Does maternal diabetes delay fetal pulmonary maturity?

258 Letters

Does maternal diabetes delay fetal pulmonary maturity? To the Editors: In their recent analysis of fetal maturity studies in diabetic and nondiabetic mothers, Piper and Langer (Piper JM, Langer O. Does maternal diabetes delay fetal pulmonary maturity? AnaJ Oasmr GYNECOL 1993; 168:783-6) conclude that well-controlled maternal diabetes does not delay fetal pulmonary maturity but that poorly controlled diabetes does. This conclusion is surprising because their Fig. I clearly shows, at every gestational age, higher rates of pulmonary immaturity with well-controlled diabetes than without diabetes. The basis for their conclusion was that contingency analysis within each gestational age stratum showed a nonsignificant difference between the two groups. However, the nonsignificance was likely caused by the relatively small sample size within each stratum, that is, a type II statistical error. The trend across gestational ages seems too consistent to ignore. We performed a Mantel-Haenszel stratified X' analysis' s on their data. This analysis adjusts for the effect of gestational age on pulmonary maturity, allowing summary analysis across strata. The results showed that women with well-controlled diabetes had a significantly higher gestational age-adjusted risk of pulmonary immaturity than did those without diabetes (summary odds ratio 2.75,95% confidence interval 1.57 to 4.81, When the wellMantel-Haenszel X4 12.01, p<0.001). controlled diabetes group was compared with the poorly controlled group, the latter had a marginally higher risk of pulmonary immaturity (summary odds ratio 1.83,95% confidence interval 1.03 to 3.26, Mantel-Haenszel X4 3.77, p=0.052). We conclude that the data of Piper and Langer show a significantly increased risk of fetal pulmonary immaturity with well-controlled diabetes. However, it is possible that this increased risk was caused not by diabetes per se but rather by the difference in the definition of maturity for those with diabetes versus those without. With diabetes their definition required the presence of phosphatidylglycerol, whereas without diabetes maturity was defined by either the presence of phosphatidylglycerol or a lecithin/sphingomyelin ratio >2. This difference in definitions alone may explain the results. It would be informative to see an analysis in which the definition of maturity is the same for all groups. C. Andrew Combs, MD, PhD, and Ronald K Jaekle, MD Department of Obstetricsand Gynecology,University of Cincinnati College of Medicine, Cincinnati, 011 45267-0526

January 1994 Am J Obstet Gynecol

the response of Combs and Jaekle to our publication. They have raised two questions. The first is related to our decision not to use a summarizing statistical technique. The second is regarding our definition of maturity. On the first question, we specifically stratified our data by gestational age categories that were based on the windows of greatest interest, the early term gestations (34.0 to 36.9,37.0 to 37.9,38.0 to 38.9 weeks). We did not use a summarizing technique (such as Mantel-Haenszel) because (1) it would be biased by the grouping of gestational ages chosen and (2) across the vast differences in prevalence between the gestational age categories our categories of greatest interest would be masked by the extremes on either side of them. Indeed, it was the individual categories we were the most interested in. Additionally, although our Fig. 1 optically appears to have some difference between the good control and nondiabetic groups at 34 to 37.9 differences found. We there no significant weeks, were would encourage caution in applying the word "trend" (paragraph 1, above letter) with its implication of significance to data that are statistically not different. Regarding the second issue, the definitions of maturity by amniotic fluid analysis used in our study were based on common clinical criteria used in our institution and many others. The presence of phosphatidylglycerol was required for diabetics, whereas nondiabetics could have either phosphatidylglycerol present or a lecithin/sphingomyelin ratio -2t2: 1. The well-controlled and poorly controlled diabetics were compared by phosphatidylglycerol only. When the well-controlled diabetics were compared with the nondiabetics by means of either phosphatidylglycerol only or both lecithin/sphingomyelin and ratio, phosphatidylglycerol there were no significant differences seen (the immaturity rates tended to be slightly higher in the nondiabetics but not significantly so). The issue we find most interesting is the differences between well-controlled diabetic controlled pregnancies. poorly and Finally, although our study included more than 800 pregnancies and almost 300 diabetic patients (one of the largest series in the literature), we recognize the limitations of our sample size when stratified. To acknowledge this we clearly delineated our stratified study population in Table I. Deanna Af. Piper, MD, and Oded Langer, MD Division of Maternal-Fetal Medicine, Department of Obstetricsand Gynecoloo University of Texas Health Science Center at San Antonio, San Antonio, TX 78284-7836

REFERENCES 1. Mantel N, Haenszel W. Statistical aspects of the analysis of data from retrospective studies of disease. J Natl Cancer Inst 1959; 22: 719-48. 2. Robins J, Greenland S, Breslow NE. A general estimator for the variance of the Mantel-Ilaenszel odds ratio. Am J Epidemiol 1986; 124: 719-23.

Reply To the Editors: We thank the AMERICAN JOURNAL OFOBSrerRucsANDGvNEco c; Y for the opportunity to comment on

Uterine size as indication for early hysterectomy To the Editors: I read with great interest the article by Friedman and Haas (Friedman AJ, Haas ST. Should uterine size be an indication for surgical intervention in women with myomas? AM J Osstrr GYNECOL1993; 168: 751-5). The authors state that there is no indication for early surgical intervention in asymptomatic women with a uterine size < 12 gestational weeks. Taking into consideration the fact that postoperative