Nausea in the first month of pregnancy is caused by HCG secretion in the body, which is a normal early pregnancy reaction. Most women experience it around 6 weeks of pregnancy and it disappears on its own around 3 months after menopause, manifesting as morning sickness, vomiting and dislike of oily diet. Most of the symptoms are mild, do not affect normal eating and can be tolerated. However, in a small number of women, the symptoms are more severe, affecting the diet and lasting longer, and may even lead to disturbance of water, electrolytes and acid-base balance, which is called severe pregnancy vomiting and requires hospitalization to adjust the disturbance of water, electrolytes and acid-base balance. If the symptoms persist, early termination of pregnancy may be necessary as a last resort.