European Journal of Cardiovascular Medicine

Intrapartum hypoxia causes fetal suffocation, acidosis, newborn brain damage, long-term morbidity, and mortality.¹ As a result, intrapartum fetal monitoring is performed to detect early indicators of fetal hypoxia and to take appropriate action as soon as possible to avoid fetal hypoxia complications. Intrapartum electronic fetal monitoring with cardiotocography has become an essential component of all labour. Edward Hon pioneered this in the late 1950s in the United States.² Electronic fetal monitoring measures the fetal heart rate rhythm and its association with uterine contractions.³ A normal CTG is reassuring, but an abnormal CTG does not usually mean fetal acidity. CTG has a significant false positive rate and is an unreliable predictor of fetal hypoxia and metabolic acidosis.⁴

As a result, a positive perinatal outcome is expected when CTG results are normal, but a negative outcome is not guaranteed when they are abnormal. In addition, the classification and interpretation of CTG vary greatly across and between observers.  It is critical to recognize newborn acidemia since these neonates are at risk of a poor outcome following delivery. These outcomes include low Apgar scores, respiratory distress syndrome, hypoxia ischemic encephalopathy, convulsions, intraventricular hemorrhage, sepsis, and death.⁵ When CTG was launched, it was expected to lower the incidence of cerebral palsy and mental retardation by 50%. However, research has found little to no improvement in long-term neurological outcomes.⁶

Acidosis is a quantifiable result in the infant and is regularly characterized as a low umbilical pH or a high umbilical base shortage, which is communicated as bad base overabundance. The ordinary scope of umbilical line pH is 7.40 ± 0.20.6 The cut-off of low umbilical pH (metabolic acidosis) differs from 7.2 to 7.01 and a base deficiency of ≥12.0 mmol/L.⁶ The American School of Obstetricians and Gynecologists expresses that umbilical string blood gas examination ought to be performed after any conveyance in which a fetal metabolic irregularity is suspected.⁷

Perinatal asphyxia and fetal acidemia are extricating a weighty cost for youth mortality and grimness. It very well may be forestalled by utilizing demonstrated and powerful fetal observation strategies. The ongoing examiner finds clashing reports on the utility of Doppler ultrasound in anticipating fetal acidemia. There is a need for such examinations in emerging countries like our own. Examining the precision of the forecast of fetal acidemia by fetal Doppler ultrasound will affect the detailing of fetal observation conventions during the antepartum and intrapartum periods. It might likewise impact our country's future preparation of the medical services framework.

1. To study the correlation between fetal Doppler ultrasound and umbilical cord blood gas analysis in detecting fetal academia.
2. To identify the maternal and obstetric determinants associated with fetal acidemia.

Study Design: Hospital-based prospective observational study.

Study area: The study was conducted in the Department of Obstetrics and Gynaecology.

Study Period:  1 year. 

Sample size:  Using a sample size calculator, expecting a correlation coefficient of r=0.300, the required sample size was calculated to be 85.

Study population: During the study period, a total of 92 pregnant women with abnormal fetal Doppler ultrasound findings, meeting the below-mentioned inclusion and exclusion criteria were eventually recruited into this study.

Sampling Technique: Simple Random technique.

Inclusion Criteria:

All pregnant women delivered by lower segment caesarean section with

1. Age 18yrs-35yrs
2. Abnormal fetal Doppler ultrasound findings
3. Gestational age of more than 28 weeks.

Exclusion criteria:

All pregnant women with

1. Diabetic ketoacidosis/metabolic acidosis
2. intrauterine fetal demise
3. intrauterine growth retardation
4. antepartum haemorrhage
5. cardiac or respiratory disease

Ethical consideration: Institutional Ethical committee permission was taken before the commencement of the study.

Study tools and Data collection procedure:

The institutional ethical committee clearance was obtained. The design and nature of the clinical study were explained to the patients and significant relatives of the patients. Informed consent was obtained from patients. The socio-demographic data was collected and recorded in the specially designed proforma. The socioeconomic class was assessed using the Socio-Economic Status Schedule. The obstetric history data was gathered and recorded in the proforma. All the patients in the sample group (n=92) were subjected to thorough clinical examination which included general physical, systemic examination and pelvic examination. Maternal blood samples for routine laboratory investigations(including tests for acidosis) were sent. All the results were entered into proforma. The pregnant women were all delivered by lower-segment caesarean section. The newborn was assessed for APGAR scores at 1 minute and 5 minutes. An umbilical cord blood sample was taken within 5 minutes of birth and sent for blood gas analysis. The results were later availed and tabulated.

Statistical Analysis:

Characteristics of the pregnant women who participated in the study were summarised as frequencies and percentages. Similarly, abnormal patterns in ultrasound Doppler parameters were also summarized as percentages. Dimensions of ultrasound Doppler parameters were described in terms of mean and standard deviation. Differences in USG Doppler indices (namely Umbilical artery RI, Umbilical artery PI, Middle Cerebral Artery RI and Middle Cerebral Artery PI) between infants who developed acidemia or not were compared using the student ‘t’ test. Similarly, various maternal characteristics and fetal acidemic status were compared using the chi-squared test. P values less than 0.05 were considered statistically significant.

This study included 92 cases with abnormal fetal Doppler ultrasound findings. Their newborns were subjected to Umbilical cord blood gas analysis.

Table 1: Distribution of cases according to age group

The cases in this study had an age group from 18 years to 35 years. Maximum number of cases (N=39, 42.4%) belonged to the 22-26 year age group. This was followed by cases in the age group of 27-30 years (N=25, 27.2%) and then by women in the age group of 31-35 years (N=23, 25%). The age group of 18-21 years had the least number of cases (N=5, 5.4%).

The majority of the cases (N=41, 44.6%) belonged to the Upper Lower SES. This group was followed by cases belonging to the Lower SES (N=35,38%). The rest of the cases belonged to the Lower middle SES (N=16,17.4%). None of the cases belonged to the Upper SES or the Upper middle SES.

Maximum number of cases were Gravida 1 (N=43, 47.3%). This was followed by groups of Gravida 2 (N=25, 27.5%) and Gravida 3 (N=15, 16.5%). The least number of cases belonged to the group of Gravida 4 or more (N=8, 8.8%). Maximum number of cases had gestational age 39 (N=34, 37%). This was followed by gestational ages of 40 weeks (N=22,23.9%), gestational age of 37 weeks (N=13, 14.1%) and gestational age of 38 weeks (N=12, 13%). These groups were followed by cases with a gestational age of 41 weeks (N=9,9.8%) and a gestational age of 42 weeks (N=2, 2.2%).

Table no.2: Distribution of abnormal findings recorded in the Fetal Doppler ultrasound

All the 92 cases had abnormal fetal Doppler ultrasound results. The Umbilical artery resistive index (UARI) values were all equal to or more than 0.7 (N=92). Maximum of the Umbilical artery pulsatility index (UAPI) values were more than 1.5 (N=91, 98.9%). Only one case had UAPI between 1-1.5 (1.1%). Participants' Middle cerebral artery resistive index (MCARI) values were all between 0.7-0.9(N=92, 100%). Whereas, the Middle cerebral artery pulsatility index (MCAPI) had all values more than 1 (N=92, 100%).

Based on cardiotocographic (CTG) findings. Maximum cases had Abnormal CTG (N=44, 47.8%). This was followed by cases with Non-reassuring CTG (N=36, 39.1%) and then by cases with Reassuring CTG (N=12, 13%).

Regarding the distribution of UCBGA pH values of newborns. The majority of the newborns had pH values of 7 or more (N=73, 79.3%). The remaining had pH values less than 7. (N=19, 20.7%). The majority of the newborns had pCO2 levels of more than 50 mm Hg (N=91, 98.9%). Only one newborn had a pCO2 level of 50mmHg or less. 80.2% (N=74) cases had UCBGA pO2 =/>20mmHg. The remaining cases (N=18, 19.6%) had UCBGA pO2 less than 20mmHG. The majority of the cases had UCBGA HCO3 values of 18mmol or more (N=73, 79.3%). The remaining had values of UCBGA HCO3 <18mmol (N=19, 20.7%). Maximum number of cases (N=74, 80.4%) had UCBGA Base excess values =/>-4. The remaining cases had UCBGA Base excess values <-4 (N=18, 19.6%).

Table 3: Distribution of values of Fetal Doppler Ultrasound Indices.

The umbilical artery resistive index (UARI) had a mean value of 1.76. The values ranged from 1.5 to 1.9. The umbilical artery pulsatility index (UAPI) had a mean value of 1.75. The values had a range from 1.2 to 1.9. The Middle cerebral artery resistive index (MCARI) was found to have a mean value of 1.76 among the 92 cases. The values of MCARI ranged from 1.3 to 2. Middle cerebral artery pulsatility index (MCAPI) findings had a mean value of 2. These values ranged from 1.3 to 4.

Table 4: Comparison of Fetal Doppler Ultrasound Indices based on fetal academic status

The above table compares the 4 different Fetal Doppler Ultrasound indices among themselves, based on the presence or absence of fetal acidemia. The data shows that among those newborns that developed fetal acidemia and those that did not, the difference in UARI values was not statistically significant (p-value = 0.31). Similarly, the difference in data of UAPI (p value=0.07) and MCARI (p value=0.53) was also not statistically significant. The MCAPI was found to be highly statistically significant between the two sets of data with a p-value of <0.0001.

Table 5: Correlation of UCBGA values with UAPI values.

The above table shows that the UAPI had a highly significant correlation with all the UCBGA results. These were statistically highly significant. An Abnormal UAPI value was statistically significant in predicting fetal acidemia.

Table no. 6: Association of Gestational Age and Fetal Acidemic Status

The above table shows the relation between gestational age and fetal acidemic status. Statistical evaluation showed the p-value to be 0.0096. This was highly statistically significant. Therefore, there exists a significant relation between gestational age and fetal acidemic status.

Table number 7: Relationship between fetal Doppler ultrasound indices and fetal acidemia

Table no.8: Association of Per Vaginal(PV) finding and fetal acidemic status

The above table and chart show the relation between per vaginal examination findings and fetal acidemic status. Statistical evaluation showed the p-value to be 0.1987. This was not statistically significant. Therefore, no significant relation exists between per vaginal examination findings and fetal acidemic status.

This study is an observational, descriptive, cross-sectional study that investigates the correlation between fetal Doppler ultrasound and umbilical cord blood gas analysis in detecting fetal acidemia. It comprises 92 pregnant women with abnormal fet al Doppler ultrasound findings.

Majority of the participants (42.4%) were belonging to the age group of 22 - 26 years. They were distributed equally in number based on their address location. 50% each belonged to urban and rural areas. When distributed as per their socioeconomic status, most of the participants (44.6%) in this study belonged to the Upper Lower socioeconomic status as per the Modified Kuppuswamy scale. Regarding booking status for antenatal care, the maximum number of participants (70.7%) were not booked at any government or private hospital. Most (43.5%) of participants in this research had a married life of 6-10 years. 69.6% of women who were recruited into the study had a third-degree consanguinity in marriage.

Among the participants, the majority of women were primigravida (47.3%). Women with gravida 4 or more formed the group with the least number of cases (8.8%). The gestational age cut-off for recruitment into this study was kept at 38 weeks. Among the 92 cases recruited, maximum number of participants had gestational age of 39 weeks (37%). When enquired about the presence of any significant past medical history, none of the participants had any such history. Also, none of the 92 cases had any significant family history.

The general physical examination of the participants revealed that only one case had pallor. The patient’s blood investigations further revealed that she had anaemia. Therefore, only one case had a medical comorbidity of anemia. However, the remaining 91 cases had no abnormality on either general physical examination or on investigation. Systemic examination of all 92 participants was within normal limits. This was corroborated by the normal values found in conducting relevant investigations on all participants. All the participants were subjected to per vaginal examination and their labour status was documented. The majority of the cases (64.1%) were in early labour.

Cardiotocographic investigation of the cases during labour revealed that the majority of the cases had abnormal cardiotocographic findings (47.8%). APGAR scores of the newborn at one minute revealed that the maximum number of newborns had APGAR scores in the range of 7-10 (73.9%). When examined at 5 minutes, the majority of APGAR scores at 5 minutes were in the range of 7-10 (79.3%). All 92 newborns were delivered by lower-segment caesarean section.

The participants in this study had to be cases with abnormal fetal Doppler ultrasound investigation. All of the 92 cases had abnormal fetal Doppler ultrasound results. The Umbilical artery resistive index (UARI) values were all equal to or more than 0.7 in all the cases (100%). UARI Mean value was 1.76. The majority of the cases had Umbilical artery pulsatility index (UAPI) values of more than 1.5 (98.9%). Only one case had UAPI between 1-1.5 (1.1%). UAPI Mean value was 1.75. Participants' Middle cerebral artery resistive index (MCARI) values were all between 0.7-0.9(100%). The mean value of MCARI was 1.76. However, the Middle cerebral artery pulsatility index (MCAPI) had all values more than 1 (100%). MCAPI Mean value was 2.

The newborns were all subjected to umbilical cord blood gas analysis. As there is no consensus on the definition of fetal acidemia, the criteria set by Swanson et al3 in the American journal of Obstetrics and Gynaecology were used in this study. The criteria were:

Fetal acidemia will be diagnosed in any umbilical cord blood gas analysis result showing:

• umbilical cord arterial pH <7.0 and
• umbilical cord arterial base deficit equal to or more than 12mEq/L.

In blood gas analysis, a positive number is called a base excess and indicates a metabolic alkalosis. A negative number is called a base deficit and indicates metabolic acidosis. These criteria were chosen as they also incorporated the base deficit/excess component. This prevented detecting false positive fetal acidemia, in cases where there was undetected maternal acidosis. The inclusion of the stricter above-mentioned criteria helped detect true fetal acidemia. Using these criteria, a total of 19 newborns were diagnosed to have fetal acidemia. Their UCBGA pH results were less than 7(20.7%). UCBGA also revealed the blood pCO2 levels. Maximum number of newborns had pCO2 levels more than 50mmHg (98.9%). Only one newborn had a pCO2 level of 50mmHg or less. With regards to the UCBGA pO2 levels, most of the newborns (80.2%) had UCBGA pO2 =/>20mmHg. The majority of the newborns had UCBGA HCO3 values of 18mmol or more (79.3%). The Base excess/deficit values on UCBGA revealed that most of the newborns (N=74, 80.4%) had UCBGA Base excess/deficit values less than or equal to -4. The findings of the incidence of fetal acidemia in this current study are lower than that of a few other studies.

An Indian study by Deshpande et al⁸ in 2019 investigated 120 pregnant women. Their study found that 61 newborns had fetal acidemia. This brought the incidence of fetal acidemia to 50.83%. Bernardo et al⁹ in 2020 published findings of a retrospective cohort study on 352 cases. They evaluated umbilical blood gas analysis results. Their study revealed the incidence of umbilical artery pH < 7.12 to be 33.8% (N = 119). The difference in the incidence could be due to the stringent criteria used in this study. We have not only used cord blood pH value but also base deficit/base excess, in diagnosing fetal acidemia. A delay in sending cord blood samples can also affect the results. In this study, cord blood samples were sent for evaluation within 5 minutes of delivery.

In the current study, the investigator compared four different fetal Doppler ultrasound indices based on the presence or absence of fetal acidemia. The results revealed that the Middle cerebral artery pulsatility index (MCAPI) was significantly associated with the presence of fetal academia (p-value of <0.0001). The statistical analysis revealed no significant differences in the UARI (p value = 0.31), UAPI (p value=0.07) and MCARI (p value=0.53). As the data was analysed further, UAPI was found to have a significant correlation with the individual tests of umbilical cord blood gas analysis. The p-value was <0.0001 suggesting a highly significant correlation. Thus, the MCAPI and the UAPI were found to be good predictors of fetal acidemia in this study.

These findings are different when compared to earlier studies. Feinkind et al¹⁰ studied 273 patients and found no correlation between umbilical artery Doppler indices and umbilical cord blood pH, bicarbonate, base excess/deficit, pCO2, pO2, or oxygen saturation. Then Feinkind et al¹¹ delved deeper and investigated 16 at-risk pregnancies within the above-mentioned study population and found positive and negative correlations between umbilical S/D ratios(systolic/diastolic), base excess/deficit and pH. They failed to find any correlation between the umbilical artery Doppler indices and pCO2, pO2, oxygen saturation and bicarbonate, even in the at-risk group.

Malcus et al¹² investigated a larger sample of 575 women in various stages of labour. Their study too failed to find any significant correlation between abnormal Doppler ultrasound findings and fetal acidosis. They suggested that fetal Doppler ultrasound is not a good ‘admission test’ as it fails to predict fetal distress. Puzey et al¹³ studied 42 patients and found that there was a significant negative correlation between umbilical vein pH and pulsatility index (r=-0.59). In a study conducted by Stuart et al¹⁴ in 36 women with singleton pregnancies, they failed to find any significant relation between the fetal Doppler ultrasound indices and cord blood pH. The differences in the findings of these studies may arise from the heterogeneous population groups that they studied. The sample size also varied among these studies.

The current study analysed any significant correlation between the maternal and obstetric determinants and development of fetal acidemia, as a secondary objective. The only significant correlation found was between gestational age and fetal acidemia (p value=0.0096). An increase in gestational age (41 weeks and above) was found to be protective from fetal acidemia. This finding is contrary to the research published by Caughey et al¹⁵ in 2005. They conducted a retrospective cohort study between 1976 and 2001. Their research evaluated 32,679 pregnant women. Their study revealed that fetal acidemia increased in incidence after gestational age of 40 weeks. The opposite findings in the current study could be because only 11 cases had a gestational age of 41 weeks or more, in this study. The findings from such a small sample need to be confirmed by conducting further studies using a large sample size of pregnant women with a gestational age of 41 weeks or more. None of the other determinants such as maternal age, address location, socioeconomic status, antenatal care booking status, marital life duration or degrees of marital consanguinity had any significant correlation with fetal acidemia.

Based on the statistical analysis of the data, it is safe to assume that fetal Doppler ultrasound can predict the development of fetal acidemia. Two indicators, the Middle cerebral artery pulsatility index and the Umbilical artery pulsatility index, are strong predictors of fetal acidemia. Similarly, determinants like obstetric score, medical comorbidity, general physical examination and status of labour per vaginal examination were also not found to be significantly associated with fetal acidemia.

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