According to US and UK data from public health authorities, morning sickness affects over half of all pregnant mothers. It is generally related to an increase in estrogen levels, low blood sugar counts, and a greater susceptibility to some smells. Often, morning sickness occurs in the early hours of the morning and will ease up somewhat as the day goes on.
At times, morning sickness can be mild. However, the pregnant mother may at other times feel so nauseous that she will vomit. In most cases, morning sickness settles down by the end of the first trimester.