Morning Sickness Usually Begins Within a Three-day Window

Researchers have narrowed down the time frame during which nausea and vomiting can potentially occur during pregnancy to just three days for most women, opening the door for scientists to identify a biological cause for this condition. By tracking the onset of symptoms based on a woman’s ovulation date rather than the date of her last menstrual period, they have demonstrated that symptoms occur earlier in pregnancy than previously thought and that the time frame for their occurrence is narrower.

Morning Sickness Begins Earlier

Nausea and vomiting during pregnancy, also known as morning sickness, are among the most common complaints in early pregnancy and affect about 70–80% of all pregnant women. Symptoms usually begin between the 4th and 7th weeks of pregnancy, peak around the 8th to 10th week, and subside in most women by the 12th to 14th week of pregnancy. The primary causes are hormonal changes, particularly the rise in the pregnancy hormone hCG and increased estrogen levels. Although the condition is often referred to as “morning sickness,” the symptoms can occur at any time of day. In most cases, the symptoms can be alleviated by eating small, regular meals, staying well-hydrated, and avoiding strongly scented or greasy foods. A severe form of pregnancy nausea is hyperemesis gravidarum, in which persistent, severe vomiting can lead to weight loss, dehydration, and electrolyte imbalances and often requires medical treatment. Despite the distress it causes, typical pregnancy nausea is generally harmless and poses no risk to either the mother or the unborn child.

In the past, the cause was often considered psychological, but a study supports the view that the cause is biological in nature and related to a specific stage of pregnancy development. Researchers at Warwick Medical School and the Department of Statistics at the University of Warwick drew their conclusions from a unique dataset collected at the Clearblue Innovation Center by SPD Development Company Ltd. Their findings, published in the journal BMC Pregnancy and Childbirth, identify a specific period during pregnancy that could provide scientists with clues to an anatomical or biochemical cause of this condition.

A woman’s last menstrual period is typically used to determine the start of pregnancy, but the timing of ovulation is considered a more accurate starting point, as menstrual cycles can vary greatly from person to person and even from cycle to cycle in the same person. The researchers used data from daily symptom diaries kept by 256 pregnant women to compare the onset of their nausea and vomiting symptoms with the date of their last menstrual period and the date of ovulation determined by urine test. When the ovulation date is used as the start of pregnancy, the first symptoms of morning sickness appeared in most women after 8 to 10 days, compared with 20 to 30 days when calculated from the last menstrual period. This not only showed that morning sickness begins earlier than previous studies suggested, but also that using the ovulation date narrows the time frame for the onset of symptoms to 3 days—compared to 11 days when the last menstrual period is used as a benchmark.

A Biological Issue Related to Early Fetal Development

Lead author Professor Roger Gadsby of Warwick Medical School said: “The exact course of morning sickness is unknown, but this study shows that it occurs at a specific stage of development and within a specific time window. “For us researchers, this narrows the focus when it comes to where we look for the cause. Knowing that symptoms occur within a very narrow time window of 8 to 10 days after ovulation allows researchers to concentrate their efforts on this specific stage of development to investigate the cause of the condition, both anatomically and biochemically.” In the past, the symptoms of women suffering from nausea and vomiting during pregnancy were downplayed and overlooked, as it was assumed that the symptoms had a psychological cause. This study reaffirms once again that nothing could be further from the truth and that this is a biological issue related to the development of the early fetus.

The study also found that 94% of women experienced symptoms of morning sickness—a higher percentage than in previous studies, which typically estimated this figure at around 80%. This is likely because data were collected regularly from participants starting before their pregnancy and continuing up to 60 days after their last menstrual period, whereas most other studies ask women to recall their symptoms after the fact. Professor Roger Gadsby added: “We have shown that more people develop symptoms of pregnancy-related nausea than previously thought, and one of the reasons for this is that this study captured mild early symptoms that typically subside by the 7th to 8th week. In other studies, these symptoms would have already subsided by the time the study began.” Previous research by the same team has shown that the term “morning sickness” is misleading, as nausea and vomiting can occur at any time of day, and argues that “nausea and vomiting in pregnancy” or “pregnancy-related nausea and vomiting” are more appropriate and avoid trivializing the condition.

How to Relieve Morning Sickness

To relieve morning sickness, various non-medicinal measures can be tried first. It is often recommended to eat several small, easily digestible meals throughout the day, as an empty stomach can worsen the symptoms. In addition, fatty, heavily spiced, or strongly scented foods should be avoided as much as possible, as these can trigger or worsen nausea and vomiting. Adequate fluid intake is also important, though small amounts spread throughout the day are often better tolerated than large amounts consumed all at once. Some studies show that ginger—for example, in the form of tea, capsules, or candies—can effectively relieve symptoms. Similarly, getting enough rest and avoiding stress can help improve symptoms. If these measures are not sufficient, medications such as vitamin B6 (pyridoxine) or other antiemetics suitable for pregnancy may be used after consulting a doctor. In cases of severe symptoms, particularly hyperemesis gravidarum with persistent vomiting, weight loss, or signs of dehydration, early medical treatment is necessary. In such cases, treatment with intravenous fluids to replenish fluids and electrolytes, as well as medication, may be necessary to prevent complications for both mother and child.