A Population-Based Study of Meconium Aspiration Syndrome in Neonates Born between 37 and 43 Weeks of Gestation.

The epidemiology of meconium aspiration syndrome (MAS) in term neonates is described in a population-based retrospective study of data recorded for all births from 2000 to 2007 in a French region (Burgundy). Of the 132 884 eligible term newborns, the rate of meconium-stained amniotic fluid (MSAF) was 7.93%. The prevalence of severe MAS was 0.067% in the overall population. MAS rate was 0.11% at 37-38 weeks of gestation (WG), 0.20% at 39-41 WG, and 0.49% at 42-43 WG. Factors independently associated with severe MAS were identified by a case-control study, that is, thick meconium amniotic fluid, fetal tachycardia, Apgar score ≤3 at 1 minute, and birth in a level III facility. Our results confirm the high prevalence of MSAF after 37 WG but also show the low frequency of severe MAS in a period corresponding to the new international recommendations on the management of birth with MSAF.

Umbilical vein blood volume flow rate and umbilical artery pulsatility as 'venous-arterial index' in the prediction of neonatal compromise.

OBJECTIVE: To assess the diagnostic power of the umbilical venous-arterial index (VAI) for the prediction of poor fetal outcome. SUBJECTS AND METHODS: This was a retrospective, cross-sectional clinical study in which normalized umbilical vein blood volume flow rate (nUV) (mL/min/kg estimated body weight), umbilical artery pulsatility index (UAPI), the newly developed VAI (nUV/UAPI), and the uterine artery resistance index (UTRI) were determined in 85 fetuses once (17-41 gestational weeks) during pregnancy using standard ultrasound Doppler equipment. A risk score based on umbilical blood pH, 1-min Apgar score, birth weight, duration of gestation, type of respiratory support, and referral to the pediatric department was constructed, and fetuses were assigned to a control or a pathological group accordingly. Logistic regression and analysis of fitted receiver-operating characteristics curves were performed to evaluate the diagnostic power of nUV, UAPI, UTRI, and VAI. RESULTS: The incidence of compromised neonates was 17.6%. The area under the receiver-operating characteristics curve was larger for VAI than for UTRI or for UAPI (P < 0.002). At a cut-off value of 100 mL/min/kg, the sensitivity of VAI to predict poor neonatal outcome was 85% with a 15% false-positive rate. CONCLUSION: Determination of the VAI has a greater diagnostic power to predict poor fetal outcome than the pulsatility index in the umbilical artery or the resistance index in the uterine artery.

Unloading of baroreceptors by carotid occlusion does not increase heart rate in fetal sheep.

UNLABELLED: Unloading of baroreceptors by carotid occlusion does not increase heart rate in fetal sheep; OBJECTIVES: To test the hypothesis that in fetal sheep reduction of carotid sinus pressure by carotid occlusion increases heart rate. STUDY DESIGN: Fetal sheep (gestational age 121-132 days) were chronically instrumented with bilateral carotid occluders, catheters and electrodes (ECG) to measure systemic arterial and carotid sinus (CSP) blood pressures, and fetal heart rate. RESULTS: Bilateral carotid occlusion (BCO) increased mean arterial blood pressure from 46+/-7 mmHg to 53+/-8 mmHg (mean+/-S.D.) while CSP decreased from 44+/-7 mmHg to 17+/-7 mmHg. Fetal heart rate fell during occlusion significantly from 186+/-34 bpm to 159+/-26 bpm (n=20 animals). Infusion of phenylephrine (8.5-20 microg min(-1)kg(-1)) or methoxamine (60-200 microg min(-1)kg(-1)) increased mean blood pressure from 44+/-6 to 61+/-9 mmHg, and fetal heart rate decreased from 186+/-30 to 132+/-31 bpm (n=12). BCO increased systemic arterial pressure further to 70+/-11 mmHg whereas carotid sinus pressure was reduced to 31+/-13 mmHg. However, average heart rate did not increase significantly (136+/-28 bpm). CONCLUSION: We conclude that in contrast to adult animals, in fetal sheep carotid occlusion with subsequent unloading of baroreceptors does not increase heart rate even when the baroreflex had been activated by arterial hypertension. It seems likely that stimulation of carotid chemoreceptors prevents the expected baroreceptor mediated heart-rate response.

Efficacy of carotid collateral perfusion in anaesthetized sheep fetuses.

The purpose of this study was to learn to what extent carotid collateral circulation is efficient in maintaining cephalic blood flow in the sheep fetus. Under halothane anaesthesia six fetal sheep at 124-135 days of gestation were instrumented with inflatable occluders around both common carotid arteries, an inductive flow probe around one external carotid artery, and arterial catheters to measure carotid sinus and aortic pressure. In acute experiments, the occluders were inflated on one side, or the other, or both sides simultaneously, while carotid blood flow, driving pressures and fetal heart rate were determined. Ipsi- and bilateral occlusion reduced carotid blood flow from about 42 ml/min to 10-0 ml/min and decreased sinus pressure from 39 mmHg to 29.1+/-2.9 (mean+/-s.d.) and 16.7+/-3.7 mmHg, respectively. Occlusion of the contralateral carotid artery increased ipsilateral carotid blood flow from 45+/-10 ml/min to 64+/-14 ml/min within 0.2 sec. Heart rate and aortic and sinus pressures did not change appreciably. Analysis of an analogue resistance network demonstrated that the observed carotid flow increases (less than twice normal) do not require changes of vascular resistances.It is concluded that the fetal sheep, as in the adult of many species, possesses an efficient carotid collateral system.

The effect of oxytocin, prostaglandin E2 and acetylsalicylic acid on flow distribution and on the transfer of alanine, glucose and water in isolated perfused guinea pig placentae.

The influence of oxytocin (OXY), sulproston (SUL) and acetylsalicylic acid (ASA) on L-alanine- (ALA), D-glucose- (GLU) or water- (H(2)O) uptake (maternal side) in the isolated perfused guinea pig placenta was investigated. Uptake was measured with a single injection, paired tracer dilution method. 'T50' values were derived from venous concentration curves (extracellular marker) as the distance (sec) between two concentration values at 50 per cent of peak concentration. T50 values were regarded to reflect the change of flow distribution on the maternal side. On average, there was a significant apparent inhibition of GLU uptake (by 27.2 per cent from control values) by OXY as well as of ALA uptake by OXY (26. 0 per cent), by ASA (56.6 per cent), and by SUL (56.7 per cent). The respective mean T50 values decreased significantly in the above groups by 15.9 per cent, 18.7 per cent (ns), 42.2 per cent and 56.7 per cent. However, it was not possible to generate dose-response curves whereas significant correlations of uptake values with T50 values were found. There was no dose-response relationship between T50 values and OXY or ASA concentrations but decreased mean T50 values were found. For SUL a weak correlation of T50 and SUL concentration was found. The r -value of GLU uptake and T50 was 0.57, for H(2)O uptake this value was 0.70, for ALA uptake the r -values were 0.51 (OXY), 0.35 (SUL) and 0.31 (ASA). Correlation of uptake and concentrations were not significant. We conclude that the 'inhibitory' effects of OXY, ASA and probably SUL on placental transfer are unspecific and the consequence of flow shifts from the placental exchange area to the uterine muscle.

Diffusive transfer of water and glucose across the chorionic plate of the isolated human term placenta.

This study investigated systematically the diffusive transfer of water and glucose across the chorionic plate of the human placenta. Isolated sections of human term placentae were perfused at the fetal side (open loop) with modified Ringer's solution (n=31). An artificial amniotic compartment was created on top of the chorionic plate. 3H- and 14C-labelled tracer pairs were added (donor side) to the fetal perfusion fluid or to the 'amniotic' fluid. Transfer fractions (TF, ratio of acceptor side to donor side radioactivity) were calculated as percentages. TF of water and L-glucose from perfusion fluid into the 'amniotic' fluid were 3.9+/-0.5 per cent (mean+/-SEM) and 1.2+/-0.3 per cent after 60 min and significantly different (n=6). In each sample of the following experiments the transfer fraction of the D-hexose was larger than that of the L-isomer. At 60 min, the TF were 1.6+/-0.2 and 1.1+/-0.2 per cent (D-glucose/L-glucose; fetal to amniotic compartment, n=8), from amniotic compartment to fetal perfusate 0.6+/-0.1 and 0.4+/-0.1 per cent (D-glucose/L-glucose, n=11), and 0.8+/-0.1 and 0.6+/-0.1 per cent (3-O-methyl-D-glucose/L-glucose, n=6). The difference between the latter TF lost its significance after cytochalasin B (0.1-0.2 mmol/l) had been added to the amniotic compartment. It is concluded that a limited diffusive pathway across the chorionic plate of the human placenta exists and that the transfer of D-glucose depends in part on facilitated diffusion.

Doppler ultrasound evaluation of ductus venosus blood flow during acute hypoxemia in fetal lambs.

It has been demonstrated with invasive techniques in fetal lambs that the ratio of ductus venosus to umbilical vein blood flow rate (DV/UV ratio) increases during hypoxemia and infusion of catecholamines. Recently it was found in human fetuses using pulsed wave Doppler ultrasound equipment that the DV/UV ratio in fetuses with intrauterine growth restriction was significantly increased. The aim of the present study was to show in fetal lambs whether routine Doppler ultrasound devices were capable of determining the DV/UV ratio with sufficient reliability. The experiments were performed on seven near-term instrumented fetal lambs using pulsed wave Doppler ultrasound to measure flow rates (derived, in milliliters per min, from the intensity-weighted mean velocity (Vmean) and the vessel's cross-sectional area) in the ductus venosus and intra-abdominal umbilical vein. Fetal hypoxemia was induced by administering a low-oxygen gas to the ewe (5-7% oxygen, 2% carbon dioxide). Fetal arterial pO2 and heart rate decreased significantly during maternal hypoxia. The proportion of umbilical venous return passing through the ductus venous in controls was 36 +/- 5% (mean +/- SD). This increased to 53 +/- 6% (p < 0.001) because the umbilical venous blood flow fell during late hypoxemia when the heart rate had decreased by 20%. Severe hypoxemia tended to reduce the mean velocity (Vmean) and the minimum velocity (Vmin) (based on the maximum velocity envelope curve) in the ductus venosus, descending aorta and inferior vena cava. The pulsatility index of the umbilical artery significantly increased at the end of hypoxemia. We conclude that determination of the proportion of umbilical vein blood flow entering the ductus venosus by Doppler ultrasound in a clinical setting may contribute to the detection and evaluation of fetal distress.

Blood flow through the ductus venosus in singleton and multifetal pregnancies and in fetuses with intrauterine growth retardation.

OBJECTIVE: It is known from animal experiments that blood flow through the ductus venosus changes with fetal strain. Therefore the ratio of umbilical vein to ductus venosus flow rate in human intrauterine growth retardation and multifetal pregnancies was investigated and compared with that in control subjects. STUDY DESIGN: Blood flow rates in the umbilical vein and in the ductus venosus, as well as peak velocity, minimum velocity, mean velocity, and pulsatility index (maximum velocity envelope curve) in the ductus venosus, were measured in women with normal pregnancies (n = 55), intrauterine growth retardation (n = 20), and multifetal pregnancies (10 women with 20 fetuses) with color Doppler ultrasonography. RESULTS: Average ductus venosus blood flow rates (mean +/- SD), normalized for estimated fetal body weight, were 60 +/- 30, 69 +/- 35, and 77 +/- 28 (ml x min(-1) x kg(-1)) in control subjects, intrauterine growth retardation, and multifetal pregnancies, respectively. Umbilical vein blood flow rates amounted to 140 +/- 59, 111 +/- 54, and 141 +/- 47 (ml x min(-1) x kg(-1)). Both absolute flow rates increased with gestational age, whereas normalized flow rates decreased. The percentage of umbilical blood flow passing through the ductus venosus in the control group was 43% + 9%. It was significantly increased in both intrauterine growth retardation (62% +/- 8%) and in multifetal pregnancies (55% +/- 12%). Peak velocity, minimum velocity, mean velocity, and pulsatility index in the ductus venosus were not significantly different between groups. CONCLUSION: The increased ratio of ductus venosus blood flow to umbilical vein blood flow may indicate fetal strain.

The transport of vitamin C in the isolated human near-term placenta.

We investigated the specific uptake (reference: [H3]-L-glucose) as a measure of membrane transfer of [C14]-labeled L-ascorbic acid (AA), L-dehydroascorbic acid (DHA) and diketogulonic acid using the single injection, double tracer dilution method in the artificially perfused lobe of the near-term human placenta. The uptake of DHA (40-60%) on both the fetal and the maternal side was 3-6 times higher than the uptake of AA, whereas an uptake of diketogulonic acid was not detected. AA transport was slightly higher on the maternal side. Uptake of DHA was suppressed by phloretin and cytocholasin B, whereas AA transfer was not affected. Low sodium concentrations inhibited the uptake of DHA. D-glucose (> 20 mmol/l) inhibited the DHA uptake, and DHA inhibited D-glucose uptake but not L-alanine uptake. The Km value (self inhibition) for DHA was 6-14 mmol/l. Vitamin C enters the trophoblast predominantly as L-dehydroascorbic acid. Its transfer through the microvillous and basal membrane might use the glucose transporter, however, a specific sodium-dependent pathway is not ruled out. Our transfer data suggest an intracellular pool of vitamin C which fills up with increasing plasma DHA-concentrations.

[Estimating the peripheral vascular resistance of the aorta of fetal sheep by external Doppler ultrasound diagnosis]. / Abschätzung des peripheren Gefässwiderstandes in der Aorta des fetalen Schafes durch externe Dopplersonographie.

OBJECTIVE: Do external Doppler indices correlated sufficiently to the peripheral resistance? METHODS: The resistance of 7 fetal sheep was measured inductively and was correlated to external Doppler measurements. The correlation of different indices and methods was compared. RESULTS: Only bloodflow velocities and the harmonic component index (HCI) yield good correlations (r > or = 7) to the peripheral resistance. PI, RI, S/D-Ratio and Vpeak/Vmean showed r-values from .47 to .59. None of the Doppler parameters reached the values of indices derived from the inductive flow probe. CONCLUSIONS: The blood flow velocities and the HCI seem to be superior to the classical indices in estimation of blood flow in the fetal aorta.