SGA: infant born with birth weight below 10th centile for its gestational age
Low birth weight (LBW): infant with birth weight <2500 g
Fetal growth restriction: a pathological process has restricted genetic growth potential
Aetiology
Normal (constitutionally) small
50 to 70% of SGA fetuses/infants are constitutionally small, identified by small size at all stages but growth following the centiles
No pathology is present
Contributing factors include ethnicity, sex, and parental height
Placenta mediated growth restriction
Growth is usually normal initially but slows in utero - common cause of FGR
Maternal factors that can result in placental insufficiency include low pre-pregnancy weight, substance abuse, autoimmune disease, renal disease, diabetes and chronic hypertension
Non-placenta mediated growth restriction
Infection e.g. rubella, CMV, toxoplasma
Congenital anomilies e.g. absent kidneys
Chromosomal abnormalities e.g. Down syndrome
Investigations
At booking, and again at 20 weeks gestation, all women should be assessed for risk factors for SGA
Ultrasound is used for the diagnosis and surveillance of an SGA fetus
Ultrasound biometrics, including EFW and AC, are plotted on customised centile charts
Other investigations that may be appropriate include:
Detailed foetal anatomical survery
Uterine artery Doppler
Karyotyping
Screening for infections e.g. congenital cytomegaolovirus, toxoplasmosis, syphilis, malaria
Management
Prevention
Modifiable risk factors should be managed to help prevent SGA, including promoting smoking cessation and optimising maternal disease
150 mg aspirin at night from 12 weeks in women with risk factors for pre-eclampsia or uterine artery notching at anomaly scan
Surveillance
Serial scans for growth with umbilical Doppler and liquor volume as minimum
Schedule individualised according to risk factors
Delivery
Below 3rd centile offer delivery from 37 weeks and aim to have delivered by 37+6 weeks
Between 3rd and 10th centile offer delivery at 39 weeks
If no other obstetric indication and Dopplers normal, aiming for vaginal delivery via induction of labour usually appropriate
Abnormal umbilical Doppler increases chance of fetal distress in labour therefore caesarean section may be offered
Continuous CTG monitoring in labour imperative
If early delivery indicated:
Offer steroids between 24 and 35+6 weeks (sometimes up to 38 weeks)
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