Polyhydramnios

Question 1

Polyhydramnios - definition

Answer 1

• Excess amniotic fluid volume in pregnancy
• DVP/SDP >/= 8cm
• AFI >/= 24cm (SMFM definition, older texts may use >/= 25cm)

Question 2

Polyhydramnios - severity:

Answer 2

Using DVP:
- Mild: 8-11.9cm
- Moderate: 12-15.9cm
- Severe >/= 16cm

AFI:
- Mild: 24 to <30cm
- Moderate: 30 to <35cm
- Severe: > 35cm

Question 3

Polyhydramnios - physiology

Answer 3

• Reflects a balance between fetal urine/ lung fluid production and fetal swallowing/ intramembranous absorption.
• Clinically, poly often implies either:
  1. Increased fluid production, or
  2. Reduced fetal swallowing/ clearance

Question 4

Polyhydramnios - causes:

Answer 4

Idiopathic (most mild cases)

Maternal:
- Diabetes mellitus/ gestational diabetes

Fetal structural/ genetic:
(conditions that impair swallowing or are associated with increased fluid):
- GI obstruction (e.g. oesophageal/ duodenal atresia)
- Neurological anomalies
- Other major structural anomalies
- Genetic syndromes /chromosomal abnormalities

Other causes:
- Multiple pregnancy
- Congenital infection
- Alloimmunisation

Question 5

Risks of polyhydramnios - maternal/intrapartum + fetal risks:

Answer 5

Maternal / intrapartum:
- Maternal discomfort
- Dyspnoea
- Preterm contractions / preterm labour
- PROM
- Malpresentation
- Umbilical cord prolapse
- Placental abruption
- Increased CS / operative birth
- Postpartum haemorrhage from uterine overdistension

Fetal risks:
- Risk of anomaly / genetic disorder
- Possible macrosomia (especially with diabetes)
- Prematurity if severe / symptomatic / underlying pathology present

Question 6

Polyhydramnios - assessement

Answer 6

1) Confirm diagnosis
- DVP or AFI
- Severity
- Fetal presentation
- Placental location
- EFW

2) Look for cause
- Screen for diabetes if not already done, or repeat if clinically indicated
- Detailed USS for: fetal structural anomalies, swallowing/GI abnormalities, growth (incl macrosomia or sometimes growth restriction)
- Consider: infection testing, group and antibodies (alloimmunisation), genetic testing or amniocentesis if anomalies seen

3) Assess sx and severity
- Breathlessness
- Abdo pain/tightness
- Contractions
- RFMs
- Sudden abdominal enlargement

Question 7

Polyhydramnios - management

Answer 7

Depends on:
- Severity, sx, gestation, underlying cause

Mild idiopathic:
- Usually no specific rx
- Often managed w observation and routine/individualised FU
- SMFM: antenatal fetal surveillance is not required for the sole indication of mild idiopathic poly

Rx the cause:
- If due to diabetes, optimise glycaemic control
- If due to anomaly, infection, alloimmunisation, or multiple pregnancy, manage that underlying condition

Severe or symptomatic poly:
- If severe maternal discomfort or dyspnoea: amnioreduction can be considered
- Indomethacin should not be used solely to reduce fluid in poly

Question 8

Timing of birth for polyhydramnios:

Answer 8

• Mild idiopathic: allow labour to occur spontaneously at term
• If IOL is planned, do not induce before 39+0 without another indication
• Mode of birth: based on usual obstetric indications
• Severe poly: delivery should occur in a tertiary centre, because of the higher chance of significant fetal anomaly and potential intrapartum complications

Question 9

Intrapartum considerations for polyhydramnios:

Answer 9

• Confirm presentation (higher risk malpresentation)
• Be alert for:
  > cord prolapse after ROM
  > abruption
  > labour dystocia
  > PPH after birth due to uterine overdistension
• Moderate/severe cases are best managed in a setting where rapid obstetric intervention is available

Question 10

“Exam-ready answer” for how to manage poly

Answer 10

• Confirm by USS (DVP >/= 8cm or AFI >/= 24cm)
• Grade severity
• Look for a cause: especially diabetes and fetal anomaly
• Do a detailed scan and consider infection/ antibody/ genetic work-up if indicated
• Mild idiopathic causes usually need no treatment and can be observed
• Severe/symptomatic causes may need amnioreduction
• Do not use indomethacin solely to reduce fluid
• Do not induce mild idiopathic poly before 39w without other indication (or ideally at all if otherwise low risk)
• Plan birth based on usual obstetric indications, but severe cases should deliver in a tertiary centre

Question 11

What is the most common cause of polyhydramnios overall?

Answer 11

• Idiopathic (esp if mild - most)

Question 12

Indications for indomethacin?

Answer 12

1) Short-term tocolysis in PTL <32 weeks (avoid after this because of risk of premature closure of ductus arteriosus)

2) Sometimes symptomatic uterine irritability with severe polyhydramnios <32 weeks (NOT just to reduce liquor)

3) Degenerating fibroid pain in pregnancy (short course)

Do NOT use for:
- Tocolysis > 32w
- The sole rx for poly to reduce fluid volume