Correlation between uterine wall thickness measured via trans-abdominal ultrasonography and cervical characteristics measured via trans-vaginal ultrasonography and Prediction of Preterm delivery

DISCUSSION

The studied cases have been divided into 50 pregnant women who have risk factors of preterm labor and 50 pregnant women without risk factors for preterm birth. There was statistically significant decrease in gestational age at delivery in cases with risk factors for preterm labor (mean was 35.7 ± 1.76 weeks) than in those without risk factors for preterm birth (mean was 37.88 ±1weeks) (P<0.001). There was no statistically significant difference among both studied groups with respect to the mean age of pregnant women (P=0.225), prior parity (P =0.494), mean BMI (P =0.261).

Experience of prior preterm birth was acknowledged as the most significant risk factor for PTB. This was in line with the former findings where women with previous PTD were at increased risk in their next pregnancy.^{6, 7}

Preterm was the largest direct trigger of neonatal mortality and may be concomitant with severe morbidity in the surviving infants.⁸

There is a consensus that preterm neonates are at higher risk of NICU admission, prerequisite for oxygen therapy, hypoglycemia, neonatal demise and other neonatal morbidities when contrasted to full term counterparts. Neonatal mortality was reported to be around 2.3 times higher in 37 weeks paralleled to 39 weeks neonates. The American College of Obstetricians and Gynecologists (ACOG) reinforced on the significance of delaying, when feasible, the elective resolution of pregnancy to after 39 weeks, instead of intervening at 37 or 38 weeks.^{9, 10}

Furthermore our results revealed that CL was shorter in cases who had risk of preterm labor (24.84± 3.19 mm) compared to that of those without risk (26.8±1.98 mm) (P <0.001). While the cut off value of cervical length was 25.5 (mm) for anticipating the risk of preterm labor, the sensitivity was 62%, specificity was 76%. However, the mean UCA and inner to inner cervical diameter (mm) showed no statistically significant difference among both studied groups (P >0.05). 

Shazly et al.¹¹ reported that the average CL in preterm group was 3.1 mm while it was 4.6 mm in the term group 2  with a significant discrepancy between both groups (p=0.021). They stated that the most noteworthy indicator discriminating women with PTD from those who delivered at term was the overall aberrant cervicometric results.

Mabrouk et al.² revealed that, the predictive role of CL measurement evaluated by the ROC curve between 20 to 24 weeks at cut off value of < 26 mm had sensitivity 100%, 48.9% specificity with 54% accuracy.

The sensitivity and specificity of CL measurement of 25 mm in low risk women was estimated in Dalili et al.¹² study were 55.5% and 93.6% respectively.

PTB is hard to be predicted. Up till now, there are no strict and absolute standard parameters for its anticipation, but there has been substantial interest in ways of distinguishing at-risk women of giving birth prematurely via clinical symptoms & signs, biochemical indicators, as well as CL.¹³

In the PTB prediction, the prominent sonographic variable beyond a doubt is the CL since short cervix has been ascertained to be meticulously concomitant with an increased PTB risk. Though the procedure for measuring CL is unchanged in most studies, considerable variances were present, explicitly; definition and PTB criteria exhibit great variability among studies. Next, most of the CL measurements were performed at admission but not after tocolysis.¹⁴

However, universal CL screening of singleton gestations without a prior PTB history is still a matter of debate.^{15, 16}

A published meta-analysis of randomized controlled trials (RCTs) did not find satisfactory evidence to advocate for or against routine CL screening, basically owing to limitations in the methodology of the included trials.¹⁷

For ease of clinical utility, 25 mm has been elected as the ''cut-off'' beyond which a cervix can be considered as normal, and underneath which it can be called as short and may be indicative of PTB.   Women with a CL 18

Mabrouk et al.² found that the CL estimated at 20-24 weeks in preterm group was significantly shorter in spontaneous PTB (sPTB) women in contrast to women who gave birth at full term.

Numerous additional ultrasound indicators have been studied to determine the risk of PTD, including cervical canal dilation, membrane distinguishability, gland area appearance, perfusion of the lower uterine segment, and if the canal was straight or curved. Regrettably, the data did not support any of these markers in the same way that our results did.¹⁹

There is some confirmation, that a wider UCA is allied to PTB before 34 weeks of gestation. Daskalakis et al.²⁰ assessed the existing body of literature about 3,000 women. The authors determined that 2^nd trimester UCA measurements could be a beneficial measurement in the likelihood of PTB prior to 34 weeks. The most frequently reported cut-off measurements were 105° and 95°.

 In agreement to our results earlier prospective cohort analysis that studied threatened PTL between the 20^th  and 31^st  weeks reported an average UCA of 103 degrees without statistically significant difference from the term group (P = 0.924).²¹

 Our study showed the mean thickness of both lower anterior and mid anterior uterine wall was significantly thinner in women with risk of preterm labor than those without (5.42±0.49 (mm) vs. 5.88±0.36 (mm)), (P<0.001) & (5.45±0.49 (mm) vs. 5.89±0.37 (mm) respectively) (P<0.001).Furthermore, there was statistically significant decrease in fundal thickness and posterior uterine wall thickness in women with risk of preterm delivery than those without risk (5.48±0.47 vs. 5.9±0.37, and 5.6 ± 0.46 vs. 6.01 ± 0.38 mm; respectively) (p<0.001). ). All uterine wall thickness as well as cervices length had statistically significant positive correlation with gestational age at delivery (P<0.001), neonatal birth weight (P<0.001), and negative correlation with inter pregnancy intervals less than 18 months (P<0.05). Finally, statistically significant negative correlation was observed between cervices length and each of NICU admissions more 2 weeks (r=-0.293, P=0.003), as well as RDS (r=-0.248, P=0.013).

ROC curve showed that the optimum cut-off values for low anterior and mid anterior uterine wall thickness were 5.51 and 5.52 (mm) for predicting risk of PTD with sensitivity 58% of both markers and specificity 90% and 92%; respectively (P<0.001). Also, fundal thickness and posterior uterine wall thickness had cutoff values of 5.615, and 5.735 (mm); respectively with sensitivity 60% and 58% and specificity 88% and 86% of both markers respectively. There is a paucity of studies regarding correlation between uterine wall thickness evaluated via trans-abdominal ultrasonography and prediction of PTD.

Woraboot et al.⁴  reported that where trans-abdominal ultrasonography (TAUS) was performed to estimate the lower uterine wall thickness (LUS) and TVUS was performed to measure the CL in 166 singleton pregnant women, an extremely positive correlation between LUS with cut-off value was 4.4 mm, and CL at 16-32 weeks of gestation (rs ¼0.767, n¼166, p<0,001). So they believed that it’s practical to imply that when the cervix is found long, the lower uterine wall would be thick, and when the cervix becomes shorter, the lower uterine wall would transform in the same direction i.e.  becomes thinner.

Mabrouk et al.² reported that there was statistically significant decrease in mean thickness of lower anterior in addition to mid anterior uterine wall, fundal and posterior wall thickness in women at risk of PTD than those without. Nonetheless, their study showed that there were no significant differences in myometrium thickness in diverse locations between cases at risk of preterm and the non-risky group. Using ROC curve, they reported that a posterior uterine thickness ≤6.0 mm had highest diagnostic characteristics in predicting preterm delivery among risky group with sensitivity 84.6%, specificity 62.2% and with 68% accuracy.

While Sfakianaki et al.²² study, assessed myometrium thickness (MT) serially in 92 twin pregnant females to establish pregnancy outcomes via TAUS they reported that patients with LUS-MT thickness in 2^nd trimester of (4.5 mm – 6.0 mm) were delivered at full term after 35 week' gestation, while patients with LUS-MT thickness of (3.5 mm-5.6 mm) had PTD before 35 week' gestation. Hamdi et al.²³ found that MT of the upper uterine segment continues as constant in the first and second pregnancy trimesters, while a significant linear tendency was found between thinning of the LUS and progressing gestational age.

Kim et al.²⁴ in the 2^nd trimester, uterine wall thickness displayed  that with the cut-off value of above 4.6 cm in uterine wall thickness, the sensitivity, specificity were 57.1%, 86.1%  respectively. When they evaluated the diagnostic performance of uterine wall thickness in the 1^st and 2^nd  trimester, uterine wall thickness in the 2^nd pregnancy trimester exhibited significantly greater area under the curve (AUC) value for prediction of  the subsequent PTD (p = 0.007).

Erzincan et al.¹⁴ studied the fundal, mid-anterior walls MT estimated trans-abdominally and the LUS as well as CL measurements and the ratio between them to distinguish and recognize the at-risk cases for PTB following an experience of threatened PTB in 46 singleton pregnancies. In line to our work, they concluded that the optimal cut-off values for CL, fundal MT: CL and mid-anterior MT: CL ratios in anticipating PTB were estimated to be 31.1 mm, 0.19 and 0.20, respectively.  They also reported that fundal MT: CL ratio predicted PTD with 71% sensitivity, 72% specificity values. For mid-anterior MT: CL ratio, sensitivity & specificity values were 76% for both. They found that fundal MT: CL and mid-anterior MT: CL ratios can anticipate PTB. They recommended that besides CL measurement, a fundal MT: CL ratio < 0.19 or mid-anterior MT: CL ratio < 0.20 can be used as an outpatient setting. This proofs our result in probability of expectation of PTL MT measurement via TAUS.

Elnasr et al.⁵ in their recent work showed that there was a statistically significant positive correlation between CL and LUS assessed trans-vaginally in preterm labor prediction in twin pregnancies with 4.26 mm was their reported cut-off value for LUS.

Thereby, the uterine wall thickness during pregnancy can be considered as predictors for PTB.

CONCLUSION

The lower uterine wall thickness measured trans-abdominally could be utilized with the intention of predict cases at-risk for PTB. It may represent an effective, precise, appropriate, and harmless procedure in anticipating the preterm labor with high validity than cervical length, so further research in this sector is necessary to validate the findings, as there are currently no large-scale prospective randomized trials to verify their practicality.