Final answer:
Hyperemesis gravidarum may be caused by hormonal changes, stress, or carrying multiples such as twins or triplets, correlated with increased pregnancy-related hormones.
Step-by-step explanation:
Three possible causes of hyperemesis gravidarum are hormonal changes, stress, and carrying multiples such as twins or triplets. Hyperemesis gravidarum is a severe form of nausea and vomiting during pregnancy that can lead to dehydration and weight loss, and differs from the more common and less severe morning sickness. This condition is thought to be associated with the increased levels of pregnancy-related hormones like circulating estrogen, progesterone, and hCG (human chorionic gonadotropin) which affect gastrointestinal function and can increase nausea and vomiting sensitivity. Additionally, the presence of more than one fetus may exacerbate the production of these hormones.