NVP occurs in up to 50% to 80% of pregnant women.[2]American College of Obstetricians and Gynecologists. Practice bulletin no. 189: nausea and vomiting of pregnancy. Jan 2018 [internet publication].
https://www.acog.org/clinical/clinical-guidance/practice-bulletin/articles/2018/01/nausea-and-vomiting-of-pregnancy
Hyperemesis gravidarum occurs in 0.3% to 3% of pregnancies and is a severe form of NVP.[2]American College of Obstetricians and Gynecologists. Practice bulletin no. 189: nausea and vomiting of pregnancy. Jan 2018 [internet publication].
https://www.acog.org/clinical/clinical-guidance/practice-bulletin/articles/2018/01/nausea-and-vomiting-of-pregnancy
Its incidence is increased with multiple gestation, gestational trophoblastic disease, triploidy, trisomy 21, and hydrops fetalis.[1]Goodwin TM. Hyperemesis gravidarum. Clin Obstet Gynecol. 1998 Sep;41(3):597-605.
http://www.ncbi.nlm.nih.gov/pubmed/9742356?tool=bestpractice.com