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Acute Fatty Liver of Pregnancy (AFLP): Comprehensive Analysis

Overview

Acute fatty liver of pregnancy (AFLP) is a rare but potentially life-threatening, obstetric emergency unique to human gestation. It is characterized by microvesicular fatty infiltration of hepatocytes leading to varying degrees of hepatic failure, from mild transaminase elevation to fulminant hepatic failure with encephalopathy, coagulopathy, and multiorgan dysfunction. It occurs almost exclusively in the third trimester and constitutes a true obstetric emergency requiring immediate recognition and delivery.
  • Robbins, Cotran & Kumar Pathologic Basis of Disease
  • Sleisenger and Fordtran's Gastrointestinal and Liver Disease

Epidemiology and Risk Factors

The reported incidence varies widely across studies:
  • Approximately 1 in 6,700 third-trimester pregnancies (Sleisenger and Fordtran's)
  • 1 in 7,000 to 1 in 20,000 pregnancies (Goldman-Cecil Medicine; Creasy & Resnik)
  • 5 per 100,000 pregnancies in some population-level estimates (Comprehensive Clinical Nephrology)
A prospective UK study of over 1 million pregnant women identified only 57 confirmed cases using strict Swansea criteria, underscoring both the rarity and the existence of many subclinical, undiagnosed cases.
Established risk factors include:
Risk FactorNotes
PrimigravidasMost common in first-time mothers
Multiple gestations (twins)Significantly overrepresented
Male fetusGreater than expected frequency
Low BMI (<20)Underrepresented nutritional reserves
Fetal fatty acid oxidation disordersEspecially LCHAD deficiency
PreeclampsiaCo-occurs in 21-64% of cases
  • Creasy & Resnik's Maternal-Fetal Medicine, Principles and Practice
  • Comprehensive Clinical Nephrology, 7th Edition

Pathogenesis and Molecular Mechanisms

The pathogenesis of AFLP involves a convergence of fetal metabolism, maternal genetic susceptibility, and placental biology.

The LCHAD Hypothesis

The central molecular mechanism involves defects in mitochondrial fatty acid beta-oxidation, of which long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency is the best characterized:
  1. During normal pregnancy, the fetal-placental unit metabolizes free fatty acids (FFAs) for fetal growth and energy. Placental enzymes catabolize triglycerides into FFAs that are transferred to the fetus.
  2. When the fetus carries autosomal recessive mutations in the HADHA gene (encoding the alpha-subunit of the mitochondrial trifunctional protein, which includes LCHAD activity), the fetus cannot properly oxidize long-chain fatty acids.
  3. Intermediate fatty acid metabolites - particularly 3-hydroxy fatty acids - accumulate in the fetal-placental unit and enter the maternal circulation.
  4. These toxic intermediates and associated reactive oxygen species are taken up by the maternal liver, causing:
    • Microvesicular fatty infiltration of hepatocytes
    • Activation of inflammatory cascades
    • Hepatocellular dysfunction and death
  5. Both mother and father must be heterozygous carriers of the LCHAD mutation. The mother, as a carrier, has reduced hepatic capacity to metabolize long-chain fatty acids - sufficient in the non-pregnant state, but overwhelmed during pregnancy by the additional metabolite load from the affected fetus.
This mechanism elegantly explains why AFLP is described as a rare instance of the fetus causing metabolic disease in the mother, and why the syndrome resolves after delivery.
However, LCHAD deficiency accounts for only approximately 20% of AFLP cases. The remaining 80% have no identified fatty acid oxidation defect - the pathogenesis in these cases likely involves other metabolic or inflammatory factors, possibly related to normal fluctuations in lipid metabolism during pregnancy combined with yet-uncharacterized enzyme defects.
  • Goldman-Cecil Medicine International Edition
  • Robbins, Cotran & Kumar Pathologic Basis of Disease
  • Creasy & Resnik's Maternal-Fetal Medicine

Kidney Injury Mechanisms

Renal disease in AFLP is multifactorial:
  • Tubular FFA accumulation (abnormal fatty acid oxidation)
  • Hemodynamic changes resembling hepatorenal syndrome
  • Thrombotic microangiopathy
  • Coexisting preeclampsia
  • Comprehensive Clinical Nephrology, 7th Edition

Clinical Presentation

AFLP typically presents between 34 and 37 weeks of gestation, though cases as early as 19-20 weeks have been reported. Rarely, onset occurs postpartum.

Prodromal/Early Symptoms (Days to Weeks Before Diagnosis)

  • Nausea and vomiting (most common initial complaint)
  • Fatigue and malaise
  • Anorexia
  • Right upper quadrant or epigastric abdominal pain
  • Pruritus (rare overlap with intrahepatic cholestasis)

Progressive/Established Disease

  • Jaundice - common but not invariable
  • Encephalopathy - confusion, altered consciousness (hepatic encephalopathy)
  • Polydipsia and polyuria - from transient diabetes insipidus (seen in a subset of patients)
  • Vaginal bleeding
  • Decreased fetal movement
  • Premature labor

Complications of Advanced Disease

  • Disseminated intravascular coagulation (DIC)
  • Ascites and pleural effusion
  • Acute pancreatitis
  • Acute kidney injury (AKI) - present in 75% of cases in one series
  • Respiratory failure / ARDS
  • Infection and sepsis
  • Hypoglycemia and hyperammonemia
  • Myocardial infarction (rare)
  • Pulmonary fat emboli (rare)
  • Transient diabetes insipidus
One cohort of 51 women with AFLP demonstrated:
  • 55% required blood and component transfusion
  • 16% developed pancreatitis
  • 14% required ICU admission
  • 75% had acute renal failure (creatinine >1.5 mg/dL)
  • 4% maternal mortality
  • 12% risk of stillbirth
  • 2% required dialysis
  • Creasy & Resnik's Maternal-Fetal Medicine
  • Sleisenger and Fordtran's Gastrointestinal and Liver Disease

Laboratory Findings

AFLP produces a distinctive pattern of multi-system laboratory derangements:
ParameterTypical Finding
Serum aminotransferases (AST/ALT)Moderately elevated (~750 U/L); rarely very high or even normal
BilirubinElevated (hyperbilirubinemia); >0.8 mg/dL
Prothrombin time (PT)Prolonged (>14 sec) - coagulopathy
aPTTProlonged (>34 sec)
Serum fibrinogenDecreased (hypofibrinogenemia)
Antithrombin IIIDepressed
LeukocytosisWBC >11,000/mm³
Serum ammoniaElevated (>47 μmol/L)
Blood glucoseLow (<4 mmol/L / 72 mg/dL) - hypoglycemia
Serum urate/uric acidElevated (>340 μmol/L / 5.7 mg/dL)
Serum creatinine/BUNElevated (renal dysfunction)
PlateletsDecreased (thrombocytopenia)
Fibrin split productsElevated (DIC marker)
Important caveat: Very low or normal AST/ALT can paradoxically indicate severe disease, as it may reflect near-total hepatocyte failure with loss of transaminase-producing capacity. The transaminase level should never be used as the sole marker of disease severity.
  • Creasy & Resnik's Maternal-Fetal Medicine
  • Rosen's Emergency Medicine

Diagnostic Criteria: The Swansea Criteria

The Swansea Criteria (Ch'ng et al., 2002; Knight et al., 2008) are the standard diagnostic tool. Six or more of the following features are required, in the absence of another explanation:
Clinical features:
  • Vomiting
  • Abdominal pain
  • Polydipsia / polyuria
  • Encephalopathy
Laboratory values:
  • Bilirubin >0.8 mg/dL (>14 μmol/L)
  • Hypoglycemia <72 mg/dL (<4 mmol/L)
  • Uric acid >5.7 mg/dL (>340 μmol/L)
  • Leukocytosis >11 × 10⁹/L
  • ALT or AST >42 U/L
  • Ammonia >47 μmol/L
  • Renal impairment: creatinine >1.7 mg/dL (>150 μmol/L)
  • Coagulopathy: PT >14 sec or aPTT >34 sec
Imaging/Histologic:
  • Ascites or bright liver on hepatic ultrasound
  • Microvesicular steatosis on liver biopsy
The Swansea criteria have high sensitivity and are the basis for clinical diagnosis without requiring biopsy in most cases.
  • Sleisenger and Fordtran's Gastrointestinal and Liver Disease, BOX 40.3
  • Comprehensive Clinical Nephrology, 7th Edition, BOX 44.5
  • Rosen's Emergency Medicine, BOX 76.3

Diagnosis: Approach and Investigations

Clinical Diagnosis (Primary Approach)

Diagnosis of AFLP is almost always made on clinical and laboratory grounds - the combination of third-trimester presentation, typical symptoms, and characteristic lab derangements meeting ≥6 Swansea criteria. Histologic confirmation is not required in most cases.
Step-by-step diagnostic approach:
  1. History and clinical assessment - gestational age, symptom timeline, risk factors
  2. Laboratory panel - LFTs, CBC, coagulation studies (PT/aPTT/fibrinogen), metabolic panel (glucose, creatinine, BUN, urate, ammonia, bilirubin)
  3. Apply Swansea criteria - ≥6 criteria = AFLP diagnosis in absence of other explanation
  4. Hepatic imaging (ultrasound) - confirms hepatic steatosis ("bright liver"), evaluates for hepatic hematoma, rupture, or infarction. CT or MRI may add detail.
  5. Liver biopsy - usually unnecessary but may be performed if diagnosis remains uncertain. Transvenous (transjugular) route preferred due to coagulopathy.

Liver Histology (When Performed)

The histologic hallmark is microvesicular steatosis:
  • Small-droplet fatty infiltration most prominent in zone 3 hepatocytes (centrilobular, surrounding central veins)
  • Spares periportal hepatocytes (zone 1)
  • May appear relatively homogeneous on H&E staining - requires special techniques:
    • Oil Red O staining of frozen sections (confirms fat)
    • Electron microscopy (shows mitochondrial abnormalities)
  • Severe cases may show lobular disarray, hepatocyte dropout, reticulin collapse, and portal inflammation (mimicking viral hepatitis)
  • Cholestasis may coexist
  • Robbins, Cotran & Kumar
  • Sleisenger and Fordtran's

Differential Diagnosis

AFLP must be distinguished from several overlapping pregnancy-related and non-pregnancy conditions:

AFLP vs HELLP Syndrome

This is the most clinically challenging distinction, as both present with liver dysfunction and multi-system involvement in the third trimester:
FeatureAFLPHELLP
Nausea/vomiting (new onset)Prominent, often earlyLess prominent
HypoglycemiaYes (synthetic failure)Rare
Coagulopathy/DICMarkedPresent but usually less severe
HyperbilirubinemiaOften markedMay be mild
Creatinine elevationProminentVariable
Uric acidMarkedly elevatedElevated
Polyuria/polydipsiaYesNo
Hemolysis (microangiopathic)Less prominentHallmark
ThrombocytopeniaYesHallmark
AmmoniaElevatedUsually normal
Features favoring AFLP: polydipsia/polyuria, coagulopathy, hypoglycemia, encephalopathy, elevated ammonia. Additional organ involvement (pulmonary, renal) also more suggestive of AFLP.

Other Differential Diagnoses

  • Viral hepatitis (especially hepatitis E in endemic areas - can cause fulminant failure in pregnancy)
  • HSV hepatitis (usually anicteric, high transaminases, typical in third trimester)
  • Intrahepatic cholestasis of pregnancy (pruritus dominant; rare AFLP overlap)
  • Preeclampsia with severe features (may co-exist in up to 64% of AFLP cases)
  • Thrombotic microangiopathy (TTP, aHUS)
  • Biliary obstruction / choledocholithiasis
  • Drug-induced liver injury
  • Reye syndrome (in non-pregnant patients with fatty acid oxidation defects)
  • Goldman-Cecil Medicine
  • Comprehensive Clinical Nephrology, 7th Edition

Management

AFLP is managed as an obstetric emergency. The cornerstone of treatment is prompt delivery combined with aggressive supportive care.

1. Prompt Delivery

  • Immediate delivery is the definitive treatment, regardless of gestational age
  • Route: vaginal delivery preferred if feasible, but cesarean section performed when obstetric indications present or rapid stabilization needed
  • Most patients show clinical improvement within days of delivery
  • The syndrome typically remits after birth with no residual hepatic or renal impairment

2. Supportive Intensive Care

All patients require close monitoring; one-third need ICU-level care:
Glycemic control:
  • Continuous IV glucose infusion to correct and prevent hypoglycemia
  • Regular blood glucose monitoring
Coagulopathy management:
  • Fresh frozen plasma (FFP) for coagulopathy correction
  • Cryoprecipitate for low fibrinogen (<1 g/L)
  • Platelet transfusions for thrombocytopenia with bleeding or prior to procedures
  • Blood and component transfusion (needed in ~55% of cases)
Renal support:
  • Aggressive fluid management
  • Renal replacement therapy (dialysis) if needed (required in ~2% of cases)
Hepatic encephalopathy:
  • Lactulose, management of ammonia
  • Avoid hepatotoxic medications
Fluid and electrolyte management:
  • Aggressive fluid and electrolyte support
  • Management of ascites
Respiratory support:
  • Ventilatory support if ARDS or respiratory failure develops
Glucose and nutrition:
  • IV dextrose; enteral/parenteral nutrition as needed

3. N-Acetylcysteine (NAC)

NAC has been used clinically for AFLP (as in other forms of acute liver failure), but is not uniformly recommended due to insufficient evidence.

4. Liver Transplantation

Rarely, progressive liver failure despite delivery may require liver transplantation, though this is uncommon.
  • Rosen's Emergency Medicine
  • Creasy & Resnik's Maternal-Fetal Medicine
  • Comprehensive Clinical Nephrology, 7th Edition

Prognosis and Outcomes

Maternal Outcomes

  • With prompt diagnosis, delivery, and intensive care: survival approaches nearly 100% in high-resource settings
  • Maternal mortality: reported as 2-4% in recent high-income country series; historically as high as 70-85% before modern intensive care
  • Most women recover completely with no residual hepatic or renal damage
  • Return to baseline creatinine typically takes 8-9 days on average

Perinatal Outcomes

  • Perinatal/neonatal mortality: <7% to ~10% in recent series (though up to 58% in older series, partly attributed to prematurity)
  • Surviving neonates - particularly those with LCHAD deficiency - may develop:
    • Non-ketotic hypoglycemia
    • Obtundation
    • Neuropathy, cardiomyopathy, myopathy (features of LCHAD deficiency)

Recurrence

  • AFLP can recur in subsequent pregnancies, particularly in women with LCHAD deficiency
  • Women, their partners, and affected children should be tested for the G1528C LCHAD mutation in all confirmed cases of AFLP
  • Neonatal screening for fatty acid oxidation disorders (including LCHAD deficiency) after AFLP-affected pregnancies has been advocated, though not yet routine in all centers
  • Sleisenger and Fordtran's Gastrointestinal and Liver Disease
  • Comprehensive Clinical Nephrology, 7th Edition

Postpartum and Long-term Considerations

  • Complete liver and kidney recovery is expected in the vast majority of cases after delivery
  • Genetic counseling for the couple regarding LCHAD mutation status and risk in future pregnancies
  • Neonatal evaluation for LCHAD deficiency and other fatty acid oxidation disorders
  • Subsequent pregnancy planning should involve a multidisciplinary team (hepatology, maternal-fetal medicine, genetics)
  • Per the 2024 AGA Clinical Practice Update (PMID 39140906), management of pregnancy-related liver disease should involve multidisciplinary care, particularly for complex presentations

Summary Table: Key Facts at a Glance

AspectKey Points
Incidence1 in 7,000-20,000 pregnancies
Timing3rd trimester (34-37 weeks); rarely earlier or postpartum
MechanismFetal LCHAD deficiency → accumulation of toxic fatty acid intermediates → maternal hepatotoxicity (in ~20% of cases)
HistologyMicrovesicular steatosis, zone 3 predominance; Oil Red O or EM to confirm
DiagnosisSwansea Criteria (≥6 of 14 features); biopsy rarely needed
Key labs↑ bilirubin, ↑ PT/aPTT, ↓ fibrinogen, ↓ glucose, ↑ creatinine, ↑ urate, ↑ ammonia, leukocytosis
ManagementEmergency delivery + ICU support (glucose, coagulopathy, renal support)
Prognosis~100% maternal survival with prompt care; ~10% perinatal mortality
RecurrencePossible, especially in LCHAD mutation carriers
Genetic testingG1528C LCHAD mutation in mother, father, and neonate
Sources:
  • Sleisenger and Fordtran's Gastrointestinal and Liver Disease, Chapter 40
  • Creasy & Resnik's Maternal-Fetal Medicine: Principles and Practice, Chapters 57 & 64
  • Comprehensive Clinical Nephrology, 7th Edition, Chapter 44
  • Robbins, Cotran & Kumar Pathologic Basis of Disease
  • Goldman-Cecil Medicine International Edition, Chapter 221
  • Rosen's Emergency Medicine: Concepts and Clinical Practice, Chapter 76
  • Kothari S, et al. "AGA Clinical Practice Update on Pregnancy-Related GI and Liver Disease." Gastroenterology 2024 Oct. PMID 39140906
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