Intrauterine Growth Restriction (IUGR)

Introduction

Intrauterine growth restriction (IUGR), also known as foetal growth restriction (FGR), is when a foetus does not grow to its genetic potential in the uterus. IUGR is associated with an increased risk of morbidity and mortality.

The terms IUGR and small for gestational age (SGA) are often incorrectly used synonymously.

SGA is defined as any foetus with a foetal abdominal circumference (AC) or estimated foetal weight (EFW) less than the 10^th centile for its gestational age. The foetus may be constitutionally small without being at increased risk of complications.

In contrast, IUGR is a pathological in-utero growth restriction with an increased risk of foetal compromise.^1,2

Aetiology

Asymmetrical IUGR

Asymmetrical IUGR refers to disproportionate growth restriction with a greater decrease in foetal body and limbs compared to head circumference. It is caused by extrinsic factors such as placental insufficiency.

In asymmetrical IUGR, oxygen and nutrients are directed towards vital foetal organs (brain and heart) bypassing other organs (e.g. foetal liver, muscle and fat tissue). This affects the foetus later in gestation.

Symmetrical IUGR

Symmetrical IUGR refers to proportional growth restriction in all parts of the foetus. It is caused by intrinsic factors such as genetic abnormalities and intrauterine infections. This affects the foetus early in gestation.

Risk factors

Risk factors for IUGR can be divided into maternal, uteroplacental and foetal risk factors.

Maternal risk factors

Maternal risk factors include:

• Maternal medical conditions: pre-existing diabetes mellitus, chronic hypertension, gestational hypertension, pre-eclampsia, systemic lupus erythematosus, antiphospholipid syndrome, sickle cell disease, severe anaemia, anorexia nervosa
• Substance use: tobacco, alcohol, cocaine, or narcotics
• Exposure to teratogenic drugs: ACE-inhibitors, warfarin, carbamazepine, phenytoin, cyclophosphamide or valproic acid
• Previous pregnancy with IUGR

Uteroplacental risk factors

Uteroplacental risk factors include:

• Placental insufficiency caused by maternal conditions (e.g. chronic hypertension, diabetes mellitus, sickle cell disease or anorexia nervosa) or pregnancy-related conditions (e.g. Rh- incompatibility or pre-eclampsia)
• Placenta praevia or placental abruption
• Umbilical artery thrombosis or infarction
• Uterine abnormalities (e.g. fibroids)
• Multiple gestation

Foetal risk factors

Foetal risk factors include:

• Congenital/early intrauterine infections: toxoplasmosis, rubella, cytomegalovirus infection, varicella, tuberculosis, herpes infections, HIV infection, syphilis, or malaria
• Genetic abnormalities: aneuploidy
• Congenital anomalies: tracheoesophageal fistula, cyanotic congenital heart disease, gastroschisis, or neural tube defects

Clinical features

History

A thorough obstetric history is crucial to identify any risk factors for IUGR.

Signs and symptoms will depend on the underlying cause of IUGR. For example, a patient may present with abdominal pain due to placental abruption or headache, visual disturbances, and epigastric pain due to pre-eclampsia.

Clinical examination

Typical clinical findings in suspected IUGR include:³

• Symphysial-fundal height (SFH) is decreased compared to gestational age (at least 3cm less than gestational age in weeks)
• Foetus is small for gestational age
• Foetal movements are reduced or absent

Investigations

Bedside investigations

Relevant bedside investigations include:

• Maternal vital signs (basic observations): blood pressure, heart rate, respiratory rate, oxygen saturation, temperature
• Urine dipstick
• Cardiotocography (CTG): to assess foetal compromise. It may show late decelerations of the foetal heart rate and foetal bradycardia in IUGR.¹

Laboratory investigations

Appropriate laboratory investigations are performed based on the suspected underlying cause of IUGR.

For example, oral glucose tolerance test (OGTT) for gestational diabetes mellitus and serological screening for congenital intrauterine infections.

Imaging

Relevant imaging investigations include:^1,4

• Serial ultrasound scans: to assess foetal biometry and estimated foetal weight which are plotted on a customised growth chart. Ultrasound also provides detailed information on foetal anatomy, placental morphology, and amniotic fluid volume. Findings may include decreased foetal growth with foetal weight below the 10^th centile of a given gestational age, small placenta and oligohydramnios.
• Umbilical artery Doppler (UA Doppler): shows abnormalities such as reduced or reversed diastolic flow.
• Biophysical profile (BPP): is a non-invasive test that integrates different parameters to assess foetal well-being. Typical findings in IUGR include amniotic fluid measurement of <5 (oligohydramnios), absent foetal breathing movements, and decreased foetal movements and tone. A BPP score of ≤ 4 indicates the need for delivery.

Diagnosis

The diagnosis of IUGR is made from serial ultrasound scans and umbilical artery Doppler (UA Doppler) showing estimated foetal weight <10th centile, oligohydramnios, abnormal UA Doppler and/or poor interval growth velocity and/or EFW <3rd centile.¹

Management

Conservative management

Conservative management involves optimising modifiable risk factors during pregnancy, including smoking cessation, drug counselling, and healthy diet and exercise.

Medical management

It is important to treat any underlying maternal condition (e.g. treatment of gestational diabetes mellitus or pre-eclampsia) and medically optimise any co-morbidities before and during pregnancy.

Maternal vital signs should be closely monitored alongside foetal status.

Surgical management/delivery

Delivery should be performed if there are signs indicating non-reassuring foetal status or maternal compromise.

The optimal timing and mode of delivery (either induction of labour or caesarean section) for IUGR require careful consideration of both maternal and foetal risks of continued intrauterine existence, premature delivery, labour and caesarean section.

The goal is to delay delivery and prolong intrauterine life to gain foetal maturity, improve survival and reduce the risks of morbidity and mortality.¹

Induction of labour is offered to all patients. However, a caesarean section is strongly recommended when there are signs of foetal compromise such as absent and reduced end-diastolic flow (AREDF) in the umbilical artery.¹  

Magnesium sulphate should be administered in gestations less than 33⁺⁶ weeks for foetal neural protection, where delivery is contemplated.⁵

Prenatal corticosteroids should be administered to women with IUGR foetus between 24⁺⁰ to 33⁺⁶ weeks gestation when preterm birth is imminent. Corticosteroids should be discussed with women undergoing a planned caesarean section up until 38⁺⁰ weeks.^1,5

When EFW is <10th centile and UA Doppler is normal, delivery can be delayed until at least 37 weeks, and even until 38-39 weeks of gestation in some cases.^1,6

Complications

Complications of IUGR include:^1,3,4

• Preterm labour and delivery
• Stillbirth
• Perinatal asphyxia
• Necrotising enterocolitis
• Cognitive delay and behavioural issues
• Adult-onset diseases (e.g. diabetes mellitus, obesity, coronary artery disease, hypertension)
• Motor and neurological disabilities
• Intrauterine/neonatal death

Key points

• IUGR occurs when a foetus does not grow to its normal gestational size because of underlying pathology
• There are maternal, foetal and uteroplacental factors that increase the risk of IUGR
• Serial ultrasound scans and UA Doppler are the key diagnostic investigations
• Management includes treating the underlying maternal condition, and delivery of the baby if there are signs of maternal or foetal compromise
• Prevention strategies include assessing the underlying causes, smoking cessation and low dose aspirin
• Complications of IUGR can include intrauterine death, preterm labour and delivery, and neurodevelopmental issues

Reviewer

Dr Karim Botros

RCSI Honorary Clinical Lecturer
Senior Registrar in Obstetrics & Gynaecology
University Hospital Waterford, Waterford, Ireland

Editor

Dr Chris Jefferies

References

1. Institute of Obstetricians & Gynaecologists Royal College of Physicians of Ireland. Fetal Growth Restriction – Recognition, Diagnosis & Management. Published in 2014. Available from: [LINK]
2. Patient.info Professional References. Intrauterine Growth Restriction. Published in 2016. Available from: [LINK]
3. UpToDate. Fetal growth restriction: Screening and Diagnosis. Published in 2021. Available from: [LINK]
4. AMBOSS. Intrauterine Growth Restriction. Published in 2021. 
5. National Institute for Health and Care Excellence. Preterm Labour and Birth. Published in 2015. Available from: [LINK]
6. Royal College of Obstetricians & Gynaecologists. The Investigation and Management of the Small-for-Gestational-Age Fetus. Published in 2013. Available from: [LINK]
7. The American College of Obstetricians and Gynecologists. Fetal Growth Restriction. Published in 2019. Available from: [LINK]