Nausea and Vomiting of Pregnancy

Nausea and vomiting of pregnancy (NVP) is one of the most common conditions of early pregnancy. Despite the popular term "morning sickness," symptoms can occur at any time of day and are often present continuously. Virtually everyone who develops NVP has some symptoms by 9 weeks' gestation, more than half by 6 weeks, and most improve by 16 weeks — though a meaningful minority have symptoms that persist beyond 20 weeks.^[1] At the severe end of the same spectrum is hyperemesis gravidarum (HG): intractable vomiting causing dehydration, electrolyte disturbance, nutritional deficiency, and weight loss that can threaten both maternal and fetal wellbeing, and that must prompt investigation for other causes before being accepted as the diagnosis.^[2] The single most important counselling point in this chapter is that treating NVP appropriately — not avoiding treatment out of fear of medication exposure — is the safer choice for mother and fetus, since untreated severe NVP and HG carry real, well-documented risks of their own.

Typical presentation

Nausea, with or without vomiting, beginning in the first trimester — onset after 9 to 10 weeks' gestation is atypical for NVP and should prompt a search for an alternative cause.^[1] Symptoms are frequently accompanied by hypersalivation (ptyalism), a heightened sense of smell, food aversions, and sensitivity to previously tolerated odours.

Hyperemesis gravidarum

HG is the severe end of the NVP spectrum: intractable, often continuous vomiting starting in the first trimester that can persist throughout pregnancy, producing dehydration, electrolyte disturbance, nutritional deficiency, and weight loss severe enough to threaten maternal and fetal wellbeing. Because no single confirmatory test exists, HG is a diagnosis of exclusion — reserved for protracted NVP with objective evidence of dehydration and electrolyte imbalance alongside substantial weight loss, once other causes of vomiting in pregnancy have been reasonably excluded.^[2]

• Multifetal (twin or higher-order) pregnancy.
• Molar (hydatidiform) pregnancy.
• NVP or hyperemesis gravidarum in a previous pregnancy.
• A first-degree relative with a history of NVP or hyperemesis gravidarum.
• History of motion sickness.
• History of migraine.
• Nulliparity.
• Pre-existing gastrointestinal disorders (e.g., gastroparesis, prior Helicobacter pylori infection) that can compound NVP severity.

History

• Frequency, severity, and timing of nausea and vomiting in relation to meals, time of day, and emotional stressors.
• The relationship between nausea and vomiting, and, if vomiting occurs, the amount and character of the vomitus.
• Whether the presentation is consistent with pregnancy-related nausea or suggests another cause.
• A full gastrointestinal review — bowel habit, early satiety, postprandial symptoms, abdominal pain, or unintended weight loss.
• Other symptoms such as headache, focal pain, or vertigo.
• Diet history, including new foods, food intolerances, and possible contaminated-food exposure.
• Exposure to gastroenteritis or other infectious illness.
• Past history of migraine, endocrine disorders, or malignancy.
• A complete medication history, including prescription, non-prescription, herbal, and recreational drug use (including cannabis), alcohol, and supplements — and any recent changes to the medication regimen that correlate with symptom onset.
• Psychosocial stressors and the patient's own concerns, functional impact, and treatment preferences.

Physical examination

• Vital signs, including blood pressure, pulse, respiratory rate, and temperature.
• Hydration assessment — jugular venous pressure, mucous membranes, skin turgor, and postural changes in blood pressure and heart rate.
• Abdominal examination to look for an alternative cause when the history is not clearly typical of NVP.
• A focused examination directed at any suspected underlying cause (e.g., neurologic exam for suspected migraine, assessment for bowel obstruction if postsurgical or malignancy history, nystagmus in vertigo-associated nausea, fundoscopy for papilledema).
• Intermittent fetal auscultation or a non-stress test in the second and third trimester; a biophysical profile if fetal compromise is suspected.

Severity scoring — PUQE-24

The modified Pregnancy-Unique Quantification of Emesis (PUQE-24) index is a validated, simple point-sum tool used to grade severity and track response to treatment over time.^[3] Score each of the 3 questions from 1 to 5 and sum the total (range 3 to 15).

Total score interpretation: mild NVP is a score of 6 or under; moderate NVP is a score of 7 to 12; severe NVP is a score of 13 or higher.

Other investigations, if indicated by history and exam

• Electrolytes, glucose, and a metabolic panel — e.g., calcium in suspected malignancy, glucose in a diabetic patient, potassium/sodium in a patient on diuretics, lipase/amylase if pancreatitis is suspected.
• CBC and differential if an infective cause is suspected.
• Serum creatinine to assess for a renal cause.
• Relevant drug levels (e.g., digoxin, anticonvulsants) if applicable.
• Liver function tests.
• Thyroid function or fasting cortisol if an endocrine cause is suspected.
• Ultrasound of the pregnancy to assess for multiple, molar, or ectopic pregnancy if not already established.
• Ultrasound of the liver, gallbladder, or pancreas if indicated.
• Abdominal x-ray if bowel obstruction is suspected, or an upper GI series if reflux or gastroparesis is suspected — imaging decisions should weigh maternal benefit against fetal radiation exposure, with the patient involved in that decision.
• Upper GI endoscopy or CT of the abdomen, again weighing maternal benefit against fetal risk.
• CT of the head if an intracranial cause is suspected.

• Eliminate nausea and vomiting; where that is not possible, reduce severity, frequency, and duration as much as possible.
• Prevent complications of nausea and vomiting, including dehydration, ketosis, and nutritional deficiency.
• Prevent recurrence once symptoms are controlled.
• Reduce time off work and disruption to daily function.
• Correct any consequences of persistent nausea, such as electrolyte abnormalities or nutritional compromise, once they occur.
• Prevent Wernicke encephalopathy in any patient with prolonged vomiting through timely thiamine supplementation.

• Reassure patients that most mild to moderate NVP is a normal part of pregnancy, is not harmful to the fetus, and usually improves as pregnancy progresses.
• Recommend small, bland, frequent meals; avoid fatty, fried, or spicy foods.
• Eat at times of day when nausea is less severe, and eat something before getting out of bed in the morning.
• Avoid strong food odours; separate solid and liquid intake, drinking small amounts of fluid regularly between meals rather than with meals.
• Avoid raw or undercooked meat, fish, or eggs, sprouts, and unpasteurized dairy or juice, given the risk of foodborne illness in pregnancy.
• If a standard prenatal vitamin worsens nausea (often due to its iron content or tablet size), switch to folic acid alone or a low-iron multivitamin for the first trimester.
• Avoid becoming overheated, increase rest, and reduce work hours or stress where feasible.
• Ginger (250 mg PO every 6 hours, up to 1 g per day) has evidence supporting benefit over placebo in randomized trials for mild to moderate NVP, with effectiveness reported as comparable to pyridoxine and to dimenhydrinate in head-to-head trials — a reasonable option for patients who wish to avoid or delay prescription antiemetics.
• P6 (Nei Guan) acupressure — located about 5 cm proximal to the wrist crease, between the tendons of palmaris longus and flexor carpi radialis — can be self-applied with fingertip pressure or an acupressure wristband; some practitioners suggest about 5 minutes of pressure every 4 hours. Evidence for acupressure and acupuncture is mixed and has not clearly shown superiority over dietary or lifestyle advice, but the manual technique is safe and low-cost, making it a reasonable adjunct for patients who want a non-drug option.
• Discuss cannabis use directly with every patient presenting with NVP — reported use is increasing, cannabis is not an effective or recommended treatment for NVP, and chronic use can itself cause cannabinoid hyperemesis syndrome. Cannabis crosses the placenta, and in-utero exposure has been linked to neonatal withdrawal-like symptoms and longer-term neurodevelopmental effects. Health Canada advises against cannabis use in those who are pregnant, breastfeeding, planning a pregnancy, or of childbearing age without reliable contraception.

Pregnancy — trimester-specific considerations

Every agent recommended above has a reassuring pregnancy-safety record when used as directed. Ondansetron is the notable exception: a large cohort study found no increased risk of cardiac malformations or congenital malformations overall after adjusting for confounders, but did find a small increased risk of oral clefts with first-trimester exposure, and other cohorts have reported conflicting signals for cardiac septal defects specifically.^[5] Health Canada updated the Zofran and Zofran ODT product monograph in November 2020 to reflect this signal and states that ondansetron use in pregnancy is not recommended; ondansetron is not authorized in Canada specifically for NVP.^[6] In practice, ondansetron continues to be used for NVP and hyperemesis gravidarum refractory to other agents given the genuine difficulty of managing severe symptoms otherwise — this should only follow explicit counselling on the oral-cleft signal and the conflicting cardiac data, with a shared decision to proceed, and use after the first trimester where the option to delay exposure exists. Systemic corticosteroids carry a weak signal for oral clefts with first-trimester exposure, so reserve them for after the first trimester wherever the clinical situation allows.

Breastfeeding

The agents used for NVP and HG in pregnancy are also generally considered compatible with breastfeeding.^[1]

Pediatric

Not applicable — NVP and hyperemesis gravidarum are pregnancy-specific conditions.

Renal/hepatic impairment

Reduce the ondansetron dose in moderate-severe hepatic impairment (no more than 8 mg per day). Reduce the metoclopramide dose in significant renal or hepatic impairment. No specific adjustment is required for doxylamine-pyridoxine, dimenhydrinate, diphenhydramine, promethazine, ginger, pyridoxine, or thiamine at standard NVP doses, though standard caution applies in severe organ impairment.

Multiple or molar gestation

Both carry an increased risk of NVP and hyperemesis gravidarum; confirm the diagnosis with ultrasound if not already established, since management and counselling differ from a singleton, non-molar pregnancy.

Reassess symptom severity (informally, or with a repeat PUQE-24 score) and track weight at each follow-up visit. Review the effect of a new or escalated antiemetic within a few days of starting it rather than waiting for a routine visit, since ineffective therapy should be escalated promptly rather than continued unchanged. For hospitalized HG, check electrolytes and weight daily while on IV fluids, and step down to oral therapy as soon as it is tolerated. Watch for medication-specific issues at every review: extrapyramidal symptoms or oculogyric crisis with dopamine antagonists (stop immediately if these occur), QTc-prolongation risk factors before and during ondansetron use, and hyperglycemia or infection signs during corticosteroid therapy. Reinforce that thiamine must be given before or with any dextrose-containing fluid in a patient with prolonged vomiting. Assess hospitalized HG patients for thromboprophylaxis with low-molecular-weight heparin unless contraindicated, and reassess Wernicke encephalopathy risk (visual changes, ataxia, confusion) at every review of a patient with prolonged vomiting.

1. Confirm the current regimen is actually being taken as prescribed before escalating — including whether the patient can keep oral doses down at all.
2. Add a second antiemetic from a different drug class rather than simply increasing the dose of the first.
3. If first-line antihistamine-based therapy (doxylamine-pyridoxine, dimenhydrinate, diphenhydramine, or promethazine) is inadequate, add or switch to a dopamine antagonist (metoclopramide, prochlorperazine, or chlorpromazine).
4. If symptoms remain refractory, consider ondansetron after explicit safety counselling, and reassess for hyperemesis gravidarum.
5. If the patient cannot tolerate oral intake, has ketosis, significant weight loss, or electrolyte disturbance, admit for IV fluid and electrolyte correction, giving thiamine before or with any dextrose-containing fluid.
6. If HG persists despite IV fluids and combination antiemetic therapy from at least two drug classes, consider a corticosteroid (methylprednisolone or hydrocortisone IV, then an oral prednisone taper), preferably after the first trimester.
7. At any step, reassess for an alternative diagnosis if the pattern deviates from typical NVP — persistent abdominal pain, fever, onset after 9 to 10 weeks, or persistence beyond 20 weeks without improvement.

• Withholding effective antiemetic therapy out of unfounded fear of medication risk to the fetus — untreated severe NVP and HG carry real maternal and fetal risk, and appropriate treatment is the safer choice.
• Starting a dextrose-containing IV fluid in a patient with prolonged vomiting before giving thiamine, risking precipitation of Wernicke encephalopathy.
• Continuing metoclopramide beyond 5 days or exceeding its maximum daily dose, given the dose- and duration-dependent risk of extrapyramidal effects and tardive dyskinesia.
• Reaching for ondansetron as a first-line agent without first trying better-established options, or without counselling the patient on its evolving safety evidence.
• Combining dimenhydrinate and diphenhydramine, unintentionally duplicating the same active antihistamine.
• Attributing every case to routine "morning sickness" without asking about abdominal pain, fever, or a symptom pattern atypical for NVP.
• Missing hyperemesis gravidarum until dehydration or weight loss is already advanced, rather than escalating care at the first signs of inability to tolerate oral intake.
• Not asking about cannabis use, or assuming it is a safe or effective treatment for NVP.
• Forgetting to reassess and step down therapy as symptoms improve toward the expected resolution window.

How to use this table: doses are adult doses for NVP/HG specifically and require patient-specific confirmation. Drug pricing is intentionally omitted. Select any drug name to open its complete Pharmasist Drug Database page.

Antihistamines (H1-receptor antagonists)

First-line alternatives to doxylamine-pyridoxine for moderate-severe NVP.

Combination Product — Doxylamine/Pyridoxine

Doxylamine succinate/pyridoxine hydrochloride (delayed-release, marketed in Canada as Diclectin) is the only medication specifically approved by Health Canada for NVP, with one of the largest cumulative pregnancy-safety experiences of any medication used in pregnancy. Its predecessor combination (marketed in the United States as Bendectin, which also contained the antispasmodic dicyclomine) was voluntarily withdrawn from the US market in 1983 amid litigation alleging a teratogenic effect, despite an absence of supporting epidemiologic evidence; the doxylamine-pyridoxine combination without dicyclomine was later re-approved in the US as Diclegis and, as a once-nightly extended-release formulation, Bonjesta — only the original delayed-release formulation (Diclectin) is marketed in Canada. A 2018 reanalysis of previously unpublished trial data found no significant benefit of the combination over placebo,^[7] which is why a trial of pyridoxine alone (see Natural Health Products below) is also a reasonable evidence-based first step — but the combination remains recommended as first-line pharmacotherapy by SOGC and ACOG^[1][4] given its exceptional safety record; the debate concerns the size of its benefit over pyridoxine alone, not its safety.^[8]

Natural Health Products

Reasonable first steps for mild NVP, or as an adjunct to prescription therapy.

Dopamine Antagonists (Phenothiazines and Prokinetics)

Second-line — use when first-line antihistamine-based therapy is inadequate. Domperidone is used for this indication in some jurisdictions but carries a dose-related QT-prolongation warning and is not covered in this table.

Serotonin 5-HT3 Receptor Antagonist

Reserve for refractory NVP or hyperemesis gravidarum after explicit safety counselling — see Special Populations.

Corticosteroids (Refractory Hyperemesis Gravidarum)

Reserve for HG refractory to IV fluids and combination antiemetic therapy, and use after the first trimester where possible given a weak signal for oral clefts with first-trimester systemic corticosteroid exposure.

Thiamine — Wernicke Encephalopathy Prevention

Give thiamine before or with any dextrose-containing fluid or parenteral nutrition in a patient with prolonged vomiting — administering dextrose to a thiamine-deficient patient can precipitate Wernicke encephalopathy.^[2]