Stroke and migraine in pregnancy

Strokes in pregnant women who suffer from migraine headaches are very rare.  This is a letter I submitted to the British Medical Journal  in response to an article they just published on this topic:

The large amount of data and the statistical analyses in this paper look impressive and unfortunately may fool many readers into believing the conclusions made by the authors.  The authors do acknowledge that the discharge diagnostic codes miss many patients who suffer from migraine headaches.  This diagnosis is not only missed upon discharge, but it is an established fact that migraine is significantly underdiagnosed by the majority of primary care doctors.  Obstetricians are not likely to do a better job in distinguishing sinus and tension-type headaches from migraines, or diagnosing a migraine aura, particularly when managing a pregnant woman in the hospital.  It is true that migraines improve in pregnancy, but considering that about 18% of women suffer from migraine headaches, it is hard to believe that only one in 100 of these women will continue having migraines during pregnancy.  Obviously, when a complication, such as stroke occurs the diagnosis of migraine is much more likely to be recorded than when no complications occur. 
The authors provide many disclaimers and state that “On the basis of the select group of pregnant women with migraines coded during the hospital admission, this may not represent the population of women with migraine as a whole”.  Nevertheless, they go on to present and analyze this highly inaccurate data and even draw conclusions.  It is very unfortunate that the publicity associated with this paper (I first saw it reported on Yahoo.com) will cause unnecessary anxiety to millions of pregnant women.