An HG pregnancy refers to a pregnancy complicated by hyperemesis gravidarum, the most severe form of nausea and vomiting during pregnancy. Unlike typical morning sickness, HG involves persistent vomiting so intense that it causes dehydration, weight loss of 5% or more of pre-pregnancy body weight, and disruptions to electrolyte balance. It affects up to 3% of pregnancies and often requires medical treatment, including IV fluids or hospitalization.
How HG Differs From Morning Sickness
Most pregnant women experience some nausea during the first trimester, and for the majority, symptoms resolve by around week 12 to 14. About 10% of women continue to feel nauseous beyond 22 weeks, but the nausea is manageable and doesn’t interfere with eating or hydration in a serious way.
HG is a different condition entirely. Women with HG vomit so frequently that they can’t keep food or fluids down for days at a time. The vomiting leads to measurable changes in the body: elevated markers of dehydration in blood tests, ketones in the urine (a sign the body is burning fat for energy because it’s not getting enough food), and imbalances in key minerals like potassium and chloride. Some women with HG remain symptomatic through the entire pregnancy, all the way to delivery.
Doctors sometimes use a scoring tool called the PUQE (Pregnancy-Unique Quantification of Emesis) to measure severity. It rates nausea, vomiting, and retching on a scale of 3 to 15. Scores of 13 or higher point toward severe nausea consistent with HG, while scores below 7 indicate mild, typical pregnancy nausea.
What Causes It
For decades, the cause of HG was poorly understood, and women were sometimes told it was psychological. A 2023 study published in Nature identified a key biological mechanism. The fetus produces a protein called GDF15 starting early in pregnancy, and levels rise sharply in the first trimester. This protein activates a receptor in the hindbrain that directly triggers nausea, vomiting, and food aversion.
The critical factor isn’t just how much GDF15 the fetus produces. It’s how sensitive the mother’s brain is to it. Women who had lower baseline levels of GDF15 before pregnancy appear to be more vulnerable because their bodies haven’t been “desensitized” to the protein. In animal studies, prior exposure to GDF15 reduced the severity of the response when levels spiked later, much like building a tolerance. This explains why HG can run in families and why some women are affected in every pregnancy while others never experience it.
Recurrence Risk
If you’ve had HG in one pregnancy, there’s a significant chance it will return. Studies report recurrence rates ranging from 15% to 81%, a wide range that reflects differences in how HG is defined and measured across research. The general pattern is clear, though: having HG once makes it more likely in subsequent pregnancies, and many women factor this into their family planning decisions.
Treatment Options
Treatment follows a stepwise approach, starting with milder interventions and escalating if symptoms don’t improve. The first option is vitamin B6, taken alone or combined with an antihistamine called doxylamine. This combination is available as a single tablet and helps many women with moderate symptoms.
When that’s not enough, doctors add stronger anti-nausea medications from the antihistamine or dopamine-blocking families. These are more effective but can cause significant drowsiness. For women who don’t respond to any of these, short courses of a steroid medication may be considered, though this is generally avoided in the first 10 weeks of pregnancy due to potential risks to the developing fetus.
Women who become dehydrated often need IV fluids, typically saline with added potassium, guided by daily blood work to monitor electrolyte levels. One important part of hospital care is thiamine (vitamin B1) supplementation, which is given to any woman admitted with prolonged vomiting or severely reduced food intake. This matters because thiamine deficiency can lead to a dangerous neurological condition if left untreated.
Risks of Untreated HG
When HG goes unmanaged, the consequences extend well beyond discomfort. Severe, prolonged vomiting can deplete thiamine stores, leading to a condition called Wernicke’s encephalopathy, which causes confusion, difficulty with balance, and vision problems. This condition is most commonly associated with chronic alcohol use, but it also occurs in HG. Without timely treatment, it can cause permanent brain damage and is fatal in 10 to 20% of cases that progress to an advanced stage. Severe dehydration can also damage the kidneys and liver.
These extreme outcomes are rare, but they underscore why HG requires genuine medical attention rather than a wait-and-see approach.
Effects on the Baby
One of the biggest concerns for women with HG is whether their baby will be harmed. The reassuring finding from a large Norwegian study of over 71,000 pregnancies is that babies born to mothers with HG had no significant difference in birth weight once maternal weight gain was accounted for. Pregnancies with HG did tend to be about one day shorter on average, a difference with no clinical significance. In short, with proper treatment and nutrition support, HG does not appear to affect fetal growth.
The Mental Health Toll
HG takes a serious psychological toll that is often underestimated. Rates of depression among women with HG reach approximately 50%, and anxiety affects a similar proportion, around 47%. The condition is also linked to post-traumatic stress disorder. Research shows the relationship is dose-dependent: for every additional point on the PUQE severity scale, the odds of developing anxiety increased by 41% and the odds of PTSD increased by 49%.
The mental health impact comes from the relentlessness of the symptoms, the isolation of being unable to function normally, and in many cases, the dismissiveness women encounter from people who equate HG with ordinary morning sickness. Women who have experienced HG frequently describe it as one of the most difficult things they have ever endured, and some choose not to have additional children specifically because of it.