El Doppler de la arteria vertebral como alternativa al Doppler de la arteria cerebral media en el diagnóstico de la restricción del crecimiento fetal
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2017
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29-09-2017
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Morales Roselló, José
Perales Marín, Alfredo
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Abstract
THE VERTEBRAL ARTERY DOPPLER AS ALTERNATIVE TO THE MIDDLE CEREBRAL ARTERY DOPPLER IN THE DIAGNOSIS OF GROWTH-RESTRICTED FETUS.
Vascular supply to the fetal brain comes from two vascular gates: the internal carotid artery (ICA) and the vertebral artery (VA). The first derives from the anastomosis between the third branchial artery and the most cranial segments of the aorta, whereas the second originates from the anastomoses of the first six cervical intersegmental arteries. From a phylogenetic point of view, VA supplies the older areas of the brain, brain stem, and cerebellum, which have been shown to present better adaptive mechanisms to hypoxia than the neocortex irrigated by the ICA and its continuation to the middle cerebral artery (MCA). These differences, which might be partially the result of different arterial responses to hypoxemia, prompted us to initiate a research line on the fetal VA Doppler.
Compared to adequately developed fetuses, fetuses with fetal growth restriction (FGR) have higher rates of mortality, birth asphyxia, hypothermia, hypoglycemia, meconium aspiration, and neurological sequelae. They also account for 40% of unexplained stillbirths, 30% of deaths due to sudden death and have an infant mortality 8 times higher than fetuses with a suitable weight for their gestational age. In addition, there is an hypothesis that states they are exposed in adulthood to diseases such as hypertension, atheromatosis or impared glucose tolerance.
Evolution provided the developing brain with a vascular self-protection system: brain-sparing. Both VA and MCA are able to vasodilate during FGR. However, only the second one has been studied in depth, but the result of a recent meta-analysis showed its correlation with poor perinatal outcome and cognitive and behavioral anomalies in childhood.
In conclusion, the aim of the study is to determine the utility of VA Doppler in fetal medicine, to determine if the VA Doppler could be more valid than MCA Doppler to assess the intrauterine growth retardation; or at least to be comparable or provide us with more information at those times when it is not possible to perform MCA doppler.
This is an observational, prospective, cross-sectional study that includes patients undergoing ultrasound examination during pregnancy (one study per patient). Performed at 19 to 41 weeks gestation on singleton pregnant women whose last menstrual period was accurately determined with a first trimester ultrasound. During each examination, a complete fetal biometry and a Doppler measurement of the VA, MCA, and umbilical artery (UA) resistance index (RI) and pulsatility index (PI) were performed. Cerebral-placental (CPR) and vertebro-placental (VPR) ratios are calculated. Data from fetuses with malformations were excluded. However, fetuses with growth disorders and preterm deliveries were included as were considered part of the general population. Data on gestation and delivery are collected.
First of all, the methodology of the VA Doppler measurement is determined.
Then, the normal reference values of the Doppler of the fetal vertebral artery are determined. We included 2248 patients in whom the described data were evaluated. Values were tested for normality using the D’Agostino and Pearson Omnibus normality test, and the 3rd, 5th, 10th, 50th, 90th, 95th and 97th percentiles were calculated using percentile regression. A table with the values of the IP, IR and VPS of the VA throughout the gestation is made, classifying it in centiles. It is observed that the VA has a similar behavior as the ACM.
Subsequently, a study was performed to compare the Doppler of AV and MCA in fetuses suitable for gestational age (AEG), small for gestational age (SGA) and in FGR. Patients were defined and classified into 3 groups: AEG (N: 1915), PEG (N: 177) and FGR (N: 157). PI measurements and VPR and CPR measurements were compared with box and whisker diagrams converting values into multiples of the median (MoM), which was calculated dividing the observed value by the 50th P. Statistical significance was determined using Mann–Whitney U tests with a p < 0.05. The results show that there are no differences between the AEG and SGA groups, however, statistically significant differences were observed in the Doppler between these two groups and fetuses with FGR. It is observed that there are no differences between the MCA and the VA Doppler, and that they have a similar behavior in all the groups.
Finally, a study was carried out to observe a possible association between the neonatal acid base status and the cerebroplacental ratios determined on ultrasound examinations performed prior to childbirth. 3D graphs are made including 3 parameters: venous pH at delivery, fetal weight centiles and CPR-VPR. The results show that there is no association between pH at birth with VPR, but no association is observed with CPR. Therefore, none of the two ratios are a good predictor of the acid-base neonatal status in fetus. Probably because of the importance of the events that occur during childbirth.
In conclusion, it is possible to study the fetal VA by Doppler, describing its normal reference values between weeks 19 and 41. These values present a similar behavior to the CAM Doppler values throughout gestation. It seems that VA Doppler behaves in the same way as MCA Doppler in fetuses with normal weight and SGA. However, there are statistically significant differences between these two groups and fetus with FGR. There appears to be no association between the acid-base neonatal status and the VPR/CPR determined on a fetal ultrasound. Therefore, it seems that VA may be useful in the diagnosis of FGR and it would be interesting to carry out further studies to confirm these results.