Less than 1% of pregnant women with morning sickness will experience excessive vomiting to the point that they become dehydrated. The medical term for this is 'Hyperemesis Gravidarum' and for some reason it is more common for women having their first baby (but can still be experienced by women having subsequent babies).
If you are vomiting several times a day and are unable to keep food or fluids down for a couple of days or more, you may need to be admitted to hospital to have a drip placed in your vein to administer fluids. You may also be prescribed an antihistamine or Maxalon medication (usually as an injection) for the vomiting (you can read more on the previous page in Medical treatments). These can make you feel drowsy. You may just stay in hospital overnight or for a few days, depending on how unwell you are and how quickly the vomiting settles. Often resting in hospital becomes somewhat of a remedy. A few women find they are in and out of hospital over a period of several weeks during early pregnancy, whenever the vomiting becomes severe.
NOTE:Not all cases of excessive vomiting are caused by severe morning sickness during early pregnancy. You may have a virus or food poisoning, meaning it could be caused by a health condition or illness totally unrelated to the pregnancy. If your doctor is concerned they will probably perform a range of blood tests and other investigations to make sure the vomiting isn't being caused by something else. In very rare circumstances, excessive vomiting may be caused by a pregnancy variation called a molar pregnancy.
Jewell D, Young G Interventions for nausea and vomiting in early pregnancy (Cochrane Review). In: The Cochrane Library, Issue 2, 2002. Oxford: Update Software.
Kizior RJ and Hodgson BB. Saunders drug handbook for health professionals. 2nd ed. 2002 W B Saunders, Philadelphia.