“Stress can double the risk of infertility for women,” The Daily Mail reports. However, the evidence provided by the latest study is not as clear cut as the reporting implies.
This research recruited around 400 US couples who were trying to conceive. The women gave two samples of saliva: one when they enroled in the study and another just after their first period during the study.
The researchers looked at whether levels of two stress hormones measured in the saliva – cortisol and an enzyme produced in response to adrenaline levels (alpha amylase) – affected the likelihood of getting pregnant over the course of a year. Women were also asked to complete daily “stress journals”.
Most couples in this study (87%) successfully conceived over the 12 months.
According to results, women with the highest third of alpha amylase levels had borderline decreased odds of becoming pregnant compared to women with levels in the lowest third.
They were also twice as likely to not conceive over the 12 months.
There are several limitations to this study, however. Measuring stress hormones on only two occasions provides, arguably, a very limited assessment of daily stress, as does the use of “stress journals”.
The analysis may have had a detrimental effect in itself, with participation in the study possibly increasing stress and anxiety levels about becoming pregnant. This factor could mean these couples are not representative of the general population trying to conceive.
Overall, this is another study suggesting the possible association between stress and chances of conceiving, but it doesn't provide conclusive answers.
The study was carried out by researchers from The Ohio State University College of Medicine, Division of Intramural Population Health Research at the Eunice Kennedy Shriver National Institute of Child Health and Human Development, and Texas A&M Health Science Center (all in the US). This study was supported by the Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development.
The study was published in the peer reviewed medical journal Human Reproduction.
The UK media’s reporting of this story was generally accurate, although more of an effort could have been made to highlight the numerous limitations of the study.
They have also used the US definition of infertility reported in this study, which uses a one-year timescale, rather than the UK definition, which is classed as “failure to conceive after frequent unprotected sexual intercourse for one to two years in couples in the reproductive age group”.
Stress was assessed using levels of “stress hormones” in the saliva, which are said to be stimulated when a person feels continually tense and anxious.
The study followed a total of around 400 couples who were trying to conceive.
The researchers state that numerous pieces of previous research had demonstrated a link between stress and fertility. However, the direction of that relationship has been unclear – that is, whether increased stress leads to lower chances of conceiving, or whether failure to conceive increases stress.
The researchers aimed to objectively measures the body’s response to stress. When we are continually anxious, stress hormones are produced in two ways:
Therefore, the researchers measured levels of both cortisol and alpha-amylase in the saliva, to try and objectively measure stress levels.
This research included 501 couples enrolled on an ongoing US cohort study between 2005 and 2009. The study enrolled people who were discontinuing use of any contraceptives, with the aim of getting pregnant. They said that in the absence of any established methods of recruiting a sample of people intending to get pregnant, they made use of a fish/hunting license registry in 16 counties in Michigan and Texas. They recruited people who met the following criteria:
When an eligible couple agreed to participate, the man and woman were interviewed separately at home, and were trained in the use of daily journals, fertility monitors and pregnancy tests. The woman collected a sample of her saliva first thing in the morning on two occasions:
Levels of salivary cortisol and alpha-amylase were measured in the laboratory.
The women were asked to fill out a daily journal, which included the question: “Please tell us your overall stress level each day”. The possible answers were:
The couples were followed for up to 12 months – or if pregnancy occurred, they were followed up throughout pregnancy. The main outcome the researchers were interested in was the time it took to conceive, as defined by a positive home pregnancy test.
They also looked at the specific probabilities of becoming pregnant during the peak six-day window around ovulation, as indicated by the fertility monitor.
The final outcome was “clinical infertility”. This was defined by the researchers in this study as a failure to achieve pregnancy, despite 12 months of regular, appropriately timed unprotected intercourse.
Outcomes were adjusted for the following confounders:
Of the 501 couples who enroled in the study, 100 (20%) withdrew; this was mostly due to a lack of interest in participating. Of the 401 (80%) women who completed the study, 347 (87%) became pregnant and 54 (13%) did not. Among those 401 women, 373 women (93%) had complete saliva data for this analysis.
There was no significant change in the levels of stress hormones measured in the saliva at the study’s enrolment and the second measure, taken after the woman’s first period.
There were no differences between those who did and did not become pregnant as to the number of times intercourse was had during the fertility window, or in their levels of salivary stress hormones.
There was also no difference in the level of daily stress reported by women each month.
When the researchers studied the likelihood of becoming pregnant and time to pregnancy, they did find some associations with levels of salivary hormones. They found that women with salivary alpha-amylase levels in the highest third were around a third less likely to fall pregnant, compared with women with levels in the lowest third.
Across each menstrual cycle, there was a general trend for women in the highest third of stress levels to be less likely to be pregnant than women with the lowest levels, though results were not statistically significant at all time points.
The researchers also found that women with salivary alpha-amylase levels in the highest third were twice as likely as women with levels in the lowest third to have not conceived by the end of the 12 months. As such, they meet the US definition of clinical infertility used in this study (relative risk (RR) 2.07, 95% CI 1.04 to 4.11).
There were no significant differences observed between women in the middle third of salivary alpha-amylase levels compared to women with the lowest levels.
There was no significant associations observed between likelihood of pregnancy and salivary cortisol levels.
The researchers say this was “the first US study to demonstrate a prospective association between salivary stress biomarkers and time to pregnancy, and the first in the world to observe an association with infertility”.
This study found that higher levels of stress, as measured by a woman’s salivary alpha-amylase levels, were associated with a longer time to pregnancy. There was also a link between alpha-amylase levels and an increased chance of a couple failing to conceive within 12 months of regular, unprotected sex.
This study benefits from a relatively large sample of couples recruited from the general population. Previous studies of this type tended to include couples recruited from fertility clinics, meaning they were not representative of the population at large.
Stress hormones were measured only on two occasions – at enrolment and after their first period. By assessing women early on, they could be less stressed about whether or not they would actually conceive than they may have been if assessed several months after trying. This may help the researchers in trying to examine the temporal nature of the relationship – whether stress levels influence the chances of becoming pregnant, or the reverse scenario, that failing to become pregnant influences stress levels. However, it still cannot very reliably tell us how or if stress and successful conception are related. It is likely to be a combination of both factors.
If repeated saliva samples had been taken on numerous occasions throughout the time the woman was trying to conceive, this may have given different results.
Other limitations to consider include the fact that:
Overall, this is another study suggesting the possible link between stress and chances of conceiving. However, it doesn't provide conclusive answers, and those trying to conceive should not be concerned by the results.
Ultimately, getting stressed about the notion that stress could make it more difficult to conceive is self-defeating.
If you do find yourself struggling with stress, visit the NHS Choices Moodzone, which contains a range of useful articles about how to combat feelings of stress and anxiety.