I suffered from Hyperemesis Gravidarum (HG) during my pregnancy. I vomited for 30 weeks straight and felt nauseous every single day until I gave birth. It wasn’t just morning sickness—it was a relentless, all-consuming illness that completely took over my life.
HG took a major toll on my mental health. I felt isolated, helpless, and at times, I wondered how I would make it through. Even now, thinking about my pregnancy brings up a lot of emotions—the trauma of it lingers. I wish I had more answers when I was going through it, which is why I’m passionate about understanding the root causes of HG and what we can do to support women facing this debilitating condition.
While HG is still widely misunderstood, emerging research is shedding light on potential triggers—from hormonal imbalances and histamine intolerance to thyroid dysfunction and iodine levels. In this post, I’ll explore what we currently know about HG, its possible root causes, and what might help.
What Causes Hyperemesis Gravidarum? A Multifactorial Condition
Despite how severe HG is, there is still no clear-cut answer as to what causes it. However, research suggests that hormonal fluctuations, genetic factors, gut health, and immune dysfunction may all contribute.
1. Hormonal Imbalance & hCG Sensitivity
One of the strongest links to HG is elevated human chorionic gonadotropin (hCG)—the pregnancy hormone that surges in early pregnancy.
Higher hCG levels are associated with worse nausea, which is why HG is more common in twin pregnancies.
Some women may have a heightened sensitivity to hCG, making them more prone to extreme nausea.
Estrogen & progesterone fluctuations may also slow digestion, making symptoms worse.
2. Genetics & Family History
Women with a family history of HG are much more likely to experience it.
Genetic mutations (GDF15 & IGFBP7), which affect nausea regulation, may play a role.
HG is more common in identical twins, further supporting a genetic link.
3. Gut Health & Helicobacter Pylori Infection
H. pylori, a bacteria linked to stomach ulcers, is found at higher rates in women with HG.
Poor gut motility (slow digestion) may also play a role in prolonged nausea and vomiting.
4. Immune System Dysregulation & Mast Cell Activation
Some women with HG may have immune system overactivation, leading to excess histamine release, which triggers nausea.
Women with autoimmune conditions, histamine intolerance, or Mast Cell Activation Syndrome (MCAS) may be more prone to severe nausea.
5. Nutrient Deficiencies & Metabolic Factors
Low vitamin B6 & B1 (thiamine) can worsen nausea.
Thyroid dysfunction (hypothyroidism or hyperthyroidism) is common in women with HG.
The Histamine Connection: Why Are Antihistamines Used for HG?
One of the most common treatments for HG is antihistamines like Diclectin (doxylamine + B6), Unisom, or Benadryl. But why?
Histamine is a neurotransmitter that plays a role in nausea. It binds to H1 receptors in the brain’s vomiting center, which can trigger intense nausea.
How Histamine May Worsen HG:
Estrogen increases histamine levels (by slowing its breakdown).
Low diamine oxidase (DAO) enzyme levels make it harder to clear histamine.
Mast cell activation releases histamine, worsening nausea and inflammation.
Why Antihistamines Help:
They block histamine’s effect on the vomiting center.
They stabilize mast cells, preventing excess histamine release.
They reduce inflammation, calming nausea signals.
Dietary Tip: People with histamine intolerance may feel better by avoiding high-histamine foods, such as aged cheese, fermented foods, processed meats, and alcohol. Although we want to get to the root cause of histamine intolerance, it can be helpful to avoid high-histamine foods while you investigate and heal the root causes. You can check out a post I wrote on histamine intolerance, the root causes, and how to heal here.
The Role of Iodine & Thyroid Function in HG
Thyroid function is closely linked to nausea and metabolism, and iodine is essential for thyroid health. However, both too little and too much iodine may contribute to HG.
1. Iodine Deficiency & HG Risk
Low iodine can cause hypothyroidism, which may worsen nausea.
Thyroid hormones regulate digestion, so sluggish thyroid function can slow gastric emptying and increase nausea.
Low Iodine Can Contribute to High Estrogen and histamine. Iodine plays a critical role in thyroid function and hormone balance. However, low iodine levels can contribute to estrogen dominance, which may worsen HG symptoms.
Iodine is necessary for proper estrogen metabolism. It helps regulate enzymes that break down estrogen into less potent forms.
Low iodine = inefficient estrogen clearance. If the body doesn’t metabolize estrogen properly, estrogen levels can rise, leading to higher histamine levels and worsening nausea.
Estrogen stimulates hCG production. Since hCG is one of the main triggers for HG, excess estrogen may amplify the body’s response to hCG, worsening nausea and vomiting.
Key Takeaway: If iodine levels are too low, the body may struggle to clear estrogen effectively, leading to higher circulating estrogen, histamine, and increased hCG sensitivity, all of which can contribute to severe nausea.
2. Excess Iodine & Thyroid Dysfunction
Too much iodine can cause transient hyperthyroidism, worsening nausea.
Some HG patients experience hCG-induced hyperthyroidism, which may be aggravated by high iodine intake.
Optimizing Iodine for Pregnancy:
Aim for 220 mcg/day (the RDA for pregnancy).
Get iodine from whole foods like eggs, seafood, and dairy.
Avoid megadoses of iodine supplements, which may disrupt thyroid function.
So, What’s the Root Cause of HG?
There is no single cause of HG, but the most likely contributors are:
hCG sensitivity & hormonal fluctuations
Genetic predisposition
Histamine intolerance & immune activation
Gut dysbiosis & slow digestion
Thyroid dysfunction & iodine imbalances
This is why no single treatment works for everyone—HG is not one condition but a spectrum of factors affecting women differently.
How to Support the Body During HG
If you or someone you love is struggling with HG, here are some potential supportive strategies that the doctor may be missing:
Check thyroid function & iodine levels (TSH, Free T3, Free T4, Reverse T3, TPO and TG antibodies, and urinary iodine).
Test for H. pylori.
Try a lower-histamine diet. Although you will not be able to fully address all of the root causes of histamine intolerance while pregnant (mainly due to supplement restrictions during pregnancy), you can try avoiding high-histamine foods if histamine sensitivity is suspected.
Final Thoughts: Breaking the Silence on HG
Hyperemesis Gravidarum isn’t just “bad morning sickness”—it is a severe, life-altering condition that deserves more research, better treatment, and greater awareness.
For me, HG was the hardest experience of my life—both physically and emotionally.
As I prepare for a potential future pregnancy, I have been addressing what I believe to be my root causes: suboptimal iodine, estrogen dominance, and histamine intolerance/overload—which, as you’ve seen in this post, are all interconnected.
I wish I had more answers when I was going through it, and I hope this information helps other women feel seen, heard, and supported.
Disclaimer
This post is for informational and educational purposes only and is not intended to diagnose, treat, cure, or prevent any disease or medical condition. The information provided is not a substitute for professional medical advice. Always consult with a qualified healthcare provider before making any changes to your diet, lifestyle, supplements, or treatment plan.
The author and publisher of this content are not liable for any adverse reactions, effects, or consequences resulting from the use of any information provided. Individual health needs vary, and what works for one person may not be suitable for another.
If you have a medical concern, please seek guidance from a licensed medical professional.
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