Nausea and Vomiting in Pregnancy Explained
Nausea and vomiting in pregnancy (NVP) is one of the most common clinical conditions women experience during the first trimester of pregnancy.
Nausea and vomiting in pregnancy (NVP) is often dismissed by healthcare professionals and underreported by women, yet it can severely affect quality of life, mental health, and, in extreme cases, lead to serious risks for both mother and baby, including suicidal thoughts or pregnancy termination. Concerns about medication safety and delayed appointments further discourage many from seeking timely treatment.
Nausea and vomiting in pregnancy (NVP), often misnamed “morning sickness,” refers to nausea and/or vomiting before 16 weeks of gestation once other causes are excluded. It usually begins around week 4, peaks between 9 and 16 weeks, and resolves by 20 weeks. The most severe form, hyperemesis gravidarum (HG), starts early in pregnancy and is marked by severe nausea and vomiting, inability to eat or drink normally, and significant disruption of daily activities.
Nausea and vomiting in pregnancy (NVP) are symptoms that begin before 16 weeks of gestation, often called “morning sickness” though they can occur any time of day. NVP usually starts around the fourth week, peaks between 9 and 16 weeks, and resolves by 20 weeks. The severe form, hyperemesis gravidarum (HG), is defined as early-onset nausea and vomiting—at least one being severe—leading to inability to eat or drink normally and significant disruption of daily activities.
What causes Nausea and Vomiting in Pregnancy?
The main mechanism of NVP is now thought to be hypersensitivity to the vomiting hormone, growth differentiation factor-15 (GDF-15), which is produced by the fetus.
GDF15 activates the vomiting centre of the brain, and higher circulating levels have been found in pregnant women who:
- were hospitalised with HG
- were taking antiemetics
- had second trimester vomiting
NVP may also be an evolutionary adaptation to prevent the ingestion of harmful foods. Symptoms peak during weeks 6–18 of gestation, when embryonic organ development is most vulnerable to chemical disruption.
Impact on maternal health
Maternal complications are varied and depend on the severity of symptoms; complications are more likely in women with severe NVP or HG. Complications include:
| More common complications | Less common/rare complications |
| Weight loss | Acute kidney injury |
| Dehydration | Retinal haemorrhage |
| Fatigue | Pneumothorax |
| Electrolyte imbalance | Venous thromboembolism (in women with reduced mobility) |
| Difficulty managing conditions that require medication | Wernicke’s encephalopathy (neurological disorder caused by thiamine [vitamin B1] deficiency)* |
| Nutritional and vitamin deficiencies | Splenic avulsion/rupture (rare) |
| Abnormal liver function tests | |
| Oesophagitis, gastritis |
*Vomiting can be both a cause and a symptom of thiamine (vitamin B1) deficiency. Prolonged vomiting can lead to thiamine depletion, while nausea and vomiting can be early signs of thiamine deficiency, particularly in conditions like Wernicke’s encephalopathy.
Fetal complications of NVP
Mild to moderate NVP typically does not harm the fetus if the woman is able to keep some foods down and remain hydrated.
HG or severe NVP that is untreated or poorly managed can pose risks to the baby through maternal malnutrition and dehydration.
Risks to the fetus include:
- Low birthweight
- Small for gestational age
- Preterm birth
Management of NVP – dietary and self-care advice
Self-care measures, which include:
- Resting – tiredness can make nausea worse and symptoms harder to cope with
- Avoiding foods or smells that worsen symptoms
- Eating plain, dry biscuits or crackers first thing in the morning
- Eating bland, small, frequent carbohydrate-rich meals (cold food may be easier to eat if nausea is smell-related)
- Drinking little and often, rather than large amounts.
- Eating food or drinks containing ginger
- Trying acupressure (there is some evidence that applying pressure to the inner forearm, near the wrist, may help alleviate nausea)
- Avoiding preparations that contain iron, as this can worsen symptoms
While nausea and vomiting are common in pregnancy, it’s important to know when to seek medical help. If you are unable to keep food or fluids down, notice signs of dehydration (such as dizziness, dry mouth, or very little urine), lose weight, or if the vomiting is severe and persistent, contact your healthcare provider promptly. These may be signs of hyperemesis gravidarum or other conditions that need medical attention to protect both you and your baby.
