The term "morning sickness" is somewhat misleading because pregnancy vomiting and nausea can occur any time - not just in the morning.
Although the cause of pregnancy nausea and vomiting is not precisely known, one theory is that vomiting and pregnancy nausea week in and week out are the result of the changes a pregnant woman's body undergoes when the fetus and the placenta produce additional hormones.
Another probable cause for symptoms is that hormonal changes affect the gastrointestinal system so that the stomach empties more slowly.
Roughly three quarters of all pregnant women experience morning sickness.
Symptoms usually set in at four to eight weeks of pregnancy and abate by the fourteenth to sixteenth week.
You may be surprised to learn that experts think morning sickness may play a significant role in pregnancy.
The condition may protect your unborn baby.
Several plant varieties contain chemical toxins to protect them against being eaten.
Adults have a built-in defense system (numerous detoxification substances made by the liver and the surface tissue of other organs) that protects them against the toxins found in these plants.
This defense system is not yet fully developed in the embryo or fetus.
When you ingest even a tiny amount of plant toxins, its effect on you will be minimal, but it could be lethal to the unborn baby.
Pregnancy nausea week in and week out during the first trimester, triggers the nauseous feeling you get when you smell or taste these certain foods, preventing you from eating foods that contain toxins and protecting your baby from exposure to harmful toxins.
Morning sickness symptoms may also protect your health.
When you become pregnant, your immunity is weakened or suppressed to ensure that your body won't reject the embryo developing inside your womb.
Pregnancy nausea week in and week out limits the chances that you will eat animal products containing harmful bacteria, which are particularly dangerous when your immune system is not functioning properly.
Occasional vomiting and moderate nausea week after week will not harm your baby's health.
While morning sickness may mean that you won't gain any weight during the first three months or so of your pregnancy, this won't affect your well-being or that of the baby.
Just make sure that you are not risking dehydration and are not starving and you can be sure your baby will stay healthy.
Most of the time, a pregnant woman will regain her appetite and start to put on weight as soon as her symptoms abate.
Actually, most women manage their symptoms quite well and are able to stay healthy.
Remember, though, to keep your doctor informed of any problems you may have with morning sickness.
First pregnancies and twin or multiple pregnancies often mean increased symptoms.
Some women continue to experience vomiting and pregnancy nausea week after week even after the end of the first trimester of pregnancy and others will continue to suffer from morning sickness throughout their pregnancies.
It's important to know that severe, unrelenting vomiting may cause dehydration and pregnancy complications such as higher preterm birth rates.
In some cases, acute symptoms could also lead to the birth of a below-average weight baby or a baby that is small for its gestational age.
This is why doctors often prescribe anti-nausea medicine to pregnant women whose pregnancy sickness is severe.