Diabetes, fetal lung maturity, and the lamellar body count

I've written a few posts on diabetes during pregnancy lately so thought I'd stick with it a bit longer. This time, however, the focus is on the effect that maternal diabetes has on fetal lung maturity.

It's generally believed that fetal lung maturity is delayed in women who have diabetes (gestational or otherwise). The reasons for this problem are not well understood, however high concentrations of glucose and insulin in the fetal blood have been postulated as a possible cause. Despite this, respiratory distress syndrome rarely occurs in term infants born to mothers with diabetes. Still, the issue of delayed fetal lung maturity and diabetes remains controversial.

I'll go on record for saying that there is no valid reason to perform amniocentesis solely to determine fetal lung maturity if maternal diabetes is well-controlled. However, if mom's diabetes is poorly controlled, then there may be value in performing fetal lung maturity tests. I'd like to emphasis the "may" in that last statement. As I've written before, it seems like all tests of fetal lung maturity should become obsolete. Realistically, however, they probably aren't going to go away any time soon.

Because the most widely used test of fetal lung maturity is about to disappear forever, many clinical laboratorians are planning to offer the lamellar body count test as a replacement. I've been asked several times what, if any, effect that maternal diabetes has on the results of this test.

Not surprisingly, that issue has been addressed only by a few published studies. In one study from 2002, a mature result from the LBC result was believable regardless of diabetes status (note, however, that this study did not include any neonates with RDS so a true assessment of the performance of the LBC could not be made). Another study from 2009 determined that the results of an LBC test were not influenced by maternal diabetes although it did suggest that the test was still useful in preterm pregnancies and in poorly controlled maternal diabetes.

What the take-home message? Granted, the data are limited but it's probably no more necessary to perform the LBC test in women with diabetes than it is in women without the disorder.

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