Obstetrics and Gynaecology chapters
Fetal growth restriction (IUGR) and intrauterine fetal death
How to tell a small but healthy baby from a growth-restricted one, symmetrical and asymmetrical growth restriction, the Doppler changes that guide delivery, and how intrauterine fetal death is confirmed, investigated and managed.
- SGA means estimated weight below the 10th centile; FGR means a fetus that has failed to reach its growth potential. Most SGA babies are healthy and small.
- Asymmetrical FGR (small abdomen, head spared) points to placental insufficiency; symmetrical FGR points to chromosomal problems or infection. There is no treatment: monitor with serial scans and umbilical artery Doppler and deliver at the right time.
- Intrauterine fetal death is confirmed by ultrasound; induce labour with mifepristone then misoprostol, investigate the cause and watch for coagulopathy.
On this page
Overview
A small baby is not always an unwell baby. Two terms must be kept apart:
- Small for gestational age (SGA): estimated fetal weight below the 10th centile for gestation (some units use the 3rd centile for severe smallness). This is a statistical label.
- Fetal growth restriction (FGR, IUGR): the fetus has not reached its genetic growth potential because of a disease process.
Most SGA fetuses are simply constitutionally small (small parents) and healthy. Some FGR fetuses are above the 10th centile yet still failing. FGR raises the risk of stillbirth, birth asphyxia and neonatal death, which is why this chapter pairs it with intrauterine fetal death.
SGA and FGR are not the same. Not every SGA fetus is growth restricted, and not every growth-restricted fetus is SGA.
Fetal growth restriction
Causes
| Group | Examples |
|---|---|
| Fetal: reduced growth potential | Chromosomal anomalies (e.g. trisomy 18), single-gene syndromes, structural anomalies (e.g. renal agenesis), congenital infection (CMV, toxoplasmosis) |
| Maternal | Undernutrition (poverty, eating disorders), low oxygen (high altitude, cyanotic heart disease), smoking, alcohol, cocaine |
| Placental: uteroplacental | Poor trophoblast invasion of spiral arteries (as in pre-eclampsia), chronic hypertension, sickle cell disease, antiphospholipid syndrome, multiple pregnancy |
| Placental: fetoplacental | Single umbilical artery, twin-to-twin transfusion |
Worldwide, the commonest cause of FGR is maternal undernutrition. In developed countries it is placental insufficiency from inadequate trophoblast invasion, the same lesion that causes pre-eclampsia, so the two often occur together.
Smoking raises maternal carboxyhaemoglobin, which cuts the oxygen available to the fetus.
Symmetrical versus asymmetrical FGR
| Feature | Symmetrical | Asymmetrical |
|---|---|---|
| Shape | Head and body both small | Abdomen small, head relatively spared |
| Timing | Early insult | Usually later (third trimester) |
| Typical cause | Chromosomal anomaly, congenital infection, intrinsic fetal problem | Uteroplacental insufficiency (pre-eclampsia, hypertension, smoking) |
| Liquor | Often normal | Often oligohydramnios |
Pathophysiology of asymmetrical FGR
- Placental failure lowers fetal pO2 and raises pCO2.
- The carotid bodies respond: blood is redirected to the brain, heart and adrenals and away from the kidneys, gut, limbs and skin.
- More oxygenated blood bypasses the liver through the ductus venosus, so the liver shrinks and glycogen stores fall.
- Result: relatively large head, small abdominal circumference, thin skin ("brain sparing").
- Less kidney blood flow means less fetal urine, so oligohydramnios.
- Prolonged hypoxia leads to acidaemia and, if the fetus is not delivered, intrauterine death. Contractions in labour reduce placental flow further, so these babies tolerate labour poorly.
In placental insufficiency the abdominal circumference is the measurement that falls behind first, while the head circumference is maintained.
Who is at risk
- Previous FGR baby (it tends to recur).
- Multiple pregnancy.
- Heavy smoking or drug use.
- Hypertension, diabetes (with vascular disease), cyanotic heart disease, antiphospholipid syndrome.
- Symphysis-fundal height (SFH) less than expected.
Detection
- Accurate dating: crown-rump length before about 14 weeks (or head circumference up to 20 weeks).
- SFH measurement at each antenatal visit from 24 weeks. A small or static SFH prompts a scan.
- Serial ultrasound biometry (BPD, HC, AC, femur length) in at-risk women, usually every 4 weeks and never closer than 2 weeks apart, plotted on a centile chart.
In twins, SFH and palpation cannot detect FGR; serial scans are used instead.
Is the small fetus healthy?
After finding SGA:
- Detailed anomaly scan.
- Symmetrical smallness with normal liquor raises suspicion of a genetic cause: offer karyotyping (amniocentesis).
- Asymmetry, oligohydramnios and high-resistance umbilical artery Doppler suggest placental insufficiency.
Doppler and monitoring
| Vessel | Change as FGR worsens | Meaning |
|---|---|---|
| Umbilical artery | Reduced, then absent, then reversed end-diastolic flow | Rising placental resistance; absent or reversed flow means delivery in the near future |
| Middle cerebral artery | Increased diastolic flow | Redistribution to the brain (brain sparing) |
| Fetal aorta | Absent diastolic flow | Fetal acidaemia |
| Ductus venosus | Rising pulsatility; reversed a-wave | Heart failure and acidaemia; death is imminent |
| CTG | Reduced variability, no accelerations, decelerations | Hypoxia |
Management
- There is no effective treatment once FGR from placental failure is established.
- Stop smoking, alcohol and drugs; optimise maternal health.
- Low-dose aspirin may help prevent FGR in high-risk women but does not treat established FGR.
- Surveillance: biometry and liquor at least 2-weekly, umbilical artery Doppler and CTG.
- Timing of delivery balances the risk of stillbirth against the risks of prematurity. Give antenatal corticosteroids if delivery is likely before 34 weeks.
- Absent or reversed umbilical end-diastolic flow, or abnormal venous Doppler or CTG, pushes towards delivery. Caesarean section is common because the fetus may not tolerate labour.
Prognosis and complications
- Fetal and neonatal: stillbirth, intrapartum asphyxia, hypoxic-ischaemic encephalopathy, hypoglycaemia (poor glycogen stores), hypothermia, infection, necrotising enterocolitis, cerebral palsy.
- Long term: most survivors show catch-up growth, but low birthweight is linked with hypertension, ischaemic heart disease, stroke and type 2 diabetes in adult life.
"Small belly, big head, quiet kidneys": asymmetrical FGR has a small AC, a spared head and oligohydramnios.
Intrauterine fetal death (stillbirth)
Definitions
- Stillbirth: a baby born dead after 24 weeks (UK definition used by Ten Teachers). For international comparisons, the WHO uses a 28-week threshold; check which definition your exam or national data use.
- Intrauterine fetal death (IUFD): death of the fetus in the uterus, before labour or during it.
Causes
| Group | Examples |
|---|---|
| Placental | FGR, placental abruption, pre-eclampsia |
| Maternal disease | Diabetes (stillbirth about five times commoner), hypertension, antiphospholipid syndrome, post-term pregnancy (perinatal death at least doubles beyond 42 weeks) |
| Fetal | Congenital anomalies, rhesus disease with hydrops, infection (e.g. parvovirus B19, CMV), monochorionic twin complications |
| Cord and labour | Cord prolapse or accidents, uterine rupture, intrapartum asphyxia |
| Unexplained | A large share despite full work-up |
Presentation and diagnosis
- Reduced or absent fetal movements; fetal heart not heard; uterus smaller than dates in long-standing cases.
- Ultrasound confirms the diagnosis by showing no fetal heart activity.
- Spalding sign (overlapping skull bones on X-ray or scan) is a late sign after some days.
Do not diagnose death on a Doppler handheld device alone; real-time ultrasound is needed.
Investigations (to find the cause and to keep the mother safe)
- FBC and coagulation screen (risk of DIC, especially with abruption or when the dead fetus has been retained for some weeks).
- Kleihauer test (fetomaternal haemorrhage; also needed for anti-D dosing in a rhesus-negative woman).
- Blood glucose or HbA1c, thyroid function, liver and renal tests, antiphospholipid antibodies.
- Infection screen (e.g. parvovirus, CMV, toxoplasma).
- With consent: postmortem, placental histology and fetal karyotype.
After an unexplained stillbirth, offer screening for gestational diabetes in the next pregnancy.
Management
- Break the news with care; offer bereavement support.
- Most women deliver vaginally. Labour is induced with mifepristone (an antiprogesterone) followed by misoprostol, the combination Ten Teachers reserves for intrauterine fetal death.
- Immediate delivery if there is sepsis, abruption, pre-eclampsia or coagulopathy.
- Anti-D if rhesus negative, guided by the Kleihauer result.
- Suppress lactation if the mother wishes (a dopamine agonist such as bromocriptine or cabergoline lowers prolactin).
- Next pregnancy: early booking, consultant care, serial growth scans and planned delivery.
Death of one twin
- Dichorionic: the survivor is usually safe; labour may start, or the pregnancy may continue to term.
- Monochorionic: shared placental vessels let the survivor bleed into the dead twin, causing death or brain injury in up to 30% of co-twins. Maternal DIC is reported but very rare.
Expect: SGA below the 10th centile versus FGR as failure of growth potential; causes of symmetrical (chromosomal, infection) and asymmetrical (placental, pre-eclampsia, hypertension, smoking) FGR; abdominal circumference as the first measurement to fall; oligohydramnios from fetal renal vasoconstriction; absent or reversed umbilical artery end-diastolic flow and reversed ductus venosus a-wave as markers for delivery; aspirin for prevention but not treatment; neonatal hypoglycaemia; ultrasound confirmation of intrauterine death, induction with mifepristone and misoprostol, coagulopathy and the Kleihauer test.
Quick revision
- SGA: below the 10th centile; FGR: failure to reach growth potential; not identical.
- Asymmetrical (head spared, small AC): placental insufficiency; symmetrical: chromosomal or infection.
- Worldwide cause: undernutrition; developed world: poor trophoblast invasion.
- Screen with SFH from 24 weeks; scan every 4 weeks (not less than 2) in at-risk women.
- Umbilical artery AREDF and reversed DV a-wave signal delivery.
- No treatment: stop smoking, steroids before 34 weeks, time delivery well.
- IUFD: confirm on ultrasound; check clotting and Kleihauer; mifepristone then misoprostol.
- Monochorionic co-twin death: up to 30% death or handicap of the survivor.
Written by The House Job from standard references (Obstetrics by Ten Teachers; Gynaecology by Ten Teachers).
FAQ
Why does placental insufficiency spare the fetal head?
The hypoxic fetus diverts blood to the brain, heart and adrenals and away from the liver, gut and kidneys, so the head keeps growing while the abdomen falls behind.
Why is there oligohydramnios in growth restriction?
Vasoconstriction in the fetal kidneys reduces urine production, and fetal urine is the main source of amniotic fluid in later pregnancy.
Can aspirin treat a growth-restricted fetus?
No. Low-dose aspirin started early may lower the risk in high-risk women, but it does not reverse established growth restriction.
Why check clotting after an intrauterine death?
Abruption, and a dead fetus kept in the uterus for weeks, can trigger disseminated intravascular coagulation, so clotting should be checked before delivery or any procedure.