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Risk factors for early miscarriage

This is an updated version of an article in the Winter 2005 newsletter, explaining the results of the research carried out for The M.A. at the London School of Hygiene and Tropical Medicine (LHSTM).

 

Risk

Risk is only a probability, not a certainty. Let’s take the example of your risk of heart disease. We know that your risk of heart disease goes up if you smoke, are overweight, have a family history of heart disease or have raised blood cholesterol. But my grandmother smoked 40 cigarettes a day all her life and died well in to her eighties of something totally unrelated. So smoking gave her an increased risk of heart disease, but she never actually got heart disease – or if she did, it was not severe enough to affect her life in any way. On the other hand, my brother had none of those obvious risk factors, yet he died at 38 of a heart attack.

Risk factors do not mean that you will or won’t have something happen to you and if you do have, say, heart disease, it does not mean that any known risk factors caused it. It does, of course, make sense to reduce risk factors so that heart disease (or whatever) is less likely. Some risk factors cannot be controlled; I now have a family history of early heart disease and there is nothing that can be done about that, but the best advice for me is to reduce other risks that I do have control over.

The same applies to the results of this research. If you have one of the identified risk factors for miscarriage, this does not necessarily mean that it caused or will cause a miscarriage. But it makes sense to reduce your risk where you can – though this isn’t always possible. Conversely, you might find some of the research findings rather reassuring. It may be that there are some things that you thought might have caused or at least contributed to your miscarriage, but the research findings find they are not associated with a risk of miscarriage.

Factors associated with an increased risk of early miscarriage

 In summarising the findings, let’s look first at the risk factors that were found to be associated with an increased risk of first trimester miscarriage.

Biological/social factors

Health/obstetric factors

 Psychological factors

Lifestyle factors

 REMEMBER – if any of these things apply to you, it does not mean that that is what caused your miscarriage. There may be other factors that make the difference. Nevertheless, you might want to decrease the risk wherever you can though, as I said earlier, that’s not always easy or possible. For example, pregnancy after miscarriage is often very stressful and that cannot be avoided but if you are feeling stressed due to, say, job problems or a house move, you might want to consider waiting until you are more settled before becoming pregnant, to try to reduce the risk of early miscarriage.

 

Factors associated with a decreased risk of early miscarriage

Some factors were associated with a decreased risk of first trimester miscarriage. Again, they don’t mean that you won’t miscarry, but they do seem to make it less likely.

Health/obstetric factors

 Psychological factors

Lifestyle factors

The chocolate finding is rather unexpected as while common sense might suggest a good diet helps reduce risk of miscarriage, chocolate is hardly considered part of a good diet! As discussed below, we don’t know why any of these factors reduce or increase risk. For chocolate, it might be that it is another sign of general well-being or it might be that if you feel nausea (which is a good sign) you are more likely to nibble high carbohydrate chocolate to reduce your feelings of sickness.

 

Factors not associated with a risk of early miscarriage

Some factors were found not to be associated with risk of first trimester miscarriage, despite people commonly believing that they actually increase the risk.

Biological/social factors

Health/obstetric factors

Lifestyle factors

Some of these seem surprising and perhaps contradictory. For example:

Caffeine consumption at first glance seemed to be linked with an increased risk of miscarriage. But women who felt sick during early pregnancy (a good sign) tended to go off coffee and tea, so we knew that those who continued to do so might in fact already have a failing pregnancy. When the researchers examined the findings to take this into account (allowing for the effect of nausea), the link disappeared. Nevertheless, the Department of Health recommends that you limit your intake of caffeine in pregnancy for other reasons not related to miscarriage.

Smoking did not seem to be linked to early miscarriage although again, should be avoided in pregnancy for other reasons. Occasional alcohol consumption was also not associated with early miscarriage, but frequent and/or heavy drinking was and, of course, should be avoided in pregnancy for other reasons.

Personally, I was relieved that there was no significant risk associated with full-time work, as I have always felt guilty about working full-time during my pregnancies. I hope that perhaps these findings might make you feel less guilty too.

Of course, we still don’t know why these factors might increase or decrease your risk of miscarriage. Some findings are surprising and it would be particularly interesting to find out more –for example, there doesn’t seem to be any obvious explanation as to why chocolate seems to reduce risk and previous termination seems to increase risk. We hope that further research will follow that will give more information.

 

Barbara Hepworth-Jones