On Pregnancy and Probability

Four pregnancy tests. Image: Zwager, via Wikimedia Commons.

I have never been pregnant, but from what I understand, it is full of bizarre cravings, frequent bathroom breaks, and a smorgasbord of medical scans and tests. This last part is what concerns Kate Owens. She is a visiting assistant professor in the math department at the College of Charleston, and she is also pregnant with her second child. On her blog, she recently started writing about being a “pregnant mathematician.” Owens’s two posts on the subject have focused on the value of screening tests. “It’s tough having to juggle my emotions as a mother, my knowledge of statistics as a mathematician, and my interest in minimizing unnecessary financial expenses.”

The test she has written the most about is the infamous Glucola test for gestational diabetes. She found that the sensitivity and specificity of the test are appalling, or at least were in 1994 when the research she found was published. Only 27% of women who have the condition test positive for it, as will 11% of those who don’t have it. Is that really worth $40? (Or whatever the cost will be, because of course you can’t know in advance.)

Owens runs a few numbers but doesn’t come to a clear conclusion about whether she should or shouldn’t have taken the test. “One thing I wish I did have, for this screening and all of the others I have been (or will be) offered, is data ahead of time. I want to know the false positive and false negative rates. I want to know the sensitivity and the specificity and the predictive values. And I want to know how much money it’s going to cost me, and how much of a hassle it’s going to be. Lastly, I would like to know more about the medical significance of the condition, and since I’m not a medical doctor, I need it in some kind of quantifiable metric for when I do these kinds of calculations.”

Of course, the frustration of not knowing the cost and efficacy of medical procedures is not confined to pregnancy. My parents have both had surgery in the past few years, and it was impossible for them to find out before the procedures what the costs would be. We all want to make the right decisions about our health, but most of us don’t have the necessary background information.

Owens’s blog is interesting outside of the “pregnant mathematician” series, which I sincerely hope she will continue writing. In March, she had a series of posts about the statistics of the weather, inspired by the unusually cool spring in South Carolina. “What is the probability that at least 21 of the last 27 days highs have been at or below average?” She also writes about incorporating inquiry-based learning into her classes, teaching with technology, and women in math. I hope she writes a book called The Pregnant Mathematician. I would totally buy it for all my pregnant friends.