Why Does Morning Sickness Occur in the Mornings?

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Nausea or vomiting in the early morning (also known as “morning sickness”) is so common that is usually acknowledged as a symptom of normal pregnancy. It takes place soon after waking up, often as retching rather than actual vomiting, thus it typically does not disturb the health of a pregnant women.

In a smaller proportion of cases (with an average incidence of 3.5 in 1,000 births) the vomiting tends to be more severe and persistent, and is known as hyperemesis gravidarum. In these women fluid and electrolyte disturbances can occur and they often require hospital admission.

Image Copyright: Monkey Business Images / Shutterstock
Image Copyright: Monkey Business Images / Shutterstock

Mechanism and periodicity of morning sickness

The exact factors responsible for pregnancy-related nausea and vomiting (morning sickness) are still not completely elucidated. Although several different theories have been proposed and elaborated, none of them have been definitively proven. Among the most common theories are increased hormone levels, altered motility of the gastrointestinal tract, and a  psychological or emotional causes.

An increase in estrogen and progesterone levels may cause morning sickness. As progesterone also relaxes the stomach and intestines, it can result in excess stomach acids and, subsequently, gastroesophageal reflux disease. Since these hormones trigger active reflux at night, symptoms are usually worse in the morning.

Human chorionic gonadotropin may also lead tovomiting by stimulating another endogenous hormone – vasopressin. Since vasopressin is an emetic, increased sensitivity of the physiological mechanisms for vasopressin release could be a mechanism for morning sickness.

Hypoglycemia or low blood sugar caused by the energy requirements of the placenta is another theory  of pregnancy-related nausea and vomiting. Fasting hypoglycemia can develop in anyone who has an empty stomach Thus it is no wonder this type of hypoglycemia coincides with morning sickness when a pregnant woman awakens.

Morning sickness may represent an evolutionary adaptation or trait that protects pregnant mothers (and their unborn child) from food poisoning. Since the women with morning sickness does not have the affinity for potentially contaminated food (such as the eggs, poultry or meat), the survival chances for her and her fetus are higher.

Management of morning sickness

As pregnancy-related nausea and vomiting affects a large percentage of women, health care providers and patients should be aware of the evidence-based information on various treatmentsand they should be tailored individually for each pregnant woman.

Timing of the treatment of morning sickness is pivotal, because  early treatment can stop the development of hyperemesis gravidarum and reduce the time absent from work, hospitalization, and emotional distress. Both women and health care providers should be aware that the benefits of safe treatment modalities outweigh any theoretical risks to the fetus.

Some of the treatment options are adequate diet, drinking at least two liters of fluids per day, taking prenatal vitamins, antacids, the intake of fibers for constipation, as well as spitting out excessive saliva and mouth washing. Herbal products such as ginger and vitamin B6 can also be used safely, although the medical literature shows varying degrees of effectiveness.


Further Reading

Last Updated: Feb 27, 2019

Dr. Tomislav Meštrović

Written by

Dr. Tomislav Meštrović

Dr. Tomislav Meštrović is a medical doctor (MD) with a Ph.D. in biomedical and health sciences, specialist in the field of clinical microbiology, and an Assistant Professor at Croatia's youngest university - University North. In addition to his interest in clinical, research and lecturing activities, his immense passion for medical writing and scientific communication goes back to his student days. He enjoys contributing back to the community. In his spare time, Tomislav is a movie buff and an avid traveler.


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  1. Catherine Taylor Catherine Taylor United States says:

    During pregnancy, the body makes more hydrogen sulfide to help with making new blood vessels (pretty important when making little arms and legs) and to keep the uterus from contracting. This toxic gas breaks down quickly under normal circumstances, but if we're short of molybdenum (trace mineral, element #42, and used by the body in sulfite oxidase, the enyzme that breaks down sulfite), it can get stuck at sulfite, which is also toxic. If that sulfite builds up in the GI tract during the night, then throwing up would be the body's fastest way of getting rid of some of it in the morning. I took molybdenum for morning sickness, and it basically made the nausea part of morning sickness go away (although if I ate food with a lot of added sulfite, I felt ill anyway because the body can only make so much sulfite oxidase). I put all the supporting studies for this theory together and just published it with a medical hypotheses journal: www.sciencedirect.com/.../S0306987716300986

  2. David Gosley David Gosley United Kingdom says:

    Take a look at the Nevasic app - it's been researched and proven over 90% effective in reducing and eliminating NVP.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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