Do temperature charts improve our chances of getting pregnant?
Anna McGrail looks at the latest research.
Many of us worry about stress and the effect it might have on our fertility ... and then we worry about worrying in case it makes our stress levels higher... When I was writing the book about infertility, I interviewed over 100 women and asked them about stress. For many women trying to conceive, one of the most important sources of stress was, in fact, aiming to make sure that they had sex on the 'right' night, as indicated by their temperature chart or ovulation predictor kit. But premeditation and passion rarely mix, as Andrea found: 'All of a sudden our sex life was taken over with charts and thermometers. Let's face it, announcing that your temperature's risen half a degree is hardly the most alluring come-on.'
The theory behind temperature charts is that the hormones produced in the first part of the menstrual cycle keep the temperature of the body at one level; this temperature dips slightly just before ovulation, then rises immediately afterwards under the influence of the hormone progesterone, which is secreted by the ovaries after the egg has been released.
As these variations in temperature are minute -- a matter of half a degree or so -- they can only be seen by measuring the basal body temperature (BBT), which means the temperature of the body 'at rest'. To construct a chart, therefore, you need to take your temperature first thing in the morning when you wake, before you have a cup of tea or do anything else, as any activity will cause your body temperature to rise and then you won't be able to see the pattern that you're looking for.
Mind you, even if you do everything right, interpreting charts can still be a headache. For some lucky women, the rise in temperature just after ovulation can be clearly seen between one day and the next. Other women find that any rise at all is hard to see and at other times the pattern is all over the place. Many things can interfere with BBT: illness, stress, a night on the town... and it's hard to tell exactly what your hormones are up to.
BBT charts do play an important role in the initial investigation of couples who seem to be having problems conceiving. Just because you have a period every month, for example, this doesn't necessarily mean that you are ovulating. Even in cycles where the ovaries produce no egg, you may have withdrawal bleeding, caused by the fall in oestrogen levels towards the end of the cycle. If you chart your temperature for a few months and find that your record lines remain consistently flat, then you may be ovulating irregularly or not at all. So charts can be useful in alerting couples that there might be a problem, and then they can decide what to do about it. However, remember that some women whose charts show a relatively flat line often turn out to be ovulating perfectly well!
Another benefit of making a series of BBT charts is they can give you a better estimation of when your most fertile time might be. Many textbooks talk as if women always ovulated on Day 14 but if your cycles are short (24 or 25 days, for example) or longer than the average (35 or 36 days, for example), ovulation will generally occur earlier or much later than the average of Day 14. Getting to know approximately when you will be ovulating in each cycle can be of great value, but if your periods are regularly irregular, then charts will be of less help to you.
The timing of intercourse is crucial for conception. The egg, once it is released from the ovary, only has a lifespan of between 12 and 24 hours. Sperm can live a little longer, for up to five days inside a woman's body. However, for the best chances of sperm being in the right place (the fallopian tube) at the right time (when the egg is released) intercourse has to take place about two or three days before ovulation. Recording the days on which you had intercourse on your temperature charts can show you whether you have generally been having sex near enough to ovulation to be in with a chance of conceiving each month. This may be able to reassure you that you don't have a problem, for example, if you can see that you've only ever been having sex too late in the cycle for conception to occur, or it may alert you to the fact that there might be a problem.
Yet once we start keeping charts, most of us inevitably start doing the one thing that BBT charts can not do: trying to predict when ovulation will occur in any one cycle. But the temperature rise is a response to ovulation, not a signal that it is about to happen. Even if you have intercourse immediately after you see the temperature rise, ovulation has already occurred so it may be too late for the sperm to reach the egg in that cycle anyway...
It is a great temptation to scour the graph, analyse the numbers, looking for the tell-tale dip that is supposed to signal ovulation. If we think we see it, we do our best to make sure that we have intercourse that day. Then perhaps the next day as well if the temperature dips again... And then our temperature may rise, only to fall again a few days later... with the result that we once more schedule sex in case this is the real opportunity this month and we don't want to miss it.
Many couples have blazing rows brought on by the fact that one partner has to work, say, on the evening that the chart indicates might the 'right' one. Others argue if one partner seems reluctant to 'perform' on cue. Sex carried out according a schedule, especially a schedule which is as hit-and-miss as a BBT chart, can rapidly extinguish any element of enjoyment for both partners. It becomes 'baby-making intercourse' rather than a spontaneous expression of love and desire. Many men have occasional problems with impotence under this pressure to perform, and that can make the whole relationship even more strained...
So, should you keep a chart, or not?
The Royal College of Obstetricians and Gynaecologists has recently issued a set of Guidelines to GPs to help them deal with the couples who come to their surgeries wondering if they might be infertile. These Guidelines have been put together from 'evidence-based practice', which means that they have been drawn up from research studies which show that something either works, or doesn't work, when applied to the real world. For example, one 'evidence-based' conclusion is that smoking really does damage fertility for both men and women; i.e. studies have shown conclusively that if either partner smokes, then that couple have a smaller chance of conceiving. So an 'evidence-based' recommendation from your GP would be that both of you stop smoking.
About BBT charts, the RCOG Guidelines say this: 'There is no evidence that the use of temperature charts and LH detection methods to time intercourse improves outcome and their use should be discouraged.'
In other words, studies show that the continued compilation of temperature charts and the use of ovulation predictor kits does not improve your chances of getting pregnant in the least. Charts can provide other sorts of useful information, as we saw above, but when it comes to timing intercourse, you may find that your GP actively discourages you from using them.
If a couple are having sex, without reference to the calendar, every two or three days, then the sperm will be in the right place at the right time anyway, regardless of what your chart or predictor kit says. And you will either get pregnant... or you will not if there is some deeper factor at work. If there is, this will need to be investigated.
Taking your temperature every morning can be a grim and bleak affair. If you want the highest accuracy, you will be sticking the thermometer in an orifice other than your mouth... and I can tell you, having done it myself, that that's no way to start a fresh morning! On top of everything else, temperature-taking can become a lonely ritual which reminds us, every single day, before we do anything else, that we have a fertility problem... and that's no way to begin a day, either.
It is very hard to stop making BBT charts once we have started. We develop a need to try to understand what is going on inside our own bodies. But if you can hold onto the fact that the evidence shows that once you have established your pattern, taking your temperature or using OPKs will make not the slightest bit of difference as to whether you actually conceive or not, then maybe this will give you the confidence to move away from them. You can wake in the morning thinking of things other than whether this will be the 'right' day. The pressures of performing to schedule can disappear. Once you do this, then perhaps sex can become what it used to be, an expression of love and a way of reaching closeness in your relationship, rather than just another source of stress.
Coping with infertility is stressful enough without adding to it.