Intra-observer variability of Doppler measurements in umbilical artery (UA) and middle cerebral artery (MCA) in uncomplicated term pregnancies

OBJECTIVE

To evaluate the intra-observer variability of the middle cerebral artery (MCA) and umbilical artery (UA) Doppler measurement taken under optimal conditions in term, uncomplicated pregnancies.

METHODS

A prospective study on uncomplicated singleton term pregnancies was performed. Multiple Doppler measurements were taken in the MCA and the UA by one examiner. Intra-rater agreement was calculated. Doppler indices were correlated to fetal biometric parameters and to gestational age.

RESULTS

One hundred patients were recruited. MCA indices were found to have the highest strength of intra-rater/observer agreement (K = 0.888) versus only a "good" agreement for UA pulsatility index (PI) (K = 0.755).The MCA-PI was significantly correlated with BPD (r = -0.198, p = .047), EFW (r = -0.241, p = .01) and birthweight (r = -0.208, p = .03). A statistically significant decrease was found in the MCA PI (r = -.422, p < .001) and in the CPR (r = -0.444, p < .001) with advancing pregnancy, between 37 and 42 weeks gestation. The UA PI did not change significantly (p = .099) during this period.

CONCLUSIONS

MCA PI measured at term is reproducible with a high ICC. MCA PI significantly decreases with advancing gestation at term. No correlation was found between Doppler measurements and time to delivery.

Abnormal Middle Cerebral Artery Doppler Associates with Spontaneous Preterm Birth in Normally Grown Fetuses

OBJECTIVE

Our aim was to evaluate whether Doppler changes in the fetal middle cerebral (MCA) and umbilical arteries (UA) suggesting fetal hypoxemia precede the onset of spontaneous preterm birth (PTB).

METHODS

We studied 2,340 appropriate-for-gestational-age singleton pregnancies that had MCA and UA pulsatility indices (PI) recorded at 28-32 weeks. Values including the cerebroplacental ratio (CPR) were converted into multiples of the median and evaluated according to both gestational age at the onset of labor and the interval between ultrasound and labor. ROC analysis was used to calculate the ability in the prediction of spontaneous PTB before 32, 34 and 37 weeks' gestation.

RESULTS

While no correlations were observed for the UA PI and CPR, lower MCA PI values were associated with an earlier onset of labor (p < 0.001) and a shorter ultrasound-labor interval (p = 0.028). The ROC analysis at different gestational ages and intervals to labor indicated that MCA PI values were poorly predictive of spontaneous PTB (all areas under the curve <0.7).

CONCLUSIONS

Low MCA PI values at 28-32 weeks are associated with subsequent spontaneous PTB, indicating that fetal hypoxemia unrelated with placental disease might be implicated in the onset of labor. This association, however, is unlikely to be useful in the prediction of PTB.

Proximity of term labor deepens the fall of Doppler impedance in the fetal cerebral arteries

OBJECTIVE

To determine the existence of Doppler changes in the fetal vertebral, middle cerebral and umbilical arteries prior to term labor.

METHODS

Five hundred and twenty eight Doppler examinations of the vertebral (VA), middle cerebral (MCA) and umbilical (UA) arteries resistance indices (RI) were performed between 37 and 41 weeks gestation. For each artery, values were converted into multiples of the median (MoM) and were divided into four groups according to the interval to labor and compared using Kruskal-Wallis tests. Subsequently, values were plotted in scattergrams and linear regressions and 95% confidence intervals were calculated. Finally, using multivariate analysis and model averaging, the importance and interrelationship of Doppler measurements in the explanation of the interval to labor was evaluated.

RESULTS

Univariate and multivariate analysis confirmed that, independently of gestational age, fetuses examined close to labor presented more intense Doppler changes in the cerebral arteries with a significant reduction of the VA RI and MCA RI. This reduction was larger in the MCA. No significant changes were detected in the UA.

CONCLUSION

Before the onset of term labor, the fetal cerebral flow presents an additional reduction of impedance, which is more intense in the MCA system.

Can we predict delivery date with obstetric ultrasound?

OBJECTIVE

The long-term prediction of delivery date with obstetric ultrasound.

METHOD

The cervical length (CL) and the fetal vertebral, middle cerebral and umbilical resistance indices were measured in 317 pregnancies between 30 and 37 weeks. Subsequently, multivariate analysis was applied to calculate the best model for the prediction of delivery date.

RESULTS

The best model included the examinations of the CL and the middle cerebral artery resistance index. In comparison with estimated delivery date (EDD) based on the last menstrual period, a small improvement was detected, particularly in earlier deliveries, however 34% of predictions still had an error of more than 5 days.

CONCLUSIONS

Long-term sonographic prediction of delivery date depends mainly on the CL and improves the prediction of the EDD. However, it is still too inaccurate for clinical use.

Doppler study of the fetal vertebral and middle cerebral arteries in fetuses with normal and increased umbilical artery resistance indices

OBJECTIVE

To compare the brain sparing mechanism of the fetal vertebral artery (VA), with the one of the middle cerebral artery (MCA) in fetuses with increased umbilical artery (UA) Doppler impedance.

METHOD

We retrospectively studied 1084 Doppler examinations of the VA, MCA and UA performed in 1084 fetuses between 19 and 41 week of gestation. These were divided into 3 groups according to the UA resistance index (UA RI): group 1: UA RI < 95(th) percentile (N = 965), group 2: UA RI > 95(th) percentile (N = 111) and group 3: absent UA diastolic flow (N = 8). Afterwards, values were converted into multiples of the median (MoM), and means and standard deviations were calculated. Finally, Kruskal-Wallis tests and box and whiskers charts were applied to evaluate differences.

RESULTS

For both, the VA RI and MCA RI, no differences were seen among the groups of fetuses who maintained diastolic flow in the UA. However, the VA RI and MCA RI were lower when the UA diastolic flow was absent.

CONCLUSION

The VA and MCA work in unison, decreasing impedances only when UA flow is severely affected.

Doppler study of the fetal vertebral artery in small for gestational age fetuses with intrauterine growth restriction

OBJECTIVES

The purposes of this study were to evaluate the Doppler resistive index of the fetal vertebral artery in small for gestational age (SGA) fetuses and to examine the ability of the vertebral artery resistive index in the diagnosis of intrauterine growth restriction (IUGR).

METHODS

A total of 437 Doppler examinations of the vertebral and umbilical artery resistive indices were performed in 437 fetuses between 26 and 41 weeks' gestation. According to birth weight, fetuses were classified into 5 groups: 1, above the 10th percentile; 2, between the 10th and 5th percentiles; 3, between the 5th and 3rd percentiles; 4, below the 3rd percentile; and 5, below the 3rd percentile with an umbilical artery resistive index above the 95th percentile. Subsequently, vertebral artery resistive index values were converted into multiples of the median, and box and whisker charts were generated to evaluate differences. Finally, receiver operating characteristic curves were calculated to assess the accuracy of the vertebral artery resistive index for predicting IUGR and a low Apgar score.

RESULTS

Compared to normally grown fetuses, vertebral artery resistive index values were lower in fetuses with birth weight below the 3rd percentile, and this difference was greater in fetuses with birth weight below the 3rd percentile and Doppler anomalies of the umbilical artery. The receiver operating characteristic analysis showed that the vertebral artery resistive index diagnosed SGA fetuses and low Apgar scores poorly. However, it performed better in cases of severe IUGR with high umbilical artery resistive index values.

CONCLUSIONS

Preliminary data show that the vertebral artery resistive index diminishes in growth-restricted SGA fetuses. Doppler examination of the vertebral artery seems to identify a group of fetuses with brain sparing and severe IUGR.

Doppler impedance changes at the fetal brain vessels in a pregnancy affected with a multiple combination of uteroplacental anomalies

A fetus with a very rare five-fold combination of uteroplacental anomalies, bicornuate uterus, short cervix with cervical incompetence, multilobed placenta succenturiata, accessory cotyledon within the cervical funneling, and umbilical cord insertion into the anomalous cervical cotyledon, presented an early and marked decrease at the vertebral and middle cerebral arteries Doppler resistances. This cerebral low-impedance state, usually found before labor, and considered an adaptive mechanism developed to protect the fetus at term from labor asphyxia, was present for an unknown reason at 20 weeks. After the patient was treated with vaginal progesterone, the cervix shortening improved and markedly, at the same time, the cerebral vascular resistances increased and maintained an adequate for gestational age impedance until delivery at 34 weeks. As the described uteroplacental anomalies determined a high risk of preterm delivery, due to cervical dilation, cord compresion, and placental haemorrhage, these fluctuating brain vascular changes might be the result of the fetal adaptation to the changes preceding an imminent delivery.