Thursday August 12 2010
We still do not know if stress affects conception
BBC News reports that research “has shown for the first time that high stress levels may delay pregnancy”.
The study behind this news followed 274 healthy women who were trying to get pregnant and looked at whether the levels of two stress-related chemicals in their saliva were linked to their chances of getting pregnant. It found that women with higher levels of one of the chemicals, alpha-amylase, did have a slightly lower chance of getting pregnant around the time they released an egg during their first menstrual cycle. However, there was no link between pregnancy and levels of another stress hormone called cortisol. The differing results for the two chemicals and the fact that the women were not asked how stressed they were mean that, based on this study alone, it is difficult to conclude whether fertility is related to stress.
There are likely to be a range of factors which can affect a woman’s chance of conceiving. Although this study does not conclusively prove that stress reduces your chances of getting pregnant, it is sensible to avoid stress where possible.
Where did the story come from?
Researchers from the US National Institutes of Health, Ohio State University and the University of Oxford carried out this study. It was funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, the UK NHS Executive, the DLM Charitable Trust and the Unipath Corporation (a company that sells fertility monitors, pregnancy tests and technical assistance for medical devices).
The study was published as an uncorrected proof in the peer-reviewed medical journal, Fertility and Sterility.
BBC News and the Daily Express reported on this research. They both state that stress could lead to a 12% reduction in the chances of becoming pregnant, but they do not note that this difference was not statistically significant.
What kind of research was this?
This was a prospective cohort study looking at the relationship between stress and likelihood of conceiving. The researchers say that women are often advised to relax while trying to get pregnant, but that so far only one study has looked at the link between stress and fertility. The previous study looked at reported stress levels in couples, while in the current study the researchers wanted to look at biological markers of stress in women’s bodies. The markers they used were the levels of two stress-related proteins in saliva – cortisol and alpha amylase. Levels of alpha amylase are reported to be linked to the levels of the hormone adrenaline – the so-called “fight or flight” hormone released during periods of physical or emotional stress. Cortisol is a hormone related to stress.
This was an appropriate study design to use for looking at whether there is a relationship between stress and conception.
What did the research involve?
The researchers enrolled women aged between 18 to 40 who wanted to become pregnant, and measured the levels of cortisol and alpha amylase in their saliva. They followed these women over six menstrual cycles to see if they became pregnant. They then analysed whether a woman’s levels of salivary cortisol and alpha amylase were related to whether she became pregnant and her chances of becoming pregnant on each fertile day of her menstrual cycle.
Women had to have a menstrual cycle length of 21 to 39 days and had to be planning a pregnancy, or to have already been trying to get pregnant but for less than three months. The researchers excluded any women who had a history of infertility, had been breastfeeding at the time, had used hormonal contraception in their past few menstrual cycles or used injectable contraceptives in the past year.
Women provided information on their lifestyles and kept a diary noting their frequency of intercourse and menstruation. They used fertility monitors to test their urine every day for 20 days, beginning on day six of each menstrual cycle. This test monitors the levels of hormones relating to egg release. They also collected saliva samples on day six of each cycle and sent these to researchers for testing for cortisol and alpha amylase. They carried out home pregnancy tests if they did not start to menstruate on the day expected, and repeated these tests each day until given a positive result or menstruation started. Women were also regarded as pregnant if pregnancy was confirmed by a nurse and some left the study because they were pregnant.
The researchers’ analyses looked at the time taken to become pregnant within each menstrual cycle. Of the 374 women in the study, 274 provided complete data for at least their first cycle and were included in the analyses. The researchers analysed the data in two ways:
- They looked at the relationship between cortisol and alpha amylase levels and a woman’s chances of getting pregnant, both in the first menstrual cycle in which she was trying to conceive and across all cycles.
- They used a different statistical technique to look at the relationship between cortisol and alpha amylase levels and a woman’s chances of getting pregnant each day of the fertile window of her menstrual cycle. This was defined as five days before the estimated ovulation date (based on fertility monitor results) and one day after the estimated ovulation date.
In their analyses, the researchers took into account other factors that could affect chances of becoming pregnant, including the couples’ ages, intercourse frequency and alcohol consumption.
What were the basic results?
Just under two-thirds of the women became pregnant during the study (64%, 175 out of 274 women). Couples who did not become pregnant tended to be older, with the women having fewer previous pregnancies and have the highest alcohol consumption. There were no significant differences between the average concentrations of salivary cortisol or alpha amylase observed in women with the different outcomes measured: withdrawal from the study, no pregnancy, loss of pregnancy or a live birth.
Overall, a woman’s salivary cortisol and alpha amylase levels on day six of her menstrual cycle were not significantly related to the chances of her becoming pregnant during the first menstrual cycle in which she attempted to become pregnant, or across all of the cycles.
Having a higher salivary alpha-amylase level on day six of the menstrual cycle was associated with a lower chance of getting pregnant on each day of the fertile window of the first menstrual cycle. When all cycles were pooled, this link was no longer statistically significant.
Salivary cortisol levels on day six of the menstrual cycle did not have any significant link to the chances of getting pregnant during the fertile windows of the first menstrual cycle or of all pooled cycles.
How did the researchers interpret the results?
The researchers concluded that “stress significantly reduced the probability of conception each day during the fertile window”. They say that their findings “support clinical and public health messages aimed at helping couples relax and minimise stressors when attempting to achieve pregnancy”.
This research has shown a link between the levels of alpha amylase and the daily chances of getting pregnant in the fertile window of a woman’s first menstrual cycle when trying to get pregnant. However, there are some limitations to these results, most notably that the link between alpha amylase was only significant in one of the analyses performed – that which looked at daily pregnancy chances in the fertile period of the first menstrual cycle. However, the link was not significant when the researchers looked at the fertile period across all cycles or when looking at the overall chances of getting pregnant in each cycle.
They suggest that the lack of a significant effect across all cycles may be due to couples who are the most fertile becoming pregnant in the first cycle, and to the women who contributed more than one cycle not becoming pregnant for other reasons. It is also possible that the study was not large enough for its analyses to detect a difference in the chance of getting pregnant across the whole cycle. In light of these problems the results should be interpreted cautiously.
There are other points to consider when looking at the results of this study:
- The link with fertility was only seen for alpha amylase, and not cortisol. The difference may be because these markers are involved in different stress pathways in the body.
- The markers measured were used to give an objective measurement of stress. The women were not asked how stressed they were feeling, therefore we cannot say from this study whether women with higher alpha-amylase or cortisol levels felt more stressed.
- The levels of the stress hormone were only measured on one day during each menstrual cycle, and this measurement may not reflect levels throughout the cycle.
- The researchers note that the methods used to collect saliva may have affected the results, as levels of the stress markers may vary throughout the day but women were not asked to take a sample at set times.
- As with all observational studies, factors other than stress (as measured by alpha amylase concentration) may have been influencing the results. The researchers tried to take some possible factors into account, but they and unknown or unmeasured factors may still be having an effect.
- The study concentrated on stress markers in females but not males: therefore this research cannot tell us whether stress in the male partner might affect the chance of conceiving.
The results of this study will need confirmation in further research. Despite this, stress is likely to have an effect on general wellbeing, and avoiding stress where possible seems beneficial for most people, regardless of whether or not they are trying to get pregnant.