Therapeutic interventions for oligohydramnios: amnioinfusion and maternal hydration

Extrinsic factors influencing fetal deformations and intrauterine growth restriction

The causes of intrauterine growth restriction (IUGR) are multifactorial with both intrinsic and extrinsic influences. While many studies focus on the intrinsic pathological causes, the possible long-term consequences resulting from extrinsic intrauterine physiological constraints merit additional consideration and further investigation. Infants with IUGR can exhibit early symmetric or late asymmetric growth abnormality patterns depending on the fetal stage of development, of which the latter is most common occurring in 70-80% of growth-restricted infants. Deformation is the consequence of extrinsic biomechanical factors interfering with normal growth, functioning, or positioning of the fetus in utero, typically arising during late gestation. Biomechanical forces play a critical role in the normal morphogenesis of most tissues. The magnitude and direction of force impact the form of the developing fetus, with a specific tissue response depending on its pliability and stage of development. Major uterine constraining factors include primigravida, small maternal size, uterine malformation, uterine fibromata, early pelvic engagement of the fetal head, aberrant fetal position, oligohydramnios, and multifetal gestation. Corrective mechanical forces similar to those that gave rise to the deformation to reshape the deformed structures are often used and should take advantage of the rapid postnatal growth to correct form.

Líquido amniótico, atividade física e imersão em água na gestação

O objetivo desta revisão foi avaliar a inter-relação entre volume do líquido amniótico, atividade física e imersão em água na gestação. Utilizando diferentes combinações desses termos, foram consultadas as bases de dados do MedLine e do Scielo, no período de 1980 a 2005 para a identificação de artigos relevantes ao assunto. O líquido amniótico é fundamental no desenvolvimento dos sistemas músculo-esquelético, gastrointestinal e respiratório fetal. Sua avaliação no passado era imprecisa, mas com o advento da ultra-sonografia, tornou-se fácil e não invasiva. Surgiram técnicas para a aferição do seu volume e curvas de normalidade. Mais recentemente, têm-se tentado diversas técnicas para a correção do seu volume, na tentativa de diminuir a morbidade associada. Um método não invasivo muito utilizado no Brasil é a hiperhidratação materna. Outros autores sugerem medidas como a imersão estática ou com atividade física em água, muito na moda nos dias de hoje. Ainda são poucos os estudos relativos à prática da atividade física na água para gestantes e seus benefícios maternos, fetais e perinatais. A presente revisão visa aprofundar os conhecimentos acerca dos exercícios aeróbicos sob imersão de gestantes em água, no que diz respeito ao volume de líquido amniótico e bem-estar fetal durante a gestação.

24-h hydration status: parameters, epidemiology and recommendations

Hydration of individuals and groups is characterised by comparing actual urine osmolality (Uosm) with maximum Uosm. Data of actual, maximum and minimum Uosm in infants, children and adults and its major influencing factors are reviewed. There are remarkable ontogenetic, individual and cultural differences in Uosm. In the foetus and the breast-fed infant Uosm is much lower than plasma osmolality, whereas in children and adults it is usually much higher. Individuals and groups may show long-term differences in Uosm. In industrialised countries, the gender difference of Uosm is common. There are large intercultural differences of mean 24-h Uosm ranging from 860 mosm/kg in Germany, 649 mosm/kg in USA to 392 mosm/kg in Poland. A new physiologically based concept called 'free-water reserve' quantifies differences in 24-h euhydration. In 189 boys of the DONALD Study aged 4.0-6.9 y, median urine volume was 497 ml/24-h and median Uosm 809 mosm/kg. Considering mean-2 s.d. of actual maximum 24-h Uosm of 830 mosm/kg as upper level of euhydration and physiological criterion of adequate hydration in these boys, median free-water reserve was 11 ml/24-h. Based on median total water intake of 1310 ml/24-h and the third percentile of free-water volume of -156 ml/24-h, adequate total water intake was 1466 ml/24-h or 1.01 ml/kcal. Data of Uosm in 24-h urine samples and corresponding free-water reserve values of homogeneous groups of healthy subjects from all over the world might be useful parameters in epidemiology to investigate the health effects of different levels of 24-h euhydration.

Brain natriuretic peptide and endothelin-1 in the pathogenesis of polyhydramnios-oligohydramnios in monochorionic twins

OBJECTIVE

We investigated the association between amniotic fluid levels of human brain natriuretic peptide, endothelin-1, and abnormal amniotic fluid volume in monochorionic twins with and without chronic twin-twin transfusion syndrome.

STUDY DESIGN

Amniotic fluid and fetal blood samples were obtained in utero or at cesarean delivery from monochorionic twins with (n = 20) or without chronic twin-twin transfusion syndrome (n = 10). Concentrations of atrial natriuretic peptide, human brain natriuretic peptide, and endothelin-1 (in picograms per milliliters) were determined by radioimmunoassay.

RESULTS

The amniotic fluid concentrations of human brain natriuretic peptide (P <.001) and endothelin-1 (P <.001) in the recipient fetuses were higher than the donor twins but were similar in the twins with no twin-twin transfusion syndrome. In the donor twins, amniotic fluid concentrations of human brain natriuretic peptide (P <.001) and endothelin-1 (P <.001) were lower than the twin pairs with no twin-twin transfusion syndrome. In both chronic twin-twin transfusion syndrome fetuses (P <.01) and fetuses with no twin-twin transfusion syndrome (P <.001), the amniotic fluid concentrations of human brain natriuretic peptide were high, although the concentrations of the endothelin-1 were lower than the fetal plasma concentrations. A positive association was present between amniotic fluid levels of human brain natriuretic peptide and endothelin-1 (R (2) = 0.51, P <.001, n = 60). Amniotic fluid human brain natriuretic peptide (r = 0.67, P <.001) and endothelin-1 (r = 0.57, P <.01) levels of the recipient twins correlated with the amniotic fluid index.

CONCLUSION

These data suggest that amniotic fluid concentrations of human brain natriuretic peptide and endothelin-1 were highest in the twins with polyhydramnios and lowest in the twins with oligohydramnios, which suggests the importance of these hormones in the regulation of amniotic fluid volume.

Antepartum prophylactic transabdominal amnioinfusion in preterm pregnancies complicated by oligohydramnios

OBJECTIVE

To assess the role of amnioinfusion in preterm pregnancies with oligohydramnios.

METHOD

29 women between 23 and 35 weeks' gestation were enrolled in the study. Transabdominal amnioinfusion was performed in 15 pregnancies, 14 patients were managed expectantly. The latency period and perinatal outcome of both groups were compared using the Mann-Whitney U-test and chi(2)-test.

RESULT

The amniotic fluid index significantly increased from a median value of 6 to 11 cm (P<0.0001) in the amnioinfusion group after amnioinfusion. The latency period of the amnioinfusion group was significantly longer (median 15 vs. 8 days P<0.05). Gestational week of the amnioinfusion group was earlier on admission (median 30.6 vs. 33.4 weeks, P=0.01) but at delivery this diversity disappeared (median 33.4 vs. 34.8 weeks, P=0.10). The perinatal outcomes of the two groups were similar.

CONCLUSION

Transabdominal amnioinfusion prolongs the latency period and improves perinatal outcome in preterm pregnancies complicated by oligohydramnios.

Posterior urethral valves: pre- and postnatal management

Posterior urethral valves are a common problem encountered by pediatric urologists. The diagnosis is most frequently suggested by antenatal screening ultrasound. A variety of pre- and postnatal parameters have been identified to aid in predicting ultimate renal outcome. These prognostic tools are invaluable to the clinician for counseling parents and for choosing appropriate management. Several approaches to the treatment of patients with posterior urethral valves exist, and the ideal strategy is debatable. As technology evolves, more options for early intervention become available. Whether early detection and antenatal intervention improve patient outcome remains to be proven.

Acute maternal rehydration increases the urine production rate in the near-term human fetus

OBJECTIVE

We sought to investigate the effect of a decrease of maternal plasma osmolality produced by hypotonic rehydration on the fetal urine production rate in normal near-term human fetuses.

STUDY DESIGN

Twenty-one healthy pregnant women attending the clinic for antenatal care were studied between 37 and 40 weeks' gestation. The fetal urine production rate was assessed by serial measurements of 3 diameters of the fetal bladder. The hourly fetal urine production rate was determined by linear regression analysis of the calculated bladder volumes versus time and was initially determined after a period of 4 hours of fluid deprivation. Thereafter, the women were asked to drink 1 L of water, and the hourly fetal urine production rate was assessed again. The hourly fetal urine production rate was only studied during behavioral state 1F because it is dependent on the behavioral state. The fetal behavioral state was determined by assessment of fetal heart rate, fetal eye movements, and fetal body movements.

RESULTS

Successful recordings were obtained in 10 of the 21 women. The hourly fetal urine production rate increased significantly after hypotonic rehydration (P <.02). Compared with the initial hourly fetal urine production rate after 4 hours of fluid deprivation, the hourly fetal urine production rate showed an increase of 63.2% after hypotonic rehydration, from 38.2 +/- 16.3 mL/h to 62.4 +/- 34.6 mL/h (mean +/- SD). After rehydration, the baseline fetal heart rate fell significantly, from 141 +/- 6 to 132 +/- 8 beats/min (mean +/- SD; P =.005).

CONCLUSION

The fetal urine production rate is augmented after acute maternal oral hypotonic rehydration after 4 hours of fluid deprivation. The current findings demonstrate that the near-term human fetus can handle such acute changes in fluid osmolality by increasing the urine production rate to maintain its fluid homeostasis. This mechanism implies that changes in maternal plasma osmolality and volume probably play an important role in determining amniotic fluid volume. Therefore the application of maternal hydration for the treatment of oligohydramnios should be further investigated.