There is no one cause of morning sickness during pregnancy, and the severity varies among women. An increase in hormone levels during the first few weeks of pregnancy is among the most common causes. Reduced blood sugar is another common cause of morning sickness.

Other factors can make you predisposed to morning sickness, or exacerbate symptoms. These include:

• Having twins or triplets
• Excessive fatigue
• Emotional stress
• Frequent traveling
• A past pregnancy with nausea and vomiting
• History of morning sickness in your family
• History of motion sickness or migraines

Morning sickness can vary between pregnancies. While you may have had severe morning sickness during one pregnancy, future pregnancies may be mild.