Gestational context
20 to 40 weeks
booking
12w
anatomy
24w
28w
36w
term
Maternal
- BP and urine
- growth restriction and pre-eclampsia share a placenta
- Fundal height plotted, not remembered
- Fundal height plotted, not remembered
- Smoking, substances, medications reviewed
- Smoking, substances, medications reviewed
- Aspirin from the first trimester if at risk next time
- Aspirin from the first trimester if at risk next time
Fetal
- Estimated weight and abdominal circumference centiles
- Estimated weight and abdominal circumference centiles
- Umbilical artery Doppler
- absent or reversed end-diastolic flow changes the plan
- Amniotic fluid
- oligohydramnios adds concern
- Monitoring cadence and delivery timing by Doppler and gestation
- Monitoring cadence and delivery timing by Doppler and gestation
Detection
- Fundal height from 20 weeks: roughly the gestational week in centimetres, plus or minus 2 to 3. A measurement 3 cm or more below expected, or a plateau, prompts ultrasound. Sensitivity is poor in obesity, fibroids and polyhydramnios.
- Ultrasound biometry: head circumference, abdominal circumference, femur length, estimated fetal weight plotted on a chart. Abdominal circumference is the most sensitive single measurement for growth restriction.
- Small for gestational age: estimated weight or abdominal circumference under the 10th centile. Growth restriction: under the 3rd centile, or under the 10th with abnormal Doppler or a falling trajectory.
Causes
| Placental (late, asymmetric) | Fetal (early, symmetric) | Maternal |
|---|---|---|
| Preeclampsia and hypertensive disease | Aneuploidy and genetic syndromes | Smoking, substance use |
| Placental infarction, abnormal cord insertion | Congenital infection (CMV, toxoplasmosis) | Chronic disease: renal, cardiac, autoimmune |
| Multiple pregnancy | Structural anomalies | Undernutrition, low pre-pregnancy weight |
Surveillance and delivery
- Umbilical artery Doppler is the test that separates a small healthy fetus from a compromised one. Normal: reassuring, repeat every 2 weeks with growth. Raised resistance: closer surveillance. Absent or reversed end-diastolic flow: a compromised placenta; admission, steroids, and delivery planning by gestation.
- Additional tools in early growth restriction: ductus venosus Doppler, biophysical profile, computerised CTG where available.
- Timing: absent end-diastolic flow is usually delivered by 34 weeks and reversed flow by 32 (with steroids), earlier for other concerns; SGA with normal Doppler is delivered at term.
- Mode: a growth-restricted fetus tolerates labour poorly; abnormal Doppler often means caesarean. Continuous monitoring in labour.
- Large for dates: macrosomia (over 4000 or 4500 g) raises shoulder dystocia risk; diabetes and post-dates are the common contexts. The estimate has a 10 to 15 percent error; that is part of the conversation.
On the modelPlacentaUmbilical cordFundus and cornua