What is Hyperemesis Gravidarum?
Hyperemesis gravidarum (HG) is a severe form of pregnancy-related nausea and vomiting characterized by severe symptoms (either severe nausea OR severe vomiting), beginning before 16 weeks of gestation, inability to eat and drink normally, and strongly limiting daily activities, with signs of dehydration contributing to the diagnosis 1.
Definition and Diagnostic Criteria
The internationally accepted "Windsor definition" represents a modern, patient-centered approach to diagnosing HG 1. This definition deliberately shifts away from older criteria that relied heavily on objective measures like specific weight loss percentages or electrolyte abnormalities, recognizing that these may miss patients suffering significantly from the condition.
Key Diagnostic Features:
- Timing: Onset before 16 weeks of gestation
- Severity: Either nausea OR vomiting must be severe (not necessarily both)
- Functional impact: Inability to maintain normal eating and drinking patterns
- Daily life: Marked limitation of activities of daily living
- Physical signs: Dehydration signs are contributory but not mandatory
Important caveat: Ketonuria should NOT be used to assess severity or guide treatment decisions, as it is not associated with HG severity or dehydration status in pregnancy 1. This is a Grade A recommendation based on high-quality evidence.
Epidemiology and Clinical Context
HG affects approximately 0.3-3.6% of pregnancies 1, making it the most common reason for hospital admission in early pregnancy 2. While general nausea and vomiting of pregnancy (NVP) affects up to 90% of pregnant women and typically resolves by 20 weeks in 90% of cases 1, HG represents the severe end of this spectrum.
The condition has high recurrence rates in subsequent pregnancies, ranging from 15.2% to 89% depending on diagnostic criteria used 1.
Clinical Assessment Tools
Two validated scoring systems help objectively quantify severity 1:
- PUQE (Pregnancy-Unique Quantification of Emesis): Valid for mild to moderate NVP and assessing treatment response, but NOT valid for severe NVP or HG
- HELP (HyperEmesis Level Prediction): Specifically designed for severe NVP and HG, can track treatment response over time in these severe cases
Impact on Quality of Life and Morbidity
HG profoundly affects quality of life, with women experiencing HG being three to six times more likely than those with simple NVP to have low quality of life 1. The constant nausea is the single most debilitating symptom.
Serious Complications Include:
- Wernicke encephalopathy: A potentially fatal emergency from thiamine deficiency, occurring in 5% maternal mortality rate when it develops, with chronic cognitive disorders in 65.4% and pregnancy loss in 50% of cases 1
- Venous thromboembolism: 4.4-fold increased risk during active vomiting periods 1
- Fetal growth restriction: Increased risk with low pregnancy weight gain (<7 kg) and symptoms persisting into late second/third trimester 1
- Preterm birth and low birth weight: Associated with inadequate weight gain 1
Psychosocial Burden:
The condition causes isolation, financial stress from work absence, relationship strain, lack of understanding from others, and loss of positive pregnancy experience 1. Many women report that healthcare providers are reluctant to provide adequate treatment, compounding their suffering.
Pathophysiology
While the exact cause remains incompletely understood 3, emerging evidence points to Growth Differentiation Factor 15 (GDF15) and metabolic signaling pathways, moving beyond traditional hormonal theories 4. The condition may involve genetic susceptibility combined with metabolic factors.
Clinical Significance
The annual cost to healthcare systems is substantial—estimated at £62 million in the UK NHS alone 1, 5—due to hospitalizations (typically 3-4 days), GP visits, and ambulance services. Nearly one-third of women require readmission during the same pregnancy 1.
The condition requires prompt recognition and aggressive treatment to prevent serious maternal morbidity and mortality, particularly Wernicke encephalopathy, which is preventable with appropriate thiamine supplementation 1.