Doppler in obstetrics: beyond the umbilical artery

DLK1: A Novel Biomarker of Placental Insufficiency in Stillbirth and Live Birth

OBJECTIVE

Delta-like homolog 1 (DLK1) is a growth factor that is reduced in maternal sera in pregnancies with small for gestational age neonates. We sought to determine if DLK1 is associated with stillbirth (SB), with and without placental insufficiency.

STUDY DESIGN

A nested case-control study was performed using maternal sera from a multicenter case-control study of SB and live birth (LB). SB and LB were stratified as placental insufficiency cases (small for gestational age <5% or circulatory lesions on placental histopathology) or normal placenta controls (appropriate for gestational age and no circulatory lesions). Enzyme-linked immunosorbent assay (ELISA) was used to measure DLK1. The mean difference in DLK1 was compared on the log scale in an adjusted linear regression model with pairwise differences, stratified by term/preterm deliveries among DLK1 results in the quantifiable range. In exploratory analysis, geometric means were compared among all data and the proportion of "low DLK1" (less than the median value for gestational age) was compared between groups and modeled using linear and logistic regression, respectively.

RESULTS

Overall, 234 SB and 234 LB were analyzed; 246 DLK1 values were quantifiable within the standard curve. Pairwise comparisons of case and control DLK1 geometric means showed no significant differences between groups. In exploratory analysis of all data, adjusted analysis revealed a significant difference for the LB comparison only (SB: 71.9 vs. 99.1 pg/mL, p = 0.097; LB: 37.6 vs. 98.1 pg/mL, p = 0.005). In exploratory analysis of "low DLK1," there was a significant difference between the odds ratio of having "low DLK1" between preterm cases and controls for both SB and LB. There were no significant differences in geometric means nor "low DLK1" between SB and LB.

CONCLUSION

In exploratory analysis, more placental insufficiency cases in preterm SB and LB had "low DLK1." However, low DLK1 levels were not associated with SB.

KEY POINTS

· Maternally circulating DLK1 is correlated with placental insufficiency.. · Maternally circulating DLK1 is not correlated with SB.. · DLK1 is a promising marker for placental insufficiency..

A longitudinal and cross-sectional study of placental circulation between normal and placental insufficiency pregnancies

INTRODUCTION

To longitudinally and cross-sectionally study the differences in the uterine artery pulsatility index (UTPI), umbilical artery pulsatility index (UAPI) and placental vascularization indices (PVIs, derived from 3-dimensional power Doppler) between normal and placental insufficiency pregnancies throughout gestation.

METHODS

UTPI, UAPI and PVI were measured 6 times at 4- to 5- week intervals from 11 to 13+6 weeks-36 weeks. Preeclampsia (PE) and fetal growth restriction (FGR) were defined as placental insufficiency. Comparisons of UTPI, UAPI and PVI between normal and insufficiency groups were performed by one-way repeated measures analysis of variance.

RESULTS

A total of 125 women were included: monitored regularly from the first trimester to 36 weeks of gestation: 109 with normal pregnancies and 16 with placental insufficiency. Longitudinal study of the normal pregnancy group showed that UTPI and UAPI decreased significantly every 4 weeks, while PVIs increased significantly every 8 weeks until term. In the placental insufficiency group however, this decrease occurred slower at 8 weeks intervals and UTPI stabilized after 24 weeks. No significant difference was noted in PVIs throughout pregnancy. Cross-sectional study from different stages of gestation showed that UTPI was higher in the insufficiency group from 15 weeks onward and PVIs were lower after 32 weeks.

DISCUSSION

Compared to high-risk pregnancies with normal outcome, UTPI and UAPI needed a longer time to reach a significant change in those with clinical confirmation of placental insufficiency pregnancies and no significant change was found in PVI throughout gestation. UTPI was the earliest factor in detecting adverse outcome pregnancies.

Obstetric vascular Doppler velocimetry: clinical applications and overuses

A safe and non-intrusive assessment of fetal health is not only crucial in low-risk gestations, but it is also the standard of care in high-risk pregnancies. Therefore, measuring blood flow across different vessels with non-invasive ultrasound methods has been accurately and painstakingly studied and published. Amongst these state-of-the-art techniques, umbilical artery (blood flow) Doppler velocimetry (UADV) has allowed for fetal well-being follow-ups and assess uteroplacental function, which obtains a more complete and clearer picture; particularly in regard to complicated pregnancies. Additionally, there are other modalities with diverse clinical applications that have emerged, including their clinical and research utilization in conditions such as fetal growth restriction (FGR), preeclampsia, fetal anemia, monochorionic twins vascular blood flow mismatch such as is in twin-to-twin transfusion syndrome, twin anemia polycythemia sequence, and twin reverse arterial perfusion sequence. Nevertheless, their applications regarding various other maternal-fetal diagnoses in the same way as premature births and/or multiple gestation surveillance have not been reported to hold strong clinical evidence. With that in regard, the purpose of this unique study was to give update of the multiple clinical applications of this very important obstetrical tool. Additionally, to review the pathophysiology as well as revisit their reported significant valid uses and occasional overuses. We also delved into quality control measures as related to the application of Doppler in obstetrics. Lastly, it is essential to look through and reflect on the future developments of this valuable, non-invasive, high-risk marvelous modern device.

Doppler Ultrasound of the Umbilical Artery: Clinical Application

OBJECTIVE

 To provide a survey of relevant literature on umbilical artery Doppler ultrasound use in clinical practice, technical considerations and limitations, and future perspectives.

METHODS

 Literature searches were conducted in PubMed and Medline, restricted to articles written in English. Additionally, the references of all analyzed studies were searched to obtain necessary information.

RESULTS

 The use of this technique as a routine surveillance method is only recommended for high-risk pregnancies with impaired placentation. Meta-analyses of randomized trials have established that obstetric management guided by umbilical artery Doppler findings can improve perinatal mortality and morbidity. The values of the indices of Umbilical artery Doppler decrease with advancing gestational age; however, a lack of consensus on reference ranges prevails.

CONCLUSION

 Important clinical decisions are based on the information obtained with umbilical artery Doppler ultrasound. Future efforts in research are imperative to overcome the current limitations of the technique.

Adverse perinatal outcomes in fetuses with severe late-onset fetal growth restriction

OBJECTIVE

To evaluate perinatal outcomes in fetuses with severe late-onset fetal growth restriction.

METHODS

This was a retrospective and observational cohort study in which pregnant women diagnosed with late-onset fetal growth restriction assisted at perinatal maternity birth from 2010 to 2017 were included. The outcomes were intensive care unit (ICU) admission and perinatal complications, such as neonatal death, intraventricular hemorrhage, periventricular leukomalacia, hypoxic-ischemic encephalopathy, necrotizing enterocolitis, bronchopulmonary dysplasia, and sepsis.

RESULTS

We selected 277 pregnant women, of whom 124 newborns (44.76%) went to the ICU. The chance of a newborn needing ICU decreases by 62, 7, and 9% according to an increase of one gestational week, 1 cm of the abdominal circumference, or 1 cm of the amniotic fluid index, respectively. Oligohydramnios increases the risk of going to the ICU by 2.13 times. The increase in the umbilical artery pulsatility index (PI) Doppler increases the chance of ICU admission by 7.9 times. The normal middle cerebral artery PI Doppler and the normal cerebroplacental ratio reduce the risk of ICU admission.

CONCLUSION

The estimated fetal weight, abdominal circumference, and amniotic fluid index diagnosed severe late-onset fetal growth restriction. With the decrease in middle cerebral artery PI Doppler, there is a greater probability of admission to the ICU, with the most common complications being intraventricular hemorrhage and necrotizing enterocolitis.

Fetal Sex and Fetal Environment Interact to Alter Diameter, Myogenic Tone, and Contractile Response to Thromboxane Analog in Rat Umbilical Cord Vessels

Fetal growth needs adequate blood perfusion from both sides of the placenta, on the maternal side through the uterine vessels and on the fetal side through the umbilical cord. In a model of intrauterine growth restriction (IUGR) induced by reduced blood volume expansion, uterine artery remodeling was blunted. The aim of this study is to determine if IUGR and fetus sex alter the functional and mechanical parameters of umbilical cord blood vessels. Pregnant rats were given a low sodium (IUGR) or a control diet for the last 7 days of pregnancy. Umbilical arteries and veins from term (22 day) fetal rats were isolated and set-up in wire myographs. Myogenic tone, diameter, length tension curve and contractile response to thromboxane analog U46619 and serotonin (5-HT) were measured. In arteries from IUGR fetuses, myogenic tone was increased in both sexes while diameter was significantly greater only in male fetuses. In umbilical arteries collected from the control group, the maximal contraction to U46619 was lower in females than males. Compared to the control groups, the maximal response decreased in IUGR male arteries and increased in female ones, thus abolishing the sexual dimorphism observed in the control groups. Reduced contractile response to U46619 was observed in the IUGR vein of both sexes. No difference between groups was observed in response to 5HT in arteries. In conclusion, the change in parameters of the umbilical cord blood vessels in response to a mild insult seems to show adaptation that favors better exchange of deoxygenated and wasted blood from the fetus to the placenta with increased myogenic tone.

Screening for fetal growth restriction using fetal biometry combined with maternal biomarkers

Fetal growth restriction is a major determinant of perinatal morbidity and mortality. Screening for fetal growth restriction is a key element of prenatal care but it is recognized to be problematic. Screening using clinical risk assessment and targeting ultrasound to high-risk women is the standard of care in the United States and United Kingdom, but the approach is known to have low sensitivity. Systematic reviews of randomized controlled trials do not demonstrate any benefit from universal ultrasound screening for fetal growth restriction in the third trimester, but the evidence base is not strong. Implementation of universal ultrasound screening in low-risk women in France failed to reduce the risk of complications among small-for-gestational-age infants but did appear to cause iatrogenic harm to false positives. One strategy to making progress is to improve screening by developing more sensitive and specific tests with the key goal of differentiating between healthy small fetuses and those that are small through fetal growth restriction. As abnormal placentation is thought to be the major cause of fetal growth restriction, one approach is to combine fetal biometry with an indicator of placental dysfunction. In the past, these indicators were generally ultrasonic measurements, such as Doppler flow velocimetry of the uteroplacental circulation. However, another promising approach is to combine ultrasonic suspicion of small-for-gestational-age infant with a blood test indicating placental dysfunction. Thus far, much of the research on maternal serum biomarkers for fetal growth restriction has involved the secondary analysis of tests performed for other indications, such as fetal aneuploidies. An exemplar of this is pregnancy-associated plasma protein A. This blood test is performed primarily to assess the risk of Down syndrome, but women with low first-trimester levels are now serially scanned in later pregnancy due to associations with placental causes of stillbirth, including fetal growth restriction. The development of "omic" technologies presents a huge opportunity to identify novel biomarkers for fetal growth restriction. The hope is that when such markers are measured alongside ultrasonic fetal biometry, the combination would have strong predictive power for fetal growth restriction and its related complications. However, a series of important methodological considerations in assessing the diagnostic effectiveness of new tests will have to be addressed. The challenge thereafter will be to identify novel disease-modifying interventions, which are the essential partner to an effective screening test to achieve clinically effective population-based screening.

Uterine Artery Doppler in Pregnancy: Women with PCOS Compared to Healthy Controls

The objective of this study was to investigate possible differences in uterine artery pulsatility index (UtAPI) between pregnant women with PCOS and healthy controls and to explore possible effects of metformin on UtAPI. Material and Methods. The study was conducted in a tertiary center. Forty-eight pregnant women diagnosed with PCOS before pregnancy and 124 healthy pregnant women were included. Women with PCOS were randomly assigned to metformin 2000 mg daily or a placebo. UtAPI was measured five times during 1st and 2nd trimesters of pregnancy in women with PCOS and four times in healthy controls. Results. There was no difference in UtAPI between PCOS women and healthy controls at any point in time (p = 0.34-0.77). In women with PCOS, randomly assigned to metformin 2000 mg or placebo, UtAPI was unaffected by metformin two hours after intake of the first dose of study medication (p = 0.34). All PCOS women, regardless of randomization, had higher UtAPI two hours after intake of study medication and a meal compared to before a meal (p = 0.02). Conclusions. In the first and second trimesters of pregnancy, there was no difference in UtAPI between women with PCOS and healthy controls. Metformin had no immediate effect on the UtAPI. Interestingly, blood flow decreased after a meal, suggesting that time since last meal should be taken into consideration when interpreting the results of UtAPI measurements in pregnancy. This trial is registered with ClinicalTrials.gov (NCT00466622) Metformin in Pregnant PCOS women (PregMet) (NCT00159536).

Doppler velocimetry in fetal rats exposed to enoxaparin and unfractionated heparin (UFH) during pregnancy

Purpose:

To evaluate the effects of enoxaparin and unfractionated heparin (UFH) administered in prophylactic and therapeutic doses on fetal vessels in healthy pregnant Wistar rats, according to Doppler velocimetry measurements.

Methods:

Fifty animals were assigned to one of five groups: controls (saline), prophylactic and therapeutic enoxaparin (1 and 2 mg/kg/day, respectively), and prophylactic and therapeutic UFH (72 and 400 UI/kg/day, respectively). Uterine horns were examined by ultrasound for identification of live fetuses. A sample of these fetuses underwent Doppler velocimetry. Spectral curves, peak systolic velocity (PSV), pulsatility index (PI), and resistance index (RI) of the middle cerebral artery, ductus venosus, and umbilical artery were investigated. Differences were considered statistically significant when p<0.05.

Results:

No significant differences in PSV, PI, or RI values were observed among the groups.

Conclusion:

Doppler velocimetry measurements revealed no significant effects of enoxaparin or unfractionated heparin on fetal vessels in pregnant Wistar rats.

Fetal Hemodynamic Parameters in Low Risk Pregnancies: Doppler Velocimetry of Uterine, Umbilical, and Middle Cerebral Artery

Objective. To elaborate curves of longitudinal reference intervals of pulsatility index (PI) and systolic velocity (SV) for uterine (UtA), umbilical (UA), and middle cerebral arteries (MCA), in low risk pregnancies. Methods. Doppler velocimetric measurements of PI and SV from 63 low risk pregnant women between 16 and 41 weeks of gestational age. Means (±SD) for intervals of gestational age and percentiles 5, 50, and 95 were calculated for each parameter. The Intraclass Correlation Coefficients (ICC) were also estimated for assessing intra- and intervariability of measurements. Results. Mean PI of UtA showed decreasing values during pregnancy, but no regular pattern was identified for mean SV. For UA, PI decreased and SV increased along gestation. MCA presented PI increasing values until 32–35 weeks. SV showed higher levels with increasing gestation. High ICC values indicated good reproducibility. Conclusions. Reference intervals for the assessment of SV and PI of UtA, UA, and MCA were established. These reference intervals showed how a normal pregnancy is expected to progress regarding these Doppler velocimetric parameters and are useful to follow high risk pregnancies. The comparison between results using different curves may provide insights about the best patterns to be used.

Digital auscultation of the uterine artery: a measure of uteroplacental perfusion

This observational study investigated digital auscultation for the purpose of assessing the clinical feasibility of monitoring vascular sounds in pregnancy. The study was performed at the Regional Hospital Viborg, Denmark, and included 29 pregnant women, 10 non-pregnant women and 10 male participants. Digital auscultation was performed with an electronic stethoscope bilaterally near the uterine arteries and correlated to the clinical diagnosis of preeclampsia (PE), intrauterine growth restriction (IUGR) or normal pregnancy in the group of pregnant participants. In the group of non-pregnant participants, digital auscultation was performed as control measurements in the same anatomical positions. The auscultations displayed pulse waveforms comprising systolic and diastolic periods in 20 of the 29 pregnant participants. However, in the non-pregnant and male participants, the pulse waveforms were absent. The pulsatile patterns are thus likely to originate from the arteries in relation to the pregnant uterus. In the participants displaying pulse waveforms, the presence of a dicrotic notch appeared with a sensitivity of 89% and a specificity of 100% in the discrimination of normal pregnancies (n  =  11) from pregnancies with PE or IUGR (n  =  9), (p  <  0.001). This preliminary study shows the potential of identifying vascular complications during pregnancy such as preeclampsia and intrauterine growth restriction. The morphology of the derived pulse contour should be investigated and could be further developed to identify pathophysiology.

Maternal and neonatal outcomes in obese women who lose weight during pregnancy

OBJECTIVE

To evaluate neonatal and maternal outcomes in obese pregnant women whose weight gain differed from the Institute of Medicine (IOM) recommendations.

STUDY DESIGN

Maternal and neonatal outcomes associated with weight change in pregnancy were retrospectively investigated in women with obesity (body mass index (BMI) ⩾30 kg m(-2); N=10734) who gave birth at 12 hospitals. Using a 1:1:1:1 design (n=778 matched groups), we matched women with obesity who lost, maintained, gained appropriate (IOM recommended) and gained excessive weight during pregnancy by gestational age at delivery, maternal age, race/ethnicity, prepregnancy BMI, chronic hypertension, pregestational diabetes and smoking status. Regression techniques were used to adjust for confounders and compare outcomes across weight change categories.

RESULT

Compared with IOM recommendations, weight loss was associated with twofold greater odds of low birth weight infants and a mean decrease in estimated blood loss of 30 ml; excessive weight gain was associated with doubled odds of gestational hypertension or preeclampsia, fourfold greater odds of macrosomia and a mean decrease in 5-min APGAR of 0.09. From lost to excessively gained weight, the odds of cesarean delivery increased 1.4 times and mean infant birth weight increased by 197 g. In contrast, the odds of small-for-gestational age were 1.8 times greater for women who lost than gained excessive weight.

CONCLUSION

Weight loss in obese pregnant women is associated with increased risk for low birth weight neonates but significantly decreased or maintained risk for other maternal and neonatal morbidities, as compared with appropriate or excessive weight gain. This study supports re-evaluation of the current IOM guidelines for women with obesity.

Effects of altitude changes on Doppler flow parameters for uterine, umbilical, and mid-cerebral arteries in term pregnancy: A pilot study

OBJECTIVE

We hypothesized that maternal and fetal circulations may be affected by moderately high altitudes. Therefore, we compared the differences in maternal and fetal Doppler flow parameters in women with term pregnancy living at a moderately high altitude (1890 m in Erzurum) with those of women living at the sea level (31 m in İstanbul).

MATERIAL AND METHODS

Eighty women (n=40, for each group) with full-term and singleton pregnancies underwent Doppler waveform analysis, and the pulsatility and resistance index values for the uterine, umbilical, and mid-cerebral arteries were recorded. Also, sex, birth, and placental weights during delivery were obtained from the medical records.

RESULTS

Similar mean placental weight values were found at the sea level compared with the moderately high altitude (p>0.05). The mean birth weight values were found to be lower at the moderately high altitude than those at the sea level (p<0.05). The pulsatility and resistance index values for the umbilical and mid-cerebral arteries were found to be similar between the groups (p>0.05). However, the pulsatility and resistance index values for both the right and left uterine arteries were higher at the sea level than those at moderately high altitude (p<0.05, for all).

CONCLUSION

Moderately high altitude does not affect fetal vascular Doppler parameters. However, it appears to increase the uterine artery blood flow bilaterally, and these alterations in the bilateral uterine artery blood flow may be associated with a physiological adaptation to high altitude.

Can we measure the spiral and uterine artery blood flow by real-time sonography and Doppler indices to predict spontaneous miscarriage in a normal-risk population?

Introduction: The predictive value of spiral artery flow Doppler measurements of a subsequent early miscarriage in first trimester pregnancy is explored here. Objective: The aim of this study is to determine uterine and spiral artery blood flow changes in first trimester subsequent miscarriages and correlate within the mechanisms of the Doppler indicies. Study design: The uterine artery and spiral artery pulsatility and resistance indexes, systolic and diastolic ratios, acceleration times, and blood flow of both the right and left uterine arteries were obtained by trans vaginal color Doppler ultrasonography in consecutive viable pregnancies between 5 and 12 gestational week. Women were subsequently classified as having continuing pregnancies or pregnancy loss before 20 weeks gestation. To predict subsequent pregnancy loss, Doppler findings were adjusted for maternal age, history of previous abortion, presence of subchorionic hematoma, embryonic bradycardia, and gestational age by means of multivariate logistic regression analysis. The cut-off values are used for the ROC curve. Results: Twenty-five pregnancies (11.7%) were spontaneously aborted before 20 weeks of gestational age. In 29 (13.6%) cases there were previously abortion history, 30 (14%) had bradycardia, and 37 (17.3%) had subchoronic hematoma. Regarding the parameters of uterine and spiral artery pulsatility and resistive index, acceleration time, systolic/diastolic ratios and blood flows, only uterine artery S/D low values were significantly associated with pregnancy loss in the multivariate logistic regression analysis (P = 0.0001,95% CI: 4.968-55.675). Conclusion: The uterine artery systolic/diastolic ratios have a predictive value for early pregnancy loss and seem to be useful as a marker. On the other hand, spiral artery changes could be so local that they cannot be determined by the parameters of spectral Doppler techniques. This suggests that uterine vascular bed alterations should be measured to understand the prognosis of early pregnancy loss during the first trimester.

Psychosocial predictors of fetoplacental blood flow during pregnancy

BACKGROUND

Although a number of studies have found significant associations between maternal psychological distress, anxiety and changes in fetoplacental blood flow, findings remain inconsistent. A recent pilot study by our group highlighted some of these inconsistencies. In the current study, we expanded this pilot analysis to include psychological distress, anxiety and a range of antenatal variables, with the aim of identifying predictors of fetoplacental blood flow.

METHODS

Healthy pregnant women (n=148) underwent Doppler flow studies on uterine, umbilical and fetal arteries; as well as assessments of distress, anxiety and other antenatal variables (e.g. perceived social support, resilience, nicotine and alcohol use) in each trimester.

RESULTS

Stepwise regression analyses found that state anxiety was associated with lower mid-cerebral artery pulsatility index at trimester 3.

LIMITATIONS

Subjects were recruited from selected midwife obstetric units in the same health district, so the generalizability of our results may be limited. While most subjects received Doppler assessment at trimesters 2 and 3, only approximately half of our sample was assessed at trimester 1.

CONCLUSION

The finding that anxiety is associated with increased blood flow to the fetal brain during trimester 3 of pregnancy, coincide with previous work. The findings emphasize a growing appreciation of the potential importance of psychological well-being during pregnancy for infant development. However, as associations were small and variable, further research using multivariate models to determine the precise mechanisms underlying these associations would be warranted.

Comprehensive imaging review of abnormalities of the umbilical cord

A complete fetal ultrasonographic (US) study includes assessment of the umbilical cord for possible abnormalities. Knowledge of the normal appearance of the umbilical cord is necessary for the radiologist to correctly diagnose pathologic conditions. Umbilical cord abnormalities can be related to cord coiling, length, and thickness; the placental insertion site; in utero distortion; vascular abnormalities; and primary tumors or masses. These conditions may be associated with other fetal anomalies and aneuploidies, and their discovery should prompt a thorough fetal US examination. Further workup and planning for a safe fetal delivery may include fetal echocardiography and karyotype analysis. Doppler US is a critical tool for assessment and diagnosis of vascular cord abnormalities. US also can be used for follow-up serial imaging evaluation of conditions that could result in fetal demise. Recent studies suggest that three- or four-dimensional Doppler US of the fetal umbilical cord and abdominal vasculature allows more accurate diagnosis of vascular abnormalities. Doppler US also is invaluable in assessment of fetal growth restriction since hemodynamic changes in the placenta or fetus would appear as a spectral pattern of increased resistance to forward flow in the fetal umbilical artery. Early detection of umbilical cord abnormalities and close follow-up can reduce the risk of morbidity and mortality and assist in decision making.

Doppler velocimetry of the ovarian artery as a tool to detect LH surge in stimulated cycles

Our aim was to assess the velocimetric pattern of the ovarian artery as a possible marker of LH surge in stimulated cycles. A total of 130 women undergoing ovarian stimulation for intrauterine insemination were randomized in two groups. Each woman was stimulated with 75 IU of recombinant FSH starting from the third day of the cycle. Velocimetric indices of the dominant ovarian artery were compared between patients with spontaneous LH surge and those needing HCG administration to trigger dominant follicle rupture. The pulsatility index and the ratio between peak systolic flow and lowest diastolic flow were significantly higher in women that had a spontaneous triggering of ovulation. These parameters had a high and very significant positive correlation with the dosage of luteinizing hormone. Threshold values of 2.60 for PI and 7.68 for S/D had a high sensitivity and specificity to predict LH surge. These velocimetric results demonstrated that an increased resistance in the dominant ovarian artery is correlated to LH surge in stimulated cycles. It may represent a sign of relevant clinical utility in timing of intrauterine insemination and/or natural intercourse.

The effects of spinal anaesthesia for elective caesarean section on uterine and umbilical arterial pulsatility indexes in normotensive and chronic hypertensive pregnant women: a prospective, longitudinal study

BACKGROUND

Despite the known effects of neuraxial blockade on major vessel function and the rapid decrease in uterine vascular impedance, it is unclear how the blockade affects the utero-placental circulation in the near-term. We hypothesize that among women with chronic hypertension, a loss of sympathetic tonus consequent to spinal block may cause significant changes in the utero-placental haemodynamics than the changes typical in normal pregnant women. Therefore, the main study objective was to analyse the effect of spinal anaesthesia for caesarean section on uterine and umbilical arterial impedance in pregnant women at term diagnosed with stage-1 chronic hypertension.

METHODS

A prospective, longitudinal study was performed in singleton pregnant women (203 low-risk and 33 with hypertension) scheduled to undergo elective caesarean section. The mean arterial blood pressure and pulsatility indexes for the uterine and umbilical arteries were recorded before and after spinal anaesthesia was performed using 8-9 mg hyperbaric bupivacaine (5 mg/mL) and 2-2.5 μg sufentanil (5 μg/mL). Multiple linear regression models with errors capable of correlation or with unequal variances were fitted using the generalized least squares.

RESULTS

In normotensive women, the mean arterial blood pressure decreased after administering spinal anaesthesia (p < 0.05). The pulsatility index of the uterine and umbilical arteries did not change after spinal anaesthesia. In the hypertensive women, the mean arterial blood pressure (p < 0.05) and uterine artery pulsatility index (p < 0.05) decreased. In both groups, the umbilical artery pulsatility index did not change after spinal anaesthesia.

CONCLUSIONS

In stage-1 chronic hypertensive pregnant women at term, spinal anaesthesia for caesarean section reduces uterine artery impedance but not umbilical artery impedance.