This blogpost is the summary of the recent TOG article published in January 2026. It provides an overview of polyhydramnios / oligohydramnios; various cause; its impact on mother & fetus and management of pregnancy/delivery. This is an important resource for exam questions.
I hope this blog post is helpful. Feel free to leave your feedback in the comments.
To download the original article (free access) : Click here
To Access ALL TOG articles: Click here
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Introduction
- Amniotic fluid volume (AFV) - vital measurement for fetal well-being
- Amniotic fluid - produced by fetus & comprises fetal urine and lung fluid; protects fetus from trauma, allows fetal movements & prevents cord compression
- Pathologies disrupting swallowing ± urine production or flow can directly affect AFV
- AFV correlated with gestational age & size
- Abnormal AFV could be due to placental, fetal or maternal pathology or a combination
Measuring AFV
- Most accurate method to measure AFV - dye dilution test (limited diagnostic value as it requires amniocentesis)
- Clinically AFV measured in 2 ways - Single Deepest Vertical Pocket (SDVP) or Amniotic Fluid Index (AFI)
- SDVP preferred choice for AFV assessment
- AFI measurement increases rates of oligohydramnios diagnosis
Polyhydramnios
- Defined as - increase AFV, SVDP ≥8 cm or AFI ≥24 cm
- No universal agreed classification
- Complicate 1-2% of pregnancies
- Most common cause of mild-to-moderate polyhydramnios - Idiopathic
- Fetal abnormalities account for over 30% of severe polyhydramnios
- Early severe polyhydramnios or in context of FGR or SGA confers poor prognosis
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| Ref: TOG |
- Most common cause of polyhydramnios - Idiopathic (isolated polyhydramnios)
- Accounts for 60-70% of all cases & 1% of pregnancies overall
- Most cases identified in 3rd tri - mild-to-moderate make up 80% overall & 90% of cases at term’
- Evidence for correlation b/w macrosomia & polyhydramnios
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Management of isolated polyhydramnios
- 3 options - amnioreduction, conservative or expedite delivery
- Consider individual risk factors
- GTGs recommend regular fetal biometry scan monitoring for all cases of polyhydramnios
- American Society for Maternal Fetal Medicine recommends amnioreduction only for severe maternal discomfort, dyspnoea or severe polyhydramnios
- Amnioreduction may assist in aiding diagnosis in suspected fetal genetic abnormalities
- Indomethacin - no longer used
Delivery
- Timing of delivery to be individualised - Need more studies
- NICE recommends continuous CTG for all cases of polyhydramnios regardless of severity
- IOL may be offered in moderate isolated polyhydramnios - exact timing decided on individual basis
Management after birth
- No consensus on screening neonates after birth
- Risk of neonatal abnormality with idiopathic polyhydramnios - 1% with mild 2% with moderate 10% with severe
- UK population risk 2019 -Genetic syndromes 6.3 per 10,000 births Chromosomal abnormalities 23.1 per 10,000
- Early-onset polyhydramnios & severe polyhydramnios - linked to high rates of undiagnosed genetic abnormalities
- Rate of genetic abnormalities with isolated polyhydramnios - 4.5% most common genetic abnormality - Bartter syndrome 21% (an autosomal recessive disorder that can be fatal in newborn due to polyuria, hypokalaemia, hyperchloremic metabolic alkalosis and hyperaldosteronism
Oligohydramnios and Anhydramnios
- Oligohyrdamnios - AFV below normal limits AFI ≤5 cm SDVP <2cm
- Anhydramnios - complete absence of amniotic fluid
- Oligohyramnios associated with poor fetal outcomes Higher degree of adverse outcomes if diagnosed in 2nd trimester
- Most common cause of oligohydramnios - Idiopathic
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| Ref: TOG |
Early-onset oligohydramnios
- Nearly always caused by fetal abnormalities or maternal effects
- Associated with significant fetal morbidity
- Most common causes - PPROM, bilateral renal agenesis or severe renal abnormalities (referred to as renal oligohydramnios)
- Potter’s sequence - used to describe severe early-onset oligohydramnios/ anhydramnios
- the sequence comprises of clubbed feet, pulmonary hypoplasia, cranial and skin abnormalities
- It is incompatible with life
- TOP offered
- Methods to reduce fetal morbidity - amnioinfusion, fetal surgical procedures - have varying levels of success Area of ongoing research
Isolated oligohydramnios
- Complicates 0.5 - 5% of pregnancies
- Diagnosis of exclusion
- Take a systematic approach to rule out common causes such as membrane rupture, placental disorders, FGR and fetal infection
Management of pregnancy
- ACOG & NICE recommend increased surveillance and monitoring for signs of deteriorating fetus
- Amnioinfusion in labour may be beneficial - but has methodological limitations not a common practice in UK
Timing of delivery
- Continuous CTG advised due to risk of fetal hypoxia
- IOL associated with increased risk of CS
- Timing of delivery to be individualised
- Need more research in this area
Management after birth
- Higher rate of respiratory distress & low APGAR scores in isolated oligohydramnios
- Delivery should occur in a facility with access to neonatal services
- Increased surveillance advised in subsequent pregnancies (as risk of placental disorders)
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