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A Correlational study of Umbilical Venous Flow Rate and Mode of Delivery

Original Research Article Objective: The Primary Objective of the study was to establish the relationship between Mode of Delivery and subsequent Intrapartum outcome [Fetal Distress]. The findings of the study showed higher rate of caesarean section during labor in fetuses with <20th centile of UV flow rate. The women who had spontaneous vaginal delivery had flow rates above 80th centiles and had less fetal compromise. Study Design: A prospective observational study done at SMS MEDICAL COLLEGE, jaipur. Fetal biometry and Arterial Doppler and venous flow rates were measured in 90 women immediately before established labor. Labor was then managed according to local protocols and guidelines, and intrapartum and neonatal outcome details were recorded. Results: Fetuses delivered by cesarean section for fetal compromise had significantly lower umbilical venous flow rates than those born by spontaneous vaginal delivery. Fetuses with the lowest umbilical flow rates were more likely to require emergency cesarean for presumed fetal compromise than those with the highest flow rates. Conclusion: Asssessment of umbilical venous flow can predict the diagnosis of intrapartum fetal compromise and need for emergency delivery.


INTRODUCTION
The intrapartum period represents the time during pregnancy when the fetoplacental relationship is challenged to the highest degree. Uterine contractions are associated with up to 60% decline in uterine artery flow velocities [1] and the associated reduction in placental perfusion may precipitate fetal compromise.
Intra-partum events leading to cerebral palsy and other neurological sequelae are over represented in medico-legal malpractice cases [2], and often result in the award of a large quantum of financial compensation [3]. With the possibility of affected individuals requiring a lifetime of care, and the spiraling costs of medico-legal malpractice insurance, intra-partum fetal compromise continues to represent a significant financial burden to healthcare providers. The psychological and emotional impact on both the affected individual and caregivers is enormous [4].
The final common pathway of many conditions that result in intra partum hypoxia is one of placental insufficiency [5]. Umbilical venous blood flow could be considered a direct and physiological measurement of vascular placental function, representing the quantity of oxygen and nutrients reaching the fetus.
The clinical use of umbilical venous blood flow was first suggested in the early 1980s [6] when reduced flow was demonstrated in growth-restricted fetuses. Doppler examination of the UV provides information about a compensatory mechanism in the fetal circulation. Evaluation of venous Doppler parameters has significantly contributed to the understanding of the vascular mechanisms that lead to fetal growth restriction (FGR) and subsequent fetal deterioration in the setting of progressive placental dysfunction. Indeed, Doppler measurement of umbilical venous blood flow has been found to be accurate when compared with several gold standards for in-vivo flow calculation.
Furthermore, abnormalities in umbilical venous flow have been associated with an increased incidence of operative delivery for fetal compromise. At the precision (absolute allowable error) of 10 ml/min in umbilical venous flow rate 90 cases were required, as sample.

Inclusion Criteria
 Singleton pregnancy  Women with normal term pregnancies presenting in early labor, and likely to deliver within 72 hours.

Exclusion Criteria
Known fetal anomaly  Cervical dilatation greater than 4 cm, and ruptured membranes with meconium stained liquor.

METHODOLOGY
After applying inclusion and exclusion criteria informed written consent was be taken and women with uncomplicated singleton pregnancy in early labor cervical dilation ≤ 4cm likely to deliver within 48 hours and willing to participate in the study were recruited from labor room of department of obs and gynec, SMS medical college, Jaipur.
Approval from Institutional Research, Review Board and Ethical Committee was taken. Detail history, examination and all routine investigations were done. Ultrasound assessment was done for fetal biometry (head circumference, biparietal diameter, abdominal circumference, femur length and fetal weight) and umbilical venous Doppler was assessed. All ultrasounds scans was performed by a single operator using (ALOKA PROSOUND alpha6 with convex probe).
For Doppler assessment, the umbilical vein was imaged at a free loop and pulsed wave Doppler was used to obtain umbilical vein flow velocities. The angle of insonation was maintained as close to 0 degree as possible and always less than 30 degree, to ensure accurate assessment of flow velocities. The image was magnified and internal diameter of vein was measured. An estimated fetal weight was calculated from fetal biometry.
Umbilical venous Doppler was done for the umbilical vein flow velocity and umbilical vein diameter, to calculate umbilical venous flow rate.
The following formula was used for calculation: Umbilical venous flow rate (milliliters per minute) = velocity (centimeters per second) x 0.3 x cross-sectional area (square millimeters).
Case were managed according to local protocol and guidelines and then case were subcategorized according to mode of delivery and corrected umbilical venous flow rates.

RESULTS
Patient demographics are shown in Table-1 and mode of delivery in Table- Instrumental deliveries of which 3 (60.00%) patients had it for presumed fetal compromise and 2 (40.00%) patients had instrumental deliveries for prolonged second stage. Both uncorrected and corrected flow rates were significantly different between the various modes of delivery groups. Out of 90, 26 women in our study had UV flow rate less than 200ml/min , of these 18 (69.23%) women developed fetal distress during labor, suggesting a strong correlation of decreased UV flow rate with fetal distress. 60 cases had UV flow rate between 201 and 250 ml/min out of which only 5 (8.33%) cases had fetal distress. There was no FD case in UV flow rate of >250ml/min. The number of patients who underwent LSCS for presumed fetal distress in group with umbilical flow rate below 20th centile was 6 as compared to 0 in group with flow rates above 80th centiles with relative risk of 2.28. Higher rate of caesarean section for presumed fetal compromise and diagnosis of fetal compromise at any time during labor were observed in fetuses in <20th centile group. The number of women who had spontaneous vaginal delivery in 20th centile UV flow rate was 8 as compared to 17 in group with flow rates above 80th centiles. The p-value was 0.01 with relative risk being 2.14. Fetuses with >80th centile UV flow rate were more likely to be born by SVD compare to cohort of fetuses with <20th centile flow rate. A UV flow rate of >80th centile yielded a 100% negative predictive value for cesarean section for presumed fetal compromise.

DISCUSSION
The results from this study demonstrate that assessment of the umbilical venous flow, in term infants from low risk pregnancies before active labor, can predict the diagnosis of intrapartum fetal compromise and the need for emergency delivery with good reliability. Currently, multivessel Doppler assessment of fetal well-being is considered valuable only in cases of fetal growth restriction. Our data suggests that assessment of the umbilical venous flow rate can also be of value in the apparently normally grown fetus at term. Although the risk of intrapartum fetal compromise being diagnosed is highest in infants with the lowest umbilical venous flow rate, a high umbilical venous flow rate appears to suggest better fetal tolerance to the stresses of labor, with a reduced incidence of abnormal fetal heart rate patterns necessitating emergency delivery. No infants in our study with UV flow rate>80th percentile required delivery by emergency cesarean section for presumed fetal compromise (NPV 100%). The mean umbillical venous flow rate in the study was 211.96 ± 30.98 ml/min whereas the mean of the corrected umbillical venous flow rate was 73.46 ± 9 ml/min/kg.Various studies have examined corrected UV flow rate at differing gestations,but few have examined UV flow rates in appropiately grown fetuses at term. Our study results were similar to the study done by Prior T et al., [7] the mean umbillical venous flow rate in study population was 213.6 ml/min. Similar results were also obtained by Tchirikov M et al., [8]. We compared with those with a flow rate greater than the 80 th centile, fetuses with an umbilical venous flow rate less than the 20 th centile were noted to have a significantly increased risk of being diagnosed with fetal compromise during labor and were also noted to have the highest incidence of cesarean section for presumed fetal compromise. Similar results were obtained in other studies also.

CONCLUSION
We suggest that measurement of umbilical venous flow may have a potential clinical application in the risk stratification of normal pregnancies prior to labor. Such stratification would allow more informed decisions to be made regarding the mode and place of delivery as well as a more targeted approach to intrapartum monitoring.