In my midwifery practice, I recently reviewed the records of a client who was transferring her care to us midway through her pregnancy. Along with the routine labs that I always encounter, I saw that her previous doctor had checked her vitamin D levels. That same day, as I waited on hold while calling Quest Diagnostics (who processes our clients' bloodwork and other labs), I listened to an upbeat promotion of a new blood test for vitamin D deficiency. I wondered whether I had missed something in the literature about the importance of checking vitamin D in pregnant women, or whether this was another case of a new popular test with unproven usefulness but intrinsic appeal to clinicians.

Maybe a little of both? Today, I came across a study in the March issue of the Journal of Clinical Endocrinology & Metabolism. The researchers report the findings of a small study of the association between maternal blood levels of vitamin D and the risk of having cesarean surgery. They measured the vitamin D blood levels of 253 women within the first 3 days postpartum, conducted interviews about habits such as prenatal vitamin use and alcohol consumption, and gathered personal, medical, and labor and birth information from medical records. After controlling for many variables that could affect cesarean risk, the researchers reported two significant findings:

• Women who were severely vitamin D deficient were almost 4 times more likely to have cesarean surgery.
• The lower a woman's vitamin D level, the higher her cesarean risk.

This is pretty compelling stuff. But how useful is this study, really? When I analyzed the study, I noticed a few problems that make me wonder if the association between vitamin D and cesarean is that straightforward after all.

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