Adrenomedullin is increased in the fetoplacental circulation in intrauterine growth restriction with abnormal umbilical artery waveforms

OBJECTIVE: To examine whether adrenomedullin, a novel vasoactive peptide produced by the placenta, participates in the uteroplacental hemodynamic alterations in intrauterine growth restriction, we studied the correlation between adrenomedullin levels and fetoplacental blood flow. STUDY DESIGN: Maternal and umbilical blood samples were collected in pregnancies complicated by intrauterine growth restriction with abnormal umbilical artery Doppler findings and in control pregnancies. Adrenomedullin levels were measured by means of a specific radioimmunoassay, and flow velocimetry waveforms were recorded from uterine, umbilical, and fetal middle cerebral arteries. RESULTS: Mean adrenomedullin values in umbilical plasma were higher (P <.05) in patients with intrauterine growth restriction (63.7 +/- 34.2 pg/mL; n = 16) than in control subjects (38.1 +/- 14.8 pg/mL; n = 16). A significant correlation was found between maternal adrenomedullin levels and umbilical artery pulsatility index. Moreover, fetal adrenomedullin concentrations correlated negatively with middle cerebral artery pulsatility index and positively with umbilical artery pulsatility index/middle cerebral artery pulsatility index ratio. CONCLUSION: This study provides evidence that adrenomedullin is increased in fetuses with intrauterine growth restriction in response to reduced uteroplacental blood flow and suggests that it may participate in the fetal hemodynamic modifications.     

Association between maternal-fetal Doppler velocimetry and fetal lung maturity

AIMS: To correlate maternal-fetal Doppler velocimetry parameters to indices of fetal lung maturity (FLM). METHODS: Fifty-five consecutive third trimester pregnancies in which a pulsed-wave Doppler study, including uterine resistance index (Ut RI), umbilical artery pulsatility index (UA PI), middle cerebral artery pulsatility index (MCA PI) and the UA/MCA ratio was performed within 24 hours before amniocentesis and within a week from birth. FLM was determined by amniotic fluid lamellar bodies count (LBs). RESULTS: A positive correlation between MCA PI and LBs (p < 0.007, r = 0.44) was found. MCA PI showed a trend to lower values in fetuses that developed RDS at birth (1.3 +/- 0.5 vs. 1.7 +/- 0.4, NS). LBs significantly decreased as Ut RI increased (O.R.: 0.98, C.I. 0.97-0.99, p < 0.05). A mean Ut RI > 0.64 was correlated to delayed FLM (LBs < 20,000/microl; sensitivity: 90.9%, specificity: 90.3%; positive predictive value: 76.9%, negative predictive value: 96.6%). COMMENT: In third trimester pregnancies abnormal uterine artery waveforms may be associated to a delayed FLM, as expressed by decreased amniotic fluid LBs.     

Predictive value of serial middle cerebral and renal artery pulsatility indices in fetuses with oligohydramnios

OBJECTIVE: To determine if unexplained changes in the amniotic fluid index or pulsatility indices of the fetal renal, middle cerebral, or umbilical artery are predictive of perinatal outcome in pregnancies complicated by oligohydramnios. METHODS: Changes in amniotic fluid measurements and fetal vessel velocimetry in patients with oligohydramnios were evaluated for correlation with fetal outcome. Fourteen fetuses with oligohydramnios underwent serial sonography evaluating the amniotic fluid index and fetal middle cerebral, renal, and umbilical velocimetry. Matched controls and neonatal outcomes were obtained. RESULTS: Change in amniotic fluid index and in renal artery pulsatility index were inversely correlated. Change in the middle cerebral artery pulsatility index was different in infants with normal outcome compared to infants with adverse outcome CONCLUSIONS: Serial velocimetry of the middle cerebral artery may identify fetuses with oligohydramnios at risk for adverse outcomes.     

Altered vascular function in healthy normotensive pregnant women with bilateral uterine artery notches

Objectives To assess endothelial function and vascular mechanical properties in normotensive pregnant women with high resistance in the uteroplacental circulation.
Design Cross-sectional prospective study.
Setting Doppler ultrasound laboratory at university department of obstetrics and gynaecology referral centre for high risk pregnancies.
Participants Forty-two caucasian normotensive pregnant women: 23 with uncomplicated pregnancies and 19 with bilateral uterine artery notches.
Methods Flow-mediated dilatation of the brachial artery was measured by ultrasonography at 25 gestational weeks. Concentrations of nitrite and nitrate in the plasma were established at 25 and 32 gestational weeks. The elastic properties of the common carotid artery, abdominal aorta and popliteal artery were measured with an ultrasonic echo-tracking system.
Results Flow-mediated dilatation at two minutes after cuff deflation was significantly lower in the bilateral notch group compared with the control group, 8.3% and 13.7%, respectively (   P = 0.0007  ). The ability to sustain vasodilatation was reduced in the bilateral notch group (   P = 0.02  ). Lower values of nitrite and nitrate in the plasma were found at 32 gestational weeks in the bilateral notch group than in the control group (mean 24.76 μM/L (SD 5.6) and 30.93 μM/L (8.2), respectively;   P = 0.008  ). Nitrite and nitrate levels tended to be lower in the bilateral notch group even at 25 gestational weeks (29.45 μM/L (8.3) and 35.73 μM/L (11.0) in the bilateral notch and control group, respectively;   P = 0.09  ). There was no difference in aortic, carotid or popliteal elasticity between the two groups.
Conclusions Healthy normotensive pregnant women with bilateral uterine artery notches show impaired endothelial function, but no differences in vascular mechanical properties.     

Placental ischemia and changes in umbilical and uteroplacental arterial and venous hemodynamics

Objective: To relate Doppler velocimetry findings in fetoplacental and uteroplacental circulation to placental histomorphology. Material and methods: In 14 uncomplicated and 31 high-risk pregnancies Doppler velocimetry was performed in umbilical artery and vein, and in maternal uterine veins and arteries during the second half of gestation. Histopathology of the placentas was examined, especially for signs of ischemia and inflammation. Results: All fetuses in uncomplicated pregnancies had normal flow velocity waveforms in umbilical artery; in the high-risk group, 18 fetuses had abnormal flow (increased PI or absent/reverse end-diastolic flow). The latter group had more often high ischemic score and infarctions in the placenta than found in pregnancies with normal umbilical artery flow (p?<?0.001 and p?=?0.02, respectively). Similarly, the abnormal uterine artery flow pattern (uterine artery score 3–4) occurred more often with high ischemic score and placenta infarctions (p?<?0.001 and p?<?0.001, respectively). No significant associations were found between the uterine venous flow type and placental ischemia. Conclusion: Placental ischemic morphological changes were associated with Doppler ultrasound signs of increased resistance to arterial blood flow, both on the fetal and maternal sides of the placenta. No significant relation to the uterine venous flow velocities was found.     

Continuous-wave Doppler ultrasound and decreased amniotic fluid volume in pregnant women with intact or ruptured membranes

The cause(s) of decreased amniotic fluid in the absence of fetal anomalies and intrauterine growth retardation is not clear. A prospective study was performed to evaluate umbilical and uterine artery Doppler velocimetric results in pregnancies complicated by decreased amniotic fluid. Three medically high-risk groups were studied: women with (1) normal fluid and intact membranes, (2) decreased fluid and intact membranes, and (3) decreased fluid and ruptured membranes. The decreased fluid/intact membranes group had a significantly increased incidence of abnormal uterine artery waveforms (diastolic notching or absence of end-diastolic velocity); however, uterine systolic/diastolic ratios were not significantly different. The umbilical systolic/diastolic ratios were marginally higher in the intact membranes/decreased fluid group when compared with the ruptured membranes group. This study suggests that problems with maternal blood supply to the placenta may be related to decreased amniotic fluid when membranes are intact.     

Fetal superior mesenteric artery blood flow velocimetry in normal and high-risk pregnancy

THE AIM: To record blood flow velocimetry in the fetal superior mesenteric artery in normal pregnancy and to evaluate if blood flow recordings in the vessel might predict adverse outcome in high-risk pregnancy. METHODS: The fetal superior mesenteric artery blood velocimetry was recorded in a cross sectional manner in 75 normal pregnancies between 27 and 41 weeks of gestation. Reference curves were performed for pulsatility and resistance indices. The superior mesenteric artery was also located in 48 singleton pregnancies complicated by pregnancy-induced hypertension and/or intra-uterine growth retardation. Middle cerebral artery, umbilical artery and vein and uterine artery velocimetry were also recorded. RESULTS: Superior mesenteric artery PI and RI values expressed an increase in resistance to blood flow with gestational age after 32 weeks of gestation. In all except eight high-risk pregnancies the fetal mesenteric artery PI values were within normal range. Among the pregnancies with absent or reversed blood flow in the umbilical artery, all had abnormal mesenteric artery pulsatility index (PI) (> 97.5th percentiles), one fetus died intrauterine and two others died after delivery due to prematurity, growth retardation and necrotizing enterocolitis. In the remaining fetuses with increased mesenteric artery PI, necrotizing enterocolitis was diagnosed in three cases. CONCLUSIONS: Increased vascular resistance in the mesenteric artery might be a late sign of fetal circulation redistribution and frequently related to necrotizing enterocolitis in the newborn.     

Effects of maternal dexamethasone administration on fetal Doppler flow velocity waveforms

Objective To investigate the effects of maternal dexamethasone administration on umbilical and fetal cerebral artery flow velocity waveforms.
Design Cross-sectional study.
Setting Department of Obstetrics and Gynaecology, Robert Ballanger Hospital, Aulnay-sous-Bois, France.
Sample Twenty-six pregnant women with singleton pregnancies considered at risk for preterm delivery. At baseline, all pregnancies had normal fetoplacental vascular resistance.
Methods These women were given weekly six intravenous doses of 4 mg of dexamethasone eight hours apart.
Main outcome measures Doppler studies were performed from both umbilical artery (UA) and fetal middle cerebral artery (MCA) before (day 0), during (day 2), immediately after (day 4) and shortly after (day 7) every steroid course.
Results No significant variation was noted in both umbilical artery pulsatility index (PI) and fetal heart rate through dexamethasone therapy. Compared with mean initial values, we found on day 4 a significant decrease in MCA PI of 0.28 (F = 7.17,   P < 0.001  ) and a significant increase in UA:MCA PI ratio of 0.08 (F = 3.85,   P = 0.013  ); in contrast no significant change was documented on days 2 and 7 in both MCA pulsatility index and UA:MCA PI ratio. After multiple regression analysis, only the decrease in fetal middle cerebral artery pulsatility index on day 4 remained significant (F=5.84,   P = 0.001  ).
Conclusions The current study finds in healthy fetuses a transient, significant and unexplained decrease in fetal middle cerebral artery impedance on the fourth day following maternal dexamethasone administration. Further basic research and clinical studies including larger sample sizes or pregnancies with fetoplacental dysfunction are needed.     

Histomorphology of the placenta and the placental bed of growth restricted foetuses and correlation with the Doppler velocimetries of the uterine and umbilical arteries

The aim of the present study was to evaluate the histomorphology of the placenta and the placental bed and to correlate this with the Doppler study of the uterine and umbilical arteries of intrauterine growth restricted pregnancies. The study group consisted of 47 women with intrauterine growth restricted foetuses. Twenty-five uneventful pregnancies with appropriate for gestational age foetuses were selected as controls. Doppler studies of umbilical and uterine arteries were performed within the last week before delivery. Placental bed biopsies were obtained at Caesarean section with direct visualization of the placental site. The incidence of pathologic bed biopsies in control, IUGR with normal uterine artery Doppler velocimetry and IUGR with abnormal uterine artery Doppler velocimetry was 0 per cent, 16.6 per cent and 79.3 per cent respectively (P< 0.001). Placentae from IUGR cases with abnormal umbilical artery Doppler velocimetries had a significantly increased number of villous infarcts, cytotrophoblast proliferation and thickening of the villous trophoblastic basal membrane (P=0.001, P=0.038 and P=0.02 respectively). Abnormal placental bed biopsy pathology was significantly associated with abnormal uterine artery velocimetry (OR 33.7, 6.5-173.6; P< 0.001). Abnormal placental pathology was significantly associated with abnormal umbilical artery Doppler velocimetry (OR 21.04, 3.8-115.9;P< 0.001). Women with both abnormal uterine and umbilical artery Doppler velocimetries were delivered earlier and their babies had lower mean birth and placental weight (P< 0.001). In conclusion, placental bed biopsy and placental pathologies are best reflected by abnormal uterine and umbilical artery velocity waveforms, respectively. The most severe clinical outcomes and perinatal mortality are present when both uterine and umbilical districts are altered.     

New score indicating placental vascular resistance

BACKGROUND: Umbilical artery Doppler velocimetry is a routine method for fetal surveillance in high-risk pregnancy. Uterine artery Doppler seems to give comparable information, but it can be difficult to interpret as there are two arteries, which might show notching and/or increased pulsatility index (PI) as signs of increased vascular impedance. Combining the information on vascular resistance on both sides in a new score might simplify and improve evaluation of placental circulation. METHODS: Uterine and umbilical artery Doppler velocimetry was evaluated in 633 high-risk pregnancies. The managing clinician was informed only about the umbilical artery flow. The umbilical artery flow spectrum was semiquantitatively divided into four blood flow classes (BFC), expressing signs of increasing vascular resistance. The uterine artery Doppler flow spectrum was divided into five uterine artery scores (UAS), taking into account presence/absence of notching and/or increase in PI. By adding UAS to BFC, a new placental score (PLS) was constructed with values ranging from 0 to 7, indicating general placental vascular resistance. The scores were related to three outcome variables: small-for-gestational age (SGA), premature delivery (<37 weeks), and cesarean section. RESULTS: All three score systems showed a significant relationship between signs of increasing vascular resistance and outcome. The new PLS showed the best association to adverse outcomes, with optimal cut-off at values exceeding score 3. CONCLUSION: Doppler velocimetry on both sides of the placenta showed a strong relationship to an adverse outcome of pregnancy. The new PLS showed a better relationship to adverse perinatal outcome than the BFC and the UAS. The PLS can simplify evaluation of uteroplacental and fetoplacental Doppler velocimetry.     

Relief of presumed compression in oligohydramnios: amnioinfusion does not affect umbilical artery Doppler waveforms.

The suggestion that amnioinfusion improves umbilical artery Doppler indices of downstream resistance in oligohydramnios by relieving cord compression was investigated by obtaining waveforms before and immediately after amnioinfusion in 16 pregnancies with severe oligohydramnios. There was no significant difference in the change in umbilical artery pulsatility index (PI) between 11 pregnancies in which amniotic fluid volume was restored (mean delta PI = -0.07, 95% confidence interval -0.17 to +0.07), and 5 pregnancies in which immediate vaginal leakage of infused fluid prevented restitution of amniotic fluid volume. Fetal heart rate did not change significantly in either group. End-diastolic frequencies did not return with restitution of amniotic fluid volume in the 2 pregnancies in which they were absent before infusion (absent in 1, reverse in 1). This study suggests that restitution of amniotic fluid volume in human pregnancies complicated by severe oligohydramnios does not acutely alter the umbilical artery PI.     

Uteroplacental blood flow and placental vascular endothelial growth factor in normotensive and pre-eclamptic pregnancy

Objective To determine whether placental vascular endothelial growth factor (VEGF) is increased in pre-eclampsia.
Design Prospective cohort study.
Setting Royal Prince Alfred Hospital, Sydney, Australia.
Sample Eleven normotensive women and eight women with pre-eclampsia matched for age and gestation.
Methods Uterine artery Doppler ultrasound flow velocity profiles were recorded in the third trimester and resistance index calculated as (V_s-V_d)/V_s (V_s= peak systolic flow velocity, V_d= end diastolic flow velocity). Placental tissue at delivery was examined for VEGF distribution with avidin-biotin-peroxidase immunohistochemistry.
Results Uterine resistance index [median (range)] was significantly increased in pre-eclamptic women (normotensive: 0.42 (0.36–0.51); pre-eclampsia: 0.59 (0.40–0.75);   P = 0.005  ). Notching of the uterine artery waveform, consistent with a high resistance circulation, was evident in early diastole in five women with pre-eclampsia but only one normotensive woman (   P = 0.013  ). Placental VEGF was increased in women with pre-eclampsia in the decidual trophoblast (normotensive: 34% (4–59) cells stained for VEGF; pre-eclampsia: 58% (15–95);   P = 0.033  ) and in the villous syncytiotrophoblast (normotensive: VEGF count 1.4 arbitrary units (1.1–2.1); pre-eclampsia: 1.8 arbitrary units (1.4–2.2);   P = 0.041  ). Analysis indicated that uterine artery resistance index was directly correlated with placental VEGF staining, mean arterial pressure and birthweight.
Conclusions Abnormal uterine artery Doppler ultrasound flow velocity profiles in pre-eclampsia indicate increased uteroplacental resistance. The associated increase in placental VEGF may represent a compensatory mechanism attempting to restore blood flow towards normal.     

Evaluation of the pulsatile curve of the placental blood flow profile by polynomial analysis]

The analysis of uterine and umbilical blood flow velocities using A/B ratio, resistance index and pulsatility index has shown to be a highly specific and sufficiently sensitive method in the evaluation of high risk pregnancies. In situations of high peripheral vascular resistance diastolic velocities are low and index values are high. Additional information of flow velocities curves, as diastolic notching, is not represented in the indices commonly used. A mathematical model was established using polynom analysis of blood flow velocity curves. In a group of 78 patients with intrauterine growth retardation polynome analysis of uteroplacental flow velocity curves was more sensitive than resistance index and pulsatility index.     

Uterine and fetal umbilical artery flow velocity waveforms in normal first trimester pregnancies

In 85 normal singleton pregnancies between 8 and 13 weeks gestation, Doppler flow velocity waveform recordings were attempted from the left and right uterine artery and fetal umbilical artery. Acceptable waveforms were obtained from the uterine arteries in 83 and from the fetal umbilical artery in 61 of the 85 pregnancies. There was virtually no difference between the left and right uterine artery on average. The marked decrease in pulsatility (PI) and resistance (RI) indices from both uterine arteries reflects the ongoing process of secondary trophoblast invasion into the muscular part of the spiral arteries. Absent end-diastolic velocities were observed in 59 of 61 fetal umbilical artery flow velocity waveform recordings. PI values from the fetal umbilical artery suggest unaltered umbilical placental vascular resistance during the first trimester of pregnancy.     

Abnormal Doppler velocimetry and blood flow volume in the middle cerebral artery in very severe intrauterine growth restriction: is the occurrence of reversal of compensatory flow too late?

Objectives To determine the time course of quantified volumetric flow and pulsatility index changes in the middle cerebral arteries of severe intrauterine growth restricted fetuses with absent or reversed end diastolic flow velocities (AREDFV) on umbilical artery Doppler with a view to defining the threshold for early intervention before the onset of reversal of adaptation.Setting Fetal growth clinic of a large UK teaching hospital.Sample Seventeen severe intrauterine growth restricted (AC<third centile for gestation and gender) fetuses with abnormal umbilical artery Doppler velocimetry and oligohydramnios (amniotic fluid index <third centile for gestation).Methods One to three daily Doppler velocimetry and quantified volume flow of the middle cerebral artery Doppler velocimetry of the umbilical arteries and daily cardiotocography.Results Reversal of adaptation occurred in eight fetuses, four of which ended as stillbirths and four as neonatal deaths. In two of these fetuses, this had already occurred before the diagnosis of intrauterine growth restriction. In the others, the onset was rapid and difficult to predict. Volume flow in the middle cerebral arteries decreased in those fetuses exhibiting reversal of adaptation but rose in the nine in which compensatory Doppler indices persisted. The decrease in volume flow occurred before the onset of reversal of adaptation in the pulsatility index. In the fetuses exhibiting reversal of adaptation, the rise in the pulsatility index was consistent over 48 hours compared with the physiological fluctuations in pulsatility index in some fetuses where the rise was only for 24 hours followed by a fall. Quantified volume flow fell in the fetuses before reversal of adaptation set-in. The umbilical artery Doppler indices fluctuated between absent and reversed end diastolic velocities within the same fetus irrespective of the changes in the middle cerebral artery Doppler indices.Conclusion Reversal of adaptation is of sudden onset and is associated with poor prognosis. Predicting its occurrence on Doppler indices is difficult as the changes may be very rapid. However, volume flow changes appear to be slower and of earlier onset than the pulsatility index changes. This may therefore be a more useful tool in predicting imminent reversal of adaptation and therefore early delivery.     

Significance of a diastolic notch in the uterine artery flow velocity waveform induced by uterine embolisation in the pregnant ewe

Objective To investigate the relation between placental embolisation and the diastolic notch in the uterine artery flow velocity waveform of pregnant ewes under general anaesthesia.
Methods Seven pregnant ewes at a gestation 16 to 17 weeks were anaesthesized and micro beads of gelfoam were injected into the uterine artery; changes in the uterine circulation were assessed by Doppler velocimetry.
Results Gelfoam embolisation reduced uterine blood flow in a dose-dependent manner, from a mean (95% CI) of 568 mL/min (495–641) to 159 mL/min (131–187) after the injection of 30 mg of gelfoam, and increased the uterine vascular resistance from 135 mmHg mine L⁻¹ (103–167) to 498 mmHg mino L⁻¹ (422–574). A diastolic notch in uterine artery flow velocity waveform was observed after 20 mg to 25 mg of gelfoam in two ewes and after injection of 30 mg of gelfoam in all seven animals. Injection of 30 mg of gelfoam increased the pulsatility index to 2–4 (1.9–2.9) from 0.6 (0.5–0.7). The mean uterine vascular resistance at the time of the appearance of a diastolic notch was 414 mmHg mine L⁻¹ (377–451).
Conclusion These findings suggest that an elevated pulsatility index and the presence of a diastolic notch in the uterine artery flow velocity waveform are indicators of increased uterine vascular resistance and impaired uterine circulation.     

Transvaginal color Doppler assessment of the uteroplacental circulation in early pregnancy

Transvaginal color Doppler was used to investigate the uteroplacental circulation of 45 patients with normal intrauterine pregnancies at 4-18 weeks' gestation. The main uterine artery and the radial and spiral arteries were demonstrated, and characteristic flow velocity waveforms were obtained in more than 90% of cases. The indices of impedance to flow decreased with gestation and there was a progressive fall in these indices from the uterine artery, through the radial, to the spiral artery. Blood velocity in the uterine artery increased exponentially with gestation.     

Uterine and fetal umbilical artery flow velocity waveforms in normal first trimester pregnancies

Summary. In 85 normal singleton pregnancies between 8 and 13 weeks gestation, Doppler flow velocity waveform recordings were attempted from the left and right uterine artery and fetal umbilical artery. Acceptable waveforms were obtained from the uterine arteries in 83 and from the fetal umbilical artery in 61 of the 85 pregnancies. There was virtually no difference between the left and right uterine artery on average. The marked decrease in pulsatility (PI) and resistance (RI) indices from both uterine arteries reflects the ongoing process of secondary trophoblast invasion into the muscular part of the spiral arteries. Absent enddiastolic velocities were observed in 59 of 61 fetal umbilical artery flow velocity waveform recordings. PI values from the fetal umbilical artery suggest unaltered umbilical placental vascular resistance during the first trimester of pregnancy.     

A comparison of Doppler flow velocity waveforms, amniotic fluid columns, and the nonstress test as a means of monitoring post-dates pregnancies

Five hundred thirty-four pregnancies exceeding 294 days were monitored by weekly sonographic estimations of amniotic fluid columns, daily maternal recordings of fetal movements, and thrice-weekly nonstress tests. In addition, each woman received twice-weekly studies of the uteroplacental and umbilical circulations by means of Doppler ultrasound. There were no fetal deaths in the study. Of the individual methods of fetal surveillance, absence of end-diastolic frequencies in the umbilical artery was the most sensitive, predicting 91% of fetuses who developed fetal distress in the first stage. Combining the test with sonographic estimation of amniotic fluid columns improved the prediction to 100%, with only a minimal fall in the specificity. These results strongly suggest that a combination of umbilical artery Doppler waveforms and amniotic fluid determinations is an adequate method of monitoring the post-dates pregnancy.     

Water immersion and changes in the foetoplacental and uteroplacental circulation: an observational study with the case as its own control

Objective: To evaluate the effect of immersion into water on maternal blood pressure, amount of amniotic fluid and on the foetoplacental- and uteroplacental circulation in healthy women with an uncomplicated singleton pregnancy.

Methods: Twenty-five healthy women were included. Recordings of blood pressure, deepest vertical pocket of amniotic fluid and pulsatility index (PI) measured by Doppler in the umbilical and uterine arteries were obtained. The participants were immersed into water and the measurements were repeated after 5 and 25?min in water and again 15 and 30?min post immersion.

Results: The amount of amniotic fluid increased significantly (p?p?Conclusions: Immersion into water increases the amount of amniotic fluid and decreases the maternal blood pressure. Immersion into water has no significant effect on either the foetoplacental or uteroplacental circulation. Further studies are needed in order to explore the effect of immersion in pregnancies complicated by a dysfunctional placenta.