Morning sickness, also called nausea gravidarum, affects around three quarters of pregnant women during the first trimester. It is caused by hormonal changes during pregnancy including increased hCG and estrogen levels. While unpleasant, morning sickness is not harmful for most women or their babies. Severe or prolonged vomiting may require medical treatment. Simple home remedies like eating small frequent meals, ginger, and peppermint can help provide relief for mild cases.