maternal infection screening (CMV, toxoplasmosis; consider rubella, syphilis, Zika, malaria)
- Amniocentesis (karyotype + microarray + PCR) in early-onset severe FGR with structural anomalies or absent signs of placental dysfunction, when results would change management
5. Fetal Monitoring
Multi-parameter surveillance combining:
- CTG/NST (twice weekly minimum; daily if inpatient)
- Computerized CTG (short-term variation <3 ms = deliver)
- Biophysical profile (BPP) — score ≤4 = abnormal
- UA Doppler — primary surveillance tool in SGA/FGR
- MCA Doppler / CPR — especially important in late-onset FGR
- Ductus venosus (DV) Doppler — key in early-onset FGR; absent/reversed a-wave = deliver
6. Delivery Timing (Key Table)
| Condition | Timing of Delivery | Mode |
|---|---|---|
| SGA (3rd–9th centile, normal Doppler) | 37–39 weeks | Induction |
| Uncomplicated FGR (EFW <3rd centile, normal Doppler) | 36–38 weeks | Induction |
| FGR with mild Doppler changes / oligohydramnios | 34–37 weeks | Induction or CS |
| FGR with UA absent end-diastolic velocity (AEDV) | 30–32 weeks | Caesarean section |
| FGR with UA reversed end-diastolic velocity (REDV) | 30–32 weeks | Caesarean section |
| FGR with abnormal ductus venosus | 26–30 weeks | Caesarean section |
Absolute delivery criteria (any gestational age): BPP ≤4, sinusoidal CTG, STV <2.6 ms, severe pre-eclampsia/HELLP/end-organ dysfunction
FGR alone is NOT an indication for caesarean section — induction preferred for late-onset FGR with normal UA Doppler.
7. Medical Interventions in FGR
- Antenatal corticosteroids: Offer at 24+0 to 34+6 weeks (same protocol as non-FGR); enhanced fetal monitoring required in severe FGR with AEDV/REDV
- Magnesium sulphate: For neuroprotection at 24+0 to 29+6 weeks (consider at 30+0–33+6 weeks); dose: 4 g IV bolus over 15 min → 1 g/hr infusion
- Continuous fetal heart rate monitoring during labour; deliver at an institution with appropriate neonatal care
8. Postpartum Counselling & Future Pregnancies
- Growth-restricted infants need closer postnatal follow-up (higher risk of neurodevelopmental and metabolic complications — Barker hypothesis)
- Women with history of FGR are at increased future cardiovascular risk
- Recurrence risk: <25% if previous FGR <10th centile; increases ~6-fold if <5th centile
- Aspirin recommended in subsequent pregnancies if risk factors for pre-eclampsia exist
- LMWH only in antiphospholipid syndrome with aspirin failure
- Routine antiphospholipid antibody screening is not recommended without thromboembolism history
- Surveillance of fetal growth starting at 24–28 weeks in subsequent pregnancies
- Placental histopathology should be sent after delivery — guides recurrence risk counselling (e.g., villitis of unknown aetiology: 10–50% recurrence; chronic histiocytic intervillositis: 70–100%)
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