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OG8.{4,8} | Maternal and Fetal Surveillance — SDL Guide (Part 2)

Fetal Surveillance: DFMC, NST and Biophysical Profile

Daily Fetal Movement Counting (DFMC) is the simplest and most universally accessible fetal surveillance tool, requiring no equipment and no specialist — only the woman's own perception of her baby's movements. DFMC is grounded in the physiology of fetal motor activity: a well-oxygenated term fetus performs approximately 30–40 gross body movements per day, punctuated by periodic quiet periods (fetal sleep-wake cycles lasting 20–40 minutes). The critical clinical insight is that fetal motor activity is suppressed early in the course of hypoxia — well before heart rate abnormalities or biometric changes develop — making maternal perception of movement a sensitive early indicator of deteriorating fetal wellbeing. No other fetal surveillance tool operates continuously across 24 hours without monitoring equipment; for this reason, DFMC is the entry point to the surveillance hierarchy and the intervention that most frequently triggers further investigation. The standard method taught in India (Cardiff count-to-10 method) asks the woman to count fetal movements from 9 am daily and record the time taken to reach 10 movements. Normal: 10 movements in ≤2 hours. Reduced fetal movements: fewer than 10 movements in 12 hours, or no movement for 2 consecutive hours. Women should be instructed to:
- Count in a quiet environment (reduces missed movements from distraction)
- Count from 9 am while the fetus is typically most active
- Report any day with <10 movements by noon
- Report any 12-hour period with no perceived movements immediately

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An alternative method (Dawes-Redman): ≥10 movements in a 12-hour observation period. Either method is acceptable; what matters is patient understanding of the threshold and the action to take (seek evaluation immediately).

Non-Stress Test (NST) / Cardiotocography (CTG):
The NST records the fetal heart rate (FHR) pattern using an external Doppler transducer over a 20-minute window. The criterion for a reactive NST (normal, reassuring) is:
- ≥2 accelerations
- Each acceleration ≥15 bpm above the baseline FHR
- Each lasting ≥15 seconds
- Within a 20-minute observation window
If the NST is non-reactive at 20 minutes, extend to 40 minutes (allow for fetal sleep cycle). A NST that remains non-reactive after 40 minutes is non-reactive and warrants further evaluation (BPP, Doppler, or immediate delivery if gestational age permits).

Additional CTG features assessed:
- Baseline FHR: normal 110–160 bpm; tachycardia (>160 bpm) may indicate fever, fetal anaemia, or hypoxia; bradycardia (<110 bpm) is concerning
- Beat-to-beat variability: normal 5–25 bpm; reduced variability (<5 bpm for >40 minutes) is concerning; sinusoidal pattern (smooth sine wave) indicates severe fetal anaemia
- Decelerations: early (physiological, mirror contraction), late (uteroplacental insufficiency), variable (cord compression)

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Biophysical Profile (BPP):
The BPP combines CTG (NST component) with real-time ultrasound assessment of four fetal biophysical activities, scoring each 0 (absent/abnormal) or 2 (present/normal), for a maximum score of 10:

Parameter	Normal (score 2)	Abnormal (score 0)
NST	Reactive (≥2 accelerations in 20 min)	Non-reactive
Fetal breathing movements	≥1 episode ≥30 sec in 30 min	Absent
Gross body movement	≥3 discrete movements in 30 min	≤2 movements
Fetal tone	≥1 active limb extension + return to flexion	Absent or slow return
Amniotic fluid volume (AFV)	≥1 pocket ≥2 cm in 2 perpendicular planes	Largest pocket <2 cm

BPP score interpretation: 8–10 = reassuring (low risk of fetal asphyxia within 1 week; repeat in 1–2 weeks for high-risk); 6 = equivocal (repeat within 24 hours; if score remains 6, deliver at ≥34 weeks); ≤4 = concerning (risk of fetal asphyxia; deliver if gestational age ≥32 weeks, or consider steroids + prolonged monitoring at <32 weeks with senior guidance).

Ultrasound in Pregnancy: Indications and Timing

Ultrasound is the most powerful single investigative tool in obstetrics, offering real-time anatomical and functional assessment of the fetus, placenta, and amniotic fluid. However, ultrasound is an indicated investigation, not a substitute for clinical examination — and the indications at each trimester are distinct in their purpose and clinical significance. The PCPNDT Act 1994 regulates the use of ultrasound in India, prohibiting its use for sex determination; all ultrasound requisitions must carry the PCPNDT-mandated Form F declaration. Understanding the timing and purpose of each ultrasound in pregnancy is essential both for clinical practice and for MBBS examinations — students must be able to state not just which scans are performed but why they are performed at specific gestational ages, what clinical decisions each scan enables, and what findings would trigger an additional non-routine scan. The following section organises this knowledge by trimester, covering both routine (scheduled in all pregnancies) and indicated (triggered by clinical findings) ultrasound examinations.

First-trimester ultrasound (6–13+6 weeks) indications:
- Viability scan (6–8 weeks): confirm intrauterine pregnancy, fetal cardiac activity, rule out ectopic gestation
- Dating scan (10–13+6 weeks): crown-rump length (CRL) is the most accurate method for gestational age determination; accurate to ±3–5 days — superior to LMP in women with irregular cycles or uncertain dates
- Nuchal translucency (NT) measurement (11–13+6 weeks): NT ≥3.5 mm associated with chromosomal anomalies (trisomy 21, 18, 13) and structural defects; done in conjunction with maternal serum biochemistry (free β-hCG and PAPP-A) for first-trimester combined screening
- Multiple pregnancy diagnosis: chorionicity and amnionicity determined most reliably in the first trimester (lambda sign = dichorionic; T-sign = monochorionic)

Second-trimester ultrasound (18–20 weeks) — the Anomaly Scan:
This is the most important routine scan in pregnancy. It assesses:
- Fetal anatomy systematically: cranium (BPD, HC, cerebral ventricles, cerebellum), face (lips, palate), spine, heart (four-chamber view + outflow tracts), abdomen (AC, stomach, anterior abdominal wall), kidneys, limbs
- Placental location: identify placenta praevia (fundal/posterior/anterior/praevia — if covering or within 2 cm of the os, serial scans are needed)
- Amniotic fluid volume (AFI or SDP)
- Cervical length (screen for cervical incompetence/preterm birth risk if indicated)

Routine Pregnancy Ultrasound Schedule

Third-trimester ultrasound (28–36 weeks) — Growth and Wellbeing:
- Growth scan (28–32 weeks): estimated fetal weight (EFW) by biometry (BPD, HC, AC, FL); EFW <10th centile = IUGR; serial scans every 2–4 weeks for confirmed IUGR
- Doppler velocimetry: umbilical artery pulsatility index (PI) in IUGR; absent end-diastolic flow (AEDF) or reversed end-diastolic flow (REDF) indicates severe placental vascular resistance → delivery warranted at ≥34 weeks or with steroids + monitoring at <34 weeks
- Amniotic fluid: oligohydramnios (AFI <5 cm or single deepest pocket <2 cm) warrants delivery decision at ≥34 weeks
- Placenta praevia follow-up at 32 and 36 weeks if low-lying at 20 weeks

Indicated (non-routine) ultrasound:
- SFH discordance ≥3 cm from dates
- Suspected malpresentation after 36 weeks
- Reduced fetal movements (BPP evaluation)
- Vaginal bleeding (localise placenta, assess placental abruption features)
- Suspected multiple pregnancy
- Post-dates pregnancy (≥41 weeks): AFI + BPP for delivery planning

Interpreting Surveillance Findings and Escalation Decisions

Surveillance findings are interpreted on a spectrum from reassuring to immediately concerning, and the clinical response must be proportionate to the degree of compromise indicated. This proportionality is the clinical art of fetal surveillance: over-responding to a reactive NST in a low-risk pregnancy generates unnecessary anxiety and intervention; under-responding to a non-reactive NST with late decelerations in an IUGR pregnancy at 36 weeks risks fetal death. The interpretation framework below provides the structured decision rules for each surveillance tool — but applying these rules requires contextual judgement that incorporates gestational age, the underlying clinical diagnosis, the trend across serial assessments, and the available facility capacity for neonatal care. A BPP of 4/10 at 36 weeks in a well-equipped tertiary centre is managed differently from the same score at a primary health centre with no NICU — the decision to transfer versus immediate delivery must factor in the transport time and risk. This is why fetal surveillance is a cognitive skill, not a lookup table: the framework provides the decision rules, but clinical reasoning determines how they are applied. The most dangerous management error is binary thinking — treating any abnormality as either 'fine' or 'emergency delivery required now' — without understanding the gradation of compromise and the time window for intervention.

NST interpretation framework:
- Reactive NST: low risk of acute fetal compromise; repeat based on indication (weekly for IUGR, bi-weekly for post-dates, as needed for reduced DFMC)
- Non-reactive NST after 40 minutes: intermediate risk; proceed to BPP before deciding management
- Non-reactive NST + late decelerations: high risk of acute uteroplacental insufficiency; urgent BPP and senior assessment; may require immediate delivery at term
- Sinusoidal pattern (smooth, undulating, fixed amplitude): consider fetal anaemia (fetomaternal haemorrhage, Rh alloimmunisation) — urgent assessment

BPP score interpretation:
- 8–10/10: reassuring; repeat surveillance interval as clinically indicated (typically weekly in high-risk pregnancy)
- 6/10: equivocal; if ≥34 weeks, deliver; if <34 weeks, repeat BPP in 24 hours + consider steroids if score remains 6
- 4/10: suspected fetal compromise; deliver if ≥32 weeks; if <32 weeks, corticosteroids + hospitalisation + daily BPP
- 0–2/10: acute fetal compromise; deliver immediately regardless of gestational age (survival at >24 weeks in tertiary care; discuss with family)

Doppler velocimetry interpretation:
- Normal umbilical artery PI for gestational age: placenta functioning adequately
- Elevated PI (above 95th centile): increased placental vascular resistance; increase surveillance frequency
- Absent end-diastolic flow (AEDF): 50% of fetuses will develop fetal compromise within 1 week; hospitalise, daily BPP, corticosteroids if <34 weeks, deliver at 34 weeks
- Reversed end-diastolic flow (REDF): near-certain fetal compromise; deliver immediately

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