Neonatal respiratory distress syndrome (RDS) is a respiratory condition that manifests at or shortly after birth, primarily due to a deficiency of pulmonary surfactant, a natural phospholipid essential for reducing alveolar surface tension and preventing alveolar collapse^[¹^]. Surfactant is a phospholipid-protein complex produced by type II alveolar cells, essential for reducing alveolar surface tension and preventing lung collapse during exhalation¹. Without sufficient surfactant, neonates experience impaired gas exchange, progressive respiratory distress, and increased work of breathing, often requiring intensive respiratory support^[²^].

Fetal lung maturity is a critical determinant of neonatal respiratory outcomes and is closely linked to adequate surfactant production. Assessing fetal lung maturity prenatally can help predict the risk of RDS and guide decisions regarding the timing of delivery or the need for antenatal corticosteroids^[³^].

RDS typically manifests within the first few hours after birth, presenting with tachypnea, nasal flaring, grunting, and cyanosis. The incidence of RDS is directly related to gestational age, affecting approximately 60–80% of neonates born before 28 weeks, 15–30% of those between 32–36 weeks, and is rare in term infants^[²^]. If left untreated, RDS can lead to severe complications such as bronchopulmonary dysplasia, intraventricular hemorrhage, persistent pulmonary hypertension, and long-term neurodevelopmental impairment^[⁴^]. In India, the mortality rate due to RDS varies widely, with case fatality rates reported between 20% to 57%, particularly among preterm and low birth weight neonates^[⁵^].

Early assessment of fetal lung maturity (FLM) is vital for optimizing perinatal care and improving neonatal outcomes, especially in pregnancies at risk for preterm delivery^[⁶^]. Accurate prediction of lung development helps obstetricians determine the optimal timing for delivery and implement timely interventions. One such intervention, antenatal corticosteroid therapy, has been shown to accelerate surfactant production, promote lung maturation, and significantly decrease the incidence and severity of RDS^[⁷^]. Thus, reliable evaluation of FLM is crucial for enhancing survival and minimizing morbidity in preterm infants^[⁶^].

Traditionally, amniocentesis has been the gold standard for assessing FLM by analyzing surfactant-related markers in amniotic fluid, such as the lecithin/sphingomyelin (L/S) ratio, phosphatidylglycerol (PG), and lamellar body count (LBC)^[⁸^]. However, despite its diagnostic accuracy, amniocentesis is an invasive procedure associated with potential risks, including infection, preterm labor, fetal injury, and maternal discomfort⁹. Given these limitations, there has been growing need for non-invasive techniques for assessing fetal lung maturity^[⁶^].

Doppler ultrasonography of the fetal pulmonary artery has emerged as a promising alternative, offering a safe, repeatable, and real-time assessment of fetal lung development^[¹⁰^]. Changes in pulmonary hemodynamics, reflected in Doppler parameters such as pulmonary artery acceleration time, systolic-to-diastolic (S/D) ratio, pulsatility index (PI), and the acceleration time to ejection time (AT/ET) ratio, have been correlated with lung maturation^[¹¹^]. Among these, the AT/ET ratio has shown particular promise as a non-invasive marker, with increasing values indicating advancing pulmonary maturity^[¹²^]. The use of Doppler ultrasound for predicting fetal lung maturity could potentially reduce reliance on invasive testing, facilitate timely corticosteroid administration, and improve neonatal respiratory outcomes by enabling better delivery planning^[¹⁰^].

OBJECTIVES

The aim of this study is to evaluate the role of fetal pulmonary artery Doppler in predicting fetal lung maturity and its correlation with neonatal respiratory outcomes. By investigating Doppler indices and their relationship with postnatal respiratory adaptation, this study seeks to establish a non-invasive, reliable method for assessing lung maturity, thereby improving obstetric management and neonatal care^[¹¹^].

A hospital-based, prospective observational study was done in the Department of Radiodiagnosis of Mahatma Gandhi Memorial Medical College & M.Y Hospital, Indore, Madhya Pradesh, India, after getting approval by the Ethics and Institutional Scientific Review committee (ISRC). The duration of this study was one year. A total of 170 patients among third trimester women referred to department of radiodiagnosis for routine antenatal screening for fetal well being were studied in our study in which out of 170, 44 patients delivered before 37 weeks, rest of the 148 patients were followed to 36 weeks. Among the 170 patients, 21 delivered at external facilities, and follow-up was carried out through telephone communication. Their post delivery outcome in terms of fetal respiratory distress was assessed.

Inclusion criteria -

1. Third trimester pregnant female referred to the department of radiodiagnosis for routine antenatal screening for fetal well being.

Exclusion criteria -

1. Any known fetal congenital anomaly
2. Patient requiring any acute intervention due to complication
3. Intrauterine growth restricted fetus
4. Multiple fetuses
5. Those with either oligohydraminos or polyhydraminos
6. Maternal diseases which can affect lung maturity

Study protocol-1. Pregnant third trimester females who were referred to the Department of Radiodiagnosis for routine antenatal screening for fetal well-being were followed till delivery and postnatal fetal outcome in the terms of development of fetal respiratory distress was assessed.

2. Informed consent taken after a complete description of study and handing over patient information sheet.
3. Detailed patient history including age, history of any medical disorders, history of any previous operation, menstrual history(last menstrual period , regularity of the cycle) was taken.
4. After completing the PC-PNDT Act formalities, obstetric ultrasound was performed.
5. All patients were examined in supine position using a low frequency transducer (3-5 MHz).
6. Fetus was observed for viability, gestational age and gross congenital defect.
7. Routine fetal biometry (BPD, FL, HC, AC) for measuring the gestational age of fetus, estimated fetal weight, Amniotic fluid index, Umbilical artery doppler and Middle cerebral artery doppler were taken.
8. After that a systematic examination of the fetal heart was performed (including 4-chamber view and outflow tracts) to exclude major structural heart defects.
9. At the axial view of the thorax, with the fetus stable without fetal breathing movements, three vessel view was obtained, MPA was traced until the midpoint between the pulmonary valve and the bifurcation of the right and left branches. The pulsed Doppler sample gate was kept between 2 to 3 mm and the angle of insonation kept at or around 15°.

The Doppler settings were adjusted to optimize the display of the velocity waveform, making the peak systolic velocity (PSV) and early diastolic notch clearly visible. The Main Pulmonary Artery (MPA) Doppler waveform displayed a distinctive shape, characterized by a sharp systolic peak that looks like a needle, known as a 'spike and dome' pattern. There is also a small reversed flow notch seen at the end of the systole. This specific shape is essential for differentiating the MPA waveform from the wave of the ductus arteriosus, which is more rounded, fuller, and triangular with greater diastolic flow. Once the optimal fetal MPA waveform was obtained, relevant Doppler velocity variables were manually traced three times and averaged. The variables included the systolic/diastolic (S/D) ratio, pulsatility index (PI), resistance index (RI), peak systolic velocity (PSV), and the At/Et ratio. The At/Et ratio is calculated by dividing the time interval from the beginning of the ventricular systole to the peak velocity (At) by the time interval from the start to the end of the ventricular systole (Et).

10. Neonatal RDS was diagnosed by neonatologist, blinded to fetal MPA Doppler results if at least 2 of 3 from these criterias were present:

1) Evidence of respiratory failure (tachypnea, retraction and, or nasal fairing) shortly after birth and increased oxygen requirement (fractional concentration of inspired oxygen > 0/4) for more than24 hours.

2) Radiographic evidence of hyaline membrane disease such as reticulonodular pattern, air bronchogram and ground glass appearance in the absence of other causes of respiratory disease.

3) Response to exogenous pulmonary surfactant

Stastical analysis Data were tabulated in the Microsoft Excel sheet and SPSS software was used to analyse the data. Further depiction of data was done in the form of various tables and charts. Sensitivity, Specificity, Positive predictive value and Negative predictive value of AT/ET ratio of pulmonary artery in diagnosing respiratory distress syndrome were calculated. The specific test were applied whenever necessary in the study.

CASE: A 24-Year-old G3P2

A)B-MODE- THREE VESSEL VIEW                    B)COLOUR DOPPLER- THREE VESSEL VIEW

1. C) DOPPLER FINDINGS

Mode of delivery – LSCS  APGAR score at 5 min- 4 Gestational age at delivery – 34 weeks 5days               NICU Admission- Yes AT/ET Ratio – 0.25  RDS- Present

Mode of delivery – NVD                                                                              APGAR score at 5 min- 3 Gestational age at delivery – 32 Weeks 0 days                       NICU Admission- Yes AT/ET Ratio – 0.16                                                          RDS- Present

Mode of delivery – LSCS                                                                             APGAR score at 5 min- 4

Gestational age at delivery – 37 weeks                                                       NICU Admission- Yes

AT/ET Ratio – 0.17                                                                                      RDS- Present

Mode of delivery – NVD   APGAR score at 5 min- 7 Gestational age at delivery – 37 weeks 5 days               NICU Admission- Yes AT/ET Ratio – 0.31  RDS- Present

Table No.1 Demographics- Distribution of patients according to age group, gestational age at scan and parity

Table No.2 Correlation between gestational age at delivery and development of RDS

Among the 44 preterm deliveries, 36 neonates (81.8%) developed respiratory distress syndrome (RDS), whereas only 3 out of 126 term neonates (2.4%) were diagnosed with RDS. This demonstrates a strong inverse correlation between gestational age and the occurrence of RDS, with a significantly higher incidence in preterm infants compared to those delivered at term.

Table No.3 Comparison of mean PI and mean PSV ratio in relation to presence / absence of RDS

The mean Pulsatility Index (PI) was slightly lower in neonates with RDS (1.87 ± 0.34) compared to those without RDS (1.99 ± 0.39), although this difference did not reach statistical significance (p = 0.087). The mean Resistive Index (RI) values were similar between the two groups (RDS absent: 0.83 ± 0.085; RDS present: 0.83 ± 0.08; p = 0.923). Likewise, the mean Peak Systolic Velocity (PSV) was marginally lower in neonates with RDS (73.94 ± 9.705) compared to those without RDS (74.94 ± 12.45), with no statistically significant difference (p = 0.592).

Table No.4 Comparison of mean AT, mean ET and mean AT/ET ratio in relation presence/absence of RDS

The mean Acceleration Time (AT) was significantly lower in neonates with RDS (65.46 ± 13.6) compared to those without RDS (77.52 ± 13.9), with a highly significant difference (p < 0.001). The mean Ejection Time (ET) was similar between the two groups (RDS absent: 233.6 ± 39.4; RDS present: 238 ± 48; p = 0.602). The mean AT/ET ratio was significantly reduced in neonates with RDS (0.27 ± 0.036) compared to those without RDS (0.33 ± 0.035), with a highly significant difference (p < 0.001).

Graph ROC curve between AT/ET ratio and development of RDS

The ROC curve shows a high diagnostic accuracy of the Doppler parameter in predicting neonatal RDS, with an AUC of 0.9287. This indicates excellent sensitivity and specificity, suggesting the parameter is a reliable predictor of RDS

Table No.5 Mean sensitivity, specifity, PPV and NPV of AT/ET cut off value

The present study demonstrates that an AT/ET ratio cutoff value of 0.30 serves as a highly effective non-invasive marker for predicting neonatal respiratory distress syndrome (RDS). The ratio exhibited a sensitivity of 92.3% and specificity of 91.6%, indicating its strong ability to accurately differentiate between neonates who will develop RDS and those who will not.Furthermore, the positive predictive value (76.6%) reflects a considerable likelihood of RDS in neonates with an AT/ET ratio below the cutoff, whereas the negative predictive value (97.6%) signifies a high probability of excluding RDS when the ratio is above 0.30

Table 6: Summary of maternal characteristics for RDS positive neonates

Among the neonates who developed Respiratory Distress Syndrome (RDS), the majority were delivered preterm, before 37 weeks of gestation. Out of 36 preterm cases, 20 were delivered by lower segment cesarean section (LSCS) and 16 by normal vaginal delivery (NVD). In the LSCS group, 19 neonates had an AT/ET ratio of less than 0.30, while only 1 neonate had a ratio above 0.30. Among the NVD group, 7 neonates had an AT/ET ratio below 0.30, and 9 had a ratio above 0.30. For term deliveries (between 37 and 40 weeks), 1 neonate delivered by LSCS and 2 neonates delivered vaginally had an AT/ET ratio below 0.30. No term neonates had a ratio above 0.30. Overall, a lower AT/ET ratio (<0.30) was strongly associated with the occurrence of RDS, especially among preterm neonates and those delivered by LSCS.

Respiratory distress syndrome (RDS) is one of the major causes of neonatal morbidity and mortality, affecting approximately 60–80% of neonates born before 28 weeks, 15–30% of those born between 32–36 weeks, and less than 5% of full-term infants^[13]. Early prediction of respiratory distress syndrome (RDS) plays an important role in improving outcomes for newborns. It gives healthcare providers the opportunity to act early with treatments such as antenatal corticosteroids, carefully plan the safest way and time to deliver the baby, and to provide the newborn with immediate care.

The pulmonary artery is integral to fetal lung development, as it supplies blood to the lungs, which, while not yet participating in gas exchange, are undergoing preparatory changes for postnatal function. Blood flow through the pulmonary artery is a critical indicator of lung maturation. Fetal pulmonary artery Doppler indices provide quantitative measures of this blood flow and offer insights into the functional status of the fetal lungs^[14].

Respiratory distress syndrome (RDS) is primarily caused by insufficient surfactant, which is crucial for preventing lung collapse. Surfactant production increases during the third trimester, especially between 32 and 34 weeks, making it an important period for fetal lung development. The third trimester was chosen for Doppler evaluation, as it offers an ideal window to assess lung maturity. By evaluating pulmonary artery blood flow, we can non-invasively assess lung development, with vascular resistance serving as a key indicator of surfactant production and lung maturity.   

A total of 170 pregnant women in their third trimester were included in the study. Routine antenatal and detailed  ultrasound studies of the fetal pulmonary artery were done, and the newborns were monitored after delivery to check if they developed RDS.

The age distribution of patients in our study indicates that the majority (52.3%) were between 19 and 25 years of age, followed by those aged 26 to 30 years (26.4%). Only 8.8% of patients were above 35 years, highlighting a younger maternal population, likely due to cultural and social factors.

In comparison, Namdev Seth et al. (2024)^[15] also reported a significant proportion of younger women in their study, with the majority of participants aged between 20 and 30 years.

In our study, the majority of antenatal scans were performed between 32 and 36 weeks of gestation (82.9%), with a small percentage of patients scanned earlier (8.2% between 28–31 weeks) and a few patients scanned at full term (8.8% between 37–40 weeks). Similarly, Kandil et al. (2023)^[16] conducted routine antenatal studies primarily between 32 and 36 weeks and found that these scans provided crucial insights for predicting neonatal respiratory distress syndrome (RDS).

The majority of patients in our study were primiparous (43.5%), followed by women with one (31.7%) or two (14.7%) children. Only a small percentage of patients were multiparous, with 6.4% of women being nulliparous and 2.9% having more than three children. This finding is consistent with other studies, such as that of Mohamed Laban et al. (2019), who also observed a higher percentage of primiparous women in their study.^[17]

In our study, the most common range for Peak Systolic Velocity (PSV) was 71–80 cm/sec (35.2%), followed by 61–70 cm/sec (21.1%). The majority of neonates had a Pulsatility Index (PI) between 1.50 and 1.99 (68.8%), and the most frequent Resistive Index (RI) was between 0.81 and 0.90 (37.6%). These distributions are similar to the findings reported by Baris Buke et al. (2019), who also observed that most fetuses showed PSV, PI, and RI values within these ranges^18.

Our study showed that the majority of deliveries occurred between 37 and 40 weeks (73.5%), with a small percentage of patients delivering preterm (25.8% between 32–36 weeks). Only one patient delivered between 28–30 weeks. These findings indicate that our study population consisted primarily of full-term deliveries, with a smaller subset of preterm births. This is in line with studies such as Kandil et al. (2023)^[16] and Mohamed Laban et al. (2019)^[17], who also reported higher rates of term deliveries in their studies.
Our study found a significant association between the mode of delivery and the development of respiratory distress syndrome (RDS), with 59.5% of neonates delivered via cesarean section (LSCS) developing RDS compared to only 12.8% of neonates delivered via normal vaginal delivery (NVD). These findings are consistent with Shuya Wang et al. (2021), who observed a higher incidence of respiratory issues, including RDS, in neonates delivered via cesarean section, suggesting that the absence of labor may impact the lung maturation process^[19]

On our study, out of 170 neonates, 39 (22.9%) were diagnosed with respiratory distress syndrome (RDS), while the remaining 131 (77.1%) did not develop the condition. When compared to other similar studies, such as the work by M. Aboulghar et al. (2019), which found that 26.5% of their fetuses developed RDS.

Our study demonstrated a strong inverse correlation between gestational age and the occurrence of respiratory distress syndrome (RDS), with 81.8% of preterm neonates (born before 37 weeks) developing RDS compared to only 2.4% of term neonates (37 to 40 weeks). These findings align with previous studies, such as those by Komal Yadav et al. (2022)^[20] and Saafaa Kandil et al. (2022)^[16] ,which also reported a higher incidence of RDS in preterm infants, highlighting the increased vulnerability of these neonates to respiratory complications.

Our analysis revealed a notable correlation between the mode of delivery and the incidence of respiratory distress syndrome (RDS). Specifically, 59.5% of neonates born via cesarean section (LSCS) developed RDS, in contrast to 12.8% of those delivered through normal vaginal delivery (NVD). This aligns with the observations made by Shuya Wang et al. (2021)^[19] who reported a greater prevalence of respiratory complications, including RDS, in neonates delivered by cesarean, suggesting that the lack of labor-associated physiological changes may influence lung maturity. These findings emphasize the role of delivery mode as a contributing factor in predicting neonatal respiratory outcomes, with cesarean delivery being associated with a higher risk of RDS compared to vaginal birth.

The mean Peak Systolic Velocity (PSV) among neonates who developed RDS was 73.93 ± 9.705 cm/sec, while for those without RDS, it was 74.94 ± 12.45 cm/sec. The difference was not statistically significant (p = 0.595), indicating that PSV alone may not serve as a reliable predictor for RDS.

In our study, most neonates (68.8%) had a Pulsatility Index (PI) between 1.50 and 1.99. Those diagnosed with RDS exhibited a slightly lower average PI (1.87 ± 0.34) compared to those without RDS (1.99 ± 0.39), though the difference approached but did not reach statistical significance (p = 0.063). This may suggest a trend toward lower PI in RDS cases, but PI on its own may not be a definitive predictor.

The mean Resistance Index (RI) was nearly identical in both groups: 0.83 ± 0.08 for neonates with RDS and 0.83 ± 0.085 for those without. The lack of a significant difference (p = 0.923) further indicates that RI is not a distinguishing marker for RDS in this study population.

These outcomes collectively suggest that PSV, PI, and RI may not be reliable standalone Doppler parameters for identifying neonates at risk for RDS. This is in accordance with the findings of Baris Buke et al. (2019)^[13] who also found no significant association between these Doppler indices and the development of RDS.

Conversely, our findings highlighted a significant reduction in both Acceleration Time (AT) and the AT/ET ratio among neonates who developed RDS. Specifically, the mean AT was 65.46 ± 13.6 in the RDS group versus 77.52 ± 13.9 in the non-RDS group, while the mean AT/ET ratio was 0.27 ± 0.036 compared to 0.33 ± 0.035, respectively—both results being highly significant (p < 0.001).

These results are in line with Komal Yadav et al. (2022)^[20], who also found a significantly reduced AT/ET ratio in fetuses who later developed RDS, identifying 0.30 as a cutoff with high diagnostic accuracy. Similarly, Saafaa Kandil et al. (2022)^[16] reported that an AT/ET ratio below 0.297 was strongly predictive of RDS. These findings reinforce our conclusion that a reduced AT/ET ratio is a dependable and sensitive Doppler marker for anticipating neonatal respiratory distress

This study underscores the vital role of fetal pulmonary artery Doppler assessment, particularly focusing on the acceleration time to ejection time (AT/ET) ratio, in the antenatal prediction of neonatal respiratory distress syndrome (RDS).

Through detailed Doppler evaluation conducted predominantly between 32 to 36 weeks of gestation a critical period for fetal lung maturation we established that a significantly lower AT and AT/ET ratio were highly predictive of the subsequent development of RDS in neonates. In contrast, other Doppler parameters such as peak systolic velocity (PSV), pulsatility index (PI), and resistive index (RI) did not demonstrate statistically significant associations, suggesting that they may have limited standalone predictive value for RDS.

Moreover, the study reaffirms the strong influence of gestational age and mode of delivery on neonatal respiratory outcomes. Preterm births exhibited a considerably higher incidence of RDS compared to term deliveries, highlighting prematurity as a key risk factor. Similarly, neonates delivered via cesarean section without the physiological stress of labor were found to have an increased risk of developing respiratory distress, suggesting that labor itself may contribute to promoting fetal lung maturation.

The AT/ET ratio, with a cutoff value of 0.30, achieved remarkable diagnostic performance, with high sensitivity, specificity, and predictive values, reinforcing its potential as a robust, noninvasive biomarker for assessing fetal lung maturity. Routine incorporation of pulmonary artery Doppler studies, particularly AT/ET measurements, in late third-trimester ultrasounds could thus significantly enhance antenatal surveillance, inform clinical decision-making, and allow for timely administration of interventions such as corticosteroid therapy or optimized delivery planning to improve neonatal outcomes.

In conclusion, fetal pulmonary artery Doppler evaluation, particularly the AT/ET ratio, holds great promise as an effective, non-invasive tool for the early identification of neonates at risk for respiratory distress syndrome. Its integration into routine obstetric practice could markedly improve neonatal respiratory outcomes through earlier diagnosis, better risk stratification, and more proactive perinatal care.

1. Moety GA, Gaafar HM, El Rifai NM. Can fetal pulmonary artery Doppler indices predict neonatal respiratory distress syndrome? J Perinatol. 2015;35(12):1015–9.
2. Schenone MH, Mari G, Horton AL, White J, Bahado-Singh R, McKenna D, et al. Predicting fetal lung maturity using the fetal pulmonary artery Doppler wave acceleration/ejection time ratio. Fetal Diagn Ther. 2014;36(3):208–14.
3. Abdelrahman AM, Mostafa AMA, Ali RM. Sonographic prediction of fetal main pulmonary artery (MPA) Doppler indices of lung maturity and neonatal respiratory distress syndrome (RDS) development. Egypt J Radiol Nucl Med. 2023;54(1):76.
4. Ghaleb F, El-sayed O, Gomaa M, Ahmed S. The role of different fetal pulmonary artery Doppler indices in the prediction of neonatal respiratory distress syndrome. Middle East J Radiol Nucl Med. 2021;10(1):1–9.
5. El-Sayed AM, Khalifa MA, Abdellatif MA. Evaluation of fetal lung maturity correlated by various ultrasound and Doppler parameters. Egypt J Radiol Nucl Med. 2022;53(1):76.
6. org. Assessment of fetal lung maturity [Internet]. Available from
7. American College of Obstetricians and Gynecologists (ACOG). Antenatal corticosteroid therapy for fetal maturation. ACOG Committee Opinion No. 713. Obstet Gynecol. 2017;130:e102–9.
8. Lampl M, Jeanty P. Timing of human fetal lung development. Am J Perinatol. 2004;21(3):143–52.
9. American College of Radiology. ACR–ACOG–AIUM–SRU practice parameter for the performance of standard diagnostic obstetric ultrasound. 2018.
10. Gharbi A, Aloui M, Ben Hmid R, Ayachi A, Belhadj A. Doppler assessment of fetal pulmonary artery: prediction of neonatal respiratory distress. Pan Afr Med J. 2020;36:212.
11. AbdelRazek AA, Masood SA. Role of fetal pulmonary artery Doppler indices in the prediction of respiratory distress syndrome in neonates. J Matern Fetal Neonatal Med. 2022;35(1):1–6.
12. Tekgündüz KŞ, Uzun S, Çelik Ö. The role of pulmonary artery acceleration time to ejection time ratio in the prediction of neonatal respiratory distress syndrome. Perinat J. 2020;28(3):123–8.
13. Buke B, Yavuz C, Çetinkaya M. The role of PATET ratio in predicting neonatal respiratory distress syndrome in preterm deliveries. J Obstet Gynaecol. 2019;39(5):647–53.
14. Moety GA, Gaafar HM, El Rifai NM. Doppler indices for predicting neonatal respiratory distress syndrome in preterm pregnancies. J Clin Ultrasound. 2015;43(7):420–8
15. Namdev S, Desai N, Tripathi S. Role of fetal pulmonary artery Doppler in predicting neonatal respiratory distress syndrome. J Matern Fetal Neonatal Med. 2024
16. Kandil SA, Ahmed A, Yousry H, Sayed M. Doppler evaluation of fetal pulmonary artery indices as predictors of neonatal respiratory distress syndrome. J Perinat Med. 2023;51(3):310–6
17. Laban M, Mustafa R, Al-Mahmood S. Predicting neonatal respiratory distress syndrome using fetal lung volume and PA-RI in preterm fetuses. J Perinatol. 2019;39(2):131–6.
18. Buke B, Yavuz C, Çetinkaya M. The role of PATET ratio in predicting neonatal respiratory distress syndrome in preterm deliveries. J Obstet Gynaecol. 2019;39(5):647–53.
19. Wang S, Liu X, Li Y, Zhang H. Diagnostic value of left and right peripheral pulmonary artery AT/ET in predicting neonatal respiratory disorders in GDM pregnancies. Medicine (Baltimore). 2021;100(52):e28039.
20. Yadav K, Sharma A, Prabha R, Komal YS. Predictive role of fetal pulmonary artery Doppler indices in neonatal respiratory distress syndrome. Int J Reprod Contracept Obstet Gynecol. 2022;11(8):2235–40