Written by The HG Collective · Reviewed by HG Clinicians Expert Panel · Last reviewed: July 2026
Possible complications of HG
Most people with HG will not develop the serious complications described on this page. Having HG does not mean that any of them will happen. They are included because they explain why prompt treatment, follow-up and being taken seriously matter.
Complications are more likely when HG is severe or prolonged, food and fluid intake remain very low, or treatment is delayed or ineffective. If this is happening to you, it is not your fault and you are not wasting anyone's time by asking for further help.
Dehydration, weight loss and nutritional problems
When it is difficult to eat or drink, HG can lead to dehydration, weight loss, disturbances in the body's salts (electrolytes) and vitamin deficiencies. These are recognised medical consequences of the illness. Fluids through a drip, blood tests, vitamins and nutritional support are therefore part of care when needed—not signs that you have failed to cope.
Repeated vomiting can also inflame or damage the food pipe. Always seek medical help if you vomit blood.
Vitamin K deficiency has been reported in people with severe or prolonged HG and can affect blood clotting, but the available research cannot tell us how often it occurs. It is not a routine complication for everyone with HG. If you have severe weight loss or prolonged poor intake, your team may assess for specific nutritional deficiencies and involve a dietitian or nutrition specialist.
RCOG's 2024 guideline recognises that NVP and HG can cause electrolyte imbalance and recommends daily urea and electrolyte testing for patients who need intravenous fluids. It also recommends assessment of malnutrition and escalation to oral nutritional supplements, enteral feeding or parenteral nutrition when clinically required.[1]
NHS guidance identifies dehydration and weight loss as features of HG and states that untreated HG can lead to further complications, including tears in the oesophagus. NHS advice is to obtain medical help whenever blood is vomited.[2][3]
A systematic review of vitamin K deficiency in HG included 14 case reports involving 21 women and one retrospective cohort of 109 women. It documented abnormal clotting tests and rare maternal and neonatal complications, but the authors explicitly concluded that the incidence could not be estimated from the available evidence. This supports considering vitamin K deficiency in severe malnutrition or weight loss; it does not support presenting it as common or routinely screening every person with HG.[4]
References
- [1] Nelson-Piercy C, Dean C, Shehmar M, et al. The Management of Nausea and Vomiting in Pregnancy and Hyperemesis Gravidarum (Green-top Guideline No. 69). BJOG. 2024;131:e1–e30. https://doi.org/10.1111/1471-0528.17739
- [2] NHS. Severe vomiting in pregnancy. https://www.nhs.uk/pregnancy/complications/severe-vomiting/
- [3] NHS. Vomiting blood. https://www.nhs.uk/symptoms/vomiting-blood/
- [4] Nijsten K, van der Minnen L, Wiegers HMG, et al. Hyperemesis gravidarum and vitamin K deficiency: a systematic review. British Journal of Nutrition. 2022;128(1):30–42. https://doi.org/10.1017/S0007114521002865
Wernicke's encephalopathy—rare, but why thiamine matters
Prolonged vomiting and very low food intake can deplete vitamin B1 (thiamine). In rare cases this can cause a serious neurological condition called Wernicke's encephalopathy.
This is why RCOG recommends thiamine for people admitted with vomiting or severely reduced dietary intake, especially before glucose-containing fluids (dextrose) or intravenous nutrition. It is a recognised risk that maternity teams should prevent and treat; you should not have to prove that you are already deficient before thiamine is considered.
New confusion, difficulty walking or problems with balance, double vision, blurred vision or unusual eye movements need urgent medical assessment.
RCOG recommends oral or intravenous thiamine for all patients admitted with vomiting or severely reduced dietary intake, particularly before dextrose or parenteral nutrition.[1]
The largest systematic review located 177 published cases of Wernicke's encephalopathy associated with HG. In those reports, inadequate thiamine treatment was common and intravenous glucose was reported to worsen the condition in some cases.[2] Because this review was made up of case reports and case series—not a defined population—it cannot provide a reliable prevalence estimate. The previously quoted figure of 0.04–0.13% has therefore not been retained on this page.
The same review reported neurological features including problems with walking or coordination, altered mental state and eye-movement or visual symptoms. Outcomes reported in case literature can look especially severe because unusual and serious cases are more likely to be published; they should not be treated as the expected outcome for a person with HG.[2]
References
- [1] Nelson-Piercy C, Dean C, Shehmar M, et al. The Management of Nausea and Vomiting in Pregnancy and Hyperemesis Gravidarum (Green-top Guideline No. 69). BJOG. 2024;131:e1–e30. https://doi.org/10.1111/1471-0528.17739
- [2] Oudman E, Wijnia JW, Oey M, van Dam M, Painter RC, Postma A. Wernicke's encephalopathy in hyperemesis gravidarum: a systematic review. European Journal of Obstetrics & Gynecology and Reproductive Biology. 2019;236:84–93. https://doi.org/10.1016/j.ejogrb.2019.03.006
Blood clots (VTE)
Pregnancy itself increases the chance of a blood clot. Dehydration and being much less mobile because of HG can increase it further. The overall risk for any one person is still small, but it needs an individual assessment.
RCOG recommends that people admitted with HG are offered blood-thinning injections called low-molecular-weight heparin (LMWH), unless there is a reason these would not be suitable. People treated in the community should also have their clot risk assessed.
There is now an earlier pathway in England. The NHS England Maternal Care Bundle, published in 2026, says a VTE self-assessment should be offered at the first NHS contact after a positive pregnancy test. HG counts as a high-risk trigger when it causes dehydration or immobility—defined in the bundle as being unable to drink without vomiting or struggling to stand and walk because of symptoms. Under the pathway, someone who screens high risk should be offered LMWH within 72 hours and referred for assessment in an early pregnancy unit or emergency department.
This pathway is being introduced across England, with full implementation required by March 2027, so local arrangements may still differ. It does not replace an individual clinical assessment, and you should not start, stop or change blood-thinning medication without medical advice.
Get urgent medical help for pain, redness or swelling in one leg. Call 999 or go to A&E for severe or sudden difficulty breathing, chest or upper-back pain, a very fast heartbeat or fainting.
RCOG Green-top Guideline No. 69 recommends LMWH thromboprophylaxis for patients admitted with HG and VTE risk assessment for those managed in the community.[1] RCOG Green-top Guideline No. 37a lists hyperemesis-related dehydration as a transient VTE risk factor and provides the wider pregnancy risk-assessment framework.[2]
Element 1 of NHS England's Maternal Care Bundle introduces risk assessment before the usual maternity booking appointment. Its three early high-risk triggers are previous confirmed VTE, HG causing dehydration or immobility, and a BMI above 50. It specifies LMWH within 72 hours for those identified as high risk, plus early-pregnancy or emergency assessment for those who screen positive because of HG. It also says LMWH can stop once the HG-related symptoms have resolved, following clinical review.[3]
The bundle applies to England. It was published on 6 January 2026, updated on 6 March 2026, and requires full implementation by maternity trusts and integrated care boards by March 2027. The page therefore explains the intended pathway without implying that it is already operating identically everywhere.[3]
The emergency symptoms above are based on current NHS advice for deep-vein thrombosis and pulmonary embolism.[4]
References
- [1] Nelson-Piercy C, Dean C, Shehmar M, et al. The Management of Nausea and Vomiting in Pregnancy and Hyperemesis Gravidarum (Green-top Guideline No. 69). BJOG. 2024;131:e1–e30. https://doi.org/10.1111/1471-0528.17739
- [2] Royal College of Obstetricians and Gynaecologists. Reducing the Risk of Thrombosis and Embolism during Pregnancy and the Puerperium (Green-top Guideline No. 37a). 2015. RCOG guideline page
- [3] NHS England. The Maternal Care Bundle: Element 1—Venous thromboembolism. 2026. https://www.england.nhs.uk/long-read/the-maternal-care-bundle/
- [4] NHS. Pulmonary embolism. https://www.nhs.uk/conditions/pulmonary-embolism/
Effects on the baby
This can be the most frightening part to read, so the balance of the evidence matters. NHS guidance says HG is unlikely to harm your baby when it is treated effectively. If HG causes significant weight loss or poor weight gain, there is an increased chance that the baby may be smaller than expected.
Research has found associations between HG and some outcomes, including low birthweight, being born early and admission to neonatal care. These are associations from observational studies: they do not prove that HG directly caused the outcome, and they do not tell us that an individual baby will be affected. A large 2023 review found no association with fetal loss, perinatal death or neonatal death.
If severe symptoms continue into the later part of pregnancy, your team may offer additional ultrasound scans to monitor your baby's growth. The purpose is to identify the smaller group of pregnancies that need closer observation—not because a problem is assumed.
NHS guidance states that effectively treated HG is unlikely to harm the baby, while weight loss during pregnancy is linked with an increased chance of low birthweight.[1]
A 2023 systematic review included 61 studies and more than 20 million pregnancies, although the number of studies contributing to each individual analysis varied greatly. HG was associated with preterm birth before 34 weeks, birthweight below 1,500 g, neonatal resuscitation and neonatal-unit admission. Some of these estimates came from only two studies. The review found no association with fetal loss, perinatal death or neonatal death and could not determine the mechanisms behind the associations.[2]
The studies were observational and used differing definitions and populations, so residual confounding and variation in disease severity or treatment may affect the results. The figures should not be presented as proof that untreated HG caused an outcome or as a prediction for an individual pregnancy.
RCOG advises serial growth scans where severe NVP or HG persists into the late second trimester or the third trimester.[3]
References
- [1] NHS. Severe vomiting in pregnancy. https://www.nhs.uk/pregnancy/complications/severe-vomiting/
- [2] Jansen LAW, Nijsten K, Limpens J, et al. Perinatal outcomes of infants born to mothers with hyperemesis gravidarum: a systematic review and meta-analysis. European Journal of Obstetrics & Gynecology and Reproductive Biology. 2023;284:30–51. https://doi.org/10.1016/j.ejogrb.2023.03.004
- [3] Nelson-Piercy C, Dean C, Shehmar M, et al. The Management of Nausea and Vomiting in Pregnancy and Hyperemesis Gravidarum (Green-top Guideline No. 69). BJOG. 2024;131:e1–e30. https://doi.org/10.1111/1471-0528.17739
The mental health impact
HG can have a profound emotional and psychological effect. Constant nausea, loss of independence, isolation, disrupted work and family life, fear about the pregnancy, and difficulty getting effective treatment can contribute to anxiety, depression or trauma symptoms.
In one prospective UK study, 49% of women admitted with HG screened positive for probable antenatal depression, compared with 6% of women in the control group. At six weeks after birth, the figures were 29% and 7% respectively. These were screening results from three London hospitals—not confirmed diagnoses or a national prevalence estimate—but they show why emotional wellbeing should be assessed as part of HG care.
This does not mean HG is caused by anxiety, depression or an inability to cope. RCOG is explicit that poor mental health can result from the illness rather than cause it. A pre-existing mental health condition can also become harder to manage—especially if vomiting means that regular oral medication cannot be kept down.
Please tell your GP, midwife or maternity team how HG is affecting you emotionally as well as physically. You do not need to wait for a screening questionnaire or a crisis. RCOG recommends assessment of both physical and mental health during pregnancy, psychological support or specialist referral when needed, and a review of how essential medication can be given if tablets are not staying down.
In England, the 2026 Maternal Care Bundle also requires repeated emotional-wellbeing screening during and shortly after pregnancy, followed by a compassionate conversation and referral when a screen or clinical concern identifies a need. Full implementation is required by March 2027, so this may not yet look the same in every area.
If you feel you may harm yourself or cannot keep yourself safe, call 999 or go to A&E now. In England, for urgent mental health help that is not an immediate emergency, call NHS 111 and select the mental health option. You can also call Samaritans free at any time on 116 123.
A systematic review of 59 papers, with 12 studies included in meta-analysis, found substantially higher depression- and anxiety-symptom scores among people with HG than controls. There was considerable statistical heterogeneity, so the pooled results describe a consistent burden of symptoms but should not be read as a precise rate of diagnosed depression or anxiety.[1]
A two-point prospective case-control study recruited 214 women at 12 weeks' gestation or earlier across three London hospitals: 106 women admitted with HG and 108 women attending a low-risk antenatal clinic without significant nausea and vomiting. Using the Edinburgh Postnatal Depression Scale, 49% of the HG group met the threshold for probable depression antenatally, compared with 6% of controls; at six weeks after birth the figures were 29% and 7%. The paper reported odds ratios of 14.4 antenatally (95% CI 5.29–39.44) and 5.2 postnatally (95% CI 1.65–17.21).[2]
The descriptions “about eight times” and “about four times” come from comparing the raw proportions. They are not the odds ratios reported by the researchers. The study used a screening questionnaire, so it measured probable depression rather than a diagnosis confirmed by clinical interview, and its hospital-based sample should not be treated as a prevalence estimate for everyone with HG.[2]
A 2026 mixed-methods systematic review brought together 64 international studies published between 2010 and 2025. Depression and anxiety were generally higher among people with HG than controls, and greater HG or NVP symptom severity was associated with greater depression and anxiety. The review also identified stress, psychological distress, post-traumatic stress symptoms, suicidal ideation and poorer mental-health-related quality of life. Some psychological effects persisted beyond pregnancy.[3]
Its qualitative synthesis found recurring experiences of psychological burden and trauma, invalidation and unmet care needs, disruption to daily life, identity and relationships, and the importance of support and coping. Women described dismissal and lack of validation, while valuing specialist services and psychological support. By integrating the quantitative and qualitative findings, the review concluded that psychological morbidity was associated with both symptom severity and experiences of care.[3]
A UK-wide mixed-methods study analysed an online survey of 5,071 respondents who self-reported HG or severe pregnancy sickness. It documented suicidal thoughts and termination of wanted pregnancies, and linked better support and care with more protective experiences. Because recruitment was through an HG charity, support forums and social media, the percentages are not population prevalence estimates and may over-represent people with severe disease or poor care. The study nevertheless provides important evidence that mental-health assessment, timely medication, specialist referral where required and compassionate care need to be part of HG treatment.[4]
RCOG recommends a full assessment of physical and mental health, referral for psychological support where necessary, and consideration of alternative routes for pre-existing mental-health medication that cannot be retained because of vomiting. The guideline also states that depression and poor psychological health result from NVP/HG rather than cause it.[5]
Element 4 of NHS England's Maternal Care Bundle specifies emotional-wellbeing screening before the booking, 25–28-week, 31–34-week and 10–14-day postnatal appointments. A positive response or clinical concern should lead to further assessment, a compassionate conversation during the same appointment and referral when indicated. Screening tools support—but do not replace—clinical judgement or listening to the patient.[6]
NHS crisis guidance advises emergency help when someone cannot keep themselves safe and lists Samaritans on 116 123 as a free listening service available day or night.[7][8]
References
- [1] Mitchell-Jones N, Gallos I, Farren J, Tobias A, Bottomley C, Bourne T. Psychological morbidity associated with hyperemesis gravidarum: a systematic review and meta-analysis. BJOG. 2017;124(1):20–30. https://doi.org/10.1111/1471-0528.14180
- [2] Mitchell-Jones N, Lawson K, Bobdiwala S, et al. Association between hyperemesis gravidarum and psychological symptoms, psychosocial outcomes and infant bonding: a two-point prospective case-control multicentre survey study in an inner city setting. BMJ Open. 2020;10:e039715. https://doi.org/10.1136/bmjopen-2020-039715
- [3] Mills A, Glaister P, Heys S, Hibberd C, Coxon K. Experiences of Psychological Burden and Care in Women with Hyperemesis Gravidarum and Nausea and Vomiting in Pregnancy: A Mixed-Methods Systematic Review. Midwifery. 2026;104956. https://doi.org/10.1016/j.midw.2026.104956
- [4] Nana M, Tydeman F, Bevan G, et al. Termination of wanted pregnancy and suicidal ideation in hyperemesis gravidarum: a mixed methods study. Obstetric Medicine. 2022;15(3):180–184. https://doi.org/10.1177/1753495X211040926
- [5] Nelson-Piercy C, Dean C, Shehmar M, et al. The Management of Nausea and Vomiting in Pregnancy and Hyperemesis Gravidarum (Green-top Guideline No. 69). BJOG. 2024;131:e1–e30. https://doi.org/10.1111/1471-0528.17739
- [6] NHS England. The Maternal Care Bundle: Element 4—Maternal mental health. 2026. https://www.england.nhs.uk/long-read/the-maternal-care-bundle/
- [7] NHS. Where to get help for self-harm. https://www.nhs.uk/mental-health/feelings-symptoms-behaviours/behaviours/self-harm/getting-help/
- [8] Samaritans. Contact a Samaritan. https://www.samaritans.org/how-we-can-help/contact-samaritan/
When to get urgent help
Seek urgent medical help if you have:
- vomited blood
- pain, redness or swelling in one leg
- sudden difficulty breathing, chest pain, upper-back pain, a very fast heartbeat, coughing up blood or fainting
- new confusion, difficulty walking or keeping your balance, double or blurred vision, or unusual eye movements
- thoughts of harming yourself or a feeling that you cannot keep yourself safe
Call 999 or go to A&E if symptoms are severe, there is an immediate danger to life, or you cannot keep yourself safe. If you are unsure what to do, contact your maternity unit, GP or NHS 111.