Meconium aspiration syndrome: reflections on a murky subject

Meconium aspiration syndrome: a comprehensive review

Meconium aspiration syndrome (MAS) is a complex respiratory disease that continues to be associated with significant morbidities and mortality. The pathophysiological mechanisms of MAS include airway obstruction, local and systemic inflammation, surfactant inactivation and persistent pulmonary hypertension of the newborn (PPHN). Supplemental oxygen and non-invasive respiratory support are the main therapies for many patients. The management of the patients requiring invasive mechanical ventilation could be challenging because of the combination of atelectasis and air trapping. While studies have explored various ventilatory modalities, evidence to date does not clearly support any singular modality as superior. Patient's pathophysiology, symptom severity, and clinician/unit expertise should guide the respiratory management. Early identification and concomitant management of PPHN is critically important as it contributes significantly to mortality and morbidities.

Outcomes of neonates born through meconium-stained amniotic fluid pre and post 2015 NRP guideline implementation

A shift in the Neonatal Resuscitation Program (NRP) guidelines occurred in 2015 from routine intubation and endotracheal suctioning of all meconium-stained non-vigorous infants towards less aggressive interventions based on response to initial resuscitation. This study aims to examine the impact of this change on outcomes of non-vigorous infants born through meconium-stained amniotic fluid at a level III academic NICU encompassing years before and after the change in guideline. This single-center retrospective study compared NICU therapies and clinical outcomes of 117 non-vigorous newborns pre-guideline implementation to 106 non-vigorous newborns post-guideline implementation. Nearly two thirds of infants in the pre-guideline cohort received endotracheal suctioning with recovery of meconium compared to less than a third of infants in the post-guideline cohort (p<0.01). Though a higher proportion of the pre-guideline cohort were admitted to the NICU for respiratory issues compared to the post-guideline cohort, the two groups did not differ significantly with regard to morbidity and therapies. Despite a marked reduction in rates of intubation and endotracheal suctioning, there is no difference in outcomes between pre-guideline implementation vs post-guideline implementation in non-vigorous meconium-stained infants, supporting the recent NRP guideline change and highlighting the benefit of expectant management.

Meconium-stained amniotic fluid

Green-stained amniotic fluid, often referred to as meconium-stained amniotic fluid, is present in 5% to 20% of patients in labor and is considered an obstetric hazard. The condition has been attributed to the passage of fetal colonic content (meconium), intraamniotic bleeding with the presence of heme catabolic products, or both. The frequency of green-stained amniotic fluid increases as a function of gestational age, reaching approximately 27% in post-term gestation. Green-stained amniotic fluid during labor has been associated with fetal acidemia (umbilical artery pH <7.00), neonatal respiratory distress, and seizures as well as cerebral palsy. Hypoxia is widely considered a mechanism responsible for fetal defecation and meconium-stained amniotic fluid; however, most fetuses with meconium-stained amniotic fluid do not have fetal acidemia. Intraamniotic infection/inflammation has emerged as an important factor in meconium-stained amniotic fluid in term and preterm gestations, as patients with these conditions have a higher rate of clinical chorioamnionitis and neonatal sepsis. The precise mechanisms linking intraamniotic inflammation to green-stained amniotic fluid have not been determined, but the effects of oxidative stress in heme catabolism have been implicated. Two randomized clinical trials suggest that antibiotic administration decreases the rate of clinical chorioamnionitis in patients with meconium-stained amniotic fluid. A serious complication of meconium-stained amniotic fluid is meconium aspiration syndrome. This condition develops in 5% of cases presenting with meconium-stained amniotic fluid and is a severe complication typical of term newborns. Meconium aspiration syndrome is attributed to the mechanical and chemical effects of aspirated meconium coupled with local and systemic fetal inflammation. Routine naso/oropharyngeal suctioning and tracheal intubation in cases of meconium-stained amniotic fluid have not been shown to be beneficial and are no longer recommended in obstetrical practice. A systematic review of randomized controlled trials suggested that amnioinfusion may decrease the rate of meconium aspiration syndrome. Histologic examination of the fetal membranes for meconium has been invoked in medical legal litigation to time the occurrence of fetal injury. However, inferences have been largely based on the results of in vitro experiments, and extrapolation of such findings to the clinical setting warrants caution. Fetal defecation throughout gestation appears to be a physiologic phenomenon based on ultrasound as well as in observations in animals.

Neonatal Outcomes of Term Infants Born with Meconium-Stained Amniotic Fluid

Background Meconium-stained amniotic fluid (MSAF) is considered an alarming sign of possible fetal compromise and it has recently been reported that neonatal outcome correlates with the degree of meconium thickness. Methods We retrospectively studied 400 term infants allocated in clear amniotic fluid and grade 1, 2, and 3 MSAF groups on the basis of color and thickness of AF. Multivariable logistic regression analysis was performed to evaluate the potential independent effect of delivery with MSAF of different severity on the risk of a composite adverse neonatal outcome. Results We found that delivery with grade 2 (OR 16.82, 95% Cl 2.12-33.52; p = 0.008) and 3 (OR 33.79, 95% Cl 4.24-69.33; p < 0.001) MSAF is independently correlated with the risk of adverse neonatal outcome, such as the occurrence of at least one of the following: need of resuscitation in the delivery room, blood cord pH < 7.100, occurrence of meconium aspiration syndrome (MAS), persistent pulmonary hypertension (PPH), transient tachypnea of the newborn (TTN), acute respiratory distress syndrome (ARDS), hypoxic-ischemic encephalopathy (HIE), and sepsis. Conclusions There is a positive correlation between the severity of amniotic fluid meconium staining and thickness and the outcomes of term infants. Therefore, the evaluation and grading of MSAF during labor is useful in order to plan for the presence of a neonatologist at delivery for immediate and proper neonatal care.

Association of Prenatal Acetaminophen Exposure Measured in Meconium With Adverse Birth Outcomes in a Canadian Birth Cohort

BACKGROUND

The small number of studies examining the association of prenatal acetaminophen with birth outcomes have all relied on maternal self-report. It remains unknown whether prenatal acetaminophen exposure measured in a biological specimen is associated with birth outcomes.

OBJECTIVES

To investigate the association of acetaminophen measured in meconium with birthweight, gestational age, preterm birth, size for gestational age, gestational diabetes, preeclampsia, and high blood pressure.

METHODS

This birth cohort from Sherbrooke, QC, Canada, included 773 live births. Mothers with no thyroid disease enrolled at their first prenatal care visit or delivery. Acetaminophen was measured in meconium for 393 children at delivery. We tested associations of prenatal acetaminophen with birthweight, preterm birth, gestational age, small and large for gestational age, gestational diabetes, preeclampsia, and high blood pressure. We imputed missing data via multiple imputation and used inverse probability weighting to account for confounding and selection bias.

RESULTS

Acetaminophen was detected in 222 meconium samples (56.5%). Prenatal acetaminophen exposure was associated with decreased birthweight by 136 g (β = -136; 95% CI [-229, -43]), 20% increased weekly hazard of delivery (hazard ratio = 1.20; 95% CI [1.00, 1.43]), and over 60% decreased odds of being born large for gestational age (odds ratio = 0.38; 95% CI [0.20, 0.75]). Prenatal acetaminophen was not associated with small for gestational age, preterm birth, or any pregnancy complications.

CONCLUSION

Prenatal acetaminophen was associated with adverse birth outcomes. Although unobserved confounding and confounding by indication are possible, these results warrant further investigation into adverse perinatal effects of prenatal acetaminophen exposure.

Assessment of thiol/disulfide and ischemia modified albumin level and oxidative stress in pregnancies complicated by meconium

OBJECTIVE

The purpose of this study is to evaluate antioxidant balance in pregnant women with meconium-stained amniotic fluid.

METHODS

Forty pregnant women with meconium-stained amniotic fluid and 40 pregnant women with non-meconium-stained amniotic fluid were included in the study. By checking the ischemia modified albumin (IMA) level and thiol/disulfide homeostasis in the maternal blood during labor and in newborn umbilical cord blood at the first minute after birth, antioxidant/oxidant balance was evaluated.

RESULTS

No statistically significant difference was found between the maternal albumin levels. Maternal IMA level was statistically significantly higher in the meconium group than in the control group (p = .045). Maternal native thiol (SH) and maternal total thiol levels were statistically significantly higher in the control group than in the meconium group (p = .042 and p = .009, respectively). No statistically significant difference was found between maternal disulfide/native thiol (p = .262), maternal disulfide/total thiol (p = .152), maternal native thiol/total thiol (p = .153) rates in both groups. No statistically significant difference was determined between the patients with meconium and the control group in terms of cord blood IMA (p = .474), Albumin levels (p = .664), cord blood Native thiol (p = .944), cord blood total thiol (p = .612) levels and cord blood disulfide/native thiol (p = .240), cord blood disulfide/total thiol (p = .276), cord blood native thiol/total thiol (p = .277) rates.

CONCLUSION

Determination of a decrease in SH and Total Thiol levels in maternal serum and an increase in the meconium group's IMA level was interpreted as a shift of antioxidant balance toward oxidant in this group.

Prediction of adverse neonatal outcome among newborns born through meconium-stained amniotic fluid

OBJECTIVE

To study maternal and intrapartum factors associated with adverse neonatal outcome in deliveries complicated by meconium-stained amniotic fluid (MSAF).

METHODS

A retrospective cohort study of all women with singleton gestations undergoing trial of labor with MSAF during 2011-2020. Deliveries with adverse neonatal outcome were compared with deliveries without.

RESULTS

Overall, 11 329 were included; 376 (3.3%) neonates were diagnosed with adverse neonatal outcomes. Multivariable regression analysis underlined the following factors as independently associated with composite adverse neonatal outcome: pregestational diabetes (odds ratio [OR] 3.21, 95% confidence interval [CI] 1.09-9.43, P = 0.031), polyhydramnios (OR 2.14, 95% CI 1.33-3.44, P = 0.002), fever (OR 2.52, 95% CI 1.67-3.80, P < 0.001), and amnioinfusion (OR 1.73, 95% CI 1.24-2.2438, P = 0.003). When 0, 1, 2, and 3 of the independent risk factors identified were present, the rates of adverse neonatal outcome were 2.9%, 5.5%, 10.0%, and 100%, respectively.

CONCLUSION

The current study's results suggest that special attention should be payed to deliveries complicated by MSAF and with any of the following factors-polyhydramnios, intrapartum fever, amnioinfusion, and pregestational diabetes.

Pathophysiological effects of intravenous phosphodiesterase type 4 inhibitor in addition to surfactant lavage in meconium-injured newborn piglet lungs

BACKGROUND

Nonsteroidal anti-inflammatory drugs, such as selective phosphodiesterase type 4 (PDE4) inhibitors have potential anti-inflammatory and respiratory smooth muscle relaxation effects. This study aimed to investigate the pathophysiological effects of an intravenous PDE4 inhibitor (rolipram) and surfactant lavage (SL) in a newborn piglet model of meconium aspiration syndrome (MAS).

METHODS

MAS was induced in 25 newborn piglets, which were randomly divided into control and four SL treatment groups administered with different doses of intravenous rolipram (0, 0.1, 0.5, and 1 mg/kg). Cardiopulmonary variables were monitored and recorded. The experimental time was 4 hours. Serial blood was drawn for blood gas and biomarker analyses. Lung tissue was examined for histological analysis.

RESULTS

All SL-treated groups revealed improved oxygenation during the 4-hour experiments and had significantly lower peak inspiratory pressure levels than the control group at the end of experiments. All SL plus rolipram-treated groups exhibited significantly higher lung compliance than the control group. However, the animals receiving high-dose (0.5 and 1.0 mg/kg) rolipram demonstrated significantly elevated heart rates. Lung histology of the nondependent sites revealed significantly lower lung injury scores in all SL-treated groups compared with that in the control group, but there were no differences among the rolipram-treated groups.

CONCLUSIONS

In addition to SL, intravenous PDE4 inhibitors may further improve lung compliance in treating MAS; however, it is necessary to consider cardiovascular adverse effects, primarily tachycardia. Further investigations are required before the clinical application of intravenous PDE4 inhibitor as an anti-inflammatory agent to treat severe MAS.

The effect of meconium thickness level on neonatal outcome

BACKGROUND

Despite its prevalence and potential maternal and neonatal implications, the literature on the thickness levels of meconium stained amniotic fluid (MSAF) and its impact on neonatal outcomes is relatively outdated and relies on relatively small sample sizes.

AIMS

To study if different thickness levels of MSAF correlate with adverse neonatal outcome.

STUDY DESIGN

A retrospective cohort study.

SUBJECTS

The medical records and neonatal charts of all women with a singleton pregnancy, who underwent a trial of labor, at 37 + 0/7 weeks or beyond, between 10/2008 and 7/2018 were reviewed.

OUTCOME MEASURES

The cohort was divided according to the level of meconium reported during labor into four groups: Clear (C group), Light meconium (LM group), Intermediate meconium (IM group), and Heavy meconium (HM group). Composite neonatal outcome included at least one of the following: umbilical artery pH ≤ 7.1, sepsis, need for blood transfusion, need for phototherapy, respiratory distress syndrome, meconium aspiration syndrome, need for mechanical ventilation support, necrotizing enterocolitis, intraventricular hemorrhage, hypoxic ischemic encephalopathy, periventricular leukomalacia, seizures, hypoglycemia, hypothermia, and death. Continuous parameters were compared with Anova's test or Kruskal Wallis, and categorical variables by chi-square test or Fisher exact test, as appropriate. Multivariant logistic regression was performed in order to eliminate possible cofounders.

RESULTS

Overall, 24,445 deliveries were reviewed (C-20,185, LM-1074, IM-2736, HM-450). Composite adverse neonatal outcome was more common with increasing thickness of MSAF. On multivariable analysis, IM and HM were independently associated with composite adverse neonatal outcome.

CONCLUSION

The degree of meconium thickness independently correlates with composite adverse neonatal outcome.

Meconium-stained amniotic fluid and the risk of postcesarean surgical site infection

OBJECTIVE

To investigate the association between meconium-stained amniotic fluid (MSAF) and postcesarean surgical site infections.

METHODS

This was a secondary analysis of the Maternal-Fetal Medicine Units Network (MFMU) Cesarean Registry. Women with a singleton pregnancy attempting labor or induction of labor, who ultimately had a cesarean delivery, were included in the study. Pregnancies complicated by MSAF (n = 4262) and those who did not have MSAF (n = 13,850) were compared. The primary outcome was the incidence of SSI.

RESULTS

A total of 18,112 patients were included in the study. 4262 (38%) had meconium-stained amniotic fluid. After accounting for potential confounders in a multivariable logistic regression, meconium-stained amniotic fluid was associated with an increased risk of postoperative surgical site infection (odds ratio 1.16, 95% CI 1.03-1.30).

CONCLUSIONS

Meconium-stained amniotic fluid may be associated with an increased risk of postoperative surgical site infection.

Unexpected term NICU admissions: a marker of obstetrical care quality?

BACKGROUND

Unexpected admissions of term neonates to the neonatal intensive care unit and unexpected postnatal complications have been proposed as neonatal-focused quality metrics for intrapartum care. Previous studies have noted significant variation in overall hospital neonatal intensive care unit admission rates; however, little is known about the influence of obstetric practices on these rates or whether variation among unanticipated admissions in low-risk, term neonates can be attributed to systemic hospital practices.

OBJECTIVE

The objective of the study was to examine the relative effects of patient characteristics and intrapartum events on unexpected neonatal intensive care unit admissions and to quantify the between-hospital variation in neonatal intensive care unit admission rates among this group of neonates.

STUDY DESIGN

We performed a retrospective cross-sectional study using data collected as part of the Consortium for Safe Labor study. Women who delivered term (≥37 weeks), singleton, nonanomalous, liveborn infants without an a priori risk for neonatal intensive care unit admission were included. The primary outcome was neonatal intensive care unit admission among this population. Multilevel mixed-effect models were used to calculate adjusted odds ratios for demographics (age, race, insurer), pregnancy characteristics (parity, gestational age, tobacco use, birthweight), maternal comorbidities (chronic and pregnancy-induced hypertension), hospital characteristics (delivery volume, hospital and neonatal intensive care unit level, academic affiliation), and intrapartum events (prolonged second stage, induction of labor, trial of labor after cesarean delivery, chorioamnionitis, meconium-stained amniotic fluid, and abruption). Intraclass correlation coefficients were used to estimate the between-hospital variance in a series of hierarchical models.

RESULTS

Of the 143,951 infants meeting all patient and hospital inclusion criteria, 7995 (5.6%) were admitted to the neonatal intensive care unit after birth. In the fully adjusted model, the factors associated with the highest odds for neonatal intensive care unit admission included: nulliparity (adjusted odds ratio, 1.62 [95% confidence interval, 1.53-1.71]), large for gestational age (adjusted odds ratio, 1.59 [95% confidence interval, 1.47-1.71]), and small for gestational age (adjusted odds ratio, 1.60 [95% confidence interval, 1.47-1.73]). Induction of labor (adjusted odds ratio, 0.95 [95% confidence interval, 0.89-1.01]) was not associated with increased odds of neonatal intensive care unit admission compared with women who labored spontaneously. The events associated with higher odds of neonatal intensive care unit admission included: prolonged second stage (adjusted odds ratio, 1.66 [95% confidence interval, 1.51-1.83]); chorioamnionitis (adjusted odds ratio, 3.89 [95% confidence interval, 3.42-4.44]), meconium-stained amniotic fluid (adjusted odds ratio, 1.96 [95% confidence interval, 1.82-2.10]), and abruption (adjusted odds ratio, 2.64 [95% confidence interval, 2.16-.21]). Compared with women who did not labor, the odds of neonatal intensive care unit admission were lower for women who labored: adjusted odds ratio, 0.48 (95% confidence interval, 0.45-0.52) for women with no uterine scar and adjusted odds ratio, 0.83 (95% confidence interval, 0.73-0.94) for women with a uterine scar. There was significant variation in neonatal intensive care unit admission rates by hospital, ranging from 2.9% to 11.2%. After accounting for case mix and hospital characteristics, the between-hospital variance was 1.9%, suggesting that little of the variation was explained by the effect of the hospital.

CONCLUSION

This study contributes to the currently limited understanding of term, neonatal intensive care unit admission rates as a marker of obstetrical care quality. We demonstrated that significant variation exists in hospital unexpected neonatal intensive care unit admission rates and that certain intrapartum events are associated with an increased risk for neonatal intensive care unit admission after delivery. However, the between-hospital variation was low. Unmeasured confounders and extrinsic factors, such as neonatal intensive care unit bed availability, may limit the ability of unexpected term neonatal intensive care unit admissions to meaningfully reflect obstetrical care quality.

Induction of labor at full-term in pregnant women with uncomplicated singleton pregnancy: A systematic review and meta-analysis of randomized trials

INTRODUCTION

The lowest incidence of perinatal morbidity and mortality occurs around 39-40 weeks. Therefore, some have advocated induction of uncomplicated singleton gestations once they reach full-term. The aim of the study was to evaluate the risk of cesarean delivery, and any maternal and perinatal effects of a policy of induction of labor in women with full-term uncomplicated singleton gestations.

MATERIAL AND METHODS

We performed an electronic search from inception of each database to August 2018. All results were then limited to randomized trial. No restrictions for language or geographic location were applied. Inclusion criteria were randomized clinical trials of asymptomatic women with uncomplicated, singleton gestations at full-term (ie, between 39⁺⁰ and 40⁺⁶  weeks) who were randomized to either planned induction of labor or control (ie, expectant management). Only trials on asymptomatic singleton gestations without premature rupture of membranes or any other indications for induction evaluating the effectiveness of planned induction of labor in full-term singleton gestations were included. The primary outcome was the incidence of cesarean delivery.

RESULTS

Seven randomized clinical trials, including 7598 participants were analyzed. Three studies enrolled only women with favorable cervix, defined as a Bishop score of ≥5 in nulliparous women or ≥4 in multiparous women. One trial included only women aged 35 years or older. Women randomized to the planned induction of labor, received scheduled induction usually at 39⁺⁰ to 39⁺⁶  weeks of gestation, whereas women in the control group received expectant management usually until 41-42 weeks of gestation, or earlier if medically indicated. Methods of induction usually included cervical ripening, with either misoprostol or Foley catheter, in conjunction with or followed by oxytocin for women with unfavorable cervix, and oxytocin and artificial rupture of membranes for those with favorable cervix. Five trials also used artificial rupture of membranes as a method for induction. Uncomplicated full-term singleton gestations that were randomized to receive induction of labor had similar incidence of cesarean delivery compared with controls (18.6% vs 21.4%; relative risk 0.96, 95% CI 0.78-1.19). Regarding neonatal outcomes, induction of labor at full-term was associated with a significantly lower rate of meconium-stained amniotic fluid (4.0% vs 13.5%; relative risk 0.32, 95% CI 0.18-0.57), and lower mean birthweight (mean difference -98.96 g, 95% CI -126.29 to -71.63) compared with the control group. There were no between-group differences in other adverse neonatal outcomes.

CONCLUSIONS

Induction of labor at about 39 weeks is not associated with increased risk of cesarean delivery.

In Vitro Action of Meconium on Bronochomotor Tonus of Newborns with Meconium Aspiration Syndrome

AIM

Here we studied the role of meconium in the respiratory system on live and exited newborns (weight 250-3000 g). Throughout this study is followed the response of tracheal rings in acetylcholine and histamine in different molar concentrations (10^-1, 10^-2, 10^-3, 10^-4 mol/dm³).

METHODS

To study the smooth tracheal musculature we used 23 tracheal preparations obtained from the newborns exited from meconium aspiration.

RESULTS

Based on the functional analysis of the tracheal specimen we have concluded that the meconium aspiration did not change the smooth musculature response on acetylcholine and histamine when compared to control group, exited from lung inflammatory processes (e.g., pneumonia, bronchopneumonia, atelectasis, cerebral hemorrhage), where tracheal smooth musculature response is significant (P for other causes is not significant (P > 0.01).

CONCLUSION

The conclusions suggest that meconium did not potentiate the constrictor action of acetylcholine and histamine in the tracheobronchial system and did not cause modulation of bronchomotor tonus in case of his aspiration. Meconium causes mild relaxation of smooth tracheal musculature with a mechanism which is not mediated by cyclooxygenase products, from tracheal epithelium or proteins. Also, direct activity in the smooth musculature of several tested acids seems to have no significant impact in increasing the tonus of respiratory airway of smooth tracheal musculature.

Mechanisms of Meconium Passage: Cholinergic Stimulation of Electromechanical Coordination in the Fetal Colon

OBJECTIVE

Fetal gastrointestinal function develops in utero, with evidence of enhanced motility near-term. Although colonic passage of meconium in utero may be associated with fetal maturation or stress, little is known of the mechanisms potentiating motility. We assessed the effect of bethanechol, a cholinergic prokinetic agent, on colonic muscle muscular contractile and electromyogram (EMG) activity in the near-term ovine fetus.

METHODS

Near-term (130 days, n = 8) singleton ovine fetuses were chronically prepared with vascular catheters and three sets of miniature strain gauges and bipolar EMGs on the serosal surface of the transverse colon, left colic flexure, and distal colon. Following a 60-minute control period, fetuses received intravenous bethanechol (60 microg/kg, Low-Beth; 120 microg/kg, High-Beth) at 60 and 180 minutes. Colonic activity was recorded digitally and analyzed for short-duration (2<SHORT<15 seconds) and long-duration (15<LONG<120 seconds) strain gauge and EMG contractions. Data were expressed as means +/- SEM and analyzed using one-way analysis of variance (ANOVA) and paired t test.

RESULTS

During the control period, there was significantly greater SHORT versus LONG strain gauge contractions in all segments (P <.05). As compared to control values, Low-Beth and High-Beth significantly increased SHORT strain gauge contractions in the transverse colon (160 +/- 13 to 201 +/- 36 and 307 +/- 74 spikes/30 min, respectively, P <.05), although not in left colic flexure or distal colon. Bethanecol did not affect LONG strain gauge contractions. SHORT-EMG and LONG-EMG spike bursts did not change in response to bethanecol (280 +/- 20, 59 +/- 2 spikes/30 min, respectively).

CONCLUSION

Cholinergic stimulation of fetal sheep colonic activity at 0.9 gestation occurs in the transverse colon, but not the more distal left colic flexure or distal colon. The increased strain gauge, but not EMG activity, suggests that cholinergic stimulation improves electromechanical coordination in the fetal colon. We speculate that cholinergic-induced delivery of gastrointestinal contents to the distal colon evokes local contractile/expulsive mechanisms resulting in meconium passage.

Induction of labor at full term in uncomplicated singleton gestations: a systematic review and metaanalysis of randomized controlled trials

The aim of this study was to evaluate the risk of cesarean and any maternal and perinatal effects of a policy induction of labor in uncomplicated full-term singleton gestations. Searches were performed in an electronic database with the use of a combination of text words related to "induction" and "cesarean section" from inception of each database through December 2014. We included all randomized controlled trials of uncomplicated singleton gestations at full term (ie, between 39 weeks 0/7 days and 40 weeks 6/7 days) with intact membranes randomized to induction of labor or control (ie, expectant management). The primary outcome was the incidence of cesarean delivery. The summary measures were reported as risk ratio (RR) with 95% confidence interval (CI). Five randomized controlled trials, including 844 women, were analyzed. Full-term vertex singleton gestations receiving induction of labor had similar incidence of cesarean delivery compared to controls (9.7% vs 7.5%; RR, 1.25; 95% CI, 0.75-2.08). Rates of spontaneous (75.9% vs 80.2%; RR, 0.95; 95% CI, 0.87-1.02) and operative (13.1% vs 10.6%; RR, 1.22; 95% CI, 0.83-1.81) vaginal delivery were also similar. Induction was associated with similar rates of chorioamnionitis (9.6% vs 8.0%; RR, 1.17; 95% CI, 0.38-3.39), but statistically significantly less blood loss (mean difference -57.59 mL; 95% CI, -83.96 to -31.21) compared to controls. Regarding neonatal outcomes, induction was associated with a significantly lower rate of meconium-stained amniotic fluid (4.0% vs 13.5%; RR, 0.32; 95% CI, 0.18-0.57) and significantly lower mean birthweight (mean difference -135.51 g; 95% CI, -205.24 to -65.77) compared to control group. Induction of labor at full term in uncomplicated singleton gestations is not associated with increased risk of cesarean delivery and has overall similar outcomes compared to expectant management.

Meconium aspiration syndrome: possible pathophysiological mechanisms and future potential therapies

Does meconium cause meconium aspiration syndrome (MAS) or is meconium discharge only a marker of fetal hypoxia? This dispute has lasted for centuries, but since the 1960s, detrimental effects of meconium itself on the lungs have been demonstrated in animal experiments. In clinical MAS, persistent pulmonary hypertension of the newborn is the leading cause of death in MAS. Regarding the complex chemical composition of meconium, it is difficult to identify a single agent responsible for the pathophysiology. However, considering that meconium is stored in the intestines, partly unexposed to the immune system, aspirated meconium could be recognized as ‘danger', representing damaged self. The common denominator in the pathophysiology could therefore be activation of innate immunity. Thus, a bulk of evidence implies that meconium is a potent activator of inflammatory mediators, including cytokines, complement, prostaglandins and reactive oxygen species. We hypothesize that the two main recognition systems of innate immunity, the Toll-like receptors and the complement system, recognize meconium as ‘danger', which leads not only to lung dysfunction but also to a systemic inflammatory response. This might have therapeutic implications in the future.

Antibiotics for meconium-stained amniotic fluid in labour for preventing maternal and neonatal infections

BACKGROUND

Chorioamnionitis is more likely to occur when meconium-stained amniotic fluid (MSAF) is present. Meconium may enhance the growth of bacteria in amniotic fluid by serving as a growth factor, inhibiting bacteriostatic properties of amniotic fluid. Many adverse neonatal outcomes related to MSAF result from meconium aspiration syndrome (MAS). MSAF is associated with both maternal and newborn infections. Antibiotics may be an effective option to reduce such morbidity.

OBJECTIVES

The objective of this review is to assess the efficacy and side effects of prophylactic antibiotics for MSAF during labour in preventing maternal and neonatal infections.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (30 September 2014). 

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing prophylactic antibiotics with placebo or no treatment during labour for women with MSAF.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion and risk of bias, extracted data and checked them for accuracy.

MAIN RESULTS

We included two studies with 362 pregnant women. Both studies compared ampicillin-sulbactam (N = 183) versus normal saline (N = 179) in pregnant women with MSAF. Prophylactic antibiotics appeared to have no statistically significant reduction in the incidence of neonatal sepsis (risk ratio (RR) 1.00, 95% CI 0.21 to 4.76), neonatal intensive care unit (NICU) admission (RR 0.83, 95% CI 0.39 to 1.78) and postpartum endometritis (RR 0.50, 95% CI 0.18 to 1.38). However, there was a significant decrease in the risk of chorioamnionitis (RR 0.36, 95% CI 0.21 to 0.62). No serious adverse effects were reported. Drug resistance, duration of mechanical ventilation and duration of admission to NICU/hospital were not reported. Most of the domains for risk of bias were at low risk of bias for one study and at unclear risk of bias for the other study. The quality of the evidence using GRADE was low for neonatal sepsis, postpartum endometritis, and neonatal mortality and morbidity prior to discharge (Neonatal intensive care admissions) and of moderate quality for chorioamnionitis.

AUTHORS' CONCLUSIONS

Current evidence indicates that compared to placebo, antibiotics for MSAF in labour may reduce chorioamnionitis. There was no evidence that antibiotics could reduce postpartum endometritis, neonatal sepsis and NICU admission. This systematic review identifies the need for more well-designed, adequately powered RCTs to assess the effect of prophylactic antibiotics in the incidence of maternal and neonatal complications.

Secreted phospholipase A2 is increased in meconium-stained amniotic fluid of term gestations: potential implications for the genesis of meconium aspiration syndrome

BACKGROUND

Meconium-stained amniotic fluid (MSAF) represents the passage of fetal colonic content into the amniotic cavity. Meconium aspiration syndrome (MAS) is a complication that occurs in a subset of infants with MSAF. Secreted phospholipase A2 (sPLA2) is detected in meconium and is implicated in the development of MAS. The purpose of this study was to determine if sPLA2 concentrations are increased in the amniotic fluid of women in spontaneous labor at term with MSAF.

MATERIALS AND METHODS

This was a cross-sectional study of patients in spontaneous term labor who underwent amniocentesis (n = 101). The patients were divided into two study groups: (1) MSAF (n = 61) and (2) clear fluid (n = 40). The presence of bacteria and endotoxin as well as interleukin-6 (IL-6) and sPLA2 concentrations in the amniotic fluid were determined. Statistical analyses were performed to test for normality and bivariate analysis. The Spearman correlation coefficient was used to study the relationship between sPLA2 and IL-6 concentrations in the amniotic fluid.

RESULTS

Patients with MSAF have a higher median sPLA2 concentration (ng/mL) in amniotic fluid than those with clear fluid [1.7 (0.98-2.89) versus 0.3 (0-0.6), p < 0.001]. Among patients with MSAF, those with either microbial invasion of the amniotic cavity (MIAC, defined as presence of bacteria in the amniotic cavity), or bacterial endotoxin had a significantly higher median sPLA2 concentration (ng/mL) in amniotic fluid than those without MIAC or endotoxin [2.4 (1.7-6.0) versus 1.7 (1.3-2.5), p < 0.05]. There was a positive correlation between sPLA2 and IL-6 concentrations in the amniotic fluid (Spearman Rho = 0.3, p < 0.05).

CONCLUSION

MSAF that contains bacteria or endotoxin has a higher concentration of sPLA2, and this may contribute to induce lung inflammation when meconium is aspirated before birth.

Bacteria and endotoxin in meconium-stained amniotic fluid at term: could intra-amniotic infection cause meconium passage?

BACKGROUND

Meconium-stained amniotic fluid (MSAF) is a common occurrence among women in spontaneous labor at term, and has been associated with adverse outcomes in both mother and neonate. MSAF is a risk factor for microbial invasion of the amniotic cavity (MIAC) and preterm birth among women with preterm labor and intact membranes. We now report the frequency of MIAC and the presence of bacterial endotoxin in the amniotic fluid of patients with MSAF at term.

MATERIALS AND METHODS

We conducted a cross-sectional study including women in presumed preterm labor because of uncertain dates who underwent amniocentesis, and were later determined to be at term (n = 108). Patients were allocated into two groups: (1) MSAF (n = 66) and (2) clear amniotic fluid (n = 42). The presence of bacteria was determined by microbiologic techniques, and endotoxin was detected using the Limulus amebocyte lysate (LAL) gel clot assay. Statistical analyses were performed to test for normality and bivariate comparisons.

RESULTS

Bacteria were more frequently present in patients with MSAF compared to those with clear amniotic fluid [19.6% (13/66) versus 4.7% (2/42); p < 0.05]. The microorganisms were Gram-negative rods (n = 7), Ureaplasma urealyticum (n = 4), Gram-positive rods (n = 2) and Mycoplasma hominis (n = 1). The LAL gel clot assay was positive in 46.9% (31/66) of patients with MSAF, and in 4.7% (2/42) of those with clear amniotic fluid (p < 0.001). After heat treatment, the frequency of a positive LAL gel clot assay remained higher in the MSAF group [18.1% (12/66) versus 2.3% (1/42), p < 0.05]. Median amniotic fluid IL-6 concentration (ng/mL) was higher [1.3 (0.7-1.9) versus 0.6 (0.3-1.2), p = 0.04], and median amniotic fluid glucose concentration (mg/dL) was lower [6 (0-8.9) versus 9 (7.4-12.6), p < 0.001] in the MSAF group, than in those with clear amniotic fluid.

CONCLUSION

MSAF at term was associated with an increased incidence of MIAC. The index of suspicion for an infection-related process in postpartum women and their neonates should be increased in the presence of MSAF.

New onset of meconium during labor versus primary meconium-stained amniotic fluid - is there a difference in pregnancy outcome?

OBJECTIVE

To compare pregnancy outcome between deliveries complicated by new onset of meconium during labor following prior evidence of clear amniotic fluid and labors in which meconium was present to begin with.

METHODS

A retrospective cohort study of all singleton term (≥37 + 0 weeks) deliveries complicated by intrapartum meconium-stained amniotic fluid in a tertiary referral medical center during the year 2012. Outcome was compared between deliveries with new onset of meconium during labor following prior evidence of clear amniotic fluid (secondary meconium group) and those in which meconium was already evident at the time of membranes rupture (primary meconium group).

RESULTS

Of the 9167 deliveries during the study period, 694 were eligible for the study group. Of these, 537 were complicated by primary meconium and 157 by secondary meconium. Only secondary meconium, but not primary meconium, was independently associated with an increased risk of operative vaginal delivery (OVD) and adverse neonatal outcome. Pregnancies complicated by secondary meconium were independently associated with a higher rate of OVD (28.0% versus 11.4%, p < 0.001), POP position of the fetal head (6.4% versus 2.6%, p = 0.02), and adverse neonatal outcome (17.2% versus 8.9%, p = 0.003).

CONCLUSION

Secondary meconium is associated with a higher rate of adverse obstetrical and neonatal outcome compared with primary meconium.

The frequency of meconium-stained amniotic fluid increases as a function of the duration of labor

OBJECTIVE

The purpose of this study was to determine whether there is a relationship between the frequency of meconium-stained amniotic fluid (MSAF) and the duration of labor in term singleton gestation.

METHODS

The clinical characteristics of women who delivered term singleton live newborns between 2001 and 2006 were examined. The cases involving neonates with major congenital anomalies were excluded.

RESULTS

(1) The frequency of MSAF in term pregnancies was 18.4% (806/4376); (2) MSAF was found in only 2.8% (28/1008) of women who delivered by elective cesarean, but in 23.1% (778/3368) of women who delivered after the onset of labor (p < 0.001); (3) The longer the duration of labor (first stage, second stage, or total), the higher the frequency of MSAF (p < 0.001 for each); this remained significant after adjusting for other confounding variables such as parity, duration of rupture of membranes, gestational age at delivery, and mode of delivery (p < 0.001 for each).

CONCLUSION

MSAF was found in only 2.8% (28/1008) of women who delivered before the onset of labor, but in 23.1% (778/3368) of women who delivered after the onset of labor. The longer the duration of labor, the higher the risk of MSAF in term singleton gestation.

Antibiotics for meconium-stained amniotic fluid in labour for preventing maternal and neonatal infections

BACKGROUND

Chorioamnionitis is more likely to occur when meconium-stained amniotic fluid (MSAF) is present. Meconium may enhance the growth of bacteria in amniotic fluid by serving as a growth factor, inhibiting bacteriostatic properties of amniotic fluid. Many adverse neonatal outcomes related to MSAF result from Meconium Aspiration Syndrome (MAS). MSAF is associated with both maternal and newborn infections. Antibiotics may be an effective option to reduce such morbidity.

OBJECTIVES

The objective of this review is to assess the efficacy and side effects of prophylactic antibiotics for MSAF during labour in preventing maternal and neonatal infections.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (30 September 2010). 

SELECTION CRITERIA

Randomized controlled trials (RCTs) comparing prophylactic antibiotics with placebo or no treatment during labour for women with MSAF.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed the results of the only available trial and extracted data on maternal and neonatal outcomes.

MAIN RESULTS

We included one study with 120 pregnant women. It compared ampicillin-salbactam (N = 60) versus normal saline (N = 60) in pregnant women with MSAF. Prophylactic antibiotics appeared to have no statistically significant reduction in the incidence of neonatal sepsis (risk ratio (RR) 1.00, 95% CI 0.21 to 4.76), neonatal intensive care unit (NICU) admission (RR 0.83, 95% CI 0.39 to 1.78) and postpartum endometritis (RR 0.50, 95% CI 0.18 to 1.38). However, significant decrease in the risk of chorioamnionitis (RR 0.29, 95% CI 0.10 to 0.82). No serious adverse effects were reported.

AUTHORS' CONCLUSIONS

Current evidence indicates that compared to placebo, antibiotics for MSAF in labour may reduce chorioamnionitis. There was no evidence that antibiotics could reduce postpartum endometritis, neonatal sepsis and NICU admission. This systematic review identifies the need for more well-designed, adequately powered RCTs to assess the effect of prophylactic antibiotics in the incidence of maternal and neonatal complications.

Meconium in the amniotic fluid of pregnancies complicated by preterm premature rupture of membranes is associated with early onset neonatal sepsis

OBJECTIVE

This study was to determine the significance of meconium in the amniotic fluid of pregnancies complicated by preterm premature rupture of membranes (PPROM) without labor.

METHODS

A case-control study of 31 pregnancies complicated by PPROM at 27-36 weeks gestation with meconium present (study group) and 93 pregnancies complicated by PPROM but without meconium was performed. The patients were matched for year of delivery, gestational age, race, and parity. Pregnancy and neonatal outcome variables of the 2 groups were compared.

RESULTS

The incidence of early onset neonatal sepsis was significantly increased in the study group (16.1% vs. 1.1%; P < 0.001). Similarly, chorioamnionitis (48.3% vs. 22.5%; P < 0.01), cesarean delivery for a nonreassuring fetal heart rate pattern (19.4% vs. 3.2%; P < 0.01), a 5-min Apgar score < 7 (22.5% vs. 8.6%; P < 0.05), and fetal growth retardation (FGR) (12.9% vs. 2.2%; P < 0.05) were also more common in pregnancies complicated by PPROM with meconium. The mean umbilical cord arterial pH was significantly lower in these pregnancies (7.18 +/- 0.07 vs. 7.28 +/- 0.08; P < 0.001). After controlling for confounding variables with multiple logistic regression analysis, we found that meconium in the amniotic fluid remained associated with early onset neonatal sepsis.

CONCLUSIONS

The presence of meconium in the amniotic fluid of pregnancies complicated by PPROM is associated with an increased incidence of early onset neonatal group B beta-hemolytic streptococcus (GBBS) sepsis.

Role of meconium in the reaction of airways smooth musculature in the newborn with meconium aspiration syndrome (MAS)

The role of meconium in the respiratory system was studied in newborns, who died from various causes (250 up to 3000 g of weight). We monitored tracheal rings response to dopamine, serotonin and ethanol in different concentrations (dopamine: 0,05 mg/ml, 0,5 mg/ml, 5 mg/ml; serotonin (5-HT): 10-4, 10-3, 10-2, 10-1 mol/dm3; ethanol: 0,02 ml, 0,5 ml, 1,0 ml; 96%). Tracheal smooth musculature tonus (TSM) was examined in 48 tracheal preparations taken after the newborn exitus due to different reasons. Based on functional researche of isolated preparations of tracheas, it may be concluded that: aspiration of meconium has not changed the response of TSM to dopamine, serotonin and ethanol (p>0,1) in comparison with the control group, which have died due to different lung inflammatory processes (e.g. pneumonia, bronchopneumonia, atelectasis, cerebral hemorrhage). The results suggest that meconium does not potentiate the constricting action of dopamine, serotonin and ethanol in tracheobronchial system. Meconium causes mild relaxation of the TSM through a mechanism that is not intermediated by the products of cyclooxygenases (prostaglandins, prostacyclins) from the tracheal epithelium or proteins. Also, as it seems, the direct activity of many tested acids in the smooth musculature has no significant impact on increase of the airways tonus in MAS syndrome.

Does amnioinfusion reduce caesarean section rate in meconium-stained amniotic fluid

INTRODUCTION

The purpose of our study was to evaluate the safety and efficacy of transcervical amnioinfusion during labour complicated by meconium-stained amniotic fluid, in a setting with limited peripartum facilities, to lower the incidence of caesarean section.

METHODS

A prospective study was conducted in a teaching hospital in north India, which enrolled 292 patients admitted in labour. Patients were randomly divided into two groups after taking their consent. One group received transcervical amnioinfusion, whilst in the other group amnioinfusion was not done. Caesarean sections were performed in either group if there were foetal heart rate abnormalities (bradycardia or irregularity for 10-20 min) or slow progress of labour. The outcomes studied were the incidence of caesarean sections, duration of maternal hospital stay, maternal febrile morbidity (temperature of >38 degrees C, 24 h after delivery), low Apgar score (at 1 and 5 min), respiratory death, MAS and perinatal mortality.

RESULT

There was a statistically significant reduction in the incidence of caesarean sections in the study group compared to the control group (31 vs. 61%). Amnioinfusion was associated with improved neonatal outcome as evidenced by statistically improved Apgar score at 1 min in newborns in the study group compared to the control group (10 vs. 37.2%). Amnioinfusion during labour was not associated with any significant maternal and neonatal complications. The mean hospital stay of the mother was decreased significantly in the study group patients compared to the control group.

CONCLUSION

Transcervical amnioinfusion in labour for meconium-stained amniotic fluid is a simple, safe and easy-to-perform procedure. It can be performed safely in a setup with limited peripartum facilities, especially in developing countries, to decrease intrapartum operative intervention and reduce foetomaternal morbidity and mortality.

Risk factors for meconium aspiration in meconium stained amniotic fluid

Meconium aspiration syndrome (MAS) is a life-threatening respiratory disease in infants born through meconium stained amniotic fluid (MSAF). The purpose of this study was to determine risk factors for MAS in the newborns of mothers who had meconium stained amniotic fluid in labour. A retrospective study of all full-term pregnancies with MSAF from May 2003 to October 2004 was designed at a teaching hospital. Development of MAS was the primary outcome. Maternal details, mode of delivery and neonatal details (Apgar score, reassuring or non-reassuring fetal heart rate tracing and birth weight) were evaluated. During the study period, there were 2,603 deliveries of whom 302 (11.6%) had MSAF. MAS developed in 64 of these infants (21.1%). Compared with healthy neonates with MSAF, those with MAS had higher rate of non-reassuring fetal heart rate (FHR) tracing, thick meconium and Apgar score < or =5 at 5 min. The neonatal birth weight was lower in the MAS group, maternal age, parity, gestational age and mode of delivery were not significantly different in the two group. We found the severity of meconium, low Apgar score at 5 min and non-reassuring FHR tracing was associated with MAS in MSAF pregnancies.

Albumin lavage does not improve the outcome of meconium aspiration syndrome

OBJECTIVE

Meconium aspiration syndrome is still a serious condition with high mortality and morbidity. No specific treatment is yet available, although surfactant is known to reduce the need for extracorporeal membrane oxygenation and surfactant lavage has shown promising results in animal studies. Our group has previously shown reduced oxygenation index in an experimental model of meconium aspiration syndrome in newborn pigs when mixing albumin with meconium before endotracheal instillation. Lung compliance increased when albumin was instilled after meconium as a rescue. The aim of this study was to combine the effect of albumin and lavage.

METHODS

Sixteen newborn pigs (six in the meconium-albumin group, six in the meconium group, and four control animals) were anesthetized and tracheotomized. Meconium 4 mL/kg was instilled endotracheally. After five minutes, albumin 15 mL/kg was instilled in the meconium-albumin group followed by endotracheal suctioning. The observation time was six hours. Respiratory and hemodynamic parameters were measured. The terminal complement complex and proinflammatory cytokines were analyzed in plasma.

RESULTS

Oxygenation index, ventilatory index, and the terminal complement complex (sC5b-9) increased significantly in both groups, but significantly more in the meconium-albumin group. Compliance decreased, but significantly more in the meconium-albumin group. The terminal sC5b-9 complex increased in both groups, but significantly more in the meconium-albumin group. Tumor necrosis factor-alpha, interleukin (IL)- 1beta, and IL-6 increased significantly in both groups.

CONCLUSION

Albumin-lavage did not improve the outcome of experimental meconium aspiration syndrome.

The role of complement in meconium aspiration syndrome

The complement system is part of the host defense with a number of biological effects, most of which contribute to the inflammatory reaction by activation of cells like leukocytes and endothelial cells. An intact complement system is required for protection against infection and for maintaining internal inflammatory homeostasis. However, the system is a double-edged sword as improperly or uncontrolled activation is disadvantageous and potentially harmful for the host. Meconium aspiration syndrome (MAS) is associated with a local inflammatory reaction in the lungs, frequently described as a chemical pneumonitis. Cytokines, arachidonic acid metabolites and reactive oxygen species are involved in this reaction. We have recently documented that meconium is a potent activator of complement in vitro and in an experimental piglet model of MAS, the latter presenting with an inflammatory profile closely resembling systemic inflammatory response syndrome. We postulate that complement activation may contribute to the pathogenesis of MAS.

Localization and gestation-dependent pattern of corticotrophin-releasing factor receptor subtypes in ovine fetal distal colon

Meconium passage is frequently observed in association with feto-maternal stress factors such as hypoxia and infection, but the triggering mechanism is unknown. We hypothesize that differential regulation of corticotrophin-releasing factor (CRF) receptors during gestation play an important role in determining the susceptibilities of the fetus to stress-induced in utero meconium passage at term. We examined the innervation patterns of CRF-receptor type 1 (CRF-R1), a stimulator of gastrointestinal motility and CRF-receptor type II (CRF-R2), an inhibitor of gastrointestinal motility in ovine fetal distal colonic segments from very preterm to term gestation. Both CRF-R1 and CRF-R2 receptors were present in muscularis mucosa as well as in longitudinal and circular smooth muscle layers in fetal distal colonic segments at all gestational ages. Quantitative image analysis indicated a 42% increase in CRF-R1 receptor immunoreactivity in muscularis mucosa and a 30% in longitudinal smooth muscle layers from very preterm to term. In contrast, CRF-R2 receptor immunoreactivity in muscularis mucosa as well as in longitudinal and circular smooth muscle layers decreased by 38%, 55% and 51%, respectively, at term. The percentage of enteric ganglia and the number of enteric neurons expressing CRF-R1 receptors were high at term. Western blot analysis identified 235 and 50 kDa molecular species of CRF-R1 receptors and 37 and 28 kDa molecular species of CRF-R2 receptors. In summary, we speculate that downregulation of CRF-R2 receptor abundance with concurrent increases in CRF-R1 receptor levels in myenteric-smooth muscle unit with advancing gestation sensitizes the colonic motility responses to stressors.

Obstetric approaches to the prevention of meconium aspiration syndrome

Meconium aspiration syndrome (MAS) is associated with increased risk for perinatal mortality and morbidities. To provide an overview of the advances in our knowledge concerning the obstetric approaches to the prevention of MAS. The evidence of the effectiveness of intrapartum surveillance, amnioinfusion, and delivery room management in the prevention of MAS are reviewed in the present paper. Meconium aspiration syndrome remains one of the most common but challenging conditions for obstetricians and pediatricians. The available evidence did not demonstrate a beneficial effect of either of obstetric strategies in the prevention of MAS.

Oligohydramnios and associated fetal complications

During intrauterine life the fetus is bathed in amniotic fluid which provides a low resistance space for free movement and a buffer against external trauma. This fluid is produced in early pregnancy largely as a maternal dialysate, then as a fetal transudate. Fetal urine is the most important source of amniotic fluid after 16 weeks gestation. The control of amniotic fluid is complex and poorly understood; it arises from secondary partitioning of water within the fetoplacental extracellular space and reflects fetal fluid balance.

Meconium aspiration syndrome

Meconium aspiration syndrome (MAS) is one of the most common conditions associated with aspiration during the newborn period. MAS can be defined as respiratory distress in a neonate born through meconium-stained amniotic fluid (MSAE) with symptoms that cannot otherwise be explained. It can be characterized by early onset of respiratory distress in term and near-term infants delivered through MSAE. Early presentation includes respiratory symptoms such as respiratory distress, poor lung compliance, hypoxemia, and radiographic findings of hyperinflation and patchy opacifications. This article discusses the pathophysiologv of MAS, historical and current prevention strategies, current management strategies, and prognoses for infants born through MSAE.

Role of complement and CD14 in meconium-induced cytokine formation

OBJECTIVE

Meconium aspiration syndrome has a complex, poorly defined pathophysiology. Meconium is a potent activator of complement in vitro and in vivo; the latter is associated with a systemic inflammatory response. The complement system and Toll-like receptors are 2 important upstream components of the innate immune system that act partly independently in the inflammatory network. The aim of this study was to investigate the relative role of complement and CD14 in meconium-induced cytokine production.

METHODS

Human adult (n = 6) and cord whole blood (n = 6) anticoagulated with lepirudin was collected and distributed into tubes that contained inhibitory antibodies (anti-CD14, anti-C2, anti-factor D, or combinations thereof). The tubes were preincubated for 5 minutes before addition of meconium or buffer and then incubated for 4 hours at 37 degrees C. Complement activation was measured by quantification of the terminal sC5b-9 complement complex by enzyme-linked immunosorbent assay. A panel of 27 inflammatory mediators (cytokines, chemokines, and growth factors) was measured by using multiplex technology.

RESULTS

Fourteen of the 27 mediators measured were induced by meconium both in cord and adult blood. In cord blood, 2 additional chemokines were induced and the inflammatory response was, in general, more potent. Blocking of complement or CD14 differentially reduced the formation of most mediators, anti-CD14 being more effective. Notably, the combined inhibition of complement and CD14 almost completely abolished meconium-induced formation of the cytokines and the chemokines and markedly reduced the formation of growth factors. The endogenous lipopolysaccharide content of meconium could not explain the CD14-mediated response.

CONCLUSIONS

Meconium-induced triggering of the cytokine network is differentially mediated by complement and CD14. A combined inhibition of these effector mechanisms may be an alternative approach to reduce the inflammatory reaction in meconium aspiration syndrome.

Corticotropin-releasing factor inhibition of sheep fetal colonic contractility: mechanisms to prevent meconium passage in utero

OBJECTIVE

In humans, fetal in utero meconium (MEC) passage rarely occurs before term gestation. We hypothesized the existence of inhibitory mechanism(s) preventing colonic motility and MEC passage prior to term.

STUDY DESIGN

Longitudinal smooth muscle strips prepared from distal colon of preterm ovine fetuses (130-132 d; term = 148-152 d) were examined for their contractile responses to muscarinic receptor agonist (bethanechol) and both nonspecific (atropine) and receptor subtype specific antagonists (M1: pirenzepine dihydrochloride, M2 methoctramine, M3: 4-diphenylacetoxy-N-methlpiperidine methiodide [4-DAMP] and M4: tropicamide) in an in vitro organ bath system. Effects of corticotrophin releasing factor (CRF) and Urocortin I (URO-I), known modulators of colonic motility and smooth muscle contractility, were studied on bethanechol-induced contractility. Immunohistochemical analysis was performed to confirm the expression of CRF and URO-I, and muscarinic and CRF R2 receptors in distal colon.

RESULTS

Bethanechol induced smooth muscle contractions via muscarinic receptor subtype M3. CRF and URO-I elicited a significant inhibition of bethanechol induced contraction. Immunohistochemical analysis verified the expression of muscarinic receptor subtype M3, CRF, URO-I and CRF-receptor-R2 in distal colon.

CONCLUSION

Inhibition of M3 dependent distal colonic motility by CRF system may prevent the passage of MEC in the preterm ovine fetus.

Intrapartum transcervical amnioinfusion for meconium-stained amniotic fluid

OBJECTIVE

To assess the rates of cesarean deliveries and perinatal outcome following intrapartum transcervical amnioinfusion in women with meconium-stained amniotic fluid (MSAF) in a setting with no electronic fetal monitoring or specialized neonatal care.

MATERIALS AND METHODS

In this prospective comparative study with 150 women who were in labor and had MSAF, 50 of the women received a transcervical amnioinfusion and the remaining 100 women received standard care. The inclusion criteria were a pregnancy of at least 37 weeks' duration, a single live fetus in cephalic presentation, no major medical or obstetric complications, and no known fetal malformation. The amnioinfusion was performed with 1000 mL of normal saline solution through a red rubber catheter.

RESULTS

Amnioinfusion was associated with a significant decrease in the incidence of low Apgar score (<7) at 1 min (12% vs. 47%; relative risk [RR], 0.26; 95% confidence interval [CI], 0.12-0.56); low Apgar score at 5 min (4% vs. 23%; RR, 0.17; 95% CI, 0.04-0.71); and meconium aspiration syndrome (4% vs. 18%; RR, 0.22; 95% CI, 0.05-0.92). There was also a trend towards a lesser incidence of cesarean deliveries (18% vs. 30%; RR, 0.6; 95% CI, 0.31-1.16) and perinatal deaths (4% vs. 13%; RR, 0.31; 95% CI, 0.07-1.31). The incidence of maternal hospital stays longer than 3 days was significantly lower in the amnioinfusion than in the control group (24% vs. 48%; RR, 0.5; 95% CI, 0.29-0.85). There were no major complications related to amnioinfusion.

CONCLUSIONS

Intrapartum amnioinfusion for MSAF is a simple, safe, effective, and inexpensive procedure feasible in settings where intrapartum monitoring is limited. It is associated with improved perinatal outcome and could lower cesarean delivery rates in low-resource countries.

Elevated plasma corticotrophin release factor levels and in utero meconium passage

Intrauterine meconium (MEC) passage and aspiration may result in significant newborn morbidity, though there is little understanding of the physiologic mechanisms for MEC passage. We hypothesized that stress induces fetal MEC passage via corticotrophin releasing factor (CRF), a known mediator of colonic motility in adult rats. Pregnant rats at e22 were subjected to acute hypoxia or normoxia for 35 min, after which rats were anesthetized and fetuses operatively delivered. Amniotic fluid bilirubin and intestinal alkaline phosphatase were measured as markers for MEC passage, and fetal and maternal plasma CRF and corticosterone levels determined. Hypoxic stress induced defecation in all dams and provoked visible MEC passage in all fetuses. Amniotic fluid bilirubin content was significantly higher in hypoxic fetuses versus controls (1.064 +/- 0.101 versus 0.103 +/- 0.003 O.D. at 410 nm) and intestinal alkaline phosphatase was consistently elevated in MEC stained amniotic fluid. Hypoxia significantly increased plasma CRF (maternal, 82 +/- 5 to 196 +/- 14 pg/mL; fetal, 284 +/- 15 to 1523 +/- 185 pg/mL) and corticosterone (maternal, 417 +/- 50 to 1150 +/- 50 ng/mL; fetal, 96 +/- 5 to 182 +/- 10 ng/mL) compared with controls. In view of the known action of CRF in adult colonic motility, these results suggest that hypoxic stress-mediated MEC passage in term fetal rats is mediated by a CRF dependent pathway.

The Respiratory System

One of the most critical events of birth is the conversion of the fluid-filled lung, unimportant to fetal intrauterine existence, into a hollow organ distended with air and capable of gaseous exchange sufficient to support life. Indeed, it has been argued that the major determinant of perinatal survival is respiratory function (Wigglesworth and Desai 1982).

The failure to make this conversion adequately may lead, directly or indirectly, to infant death, and the pathologist often needs to assess the contribution made by respiratory inadequacy to the sequence of events leading to death. In the preterm infant, problems are mainly related to pulmonary immaturity and associated therapy. In the mature infant, birth asphyxia primarily results in cerebral damage but can engender significant respiratory complications when associated with aspiration of meconium. Even in stillbirths, where primary pulmonary pathology is rarely a cause of death, lung pathology may provide clues to antecedent events. Poor lung growth and maturation may point to the presence of pathology elsewhere. Consequently, adequate pathological investigation of the fetal or infant respiratory system is critical in any perinatal autopsy.

Meconium-stained amniotic fluid across gestation and neonatal acid-base status

OBJECTIVE

To estimate whether the acid-base status of neonates born to women with meconium-stained amniotic fluid varies across gestation.

METHODS

We carried out a retrospective cohort study of all pregnancies that were complicated by meconium-stained amniotic fluid in 2004. Cases were identified from a perinatal pathology database that contained data on all pregnancies complicated by meconium-stained amniotic fluid. Data abstracted from the charts included gestational age at delivery, umbilical arterial pH, birth weight, and the presence or absence of labor. Cases were stratified according to gestational age at delivery. The distribution of meconium-stained amniotic fluid across gestation was computed. The mean umbilical arterial pH values (with 95% confidence intervals) across gestation were assessed by analysis of variance.

RESULTS

The mean umbilical arterial pH in women with meconium-stained amniotic fluid did not differ across gestation. The overall incidence of meconium-stained amniotic fluid was 12.0% (766 of 6,403 deliveries). The rates of meconium-stained amniotic fluid increased from 1.2% at 32 weeks to 100% at 42 weeks.

CONCLUSION

The rising incidence of meconium-stained amniotic fluid with gestational age is consistent with the hypothesis that fetal maturation is a major etiologic factor in meconium passage. Also, the lack of variation of mean umbilical arterial pH across gestation suggests that fetal acidemia is not increased when meconium passage occurs earlier in pregnancy rather than at later gestational ages.

Meconium-stained amniotic fluid--perinatal outcome and obstetrical management in a low-risk suburban population

OBJECTIVE

To determine whether amniotic fluid (MSAF) affects obstetrical interventions and immediate perinatal outcome in a low-risk suburban population.

STUDY DESIGN

A retrospective cohort study examined 11,226 deliveries at Tübingen University Hospital (1998-2003). Thousand one hundred and twenty-three women (10%) had MSAF during labor. A control group of matched pairs was created, assigning to each patient the next woman that gave birth without MSAF. Exclusion criteria were: gestational age less than 37+0 weeks, primary Cesarean (C-)section, multiple gestation, severe maternal disease, preeclampsia and fetal malformations.

RESULTS

Only small differences were noted between the meconium and non-meconium groups with regard to arterial pH and Apgar scores: mean arterial-pH was 7.26 (+/-0.7) for both. Five minutes Apgar scores <6 occurred in 0.9% versus 0.4%. Obstetrical interventions were more common in the meconium group: C-section rates were 17.4% versus 9.6%, vaginal operative delivery rates 13.9% versus 6.2% and scalp pH rates 9.5% versus 3.7%, respectively.

CONCLUSIONS

In a low-risk suburban population the effect of MSAF on the newborn during the immediate postpartum period was small. However, obstetrical management was significantly effected by the presence of MSAF, possibly reflecting a combination of more difficult labor and a lower threshold for obstetric intervention.

Lactate: creatinine ratio in babies with thin meconium staining of amniotic fluid

BACKGROUND

ACOG states meconium stained amniotic fluid (MSAF) as one of the historical indicators of perinatal asphyxia. Thick meconium along with other indicators is used to identify babies with severe intrapartum asphyxia. Lactate creatinine ratio (L:C ratio) of 0.64 or higher in first passed urine of babies suffering severe intrapartum asphyxia has been shown to predict Hypoxic Ischaemic Encephalopathy (HIE). Literature review shows that meconium is passed in distress and thin meconium results from mixing and dilution over time, which may be hours to days. Thin meconium may thus be used as an indicator of antepartum asphyxia. We tested L:C ratios in a group of babies born through thin and thick meconium, and for comparison, in a group of babies without meconium at birth.

METHODS

86 consecutive newborns, 36 to 42 weeks of gestation, with meconium staining of liquor, were recruited for the study. 52 voided urine within 6 hours of birth; of these 27 had thick meconium and 25 had thin meconium at birth. 42 others, who did not have meconium or any other signs of asphyxia at birth provided controls. Lactate and creatinine levels in urine were tested by standard enzymatic methods in the three groups.

RESULTS

Lactate values are highest in the thin MSAF group followed by the thick MSAF and controls. Creatinine was lowest in the thin MSAF, followed by thick MSAF and controls. Normal babies had an average L:C ratio of 0.13 (+/- 0.09). L:C ratio was more among thin MSAF babies (4.3 +/- 11.94) than thick MSAF babies (0.35 +/- 0.35). Median L:C ratio was also higher in the thin MSAF group. Variation in the values of these parameters is observed to be high in the thin MSAF group as compared to other groups. L:C ratio was above the cutoff of 0.64 of Huang et al in 40% of those with thin meconium. 2 of these developed signs of HIE with convulsions (HIE Sarnat and Sarnat Stage II) during hospital stay. One had L:C Ratio of 93 and the other of 58.6. A smaller proportion (20%) of those with thick meconium had levels above the cutoff and 2 developed HIE and convulsions with L:C ratio of 1.25 and 1.1 respectively.

CONCLUSION

In evolving a cutoff of L:C ratios that would be highly sensitive and specific (0.64), Huang et al studied it in a series of babies with severe intrapartum asphyxia. Our study shows that the specificity may not be as good if babies born through thin meconium are also included. L:C ratios are much higher in babies with thin meconium. It may be that meconium alone is not a good indicator of asphyxia and the risk of HIE. However, if the presence of meconium implies asphyxia then perhaps a higher cut-off than 0.64 is needed. L:C ratios should be tested in a larger sample that includes babies with thin meconium, before L:C ratios can be applied universally.