Diagnose and manage nausea and vomiting of pregnancy and hyperemesis gravidarum, including severity scoring, the antiemetic ladder, fluid and electrolyte management, and the prevention of Wernicke's encephalopathy

In one line

Nausea and vomiting affects up to 90% of pregnancies; hyperemesis gravidarum affects 0.3 to 3.6% and is defined by protracted vomiting with more than 5% pre-pregnancy weight loss, dehydration and electrolyte imbalance. Almost every serious complication of hyperemesis is caused by the treatment rather than the disease: dextrose before thiamine causes Wernicke's encephalopathy, over-rapid sodium correction causes central pontine myelinolysis, and forgetting thromboprophylaxis causes pulmonary embolism.

Where this sits. Where prolonged vomiting tips into a critically ill woman needing organ support is the Finals chapter on obstetric critical care.

Why pregnancy makes women vomit

The mechanism is not fully settled, which is itself worth knowing, but several strands are consistent and they explain the clinical pattern.

Human chorionic gonadotropin correlates with symptom severity, and its time course matches: nausea starts around 4 to 7 weeks, peaks around 9 to 12 weeks, and settles in most women by 16 to 20 weeks, following the hCG curve. Conditions with higher hCG produce more vomiting: multiple pregnancy, and gestational trophoblastic disease. The same hCG cross-stimulates the TSH receptor, which is why biochemical thyrotoxicosis so often accompanies severe hyperemesis. See Thyroid disorders in pregnancy.

Oestrogen slows gastric emptying and gut transit, and there is a dose relationship with nausea outside pregnancy too.

Progesterone relaxes smooth muscle including the lower oesophageal sphincter, contributing to reflux, which then aggravates the vomiting in a loop.

Genetic and placental factors. Recurrence is high, family clustering is strong, and reported recurrence rates in later pregnancies range widely, from about 15% in a hospital registry study to 81% by self-report, which tells you both that recurrence is common and that how you ask changes the answer.

The important framing for the woman is that this is a placental and hormonal illness, not a psychological one. Hyperemesis was for decades attributed to ambivalence about the pregnancy, and that history still leaks into how women are treated. The psychological consequences are real and severe, but they are consequences.

Making the diagnosis, and what must be excluded first

Nausea and vomiting of pregnancy is nausea or vomiting starting before 16 weeks with no other cause.

Hyperemesis gravidarum is the severe form, diagnosed on the triad:

1. Protracted nausea and vomiting
2. More than 5% pre-pregnancy weight loss
3. Dehydration and electrolyte imbalance

Two features of that definition do work. Onset before 16 weeks is required, so vomiting beginning at 22 weeks is not hyperemesis and needs another explanation. And weight loss is measured against pre-pregnancy weight, which means you must ask for it, because it will not be in the notes.

Exclude other causes by history, focused examination and investigation. The list that matters:

Two of those deserve emphasis in South African practice. A woman with type 1 diabetes vomiting in early pregnancy may be in ketoacidosis, and pregnancy ketoacidosis is often euglycaemic, so send ketones and a gas, not just a glucose (see Diabetes in pregnancy). And a uterus large for dates with severe vomiting is gestational trophoblastic disease until an ultrasound says otherwise (see GTD diagnosis).

Grading severity

Use a validated index rather than an impression. The Pregnancy-Unique Quantification of Emesis (PUQE) score is the one RCOG names. It asks three questions about the last 24 hours: hours of nausea, episodes of vomiting, and episodes of retching, each scored 1 to 5, giving a total of 3 to 15, classified as mild, moderate or severe. It tracks response to treatment as well as it classifies at presentation, which is its main practical value.

A PUQE score of 13 or more marks severe disease and is the RCOG threshold above which ambulatory day-care management is no longer appropriate.

Alongside the score, take:

• History: previous nausea and vomiting or hyperemesis, hypersalivation and spitting, weight loss, inability to tolerate food and fluids, effect on quality of life, and the exclusion questions above.
• Examination: temperature, pulse, blood pressure, oxygen saturation, respiratory rate, weight, abdominal examination, and specifically signs of dehydration and of muscle wasting.
• Investigation: urine dipstick quantifying ketonuria as 1+ or more, a midstream urine, urea and electrolytes looking for hypokalaemia, hyperkalaemia, hyponatraemia and renal impairment, and a full blood count. Thyroid function and liver function where the picture warrants it, and an ultrasound to confirm viability, exclude multiple pregnancy and exclude molar pregnancy.

Where she is managed