A new meta-analysis has waded into the issue of caffeine consumption in pregnancy.
Preliminary results suggest that a dose-response increase in miscarriage is seen with increased caffeine consumption – ie, the higher the dose, the greater the risk. So ‘low’ intake of 50mg to 149mg a day is not suggested to increase the risk of miscarriage, but a ‘moderate intake’ (150mg to 349mg a day) increases the risk by 16 per cent, ‘high intake’ (350mg to 699 mg day) increases it by 40 per cent and ‘very high intake’ (more than 700mg a day) by 72 per cent.
What does this mean in practical terms? A small daily latte or single-shot espresso won’t increase your risk at all; anything more might. This link offers more detail.
The findings are consistent with earlier studies. Does this mean that pregnant women should cease at once to drink coffee in order to minimise pregnancy risk? I would argue that in most cases the answer is a resounding no.
While the risk increase appears spectacular, the actual absolute risk remains low, relatively speaking. (That is, unless you are a caffeine fiend, consuming 700mg a day.) To explain the context, miscarriage occurs in 15 to 20 per cent of recognised pregnancies. The most common cause of sporadic (ie non-recurrent) miscarriage is a chromosomal/genetic disorder occurring at conception itself, resulting in an embryo that will miscarry regardless of any intervention.
The only patients I would personally advise to strongly avoid caffeine intake exceeding 149mg a day would be mothers with a history of recurrent miscarriage. This is because the potential mitigation of risk will go a long way to easing the worries that this group of patients will have. Knowing that you are able to manage certain risks can be empowering.
To other patients I would merely counsel that the absolute risk of even higher levels of caffeine remains extremely low. Ultimately, though, the decision rests with the individual patient.
It is important to realise that the two major studies quoted above are meta-analyses of case control and cohort studies, which by definition can only establish correlation but not causation. They are also lower levels of evidence and have issues with bias of various forms. These considerations mean that while we cannot say definitively that caffeine causes miscarriage, we can say that there appears to be an association with miscarriage and higher levels of caffeine consumption that may or may not prove to be causal.
Miscarriage is complex and, while there are definitive causes, caffeine is not one of them, even if epidemiological evidence suggests an association. A well-designed randomised trial is needed on this issue, but ethical considerations, plus the inability to control for the confounding factors, mean it will never happen.
To truly mitigate the risks of miscarriage, one should focus on general health considerations (such as smoking, weight, and pre-existing health disorders such as diabetes), or, in cases of recurrent miscarriage, insist on a referral for the investigation and treatment of any underlying conditions. Eliminating caffeine consumption is much lower down the priority list.
Disclaimer: this blog post is not an alternative to consultation with a licensed medical professional. Any decision about caffeine consumption should be made in conjunction with such consultation.