IUGR Risk Factors
All pregnant women should be systematically assessed for risk factors for fetal growth restriction at booking (by 14 weeks) to identify those requiring increased surveillance, with risk assessment updated throughout pregnancy. 1
Maternal Risk Factors
Placental and Vascular Conditions
The most critical risk factors involve suboptimal placental perfusion, which accounts for 25-30% of all FGR cases 2:
- Placenta abruption (OR 2.06) - strongest placental risk factor 3
- Placenta previa (OR 1.19) 3
- Hypertensive disorders of pregnancy - significant risk factor, particularly in primigravidas (OR 10.1 when combined with primiparity) 4, 5
- Pre-eclampsia risk - these women should receive aspirin 150 mg once daily at night from 12+0 to 36+0 weeks to reduce SGA/FGR risk 1
Modifiable Lifestyle Factors
Smoking is a critical modifiable risk factor that must be addressed aggressively 1, 6:
- Both active and passive tobacco exposure significantly increase IUGR risk
- Carbon monoxide testing should be used to identify smokers
- In-house treatment from trained tobacco dependence advisors should be offered using an opt-out referral process 1
Additional modifiable factors include 6:
- Maternal stress levels during pregnancy
- Excessive working hours and time spent standing
- Poor gestational weight gain (OR 3.0) 5
Maternal Medical Conditions
- Anemia - 29.6% of IUGR cases 4
- Epilepsy in pregnancy (OR 1.28) 3
- Hepatitis C virus infection (OR 1.53) 3
- Celiac disease (OR 2.48) - weaker evidence 3
Demographic and Constitutional Factors
- Younger maternal age (OR 0.9 per year increase) - particularly age 21-25 years shows maximum IUGR cases 4, 5
- Low socioeconomic status - leads to nutritional deficiencies and inadequate growth environment 4, 6
- Maternal height and birth weight - shorter mothers and those with lower birth weights themselves 6
- Primigravida status - especially when combined with pregnancy-induced hypertension 5
Obstetric History
Fetal and Genetic Factors
Chromosomal disorders and congenital malformations account for approximately 20% of FGR cases 2:
- Detailed obstetrical ultrasound examination should be performed with early-onset FGR (<32 weeks) 2
- Offer fetal diagnostic testing with chromosomal microarray analysis when FGR is detected with fetal malformation or polyhydramnios, or when unexplained isolated FGR is diagnosed <32 weeks 2
Risk Stratification Approach
The most recent guideline 1 stratifies women into risk categories:
High-risk women require:
- Uterine artery Dopplers between 18+0 and 23+6 weeks
- If normal uterine artery Doppler and normal fetal biometry at midtrimester scan: serial ultrasounds starting at 32 weeks
- If abnormal uterine artery Doppler (mean PI >95th centile): ultrasounds starting at 24+0-28+6 weeks
Moderate-risk women require:
- Serial ultrasound assessment starting at 32+0 weeks
- Four-week scan intervals until birth for most women
Low-risk women require:
- Serial symphysis fundal height measurement at each antenatal appointment after 24+0 weeks (no more frequently than every 2 weeks)
- First measurement by 28+6 weeks
Critical Pitfall
Do not confuse SGA with IUGR - they are distinct conditions. IUGR requires additional abnormalities beyond just size below the 10th percentile (pathological Doppler, oligohydramnios, lack of interval growth, or estimated weight below 3rd percentile) and carries greater perinatal morbidity, mortality, and long-term disease risk 7. The term "intrauterine growth restriction" should be used instead of "IUGR" in clinical practice 2.