The Fetal Airway Parameters: Potential Diagnostic and Prognostic Markers of Intrathoracic Lesions

32 Objective: Aim to study the fetal airway parameters in normal fetuses and fetuses with 33 intrathoracic lesions. Methods: This was an observational case–control study. In the control 34 group, 77 women were screened at 20-24 weeks gestational age, 12 were screened at 24-28 35 weeks gestational age, and 23 were screened at 28-34 weeks gestational age. In the case group, 36 41 cases were enrolled (6 cases of intrathoracic bronchopulmonary sequestration, 22 cases of 37 congenital pulmonary airway malformations, and 13 cases of congenital diaphragmatic hernia). 38 Fetal airway parameters (tracheal width, the narrowest lumen width, width of subglottic cavity and 39 laryngeal vestibule) were measured. The correlations between fetal airway parameters and 40 gestational age were analyzed. The fetal airway parameter differences between the control group 41 and the case group were analyzed. Results: Fetal airway parameters of both groups were 42 increased and had association with gestational age. Fetal airway parameters of the case group 43 were smaller than the control group. The tracheal width in fetuses with congenital diaphragmatic 44 hernia was the smallest in the cases studied. Conclusion: Fetal airway parameters are expected 45 to provide a novel diagnostic and prognostic method for intrathoracic lesions. 46

liquid is a major determinant of development and morphology of the fetal airway 5 . The liquid is a 54 delivery media of pressure. Fetal lung growth depends on the degree distended by luminal liquid 6 . 55 The pulmonary epithelium secretes liquid that distends the airways and plays a key role in normal 56 lung growth and development 7 . The changes of luminal pressure and biomechanics could lead to 57 changes in production and secretion of lung fluid 8 . 58 The trachea and bronchi are mainly composed of cartilage and smooth muscle; the development of 59 those two components influenced each other 9 . The smooth muscle is the major component from 60 trachea to lung 10,11 . Transmural pressure could promote growth of smooth muscles in the airway 2, 61 11 .

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Epithelial development of the airway wall is influenced by pressure such as shear stress 12 . The 63 principle is that pressure changes gene expression, promotes the release of growth factors, and 64 leads to changes in cell morphology and growth patterns 2, 13 . Those factors could influence growth identified 16 and the development of the fetal airway was also able to be identified 17 . The larynx, a 78 well-defined anatomical site, continues into the inferior trachea and forms the inlet of the fetal airway 79 18 . A deeper study of normal anatomy is the basis for prenatally detected structure deformities 19 . 80 With the measurements results affected by different sample preparations, there are 81 several limitations to airway studies on specimens 20, 21 . The ultrasonography is thought to be the 82 preferred option to study living fetal trachea 22 . The aim of this study is to use ultrasound to observe 83 fetal airway parameters' growth with gestation age and compare them with the airway parameters 84 of fetuses with intrathoracic lesions. Gynecology Hospital. The entry criteria of control group were normal singleton fetus with known 90 gestational age (by dates or by early ultrasound exam) and followed up through September 2021 91 without gross malformations. The entry criteria of case group were singleton fetuses with an 92 intrathoracic lesion without associated genetic or major anomalies. Exclusion criteria: 1. Patients in our center. Measurements were obtained using ultrasound equipment (WS80A, Samsung 102 Medison Co., Ltd., Seoul, South Korea) with a CV1-8A probe. To calculate intra-observer variation, 103 measurements were repeated at a different time and under the same conditions using 10 randomly 104 selected fetuses. The differences between the repeated measurements were evaluated by the 105 intraclass correlation coefficient (ICC).

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All the gravidas signed informed consent forms. All airway parameters were measured during fetal 107 apnea. Airway parameters included: traches width (TW), subglottic cavity width (SW), narrowest 108 lumen width (NW), and laryngeal vestibule width (LW). All airway parameters were measured in all 109 cases.

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The results differed as a result of the different methods of assessing tracheal parameters in 111 present studies 23 . Within the current study, we took the following simple approach to standardized 112 measurements. The tracheal ring is composed of a "C" type cartilage ring, with the free ends 26.0). The Kolmogorov-Smirnov test was performed on all measured parameters to assess whether they followed a normal distribution. Non-parametric test was performed when data did not 126 follow a normal distribution and when the variance was not homogeneous. The correlation 127 between airway parameters and gestational age was analyzed. The fitted growth curves of the 128 airway parameters were obtained. Independent samples t-tests were applied to calculate group 129 differences. Intra-and inter-observer reproducibility were assessed by analyzing the difference 130 between the values of 10 randomly-selected fetuses.

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Two trachea specimens of fetuses with the same gestation age were applied, one fetus with CDH

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Airway parameters in the case group were smaller than those in the control group, and showed 142 a statistical difference (p < 0.01) ( Table 1). The gestational age of two groups 143 showed no statistically significant differences (p=0.40), and the gestational age of different case 144 groups showed no statistically significant differences (p=0.085) too. Airway parameters of the two   The tracheal diameter in fetuses with laryngeal atresia was significantly higher than normal fetuses 235 33 . As observed in this study, airway parameters in fetuses with intrathoracic lesion are smaller than 236 normal fetuses. Therefore, when applying the airway parameters for diagnosis and treatment, such 237 as for fetal endoscopic tracheal occlusion on fetus and neonate, suitable instruments selection 238 should be carefully considered.

Limitations and further research:
We were unable to assess the change of airway parameters in many kinds of diseases 241 as the sample size was not sufficient to make such an analysis.