Doppler ultrasound characteristics of fetal nasal flow in pregnancies complicated by diabetes mellitus

The purpose of our study was to determine the Doppler ultrasound characteristics of fetal breathing-related nasal fluid flow velocity in pregnancies complicated by diabetes mellitus and to examine any changes in the timing parameters of fetal breath cycle relative to maternal blood glucose level. Fetal nasal fluid flow velocity was studied in 67 women at 30-41 weeks of gestation. In 37 cases, the pregnancy was uncomplicated; in 13 cases, the pregnancy was complicated by type I diabetes mellitus; and in 17 cases, the pregnancy was complicated by gestational diabetes. At the examination, subjects with diabetes mellitus were grouped by glucose control (normoglycemic and hyperglycemic) and by gestational age: 30-36 weeks and 37-41 weeks. Maternal hyperglycemia was defined as a plasma glucose value ranging from 140 to 205 mg per 100 ml. A continuous videotape record of the spectral Doppler imaging of fluid flow velocity in the nose was made during each study session. Based on a sample of 25 consecutive fetal breaths, the timing components of breath cycles were determined: time of inspiration (T_i), time of expiration (T_e), breath-to-breath interval (T_tolal), and ratio of T_i and T_e (T_i/T_e). There was a statistically significant difference between the T_total (msec) at 30-36 weeks' gestation in the cases of diabetes mellitus with maternal normoglycemia (1,050 ± 68 SEM) and uncomplicated pregnancy with maternal normal carbohydrate intolerance (1,221 ± 52). There was a similar difference in the values of T_e (552 ± 37 and 660 ± 29, respectively) at 30-36 weeks. In cases of maternal hyperglycemia at 30-36 weeks' gestation, the value of T_e (689 ± 84) was significantly higher than in cases of normoglycemia (552 ± 37). At 37-41 weeks' gestation, only the fetal T_i/T_e ratio in normoglycemic diabetic patients was significantly lower than in an uncomplicated pregnancy. No differences were found in the other timing parameters at this gestational age group in cases of diabetes mellitus relative to maternal blood glucose level. No relationship was found between the value of maternal blood glucose and either fetal T_total (r² = 0.003), or T_i/T_e ratio (r² = 0.0001) in cases of diabetes mellitus. Expiratory phase of fetal breath cycle even in well-controled normoglycemic diabetic women, is significantly shorter than in uncomplicated pregnancies before 37 weeks of gestation. Maternal hyperglycemia in these cases prolonged the duration of expiratory phase of fetal breath cycle and significantly decreased the T_i/T_e ratio more than 15% at 30-36 weeks of gestation. It is suggested that blood glucose level is involved in the regulation of fetal respiratory center in pregnancies complicated by diabetes mellitus.