Objective
To investigate the predictive value of pre-induction digital examination, sonographic measurements and parity for the prediction of non-reassuring fetal status and cord arterial pH < 7.2 prior to the induction of labor (IOL).
Method
This was a prospective observational study, including 384 term pregnancies undergoing IOL. Before the IOL, the Bishop score (BS) by digital examination, sonographic Doppler parameters and the estimated fetal weight (EFW) was assessed. The fetal cord arterial was sampled to measure the pH at delivery. Multivariate logistic regression analysis was performed to identify independent predictors of non-reassuring fetal status and low cord arterial pH.
Results
Forty four cases (11.5%) had non-reassuring fetal status, and 76 cases (19.8%) had fetal cord arterial pH < 7.2. In the non-reassuring fetal status group, the incidence of cord arterial pH < 7.2 was significantly higher than that in the normal fetal heart rate group (χ2 = 6.401, p = 0.011). Multivariate analysis indicated that significant independent predictors of non-reassuring fetal status were nulliparity (adjusted odds ratio [AOR]: 3.746, p = 0.003), EFW < 10th percentile (AOR: 3.764, p = 0.003) and cerebroplacental ratio (CPR) < 10th centile (AOR:4.755, p < 0.001). In the prediction of non-reassuring fetal status, the performance of the combination of nulliparity and EFW < 10th percentile was improved by the addition of CPR < 10th percentile (AUC: 0.681, (95%CI: 0.636 to 0.742) vs 0.756, (95%CI:0.713 to 0.795)), but the difference was not significant (DeLong test: z = 1.039, p = 0.053).. None of the above variables were predictors of cord arterial pH < 7.2.
Conclusion
The risk of fetal acidosis has increased in cases of non-reassuring fetal status. Nulliparity, small for gestational age and CPR < 10th centile are independent predictors for non-reassuring fetal status in term fetuses, though the addition of CPR < 10th centile could not significantly improve the screening accuracy.
The tissue stiffness is always an interesting issue to clinicians. Traditionally, it is assessed by the manual palpation, and this now can be measured by the ultrasound-based elastography. The basic physics is based on Young's modulus through the Hooke's law: E= S/e, where the Young's modulus (E) equals to the stress applied to the object (S) divided by the generated strain (e). With the rapid advancement of technology, the elastography has evolved from quasi-static elastography (ie, strain elastography) to dynamic elastography (i,e, shear wave elastography). The key differentiation of these two categories roots in the stimuli applied, namely mechanical or acoustic radiation force, and the response of the soft tissue. The strain elastography requires the operator to compress and decompress the tissue manually and the motion of the tissue during the stimuli is tracked to calculate the strain to reflect the tissue stiffness. While strain elastography is operator-dependent, shear wave elastography is not. Using shear wave elastography, the tissue is stimulated by the acoustic radiation force which can generate shear wave traveling through the tissue transversely. The shear wave propagation speed (V s ) is related to the shear modulus (m) of the medium: m = rV s 2 , where r is the density of the tissue and assumed to be a constant as 1000 kg/m 3 . In the incompressible biological tissue, the Young's modulus is approximately three times the shear modulus (E≈3 m). So the quantitative measurements of the tissue stiffness can be attained by shear wave elastography. The clinical application of elastography and its diagnostic capability has been extended. The knowledge of the basic physics of the various type of elastography facilitates the effective use of elastography. This review presented the clinical application and the risks of different types of elastography.
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