No one is really sure what exactly causes morning sickness but there are many factors that are thought to contribute to the likelihood of developing it. The surge in hormones that occurs during pregnancy is thought to be one of the biggest contributors. Both estrogen and the human chorionic gonadotropin (hCG) hormone increase at a rapid rate after conception in order to support the pregnancy. Since the levels of these hormones typically peak around six weeks and then level off, morning sickness typically begins to subside around this time as well.

While hormonal changes are thought to be a contributing factor of morning sickness, so too is a pregnant woman's increased sensitivity to smells. In fact, many if not most pregnant women will attest to their nearly superhuman sense of smell. Even common smells from foods, cleaning products, and perfumes which are inoffensive to the average person may trigger a bout of morning sickness in a pregnant woman. This increased sensitivity to aromas coupled with hormonal changes can be a recipe for nausea, and even vomiting. A highly sensitive digestive tract may also be a cause, making even the blandest of foods a potential trigger for an episode. Low levels of vitamin B have also been said to contribute to morning sickness.

Some women are considered to be predisposed to morning sickness during pregnancy. These women may have had one or more of the following: morning sickness with previous pregnancies, a prior sensitivity to birth control pills with estrogen, a history of migraines, a tendency to have motion sickness and a family history of nausea during pregnancy. Morning sickness also tends to occur more frequently with multiples, and surprisingly, girl babies. Studies have shown that women pregnant with girls have a 50% higher chance of having morning sickness.

Although many women may feel as though their morning sickness is serious, or is a danger to her developing baby, there are typically no adverse effects on the baby or mother. Women are advised to take their prenatal vitamins regularly, and to eat as healthfully as possible. In severe cases, however, morning sickness may be associated with a higher risk of lower birth weights and preterm labor. Women suffering with severe morning sickness may be diagnosed with hyperemesis gravidarum, which is characterized by frequent vomiting and the inability to keep fluids and food down, for more than 24 hours. This diagnosis may lead to hospitalization and treatment with IV fluids and anti-nausea medications. You should consult your health care provider about any health concerns you have.

Perhaps the most comforting fact about morning sickness is that it doesn't last forever. For the majority of women, the nausea and vomiting of their first trimester will be just a memory — one that most will forget the first time they hold their baby in their arms.