Oligohydramnios decreases platelet-derived growth factor expression in fetal rat lungs

Early Pulmonary Hypertension in Preterm Infants

Pulmonary hypertension (PH) in preterm neonates has multifactorial pathogenesis with unique characteristics. Premature surfactant-deficient lungs are injured following exposure to positive pressure ventilation and high oxygen concentrations resulting in variable phenotypes of PH. The prevalence of early PH is variable and reported to be between 8% and 55% of extremely preterm infants. Disruption of the lung development and vascular signaling pathway could lead to abnormal pulmonary vascular transition. The management of early PH and the off-label use of selective pulmonary vasodilators continue to be controversial.

Proteomic analysis of a murine model of lung hypoplasia induced by oligohydramnios

Severe oligohydramnios (OH) due to prolonged loss of amniotic fluid can cause pulmonary hypoplasia. Animal model of pulmonary hypoplasia induced by amniotic fluid drainage is partly attributed to changes in mechanical compression of the lung. Although numerous studies on OH-model have demonstrated changes in several individual proteins, however, the underlying mechanisms for interrupting normal lung development in response to a decrease of amniotic fluid volume are not fully understood. In this study, we used a proteomic approach to explore differences in the expression of a wide range of proteins after induction of OH in a mouse model of pulmonary hypoplasia to find out the signaling/molecular pathways involved in fetal lung development. Liquid chromatography-massspectromery/mass spectrometry analysis found 474 proteins that were differentially expressed in OH-induced hypoplastic lungs in comparison to untouched (UnT) control. Among these proteins, we confirmed the downregulation of AKT1, SP-D, and CD200, and provided proof-of-concept for the first time about the potential role that these proteins could play in fetal lung development.

Pulmonary hypoplasia correlates with the length of anhydramnios in patients with early pregnancy renal anhydramnios (EPRA)

BACKGROUND

Early pregnancy renal anhydramanios (EPRA) occurs when the fetus is anuric before 22 weeks gestational age (GA) and is considered universally lethal. Serial amnioinfusions have successfully ameliorated the lethal pulmonary hypoplasia associated with EPRA and have resulted in cases of neonatal survival, peritoneal dialysis, and renal transplant.

OBJECTIVE

We sought to evaluate the lung pathology of untreated fetuses and neonates that had EPRA.

STUDY DESIGN

This is a retrospective case series of all fetuses and neonates diagnosed with isolated EPRA that underwent autopsy at a single tertiary care center between 1987 and 2018. Autopsy data were correlated with ultrasound findings and GA at delivery. Fetal weights, lung weights, and lung developmental stage were recorded.

RESULTS

Nineteen cases met criteria for analysis and ranged from 16 to 38 weeks GA at termination or birth. The observed-to-expected (O/E) lung-to-body-weight ratio was significantly associated with GA (r = -0.51, p = 0.03), such that as GA increased the O/E ratio decreased. When limited to patients >22 weeks, this relationship strengthened (r = -0.75, p = 0.01). Importantly, overall O/E body weight had no relationship with GA.

CONCLUSION

This study shows that the degree of pulmonary hypoplasia in EPRA increases with the length of anhydramnios. This suggests that amnioinfusions are likely to be of most benefit the soonest they can feasibly be initiated.

Preterm prelabor rupture of membranes prior to early preterm delivery elevates the risk of later respiratory-related hospitalizations in the offspring

OBJECTIVE

Preterm prelabor rupture of membranes (PPROM) precedes 30%-40% of all preterm births. Early preterm delivery (<34 gestation weeks) is a well-established risk factor for short- and long-term respiratory morbidity in the offspring. We aimed to ascertain whether the presence of PPROM, before early preterm delivery, independently impacts long-term respiratory hospitalizations in the offspring.

STUDY DESIGN

A population-based retrospective cohort analysis was performed including all singleton early preterm deliveries. Exposure was defined as the presence of PPROM. Hospitalizations of the offspring up to the age of 18 years involving respiratory-related morbidity were evaluated. A Kaplan-Meier survival curve and multivariable Cox regression model were used to assess the association.

RESULTS

During the study period, 3309 early preterm deliveries met the inclusion criteria. In 22.4% of cases (n = 742), PPROM was documented. Rates of respiratory-related hospitalizations of the offspring up to the age of 18 years were significantly higher in the exposed group (12.5% vs 9.4% in the unexposed group, P = .023). The survival curve demonstrated significantly higher cumulative incidence of respiratory hospitalizations in the exposed group (logrank P = .018). In the Cox regression model controlled for gestational age, and other clinically relevant confounders - PPROM before early preterm deliveries was independently associated with an increased risk for long-term childhood respiratory-related hospitalizations in the offspring (adjusted hazard ratio 1.40, 95% confidence interval, 1.05-1.87, P = .021).

CONCLUSION

Fetal exposure to PPROM before early preterm delivery was associated with an increased risk for long-term respiratory hospitalizations in the offspring.

Pulmonary Hypoplasia Induced by Oligohydramnios: Findings from Animal Models and a Population-Based Study

Pulmonary hypoplasia is a substantial cause of death in newborn infants, and oligohydramnios is one of the most commonly associated abnormalities. Lung growth is influenced by physical factors such as the intrauterine space, lung liquid volume and pressure, and fetal breathing movements. During lung development, the main physical force experienced by the lungs is stretching induced by breathing movements and the lung fluid in the airspaces. Oligohydramnios reduces the intrathoracic cavity size, thus disrupting fetal lung growth and leading to pulmonary hypoplasia. The exact mechanism by which oligohydramnios alters the respiratory system structure and the effect of oligohydramnios on long-term respiratory outcomes remain unknown. In this review, we summarize the effects of oligohydramnios on lung development, discuss the mechanisms of oligohydramnios-induced pulmonary hypoplasia identified in various animal studies, and describe the long-term respiratory outcomes in childhood of oligohydramnios-exposed fetuses reported by a population-based study.

Effects of maternal retinoic acid administration on lung angiogenesis in oligohydramnios-exposed fetal rats

BACKGROUND

All-trans retinoic acid (ATRA) induces in vitro angiogenesis and vascular endothelial growth factor (VEGF) secretion. Prenatal administration of vitamin A tends to increase the pulmonary and plasma levels of VEGF in the developing mouse. The aims of this study were to examine the effects of maternal retinoic acid treatment on lung VEGF expression and angiogenesis in oligohydramnios-exposed fetal rats.

METHODS

On day 16 of gestation, pregnant Sprague-Dawley rats were randomly assigned to either the retinoic acid group (intragastric ATRA at 10 mg/kg body weight) or the vehicle group. We punctured each uterine sac to produce oligohydramnios, and fetuses in the opposite uterine horn served as controls. On day 21 of gestation, the fetuses were delivered by cesarean section.

RESULTS

Rats exposed to oligohydramnios exhibited lower lung weights and lung/body weight ratios, and ATRA exhibited no effects on the body or lung weights of oligohydramnios-exposed rats. Lung microvessel density decreased in oligohydramnios-exposed rats of maternal vehicle-treated dams. Microvessel density was comparable between the oligohydramnios + retinoic acid group and the control + retinoic acid group. VEGF expression was comparable among control and oligohydramnios-exposed rats of maternal vehicle- or retinoic acid-treated dams.

CONCLUSION

Maternal retinoic acid treatment did not increase lung VEGF expression or enhance lung development in oligohydramnios-exposed fetal rats. These results do not support the use of maternal retinoic acid to prevent oligohydramnios-induced pulmonary hypoplasia in the pseudoglandular stage.

Pulmonary effects of prolonged oligohydramnios following mid-trimester rupture of the membranes--antenatal and postnatal management

Mid-trimester, preterm prelabour rupture of the membranes (PPROM) with prolonged oligohydramnios remains a challenge for both obstetricians and neonatologists. Although survival rates have improved, morbidity remains common particularly due to pulmonary insufficiency and pulmonary hypertension. The aetiology of abnormal lung development is unknown but may depend critically on pulmonary vascular development. Antenatal evaluation of at-risk foetuses by three-dimensional ultrasound and MRI is possible but the techniques need to be further assessed. Antenatal corticosteroids given in cases of PPROM reduce the incidence of neonatal death, respiratory distress syndrome, intraventricular haemorrhage and necrotising enterocolitis without increasing maternal or neonatal infection. The true risk-benefit ratio of antibiotics, tocolysis and strategies to normalise amniotic fluid volume remains less clear. There is no consensus regarding the optimal ventilation strategy to support infants with pulmonary insufficiency following PPROM, and further work is required to determine whether and which pulmonary vasodilators improve long-term outcome in these infants.

Experimental Oligohydramnios Decreases Collagen in Hypoplastic Fetal Rat Lungs

Neonates with premature rupture of the membrane and oligohydramnios have an increased risk of acute respiratory morbidity. The aims of this study are to investigate the effects of experimental oligohydramnios on transforming growth factor (TGF)-β1 and connective tissue growth factor (CTGF) expressions and collagen level in fetal rat lungs. On day 16 of gestation, we anesthetized timed pregnant Sprague-Dawley dams, punctured the uterine wall and fetal membranes of each amniotic sac which resulted in oligohydramnios. Fetuses in the opposite uterine horn served as controls. On days 19 and 21 of gestation, fetuses were delivered by cesarean section. Rats exposed to oligohydramnios exhibited significantly lower lung weight/body weight ratios on days 19 and 21 of gestation than did the control rats. Lung type I collagen and TGF-β1 mRNA expressions and lung collagen levels were significantly decreased in rats exposed to oligohydramnios on days 19 and 21 of gestation. Type I collagen and inhibitors of metalloproteinase-1 (TIMP-1) proteins were decreased and matrix metalloproteinase-1 (MMP-1) was increased in oligohydramnios-exposed rats on days 19 and 21 of gestation. CTGF mRNA expressions were comparable between control and oligohydramnios-exposed rats on days 19 and 21 of gestation. These data suggest that downregulation of collagen might be involved in the pathogenesis of oligohydramnios-induced respiratory morbidity.

Retinoic acid fails to reverse oligohydramnios-induced pulmonary hypoplasia in fetal rats

All-trans retinoic acid (ATRA) stimulates platelet-derived growth factor (PDGF)-A expression and enhances alveolarization in rat lungs. On d 16 of gestation, pregnant Sprague-Dawley rats were randomly assigned to either a retinoic acid group (intragastric ATRA at 10 mg/kg body weight) or a vehicle group. We punctured each amniotic sac, and fetuses in the opposite uterine horn served as controls. On d 21 of gestation, the fetuses were delivered by cesarean section. Rats subjected to oligohydramnios exhibited significantly lower lung weights and lung/body weight ratios, and ATRA had no effects on the body or lung weights of oligohydramnios-exposed rats. Lung PDGF-A and -B mRNA expression was significantly lower in oligohydramnios-exposed rats compared with control littermates of maternal vehicle-treated dams. Maternal retinoic acid treatment significantly increased PDGF-A and -B mRNA expression in control and oligohydramnios-exposed rats compared with all rats and oligohydramnios-exposed rats of maternal vehicle-treated dams, respectively. Rats exposed to oligohydramnios exhibited a significantly lower generation of alveolar saccules than did control rats in the maternal retinoic acid- and vehicle-treated groups. In this model, maternal retinoic acid treatment showed no positive effects on oligohydramnios-induced pulmonary hypoplasia in the pseudoglandular stage.