Longitudinal survey of blood flow at three different locations in the middle cerebral artery in normal fetuses

Study protocol for a randomized trial on timely delivery versus expectant management in late preterm small for gestational age pregnancies with an abnormal umbilicocerebral ratio (UCR): the DRIGITAT study

BACKGROUND

The clinical inability to correctly identify late fetal growth restriction (FGR) within a group of fetuses who are identified as small for gestational age (SGA) is an everyday problem for all obstetrician-gynecologists. This leads to substantial overtreatment of healthy small fetuses but also inadequate detection of the growth-restricted fetuses that may benefit from timely delivery. Redistribution of the fetal circulation, signaled by an abnormal ratio of the Doppler velocity flow profiles of the umbilical artery and the middle cerebral artery, more specifically an increased umbilicocerebral ratio (UCR) (or its inverse: a decreased cerebroplacental ratio (CPR)), is an adaptation to chronic hypoxemia and nutritional scarcity with long-term consequences in survivors. The relevance of an abnormal UCR has been signaled extensively, and there is a general consensus that it is a signal of FGR, independent of size, with a strong association with poor outcomes. Yet, in the current literature, no comparisons of a monitoring-delivery strategy based on unfavorable UCR have been published. The objective of the Doppler Ratio In fetal Growth restriction Intervention Trial At (near) Term (DRIGITAT) is to evaluate if the timing of the delivery based on an abnormal UCR in late preterm fetuses identified as SGA improves neurodevelopmental outcomes at 2 years of age.

METHODS

The DRIGITAT study is a national multicenter cohort study of women with singleton pregnancies between 32 and 37 weeks of gestation identified as SGA, with a nested randomized controlled trial (RCT) in case of an abnormal UCR (> 0.8). Recruiting centers are in The Netherlands. In the nested RCT, women are randomized to either immediate induction of labor or expectant management from 34 weeks in case of severely abnormal size (EFW or FAC < p3) and from 36 weeks in case of mildly abnormal size (EFW or FAC p3-p10). The primary outcome measure is the 7-point average difference in the composite cognitive score (CCS) and composite motor score (CMS) on the Bayley-3 at 2 years. Secondary outcome measures include a composite outcome of neonatal morbidity, perinatal mortality, mode of delivery, maternal quality of life, costs, and predictive value of serum biomarkers. Analyses will be by intention to treat. The required sample size is determined for the nested RCT as 185 patients.

DISCUSSION

This study will provide insight into the diagnostic efficacy of UCR measurement in the evaluation of SGA fetuses in order to differentiate the healthy SGA fetus from the growth-restricted fetus and to determine if a fetus with abnormal UCR benefits from early delivery.

TRIAL REGISTRATION

Healthcare Evaluation Netherlands NTR6663 . Registered on 14 August 2017.

Hemodynamic Changes in Umbilical Artery and Middle Cerebral Artery With Oligohydramnios in Third Trimester of Pregnancy

Objective:

The objective of this study was to determine the hemodynamic changes in the umbilical artery (UA) and middle cerebral artery (MCA) with oligohydramnios, during third trimester of pregnancy.

Materials and Methods:

A cross-sectional descriptive study was done in a perinatal ultrasound center, over a 9-month period. The participant sample size was 64, and all of the women were conveniently consented and selected for the study. All individuals were referred for obstetrical sonography in the third trimester, with oligohydramnios. All fetal anomalies, such as a neural tube defect, dwarfism, an abdominal wall defect, were excluded from the study.

Results:

The mean systolic to diastolic (S/D) ratio for the UA was 3.01, within a range of 1.49 to 5.60 (± 0.79 SD). The mean pulsatility index (PI), of the UA, was 1.11, within a range of 0.41 to 5.51 cm (± 0.64 SD). The mean resistive index (RI) of the UA was 0.66, within a range of 0.33 to 1.25 cm (± 0.13 SD). The mean S/D ratio of the MCA was 5.68, within a range of 2.05 to 26.10 (± 3.10 SD). The mean PI of the MCA was 1.67 within a range of 0.75 to 2.55 cm (± 0.45 SD). The mean resistive index (RI), of the UA, was 0.82 within a range of 0.51 to 1.77 cm (± 0.82 SD).

Conclusion:

The Doppler indices may rise as pregnancy advances, especially in fetuses with oligohydramnios. In these types of patients, the flow within the MCA may decrease, with an increase in the gestational age. Consequently, it appears that oligohydramnios may lead to vascular remodeling of the UA and MCA.

Middle cerebral artery Doppler pulsatility index as a predictor of intrapartum meconium release in prolonged pregnancies

OBJECTIVES

The aim of this study was to asses the correlation of middle cerebral artery pulsatility index (MCA-PI) and perinatal outcomes in prolonged pregnancies.

STUDY DESIGN

This was a prospective study of all consecutive pregnant women beyond 41 weeks' gestation attending for obstetric surveillance during a two years period. We evaluated the predictive value of MCA-PI lower than the 5th percentile (<p5) and the occurrence of: cesarean delivery for fetal distress, 5-min Apgar score <7, arterial cord pH < 7.15, presence of thick meconium at delivery, need for admission to the neonatal intensive care and/or neonatal death.

RESULTS

Three hundred and one pregnancies met the inclusion criteria and were managed expectantly. Of them, 31 (10.3%) fetuses had an MCA-PI < p5, which showed a significant relationship with the presence of thick meconium at birth (p < 0.001), but was not related to any of the other perinatal outcomes.

CONCLUSION

In prolonged pregnancies, the finding of MCA-PI < p5 is related to meconium emission at the time of delivery, but is not associated with an increased risk of adverse perinatal outcome.

Inter- and intra-observer variability in fetal ductus venosus blood flow measurements in high-risk fetuses at 26-32 weeks

OBJECTIVES

Early preterm fetal growth restriction is a significant contributor to perinatal morbidity and mortality. The ductus venosus pulsatility index for veins (DV PIV) is proposed as a monitoring tool because it appears to improve perinatal outcomes. The test characteristics and robustness of DV PIV have been inadequately described. The aim of this study was to investigate inter- and intra-observer variability of DV PIV.

STUDY DESIGN

Nineteen women with a gestational age between 26 and 32 completed weeks were included in this study. Doppler sonographic fetal assessment was performed by two independent maternal-fetal medicine specialists. Each sonographer alternately performed three flow tracings for each participant, in the absence of the other sonographer (six tracings in total per patient). DV PIV was calculated automatically from stored tracings by a third researcher. Inter- and intra-observer variability of DV PIV and limits of agreement were assessed using the Bland-Altman method. Comparison of the distribution was performed with Kendall's related samples test, and the intraclass correlation coefficient (ICC) was calculated.

RESULTS

In total, 114 DV measurements were taken from 19 participants with a median age of 31 years [interquartile range (IQR) 26-34 years] at a median gestational age of 28 weeks (IQR 27-29 weeks). The proportional limits of agreement for intra-observer variation were -0.48 to 0.48 and -0.39 to 0.62 for the two observers. ICCs were 0.66 [95% confidence interval (CI) 0.42-0.84] and 0.68 (95% CI 0.45-0.85). The proportional limits of agreement for inter-observer variation were -0.29 to 0.19 with an ICC of 0.89 (95% CI 0.73-0.96).

CONCLUSION

Inter-observer variation was far less than intra-observer variation, probably due to mitigation of biological variation by averaging three measurements. DV PIV has acceptable test characteristics for use in a clinical setting when the average of at least three consecutive measurements is used.

[Doppler Sonography during Pregnancy - DEGUM Quality Standards and Clinical Applications]

Doppler sonography is widely established in prenatal medicine and obstetrics and is commonly used in screening for aneuploidy and preeclampsia during the first trimester. More importantly, during the 2nd and 3 rd trimester, it is used in the assessment of fetal health as well as the surveillance of underlying fetal conditions such as IUGR and anemia. Correct use of the method is vital for correct data interpretation and the inferred clinical decision process. Therefore, we aim to provide all users of doppler sonography with a guide for meeting the required quality standards. These quality standards will further be the basis of DEGUM-certified training courses. In the first part, we will introduce the technical principles of the method and potential error sources, vascular disciplines to which the method can be applied, analysis of the spectral curves, patient safety and the needed requirements for successful certification.

Assessment of the Fetal Cerebral Artery: Importance of Doppler Preset Settings

OBJECTIVES

The Doppler assessment of the middle cerebral artery (MCA) has a central role in the monitoring of high-risk pregnancies. The objective of this study was to investigate the importance of Doppler preset settings for measurement of the peak systolic velocity (PSV) and pulsatility index (PI) of the MCA.

METHODS

The PI and PSV of the MCA were determined prospectively in 350 healthy fetuses between 19 and 42 weeks of pregnancy. The first measurement of the MCA (MCA.S) was performed with the conventional settings and the second (MCA.O) with an optimized setting of the maximum achievable frame rate. For the MCA.O measurement, the width of the B-mode image and the color Doppler window were adjusted as narrowly as possible. In addition, the MCA was shown in optimized high-definition zoom. Resulting values were compared with commonly used reference values.

RESULTS

The PSV and PI values and frame rates of the MCA.O setting were noticeably greater than those of the MCA.S setting (P < .001 for all). For both settings, the PSV and PI values were increased compared to common reference values.

CONCLUSIONS

The assessment of the MCA with the optimized Doppler default setting yielded increased PSV and PI values compared to the commonly used measurement technique. Moreover, the resulting median curves differed from the established median reference curves. Therefore, an updated standardization for measuring the MCA should be set out, and current reference values should be adjusted.

Color doppler indices of proximal and distal parts of middle cerebral artery in fetuses with intrauterine growth restriction

INTRODUCTION

Intrauterine growth restriction (IUGR) is a major clinical issue for pregnant women. The purpose of this study was to evaluate color Doppler indices of the proximal and distal parts of the middle cerebral artery (MCA) of the fetus.

METHODS

In this cross-sectional study, 350 pregnant patients, with gestation age of 32-40 who were suspected to have intrauterine growth restriction, participated. The patients were referred for color Doppler sonography at the Imam Reza Hospital (Kermanshah, Iran) from May 2011 to September 2012. The following indices were measured for the proximal and distal part of the MCA: pulsatility index (PI), resistive index (RI), fetal heart rate (FHR), systolic to diastolic (S/D) ratio, and peak systolic velocity (PSV). The data were analyzed applying Tukey's-test, Paired-Samples t-test, and simple linear regression analysis using SPSS 19.

RESULTS

Average age of the mother, the frequency of pregnancy, and fetus gestational age were 27.79±0.17 years, 2.09±1.3, and 34.19±2.52 weeks, respectively. For gestation age of <36weeks, all Doppler indices of the distal part of the fetus MCA were significantly different from those of proximal part (p<0.05). Comparing indices of gestation age <36 weeks with those of >36 weeks, significant difference was found between the Doppler indices of the proximal parts as well as for the distal parts (p<0.05).

CONCLUSION

Measurement of fetus MCA indices may depend to the sampling location; however, this needs further investigation in order to find a clear probe location.

Reliability of Doppler Assessment of the Middle Cerebral Artery in the Near and Far Fields in Healthy and Anemic Fetuses

OBJECTIVES

The purpose of this study was to assess the reliability of the middle cerebral artery pulsatility index (PI) and peak systolic velocity (PSV) at the proximal portions of the near- and far-field vessel sites in healthy and anemic fetuses.

METHODS

The middle cerebral artery PSV and PI were prospectively assessed in 50 normal singleton pregnancies. The Doppler waveforms for the middle cerebral artery PI and the PSV were recorded independently by 2 operators at the most proximal portions of the near- and far-field sites. Data for the PSV and PI at the proximal portions of both the near- and the far-field sites were also retrospectively collected in 7 anemic fetuses.

RESULTS

No significant difference between the operators was detected for the middle cerebral artery PSV (P = .60) and PI (P = .88) measured in the conventionally used near-field proximal site in the 50 healthy fetuses. No significant difference between the proximal portions of the near- and far-field sites was detected for the PSV (P = .53) and PI (P = .23) in healthy or anemic fetuses.

CONCLUSIONS

The findings of this study suggest that the use of the far-field vessel is an acceptable alternative for measurement of the middle cerebral artery PI and PSV when investigation of the near-field vessel is technically difficult.

Role of cerebroplacental ratio for fetal assessment in prolonged pregnancy

OBJECTIVE

The aim of this study was to assess the role of the cerebroplacental ratio (CPR), i.e. the ratio between the middle cerebral artery and umbilical artery pulsatility indices, in detecting fetal compromise in prolonged pregnancy.

METHODS

Women attending a dedicated postdates clinic at 41 weeks' gestation were recruited for the study and CPR was calculated at 41+3 weeks. Induction of labor was offered at 42 weeks to those women still undelivered. Unfavorable outcome was defined as cord arterial pH < 7.15 with a base deficit of > 11 mM/L or operative delivery for abnormal intrapartum fetal electrocardiogram ST-segment analysis. The 5(th) centiles of the CPR, obtained from published reference ranges (0.90) and from our population (0.98), were used as lower cut-off values.

RESULTS

Three hundred and twenty women who reached a gestational age of over 41 weeks were eligible for inclusion in the study. The median gestational age at delivery was 294 (range, 289-300) days. Unfavorable outcome was observed in 58/320 pregnancies. There was no significant difference in the proportion of unfavorable outcomes between the two groups defined using either CPR cut-off value (both P > 0.05).

CONCLUSION

CPR is not predictive of unfavorable outcome in women with pregnancies lasting more than 41 weeks.

Fetal liver blood flow distribution: role in human developmental strategy to prioritize fat deposition versus brain development

Among primates, human neonates have the largest brains but also the highest proportion of body fat. If placental nutrient supply is limited, the fetus faces a dilemma: should resources be allocated to brain growth, or to fat deposition for use as a potential postnatal energy reserve? We hypothesised that resolving this dilemma operates at the level of umbilical blood distribution entering the fetal liver. In 381 uncomplicated pregnancies in third trimester, we measured blood flow perfusing the fetal liver, or bypassing it via the ductus venosus to supply the brain and heart using ultrasound techniques. Across the range of fetal growth and independent of the mother's adiposity and parity, greater liver blood flow was associated with greater offspring fat mass measured by dual-energy X-ray absorptiometry, both in the infant at birth (r = 0.43, P<0.001) and at age 4 years (r = 0.16, P = 0.02). In contrast, smaller placentas less able to meet fetal demand for essential nutrients were associated with a brain-sparing flow pattern (r = 0.17, p = 0.02). This flow pattern was also associated with a higher degree of shunting through ductus venosus (P = 0.04). We propose that humans evolved a developmental strategy to prioritize nutrient allocation for prenatal fat deposition when the supply of conditionally essential nutrients requiring hepatic inter-conversion is limited, switching resource allocation to favour the brain if the supply of essential nutrients is limited. Facilitated placental transfer mechanisms for glucose and other nutrients evolved in environments less affluent than those now prevalent in developed populations, and we propose that in circumstances of maternal adiposity and nutrient excess these mechanisms now also lead to prenatal fat deposition. Prenatal developmental influences play important roles in the human propensity to deposit fat.

Mean platelet volume: Association with adverse neonatal outcome

The aim of the study was to investigate on a possible association between maternal mean platelet volume (MPV) and oxygen-metabolic changes in pregnancies affected by altered maternal-fetal Doppler velocimetry. We considered the altered maternal-fetal Doppler velocimetry group (n = 57) pregnant women admitted to our Institution for a pregnancy complication associated to the event Pre-eclampsia (PE) and intrauterine growth retardation (IUGR), with altered Doppler velocimetry in the umbilical artery ( UA) (high pulsatility index, absence or reverse end diastolic flow (ARED), blood flow cephalisation) and/or bilateral increased resistance in uterine arteries. Out of these cases, 25 pregnancies were complicated by PE and 32 pregnancies were complicated by IUGR. We included 145 normotensive third trimester pregnant women as a normal maternal-fetal Doppler velocimetry control group. From all women, 20 ml of whole venous blood was obtained from the antecubital vein soon after Doppler velocimetry evaluation. MPV was significantly higher in women with abnormal Doppler velocimetry compared to those with normal Doppler velocimetry (8.0 fl [7.0-8.7] vs. 9.1 fl [8.0-10.6], <0.001. Values are median [interquartiles]). We performed a ROC curve in order to find an MPV cut-off able to predict an uneventful event in Doppler velocimetry compromised fetuses (neonatal O(2) support > 48 hrs or intubation and/or pH < 7.2 at umbilical blood gas analysis (UBGA)). An MPV > or = 10 fl was significantly related to the former diagnostic endpoints compared to that of non-compromised fetuses (sensitivity: 45%, specificity: 89.7%, 95 CI: 18.8-66, p < 0.01). Our study suggests that pregnancies affected by Doppler velocimetry alterations, an MPV value > or = 10 fl may be associated with severe oxygen support and/or low UA ph at birth.

Doppler velocimetry alterations related to platelet changes in third trimester pregnancies

The aim of this study was to evaluate the correlations between the haematological parameter mean platelet volume and Doppler velocimetry parameters in order to improve clinical management in third trimester complicated pregnancies (pre-eclampsia, PE, and IUGR) affected by altered uterine resistances. Fifty-one patients were included in the abnormal uterine arteries Doppler velocimetry group (25 pregnancies were complicated by PE, 26 pregnancies were complicated by IUGR). Ninety-nine normotensive pregnant women taking no drugs for at least 2 weeks prior to testing and with no difference in gestational age at evaluation, with normal Doppler velocimetry profiles at routine screen, were used as controls. From all pregnant women, 20 mL of whole blood were obtained into citrate tubes after Doppler velocimetry evaluation and analysed for red blood cell counts (RBC), mean corpuscular volume (MCV), haemoglobin (HGB), haematocrit level (HCT), white blood cells count (WBC), platelet counts (PLT), mean platelets volume (MPV) and other biochemical parameters. From all blood parameters studied, MPV was significantly higher in women with altered uterine artery Doppler velocimetry compared with those with normal Doppler profiles (9.4 +/- 1.0 vs. 8.05 +/- 1.2 fL, P<0.001). In the group with altered uterine artery Doppler velocimetry, pregnancies complicated by PE showed a MPV value higher than pregnancies affected by IUGR (9.5 +/- 1.6 vs. 8.9 +/- 1.1, P<0.001). Finally, mean uterine arteries RI values were significantly related to MPV (fL) in both PE and IUGR groups (P<0.01, r=0.37 and P<0.01, r=0.38, respectively). Our study shows that a periodical monitoring of haematological parameters such as MPV can be associated to Doppler velocimetry in order to improve the management of pregnancies with uterine arteries Doppler velocimetry alterations.

CURRENT ASPECTS OF FETAL CARDIOVASCULAR FUNCTION

Investigation of fetal cardiac function remains a challenging task. Although the response of the heart to changes in load is well-known in animal models and the adult human, the developmental changes in fetal cardiac response remain poorly characterised. However, quantitative evaluation of cardiovascular function is important to predict the clinical course and to manage the fetus optimally. To date, the routine evaluation of fetal cardio vascular function has relied largely on Doppler echocardiography which enables an estimate of haemodynamics; newer modalities such as measurement of myocardial velocities are employed less routinely. Fetal magnetic resonance imaging still lacks the resolution necessary to contribute significantly to morphological or functional assessment of the fetal cardiovascular system.

Middle cerebral artery blood flow velocities and pulsatility index and the cerebroplacental pulsatility ratio: longitudinal reference ranges and terms for serial measurements

OBJECTIVES

To establish reference ranges suitable for serial assessments of the fetal middle cerebral (MCA) and umbilical (UA) artery blood flow velocities, pulsatility index (PI) and cerebroplacental pulsatility ratio and to provide terms for calculating conditional reference intervals suitable for individual serial measurements.

METHODS

This was a longitudinal study of 161 singleton pregnancies. Using Doppler ultrasound, MCA and UA blood velocities and PI were determined three to five times at 3-5-week intervals over a gestational age range of 19-41 weeks. Polynomial regression lines for the 95th, 50th and 5th percentiles were calculated for the peak systolic velocity (PSV), time-averaged maximum velocity (TAMXV), PI and cerebroplacental ratio. Terms for calculating conditional reference intervals were established.

RESULTS

Based on 566 observations our new longitudinal reference ranges for fetal middle cerebral PSV, TAMXV and PI provided terms for calculating conditional reference intervals (i.e. predicting expected 95% confidence limits based on a previous measurement), and correspondingly for the cerebroplacental ratio (n = 550). The reference ranges were at some variance with those of previous cross-sectional studies. The narrow 95% confidence limits for the 5(th) and 95(th) percentiles ensured reliable ranges.

CONCLUSIONS

We have established longitudinal reference ranges appropriate for the serial assessment of MCA blood velocities and PI and cerebroplacental ratio. Particularly the terms for calculating conditional ranges based on a previous observation make this system more appropriate for longitudinal monitoring than are cross-sectional data.

Middle cerebral artery pulsatility index: reliability at different sampling sites

OBJECTIVES

To analyze the interobserver reliability of measurement of the middle cerebral artery (MCA) pulsatility index (PI) at two different sampling sites.

METHODS

This study included 100 consecutive singleton pregnancies between 24 and 40 weeks with normal fetal growth. The PI was calculated by two independent operators at proximal and distal sampling sites of the near-field MCA. Reliability analyses were performed between observers at each sampling site by means of the intraclass correlation coefficient (ICC) for agreement. Differences between observers were explored and agreement limits calculated by means of the Bland-Altman test.

RESULTS

Satisfactory flow velocity waveforms were obtained successfully in each fetus at both sampling sites. Peak systolic, end-diastolic and time-averaged maximum velocities were significantly higher at the proximal compared with the distal sampling site. Conversely, PI was significantly higher at the distal compared with the proximal site. ICCs for PI were 0.3 and 0.33 at the proximal and the distal sampling sites, respectively. The 95% interval of the PI differences between observers were +0.91 and -1.14 at the proximal and +1.03 and -1.08 at the distal sampling sites. In about 30% of the cases the PI difference between observers was greater than 0.5 at both sampling sites.

CONCLUSIONS

Moderate interobserver reliability in the measurement of end-diastolic and time-averaged maximum MCA flow velocities results in limited agreement of the PI calculation at both proximal and distal sampling sites. These results may preclude its clinical applicability.

A randomized trial of plasma volume expansion in hypertensive disorders of pregnancy: influence on the pulsatility indices of the fetal umbilical artery and middle cerebral artery

OBJECTIVE

The purpose of this study was to investigate the effect of plasma volume expansion on the pulsatility indices of the fetal umbilical and middle cerebral arteries.

STUDY DESIGN

Two hundred sixteen patients with severe preeclampsia, HELLP (hemolysis, elevated liver enzymes, and low platelet count) syndrome, eclampsia, hypertension-related fetal growth restriction, and gestational ages between 24 and 34 completed weeks of gestation were assigned randomly for temporizing treatment with plasma volume expansion (n = 111 patients; 250 mL hydroxyethyl starch 6% twice daily in 4 hours, and NaCl 0.9% between doses of hydroxyethyl starch and with intravenous medication) or without plasma volume expansion (n = 105; only NaCl 0.9% when necessary with medication). Measurements of the pulsatility index of the umbilical and middle cerebral arteries were performed at admission, after 16 to 48 hours, 60 to 120 hours, and 7 to 11 days.

RESULTS

Median gestational age was 30 weeks in both groups. Infused volumes of plasma volume expansion in the treatment group (total median, 813 mL/d) were associated with a significant decrease of hemoglobin concentration. Changes from baseline measurements of the umbilical and middle cerebral arteries were not different between the groups nor within subgroups during the first 7 to 11 days.

CONCLUSION

Plasma volume expansion did not influence the pulsatility indices of the umbilical and middle cerebral arteries.

Reference ranges for umbilical and middle cerebral artery pulsatility index and cerebroplacental ratio in prolonged pregnancies

OBJECTIVE

To construct normal ranges for umbilical artery pulsatility index (UA PI), middle cerebral artery pulsatility index (MCA PI) and cerebroplacental ratio (CPR) in prolonged pregnancies according to strict methodological criteria using polynomial regression analysis.

METHODS

This was a retrospective, cross-sectional observational study involving 140 women, 10 women for each gestational day between 287 and 300 days of gestation. Fetal Doppler parameters were assessed to construct normal reference ranges for UA PI and MCA PI. CPR was calculated as a ratio of MCA PI/UA PI.

RESULTS

Mathematical modeling of the data demonstrated that the optimal fit was a linear polynomial one. Mean, 5th and 95th centiles were calculated for UA, MCA and CPR and centile curves from the regression analysis were constructed.

CONCLUSIONS

Reference ranges for UA PI, MCA PI and CPR in prolonged pregnancies have been constructed. MCA PI shows a wider range than previously reported in the literature.

Middle cerebral artery Doppler indices at different sites: prediction of umbilical cord gases in prolonged pregnancies

OBJECTIVES

To assess the value of middle cerebral artery Doppler indices obtained from different sampling sites in predicting umbilical cord gases at delivery in prolonged pregnancies.

METHODS

This was a prospective study of consecutive pregnant women referred for prolonged-pregnancy surveillance. The predictive value of distal and proximal middle cerebral artery Doppler indices for cord blood gases was evaluated in women who delivered within 48 h of their last antenatal test using stepwise multiple regression.

RESULTS

There was a significant linear correlation between proximal and distal middle cerebral artery pulsatility indices (R = 0.777; P < 0.0001), the mean values being 1.49 (SD, 0.45) and 1.56 (SD, 0.47), respectively. There was also a linear correlation between proximal and distal cerebroplacental ratios (R = 0.68; P < 0.0001), the mean values being 1.85 (SD, 1.96) and 1.92 (SD, 1.89), respectively. The stepwise multiple regression analysis for umbilical artery pH showed that once the distal middle cerebral artery pulsatility index was introduced into the model, the addition of any variable did not result in a significant improvement of the predictive capacity. The model showed a coefficient of determination (R(2)) of 0.079. There was a significant correlation between umbilical artery pO(2) and both proximal middle cerebral artery pulsatility index (positive) and the occurrence of elective Cesarean section (negative). This model accounted for 21% of the variance (R(2) = 0.21). No other variables added any significant prediction for pO(2).

CONCLUSIONS

In post-term pregnancies the proximal middle cerebral artery pulsatility index significantly predicts umbilical artery pO(2) at delivery but does not predict pH. There is a weak association between distal middle cerebral artery pulsatility index and pH but, as this only explains 8% of the variance, it is of little clinical value.

Ultrasound assessment of the fetal middle cerebral artery peak systolic velocity: a comparison of the near-field versus far-field vessel

OBJECTIVE

Doppler assessment of the fetal middle cerebral artery peak systolic velocity may obviate the need for more invasive procedures in the alloimmunized patient. The purpose of this study was to compare middle cerebral artery peak systolic velocity measurements in the near field and far field.

STUDY DESIGN

Patients between 16 and 42 weeks of gestation with normal fetuses were eligible (n=151). Peak systolic velocity measurements were obtained at the proximal portion of each middle cerebral artery at its origin in the internal carotid artery, as well as the most distal portion before its division, for a total of 4 measurements per fetus. Comparisons were made among the 4 locations and the data were analyzed using a mixed-model analysis of variance adjusted for gestational age. Results were presented using both P values and 95% CIs. P values <.05 were considered statistically significant. Where appropriate, P values and 95% CIs were adjusted using the Tukey multiple comparison procedure. A subanalysis was performed using 11 patients to assess interobserver reliability, which was calculated using the intraclass correlation coefficient (ICC).

RESULTS

All four measurements were obtained for 120 fetuses (79%). The mean gestational age was 27.0 weeks. Statistically significant differences were noted between distal sites (95% CI, -0.05 to 0.01; P<.01) as well as the two sites on each vessel (95% CI, 0.03-0.07 and 0.07-0.12; P<.001 for both vessels). There was no significant difference between the two proximal locations (95% CI, -0.01 to 0.03; P=0.77).

CONCLUSION

By which of the 2 vessels the fetal middle cerebral artery peak systolic velocity is affected is selected, as well as the location on the vessel. If the near-field proximal site cannot be interrogated, the far-field proximal site may be the best alternative.

The cerebroplacental Doppler ratio revisited

OBJECTIVE

To evaluate the distribution of Doppler pulsatility index (PI) measurements of the umbilical and middle cerebral arteries in singleton fetuses of women with normal uterine artery blood flow and to construct reference ranges for the cerebroplacental PI Doppler ratio.

METHODS

The PI was determined in the mid-portion of the umbilical artery and the mid- or distal segment of the middle cerebral artery in 306 normal singleton fetuses. The cerebroplacental Doppler ratio (CPR) was determined from paired measurements. After determination of the best fit, reference ranges were constructed for each parameter against gestational age (GA).

RESULTS

The PI for the umbilical artery had a linear relationship with GA (umbilical artery PI = - 0.0246 x GA + 1.7791, r(2) = 0.4025, P < 0.001). The middle cerebral artery PI and the CPR both showed a quadratic relationship with GA (middle cerebral artery PI = - 0.0058 x GA(2) + 0.3335 x GA - 2.7317, r(2) = 0.2365, P < 0.01), (CPR = - 0.0059 x GA(2) + 0.383 x GA - 4.0636, r(2) = 0.2788, P < 0.001).

CONCLUSION

The CPR is not constant throughout gestation. Reference ranges constructed by a standardized Doppler technique may be of benefit in the monitoring of high-risk pregnancies.