Having a baby may help you live longer, according to research reported in the Lancet this week. The story is that mothers "steal" some of their baby's stem cells which can, in turn, protect them in later life against certain diseases such as multiple sclerosis or breast cancer. It's good news, but what is even more intriguing and significant is a mounting body of evidence that seems to point to the fact that pregnancy itself could act as a crystal ball as far as an individual woman's health is concerned.
The past few years have seen a growing number of studies looking at what can be deduced about a woman's future health from the way in which her body reacts to pregnancy: and while the results may make worrying reading for some, there is no doubt their implications for preventive health could be immense.
Here is the theory: when you are pregnant, your body is put under a huge amount of strain. You put on a lot of weight - in a relatively short amount of time - and by as early as 18 weeks into the pregnancy, for example, your heart is pumping twice as hard as usual. With all your body's systems working flat-out, medical experts believe, any cracks in their workings begin to show. These cracks are seen as pregnancy complications, and once the baby has been delivered the mother's body usually returns to its previous state. But what is only now being realised is that these complications may provide a vital clue to what will happen two or three decades later when advancing age again starts to put stresses on the system.
The theory isn't entirely new - it has been known for years, for example, that the 3.5% of pregnant women who develop gestational diabetes - a condition that is reversed after delivery - are between 17 and 63% likely, depending on other risk factors, to go on to develop type two diabetes in the next five to 16 years. Mothers in this situation are routinely told of the risks and given advice on how to reduce their chances of becoming diabetic by, for example, avoiding obesity and taking as much exercise as possible.
What the new studies concentrate on are the risks between complications such as pre-eclampsia, small-for-dates babies and premature delivery and the likelihood of suffering later heart disease. The evidence so far, say doctors involved in the studies, is compelling: for women who have had a number of complications the risk of heart disease could be tenfold. It sounds alarming but the alternative could be more so, says Helen Bryce. She had pre-eclampsia in both her pregnancies: her son, now 16, was born at 29 weeks and her daughter, now 12, was born at 34 weeks.
Ten years after the second delivery Bryce, then aged only 44, started getting pains on the top right side of her stomach, below her rib cage. Her doctor referred her for a gall bladder scan, but while she was waiting the pain became unbearable. She was rushed to hospital by ambulance and an ECG revealed she had had a heart attack: she lost a quarter of her heart muscle as a result, and has 50% blockage in two arteries. If she had known she was at risk, Bryce believes, she might have suspected earlier that it was her heart, and not her gall bladder, that was the problem. "Women's symptoms when they have heart attacks are very different from men's and, anyway, women aren't usually seen as likely to be having heart attacks in their 40s. If I had known that my pre-eclampsia was a warning that I might get heart trouble, I would have been able to mention it to the doctor as soon as I noticed those pains," she says.
"The other thing my story illustrates is how quickly some women might need to heed the warnings they are getting in pregnancy. If you had asked me before, I would have thought I would have until my fifties to start changing the habits of a lifetime and exercising more and losing weight - I'm not very overweight but, like everyone, I could do with losing a few pounds."
Dr Naveed Sattar, reader in endocrinology at the University of Glasgow and author of a British Medical Journal paper reviewing the evidence on links between pregnancy complications and later heart disease, says pregnancy is a window of opportunity to pick up potential problems and intervene to reduce risks.
A lot more research is needed, Sattar says, to tease out the circumstances that pinpoint future problems - it may be, for example, that there are different types of pre-eclampsia and that only certain kinds put a woman at risk. But the way the data is pointing so far suggests that multiple pregnancy problems - women who, like Bryce, have experienced pre-eclampsia in more than one pregnancy, plus early delivery, plus small-for-dates babies - are those most likely to have the heart disease risk.
"We need to do a lot more work but there's some evidence, for example, that women who have a history of these complications have stiffer blood vessels and higher levels of adhesion molecules - that also means the blood vessels are stickier and so, too, is the blood, than would normally be expected." He stresses, though, that it is all about relative risk: for many women the initial risk of heart disease may be quite small, so even doubling or trebling it still doesn't represent a high overall risk. For women whose pregnancies were beset with complications, though, it may be worth keeping a check on cholesterol and blood pressure, particularly through their forties and fifties. Important too, as Bryce discovered, is being aware of the risk: it is like holding a piece of a jigsaw puzzle which may prove crucial in providing the full picture if you do experience ill-health.
While research is concentrating on links between pregnancy and heart disease, there are plenty of other studies looking into how far other medical conditions can be foretold as a result of pregnancy. Several have investigated whether cancer, and in particular breast cancer, can be predicted: but while it is known that the younger you are when you give birth, the more you reduce your overall risk, it is not as clear how far what happens to you while pregnant is significant.
Some studies have suggested that cancer is less likely in women who have had pre-eclampsia: but a study from Jerusalem in March this year found a possible genetic link between both pre-eclampsia and various cancers. Around 37,000 women giving birth between 1964 and 1976 were included in the study, which found that 3.7% of those who got pre-eclampsia got breast cancer, compared with 2.6% of those who did not - a finding described as "significant" by the research team. They also found a link between pre-eclampsia and cancers of the stomach, ovary, lung and larynx, although doctors here believe a lot more work is needed before this link is clear.
Other studies are more obvious: in 2002 the American Association for Cancer Research released research showing that women who gained a large amount of weight and didn't lose it afterwards were at more risk of post-menopausal breast cancer. Another study a few years ago linked severe morning sickness to the later risk of a stomach ulcer - the theory is that you are carrying a bacterium which makes you more likely to feel sick because of the pregnancy hormones, and is implicated in the growth of many stomach ulcers.
What is clear, on the evidence so far, is that filing a woman's notes away at the bottom of a drawer after her six-week post-pregnancy check-up could be a mistake. They may, in fact, be an early warning system to potential problems in the decades ahead and - with luck and used wisely - they might even be the difference between a healthy old age, and one beset with medical difficulties.
