Assessment of fetal lung maturity by u/s and its impact on fetal outcome

Document Type : Original Article

Authors

1 obstetrics and gyecology department ,faculty of medicine,AL-Azhar university

2 obstetrics and gynecology department,faculty of medicine,AL-Azhar university.

3 obstetrics and gynecology department ,faculty of medicine ,Al-Azhar university

Abstract

Background: The presence of an immature foetal lung is linked to a variety of negative consequences, including respiratory distress syndrome. (RDS). The ability to continue or postpone birth is frequently the deciding factor efficiently assess lung maturity in the foetus.
Objective: To evaluate the value of assessment of amniotic fluid using ultrasonography in predicting fetal lung maturity and its impact on fetal outcome.
Patients and Methods: This prospective cohort study included three hundred pregnant women. They were later divided into two groups; RDS group and non-RDS group.
Results: Our results indicated the presence of a significant distinction between RDS group as well as non -RDS group regarding gestational age (P value=0.0005). However, there was no statistically significant difference regarding maternal age, gravidity, parity and abortion among RDS & non-RDS fetuses (P value > 0.05). Regarding the fetal biometric measurements, our results indicated a statistically significant decrease in the values of fetal biometric measurements including BPD, FL and AC among RDS group in comparison with the non-RDS group (P value < 0.001).
Conclusion: Ultrasound parameters including proximal tibial epiphysis (PTE) followed by distal femoral epiphysis (DFE) then amniotic fluid free floating particles (FFP) are precise predictors in the assessment of RDS with varying degrees of performance.

Keywords


INTRODUCTION

The liquid that surrounds a developing foetus in the amniotic sac, amniotic fluid (AF), is normally clear to pale yellow in colour. The makeup of AF is diverse, containing a variety of maternal and foetal components. The AF's composition varies with gestational age, with an average pH of 7.2 and specific gravity of 1.2. 1.0069–1.008. 13

In preterm and early term infants, lung immaturity is still the leading cause of morbidity and mortality. Although gestational age (GA) is the strongest predictor of lung maturity, respiratory distress syndrome and transitory tachypnea in the newborn are not limited to premature births (34 weeks). These problems are substantially more common in late preterm (34–36 weeks' gestation) and early term (37–38 weeks' gestation) newborns than in neonates delivered at or after 39 weeks' gestation.11

Because lung immaturity is linked to insufficient pulmonary surfactant production, respiratory distress syndrome (RDS), formerly known as hyaline membrane disease, is the most prevalent cause of respiratory distress in premature newborns. With the use of prenatal steroid medication, early provision of

 

 

positive airway pressure, and, in some circumstances, exogenous surfactant therapy, RDS can be avoided or its severity reduced.3

For nearly a quarter-century, Gray-level measurements, lung tissue mobility, and relative characteristics of lung-to-placenta or -liver imaging, among other things, have been utilised to attempt foetal lung ultrasound images without being invasive. These studies discovered a strong relationship between respiratory illness and death, but the diagnostic accuracy was insufficient to be useful for therapeutic purposes.4

The use of foetal ultrasonography to predict foetal lung maturity has long been suggested as a non-invasive alternative to amniocentesis. Gray-scale measurements, lung tissue motility, and the link between imaging features of foetal lung vs. placental or hepatic tissue have all been attempted utilising computer analysis of foetal lung ultrasound pictures over the last 25 years. 20

 

 

PATIENTS AND METHODS

Study design and setting: This was a prospective cohort study that was completed on 300 women coming for labour at El Hussein University and Shibin Elqantar public hospital in obstetrics and gynecology department from December 2019 to August 2021.

Criteria for inclusion: All women who are pregnant with a viable foetus and have an uncomplicated singleton pregnancy are eligible. Women have to be certain of their last menstrual cycle date and have it confirmed by ultrasound during the first trimester of pregnancy.

Criteria for exclusion: Multiple pregnancies, Malformations of the foetus ,complications (hypertension, diabetes, etc.) Macrosomic foetuses or intrauterine growth restriction Presence of meconium-stained fluid or antepartum haemorrhage.

Ethical considerations: Approval of ethical committee was obtained from Al-Azhar university faculty of medicine, Egypt. Verbal consent was taken from all cases before participation in this study. The nature and aims of this work were fully discussed to all women who were included in this study. No funding sources.

Methods:

All patients were subjected to the following:

Detailed personal, obstetric and medical history including: Personal history including age, smoking and level of education. Obstetric history including gravidity, parity, number of abortions, modes of delivery in previous pregnancies, first day of the last normal menstrual period and the gestational age, onset, duration. Medical history including Present or Past history

Examination: Vitalsigns are all important factors to consider. Abdominalexaminationforassessmentoffundallevelandfetalheartsounds. Palpation of the belly to detect foetal size and presentation, as well as uterine activity.

Lab assessment: Allinvestigationsobtainedaccordingtostandardprotocoloflabour inourhospitalincludingcompletebloodcount,CRPandgrouping,liverenzymes,kidneyfunctions,randombloodsugar,andurineanalysis.

Ultrasound evaluation: Allmotherswereexaminedbyultrasoundprenatallyforassessment of amniotic fluid index, umbilical artery Doppler, assessment of estimated fetal weight&fetalmaturitysign.The existence and size of epiphyseal ossification centres, placental grading (classification based on chorionic convolutions and calcifications), and other imaging measurements have all been used to determine maturity (19-21).Some mature fetuses may not have these findings at term, and some fetuses having these traits may be immature (e.g., maternal diabetes complicated by macrosomia). In general, ultrasonography assessment of gestational age in the third trimester (indirectly evaluating for maturity) is inferior to other approaches.

Technique: Abdominal ultrasound was done using mindray DP20 with center frequency 3.5MHZ. ultrasoundexaminationwasdoneOn the same day after their delivery, they went to the radiology department for an obstetric ultrasound scan. The same ultrasonographer performed the ultrasound examinationtodecreasetheintraobserver variability.

Ultrasound Findings: The placenta was graded according to Grannum's categorization. Biparietal diameter (BPD): The axial section of the foetal skull was measured with callipers from the outer table to the inner table of the skull, where a clear midline echo of the thalamus and septum pellucidum could be seen. Epiphyseal centres: The foetus' lower limbs were inspected, and callipers were used to measure the distal femoral epiphysis and proximal tibial epiphysis. Amniotic fluid linear densities: Linear densities in the amniotic fluid were observed.

Postoperative management:  Each neonate was examined by the paediatrician for the following foetal outcomes: foetal sex, weight, APGAR score at one and five minutes, signs of a respiratory problem, admission to the neonatal intensive care unit (NICU) and follow-up by the paediatrician for the duration of the hospitalisation, and any adverse neonatal morbidity or mortality up to discharge.

Sample size calculation: Based on previous studies who found that the adjusted the mean significant difference in the Mean FL between the RDS and the non-RDS, were in -RDS (1.27 ± 0.07) and non -RDS (1.47 ± 0.11) (Laban et al., 2015). Based on this assumption, the sample size was determined according to the using the formula:

 

Where

n is the sample size and Z/2 is 1.96. (The key number that separates the 95 percent of the Z distribution in the middle from the 5% in the tail.)

0.84 (Z) (The critical value that separates the lower 20 percent of the Z distribution from the upper 80 percent )

= the standard deviation of the mean MCA's estimate RI equals 0.07.µ1 = mean in FL in -RDS. (1.27).

µ2 = mean in FL in non-RDS. (1.47).

The sample size was calculated to be 300 patients in total.

Statistical analysis and data management

Data was collected, coded, updated, and entered into IBM SPSS version 20 (Statistical Package for Social Science). The qualitative data were given as numbers and percentages, the quantitative data with parametric distribution as mean, standard deviations, and ranges, and the quantitative data with non-parametric distribution as median with inter quartile range (IQR). When comparing two groups with qualitative data, the Chi-square test was utilised, but the Fisher exact test was used instead when the predicted count in any cell was less than 5. In the comparison of two groups with quantitative data and parametric distribution, the independent t-test was employed, while the Mann-Whitney test was used in the comparison of two groups with quantitative data and non-parametric distribution. The confidence interval was set at 95%, while the acceptable margin of error was set at 5%. As a result, the following p-value was declared significant: Non-significant if the P value is greater than 0.05. (NS). Significant if the P value is less than 0.05. (S). Highly significant if the P value is less than 0.01. (HS).

 

RESULTS

 

Neonatal respiratory distress syndrome (RDS)

Positive

(No.=47)

Negative

(No.=253)

Chi square test

No

%

No

%

x2

p value

 Maternalage

Mean±SD

29.62

4.96

31.55

4.97

2.454

0.015

Gestationalage

Mean±SD

35.68

0.76

36.04

0.81

2.829

0.005

Residence

Rural

25

53.2%

128

50.6%

0.107

0.743

Urban

22

46.8%

125

49.4%

Gravidity

Once upon a time

4

8.5%

38

15.0%

5.403

0.611

At least twice

8

17.0%

31

12.3%

At least three times

4

8.5%

34

13.4%

At least four times

6

12.8%

35

13.8%

At least five times

10

21.3%

30

11.9%

At least six occasions

5

10.6%

27

10.7%

a total of seven

6

12.8%

33

13.0%

a total of eight

4

8.5%

25

9.9%

Parity

zero times

1

2.1%

18

7.1%

6.630

0.577

Once upon a time

5

10.6%

44

17.4%

At least twice

11

23.4%

42

16.6%

At least three times

7

14.9%

32

12.6%

At least four times

4

8.5%

30

11.9%

At least five times

7

14.9%

26

10.3%

At least six occasions

4

8.5%

30

11.9%

a total of seven

5

10.6%

23

9.1%

a total of eight

3

6.4%

8

3.2%

Abortion

 

Zerotimes

28

59.6%

97

38.3%

8.656

0.013

Onetime

10

21.3%

106

41.9%

Twotimes

9

19.1%

50

19.8%

Table 1: Contrast between neonatal respiratory distress syndrome (RDS) and non RDS groups as regards demographic data

 

Neonatal respiratory distress syndrome (RDS)

RDS

(No.=47)

NON-RDS

(No.=253)

Independent t test

Mean

SD

Mean

SD

T

p value

BPD

82.09

2.59

88.24

3.14

12.665

<0.001

FL

60.67

3.51

67.86

2.86

15.215

<0.001

AC

278.72

13.92

307.96

8.67

19.037

<0.001

Table 2: Comparison between neonatal respiratory distress syndrome (RDS) and the non RDS as regards BPD, FL and AC.

 

 

 

 

Neonatal respiratory distress syndrome (RDS)

RDS

(No.=47)

NON-RDS

(No.=253)

Chi square test

No

%

No

%

x2

p value

PlacentalGrading

0-I

34

72.3%

46

18.2%

59.482

<0.001

II

8

17.0%

135

53.4%

III

5

10.6%

72

28.5%

Table 3: Comparison between neonatal respiratory distress syndrome (RDS) and non RDS as regards placental grading.

 

Neonatal respiratory distress syndrome (RDS)

Positive

(No.=47)

Negative

(No.=253)

Chi square test

No

%

No

%

x2

p value

COLON

I

5

10.6%

19

7.5%

11.466

0.003

II

28

59.6%

91

36.0%

III

14

29.8%

143

56.5%

Thalamicechogenicity

Echogenic

13

27.7%

194

76.7%

44.528

<0.001

Echolucent

34

72.3%

59

23.3%

Lung/liverechogenicity

 

Hyper-echoic

13

27.7%

70

27.7%

1.648

0.439

Hypo-echoic

17

36.2%

70

27.7%

Iso-echoic

17

36.2%

113

44.7%

Table 4:  Comparison between neonatal respiratory distress syndrome (RDS) according thalamic echogenicity, lung/liver echogenicity and colonic grading.

 

Neonatal respiratory distress syndrome (RDS)

Positive (No.=47)

Negative (No.=253)

Independent t test

Mean

SD

Mean

SD

T

p value

APGAR1min

2.98

0.82

5.26

0.79

18.062

0.001

APGAR5min

5.91

0.83

7.8

1.14

10.838

0.012

Table 5: Comparison between neonatal respiratory distress syndrome (RDS) according Apgar score.

 

Neonatal respiratory distress syndrome (RDS)

Positive (No.=47)

Negative (No.=253)

Chi square test

No

%

No

%

x2

p value

NICUadmission

No

21

44.7%

221

87.4%

46.276

<0.001

Yes

26

55.3%

32

12.6%

Mortality

No

45

95.7%

252

99.6%

5.966

0.015

Yes

2

4.3%

1

0.4%

Table 6: Comparison between neonatal respiratory distress syndrome (RDS) according NICU admission and mortality.

Item

AUC

Sensitivity

Specificity

-PV

+PV

P value

FFP

0.726

61.70

83.40

92.1

40.8

0.001

DFE

0.874

85.11

89.72

97.0

60.6

0.001

PTE

0.925

93.62

91.30

98.7

66.7

0.001

Table 7:  Cut of point, sensitivity and specificity of FFP, DFE and PTE among RDS.

This table shows that in FFP, DFE and PTE:

Its sensitivity is 61.7%, 85.11% and 93.62%

Its specificity is 83.4%, 89.72% and 91.30%

The positive predictive value is 40.8%. 60.6% and 66.7%

The negative predictive value is 92.1%, 97% and 98.7%

 

DISCUSSION

The pulmonary system is one of the last foetal organ systems to mature in terms of both function and structure. Preterm delivery can result in substantial newborn morbidity or mortality due to the immature pulmonary system's inability to sufficiently oxygenate the preterm neonate.6

Respiratory distress syndrome in newborns(RDS)isconsideredastheir lungs are immature, it is a primary cause of mortality and morbidity in newborns. It is more common in neonates that are born prematurely, and it is linked to inverselywithgestationalageatbirth.18

Thedecisiontocontinueordelaydeliverydependsusuallyontheabilitytoefficientlyassessfetallungmaturityforensuringtheprotectionofthefetusfromriskssuchassequelaeofrespiratorydistresssyndrome(RDS),necrotizingenterocolitis,intraventricularhemorrhage,patentductusarteriosusandneonatalsepsisasmuchaspossible.16, 11

Fetallungmaturitycanbeassessedbybiochemicaltestssuchaslecithin/sphingomyelinratio,absenceorpresenceofphosphatidylglycerolandamnioticliquid,fluorescentpolarization,foamstabilityorshaketestlamellarbodythatallrelyonamniocentesis,whichisaninvasivemethodtodeterminefetallungmaturitythatcouldcausecomplications.13

Ultrasoundbeingtheeasiest,for routine obstetric scanning, a simple, common, non-invasive, and cost-effective equipment is available. Ultrasound measures include bi-parietal diameter, femur length, epiphyseal centres of the lower limb, placental grading, colon grading, and free-floating particles in the amniotic fluid for assessing foetal lung maturity.withcontroversialdiagnosticaccuracy.4, 20

Therefore, the goal of our research was to assess thevalueofassessmentofamnioticfluidusingultrasonographyinpredictingfetallungmaturityanditsimpactonfetaloutcome.

Thisprospectivecohortstudyincludedthreehundredpregnantwomen.Theywerelaterdividedintotwogroups;RDSgroupandnon-RDSgroup.

Regardingthedemographiccharacteristicsofthestudiedcases,ourresultsrevealedthepresenceofa significant distinction betweenRDSgroupas well as non -RDSgroupregardinggestationalage(Pvalue=0.0005).Therewasnostatisticallysignificantdifferenceasregardsmaternalage,gravidity,parityandabortionamongRDS&non-RDSfetusesasillustratedinTable(1).

SuchfindingswereinagreementwithstudiesbyWang 28 et al. thatindicatedthatwith increasing gestational age, the risk of RDS reduced andShapiro-Mendoza and Lackritz25 studythatIn comparison to babies born at term, babies born between the 34th and 37th week of pregnancy had a higher risk of RDS. Additionally,Abdulla et al.3 study indicatedthatIncidence of RDSwasInfants born before 40 weeks gestation have a 12 percent chance of dying, whereas those born after 40 weeks have a 0% chance. ApreviousstudybyMehrabadi et al.19indicatedthatearly gestation RDS was substantially linked with maternal age (35 years) butprotectiveforlategestationRDS.

OurresultsindicatedastatisticallysignificantdecreaseinthevaluesoffetalbiometricmeasurementsincludingBPD,FLandACamongRDSgroupincomparisonwiththenon-RDSgroup(Pvalue<0.001)asillustratedinTable(2).

SuchfindingswereinagreementwithastudybyKandil et al.15 indicatedthedecreasedBPD,FL,andACamongRDSgroupandthatbyusingthefetalbiometryvaluesinthepredictionoffetalpulmonarymaturity,aBPDbetween8.28and9.35 cm,ACbetween29.5and32.2 cm,andFLbetween6.27and7.21 cmcorrelatedwithmaturefetallungs.

ItwasindicatedthatBPDcanbeusedforthe timetableinBPD bigger than 9.2 cm and elective caesarean section showed90% of foetuses have reached lung maturity.withhighspecificityandsensitivity(92%and87%respectively)andIn 80% of the cases, BPD 8.7 cm revealed RDS.19

Pallavi et al.21indicatedthatBPDisanaccuratefoetal lung maturity marker becausetheBPD and Correlation> 9.0 cm.The predictability of a positive shake test (in amniocentesis) was 100 percent. OurresultsindicatedastatisticallysignificantdifferencebetweenRDSgroupandnon-RDSgroupregardingplacentalgrading(Pvalue<0.001)asillustratedinTable(3).

SuchfindingswereinagreementwithDas et al.7thatindicatedthattherespiratorydistresssyndromewasfoundtobeassociatedwithgrade0andgradeIplacentaandnocasesweredetectedingradeIIorgradeIIIplacenta.

Previousstudiesby Keikhaie et al. and Sharma et al.14, 26indicatedthatgradeIIIplacentawasassociatedwithgoodfetalpulmonarymaturityandtheabsenceofrespiratorydistresssyndrome.

Ourresultsindicatedastatisticallysignificantdecreaseinfree-floatingparticles(FFP),distalfemoralepiphysis(DFE)andproximaltibialepiphysis(PTE)valuesamongRDSgroupincomparisonwiththenon-RDSgroup(Pvalue<0.001)asillustratedinTable(4).

SuchfindingsareinagreementwithAbdou et al.3thatindicatedthatthemeanepiphysealossificationcentersweresignificantlylowinneonatalwithrespiratorydistresssyndrome.ApreviousstudybyElsaeed et al.9indicatedthatAs long as the diameter is at least 1 mm.

 ultrasonography may identify each epiphyses ossification centre at a much earlier stage.However,Kandil et al.15indicatedthateven though thedetectionofossificationAlthough the presence of centres indicates foetal lung maturity, their absence does not rule out lung maturity. Furthermore, to prevent being confused with other neighbouring cartilaginous structures, these epiphyseal foci must be recognised with extreme caution. In difficult pregnancies, DFE detection of any size may not be related with foetal lung maturity.

Ourresultsindicatedadifference that is statistically significant betweenRDSgroupas well as non -RDSgroupregardingcolon(pvalue=0.003)andthalamicechogenicity(Pvalue<0.001),however,non-statisticallysignificantbetweenbothgroupsregardingLung/liverechogenicityasillustratedinTable(5).

SuchfindingswereinagreementwithstudiesbyKandil et al.15 thatThere was no evidence of a link between prenatal lung echogenicity and liver maturity or newborn RDS..Thesameresearchindicatedthalamic echogenicity was found to be a reliable predictor of foetal lung maturity witha77%and79%forsensitivityandspecificity,respectivelyandKeikhaie et al. 14 studythatthe foetal intestine was divided into four phases.AndGrade 4 foetal intestine was found to be a predictor of foetal lung maturitywith a good specificity and a low sensitivity (62.5%) (98.9 percent).

ApreviousstudybyRasheed et al.24 indicatedthatthe examination of the echogenic thalamus is advantageous and can be used as a foetal lung maturity measure.

OurresultsindicatedastatisticallysignificantdifferencebetweenRDSgroupandnon-RDSgroupregardingbirthweight(Pvalue<0.001)andnosignificantdifferencebetweenbirthgroupsregardingfetalsex(Pvalue>0.05)asillustratedinTable(6).

SuchfindingswereinagreementwithastudybyFehlmann et al.10thatindicatedthatRDShadahighincidenceinverylowbirthweightinfants,despitethefrequentuseofantenatalsteroids.

Condò et al.6studythatindicatedthatthe biggest risk factor for RDS is a low birth weight,butcontrarilywithourresults,thesamestudyindicatedthattheriskofRDSwashighwhenfetalsexismale.

OurfindingswereindisagreementwithapreviousstudybyPeacock et al.23thatindicatedthatMale preterm newborns are more likely than girls of the same gestational age to develop RDS and require more immediate respiratory and circulatory care. Furthermore, men have been linked to a higher risk of neonatal mortality and respiratory disease.

SuchhighriskwasexplainedascausedbyDuring the foetal phase, oestrogen regulates surfactant protein synthesis and promotes certain growth factors.12

OurresultsindicatedthepresenceofsignificantdecreaseinAPGARscoreatoneminuteandfiveminutespostbirthamongRDSgroupincomparisonwiththenon-RDSgroup(Pvalue<0.001)asillustratedinTable(7).

SuchresultsareinagreementwithWang et al.28thatindicatedthatanAt 5 minutes after birth, the Apgar score was 7.revealednegativeroleonthedevelopmentofRDSandindicatedpoorconditionsafterdeliveryduetotheimpairmentoftherespiratoryfunctionthatexacerbateshypoxia

Thavarajah et al.27studyindicatedthatBoth low and intermediate Apgar scores were substantially related with infant issues such as respiratory distress, feeding difficulty, hypothermia, and convulsions.

AretrospectivecohortstudybyChen et al.5indicatedMale infants with low gestational ages and low Apgar scores died at a higher rate than female neonates duetoRDSsyndrome.

OurresultsindicatedastatisticallysignificantincreaseinNICUadmission,mortalityrateandhospitalstayamongRDSgroupincomparisonwiththenon-RDSgroup.

SuchfindingswereinagreementwithEdwards et al.8thatindicatedthatneonatalrespiratorydistressisamajorreasonforincreasedmorbidityandmortalityamongnewborn,causingincreasedinfantsbeingadmittedtoneonatalunitssoearlyrecognitionofsignsandsymptomsofneonatalrespiratorydistressandpropermanagementcouldimprovetheprognosisofthesebabies.

OurresultsindicatedthatultrasoundparametersareprecisepredictorsintheassessmentofRDSincludingproximaltibialepiphysis(PTE)followedbydistalfemoralepiphysis(DFE)thenamnioticfluidfreefloatingparticles(FFP)thatshowedsensitivityvalues(93.62%,85.11%,and61.7%)respectivelyandspecificityvalues(91.30%,89.72%and83.4%)respectively.

SuchfindingswereinagreementwitharecentstudybyKandil et al.15thatindicatedthatultrasoundparametersaregoodpredictorsintheassessmentofRDSincludingepiphyses of the proximal tibiathatthe distal femoral epiphyses had the highest sensitivity (91%) and specificity (95%) after the proximal femoral epiphyses.showedThe sensitivity is 90% and the specificity is 84 percent.

ApreviousstudybyPatil et al.22indicatedthatThe foetal tibial epiphysis exhibited the best sensitivity (98.7%), specificity (88.8%), and accuracy of any of the tests (97.7 percent )followedbyfetalfemoralepiphysisthatshowedhighsensitivity(92.8%), whereaslowspecificity(60%) and a high level of precision (91.0 percent )intheevaluation ofRDS.

CONCLUSION

Ultrasound parameters including proximal tibial epiphysis (PTE) followed by distal femoral epiphysis (DFE) then amniotic fluid free floating particles (FFP) are precise predictors in the assessment of RDS with varying degrees of performance.

REFERENCES
 
1-Abd EL-Fattah, A., Yosry, L., Hammour, Z. and Chararah, D.A: Accuracy Of Ultrasound Prediction Of Fetal Maturity By Ossification Center Of Long Bones in The Cases Of Elective Cesarean Section At 38 Week Gestation. The Egyptian Journal of Fertility of Sterility. 2018; 22 (2): 2-12.
2-Abdou, A. M., Badr, M. S., Helal, K. F., Rafeek, M. E., Abdelrhman, A. A., & Kotb, M: Diagnostic accuracy of lamellar body count as a predictor of fetal lung maturity: A systematic review and meta-analysis. European Journal of Obstetrics & Gynecology and Reproductive Biology. 2020; X, 5, 100059.
3-Abdulla, TN., Hassan, QA. and Ameen, BA:Prediction of Fetal Lung Maturity by Ultrasonic Thalamic Echogenicity and Ossification Centers of Fetal Femur and Tibia. Italian Journal of Gynaecology& Obstetrics. 2018; 30 (4): 29-36.
4-Bonet-Carne, E., Palacio M., Cobo, T., et al: Quantitative ultrasound texture analysis of fetal lungs to predict neonatal respiratory morbidity. Ultrasound in Obstetrics & Gynecology. 2015; 45 (4): 427-433.
5-Chen, C., Tian, T., Liu, L., Zhang, J. and Fu, H: Gender-related efficacy of pulmonary surfactant in infants with respiratory distress syndrome: A STROBE compliant study. Medicine. 2018; 97 (17).
6-Condò, V., Cipriani, S., Colnaghi, M., Bellù, R., Zanini, R., Bulfoni, C., Parazzini, F. and Mosca, F: Neonatal respiratory distress syndrome: are risk factors the same in preterm and term infants? The Journal of Maternal-Fetal & Neonatal Medicine. 2017; 30 (11): 1267-72.
7-Das, L., Satapathy, U. and Rath, J: Correlation between Ultrasonographic Placental Maturation Study and Pregnancy Outcome, 2017; 118:1458-67.
8-Edwards, M.O., Kotecha, S.J. and Kotecha, S: Respiratory distress of the term newborn infant. Paediatric respiratory reviews. 2013; 14 (1): 29-37.
9-Elsaeed, G., Hassanin, E. and Abdelhamid, A: Sonographic detection of the distal femoral epiphyseal ossification center and its relation to the fetal age and fetal weight. Sci J. 2017; 10 (9): 77-81.
10-Fehlmann, E., Tapia, J.L., Fernandez, R., Bancalari, A., Fabres, J., D'Apremont, I., Garcia-Zattera, M.J., Grandi, C. and JM, C.C: Impact of respiratory distress syndrome in very low birth weight infants: a multicenter South-American study. Archivos argentinos de pediatria. 2010; 108 (5): 393-400.
11-Ghorayeb, S.R., Bracero, L.A., Blitz, M.J., Rahman, Z. and Lesser, M.L: Quantitative ultrasound texture analysis for differentiating preterm from term fetal lungs. Journal of Ultrasound in Medicine. 2017; 36 (7): 1437-43.
12-Gortner, L., Shen, J. and Tutdibi, E: Sexual dimorphism of neonatal lung development. Klinische Pädiatrie. 2013; 225 (02): 64-9.
13-Guan, Y., Li, S., Luo, G., Wang, C., Norwitz, E. R., Fu, Q. & Zhu, J: The role of doppler waveforms in the fetal main pulmonary artery in the prediction of neonatal respiratory distress syndrome. Journal of Clinical Ultrasound. 2015; 43(6): 375-83.
14-Kaluarachchi, A., Peiris, GR., Jayawardena, AK. et al: Hyperechoic amniotic fluid in a term pregnancy. Journal of family medicine and primary care. 2018; 7 (3): 635-7.
15-Kandil, R.A., El Shafiey, M.H. and Alarabawy, R.A: Values and validity of fetal parameters by ultrasound and Doppler as markers of fetal lung maturity. Egyptian Journal of Radiology and Nuclear Medicine. 2021; 52 (1): 1-10.
16-Kars, B., Karsidag, A.Y.K., Buyukbayrak, E.E., Telatar, B., Turan, C. and UNAL, O: Evaluation of fetal lung maturity by turbidity testing and tap test, 2011; J Turk Soc Obstet Gynecol. 8 (1): 25-31.
17-Keikhaie, K.R., Kahkhaie, K.R., Mohammadi, N., Amjadi, N., Forg, A.A. and Ramazani, A.A: Relationship between ultrasonic marker of fetal lung maturity and lamellar body count. Journal of the National Medical Association. 2017; 109 (4): 294-8.
18-Khanipouyani, F., Abbasalizade, F., Abbasalizade, S., Fardiazar, Z., Ghaffari, S. and Sarbakhshi, P: Predicting fetal lung maturity using the fetal main pulmonary artery doppler indices, Acta Medica Mediterranea. 2016;32 (Specia): 921-6.
19-Mehrabadi, A., Lisonkova, S. and Joseph, K.S: Heterogeneity of respiratory distress syndrome: risk factors and morbidity associated with early and late gestation disease. BMC pregnancy and childbirth. 2016; 16 (1): 1-10.
20-Palacio, M., Bonet-Carne, E., Cobo, T., Perez-Moreno, A., Sabrià, J., Richter, J., Kacerovsky, M., Jacobsson, B., García-Posada, R.A., Bugatto, F. and Santisteve, R: Prediction of neonatal respiratory morbidity by quantitative ultrasound lung texture analysis: a multicenter study. American journal of obstetrics and gynecology.2017; 217 (2): 196-e1.
21-Pallavi, L., Sushil, K., Lakhkar, D.L., Soniya, D., Abhijeet, I. and Pooja, S: Assessment of Fetal Lung Maturity by Ultrasonography. Annals of International Medical and Dental Research. 2017; 3 (4): p.1.
22-Patil, S.D., Patil, S.V., Kanamadi, S., Nimbal, V. and Yeli, R: A Clinical Study of Fetal Lung Maturity Correlated by Various USG Parameters. Parity. 2020; 5 (11): 12-4.
23-Peacock, J.L., Marston, L., Marlow, N., Calvert, S.A. and Greenough, A: Neonatal and infant outcome in boys and girls born very prematurely. Pediatric research. 2012; 71 (3): 305-10.
24-Rasheed, F.A., Zahraa’M, A.S. and Hussain, S.A: Evaluation of thalamus echogenicity by ultrasound as a marker of fetal lung maturity. Open Journal of Obstetrics and Gynecology. 2012; 2 (03): p.270.
25-Shapiro-Mendoza, C.K. and Lackritz, E.M: Epidemiology of late and moderate preterm birth. In Seminars in Fetal and Neonatal Medicine. 2013; Vol. 17, No. 3, 120-5.
26-Sharma, D., Padmavathi, I. V., Tabatabaii, S. A., & Farahbakhsh, N: Late preterm: a new high risk group in neonatology. The Journal of Maternal-Fetal & Neonatal Medicine. 2019; 1-14.
27-Thavarajah, H., Flatley, C. and Kumar, S: The relationship between the five minute Apgar score, mode of birth and neonatal outcomes. The Journal of Maternal-Fetal & Neonatal Medicine. 2018; 31 (10): 1335-41.
28-Wang, J., Yan, J., Han, J., Ning, Y. and Yan, C: Risk factors for respiratory distress syndrome among Chinese infants of 34-42 weeks gestational age: a multi-center observational study. Int J Clin Exp Med. 2019; 12 (4): 60-4354.