In the study, researchers used data from daily symptom diaries that 256 pregnant women kept to link the beginning of their pregnancy sickness to the date of their last menstrual period and date of ovulation. The latter was determined by a urine test.
Most women experienced the first symptoms of pregnancy sickness after 8 to 10 days when using the date of ovulation as the start of their pregnancy. If measured from their last menstrual period, the symptoms emerged after 20 to 30 days.
This showed that pregnancy sickness begins earlier than what previous research has determined, and also proves that using the date of ovulation constricts the time frame that symptoms start to 3 days as opposed to 11 days when using the last period.
“The precise course of pregnancy sickness is unknown, but this research shows that it occurs at a specific developmental stage, in a specific timeslot,” Gadsby said. “For researchers, it narrows our focus in terms of where we look for the cause. If we know that symptoms occur in a very narrow window 8-10 days after ovulation, researchers can concentrate their efforts on that particular stage of development to find the cause of the condition, both anatomically and biochemically.
Research also revealed that a higher proportion of pregnant women — 94% — experienced pregnancy sickness than previous research showed. Usually, that rate is calculated at 80%. It’s likely because data was routinely gathered from participants before they became pregnant up to 60 days after the last menstrual period. Meanwhile, the majority of studies ask women to remember their symptoms after they have become pregnant.
“What we’ve shown is that more people get symptoms of pregnancy sickness than has ever been shown before, and one of the reasons for that is that this research has picked up mild early symptoms that tend to fade by 7-8 weeks,” Gadsby said. “In other studies, those symptoms would have faded by the time the research started.”