Meconium-stained amniotic fluid

Passage of meconium usually occurs within 48 hours after birth. However, some fetuses may pass meconium in-utero leading to meconium staining of amniotic fluid (MSAF). The vast majority of fetuses pass meconium in-utero due to the physiological maturation of the fetal gut with advancing gestation leading to normal defaecation in utero. However, clinicians need to exclude ‘non-physiological’ causes of MSAF, especially an ongoing hypoxia or chorioamnionitis, to improve perinatal outcomes. Meconium aspiration syndrome (MAS) is a potentially serious fetal condition with increased risk of severe morbidity and mortality. The use of the cardiotocograph (CTG), timely recognition of ongoing hypoxia or infection, consideration of the overall clinical picture and avoidance of injudicious use of oxytocin may help avoid poor perinatal outcomes and resultant medico-legal consequences.     

Meconium in the amniotic fluid and fetal acid-base status

Of 323 pregnancies with meconium-stained amniotic fluid at 36-42 weeks' gestation, 68 (21%) had a pH less than 7.20 in umbilical arterial blood, 21 (7%) had a pH less than 7.15, and only three newborns (0.9%) had true metabolic acidemia. At birth, of the 74 newborns with normal electronic fetal heart rate (FHR) tracings, eight (11%) had an umbilical arterial pH less than 7.20. There was a significantly higher frequency of acidemia (defined as pH less than 7.20) in newborns with both baseline and periodic FHR abnormalities. Although there was a significant difference (P less than .05) in the frequency of meconium found below the cords in these neonates with an umbilical artery pH less than 7.20 compared with those with values exceeding 7.20, there was no significant difference in the frequency of clinical meconium aspiration syndrome. We conclude that meconium-stained amniotic fluid correlates poorly with infant condition at birth as reflected by umbilical cord acid-base measurements.     

Meconium-stained amniotic fluid is associated with puerperal infections

OBJECTIVE: The purpose of this study was to determine whether meconium-stained amniotic fluid is associated with puerperal infection and whether the quality of the meconium is further associated with this risk. STUDY DESIGN: We designed a retrospective cohort study of all deliveries beyond 37 weeks gestational age from 1992 to 2002 at a single community hospital. Data were collected on rates of chorioamnionitis, endomyometritis, quality of amniotic fluid, and length of labor and analyzed with bivariate and multivariate analyses. RESULTS: We found that, among the 43,200 women who were delivered at term, 18.9% of the women had meconium staining (8.8% thin, 5.5% moderate, 4.6% thick). Compared with deliveries with clear amniotic fluid, those with meconium-stained amniotic fluid had higher rates of chorioamnionitis (2.3% vs 4.1%, P<.001) and endomyometritis (1.0% vs 1.7%, P<.001). Further, the severity of meconium staining was associated with increased rates of infection. CONCLUSION: We found that the presence and severity of meconium-stained amniotic fluid is associated with puerperal infection even when being controlled for confounders.     

Meconium-stained amniotic fluid and its association with obstetric infections

Meconium-stained amniotic fluid (MSAF) complicates the intrapartum course of 1.5% to 18% of pregnancies. In addition to predisposing to the meconium aspiration syndrome, MSAF is also an established risk factor for neonatal sepsis and for intrapartum and postpartum maternal infection. Meconium enhances the growth of bacteria in amniotic fluid by serving as a growth factor, inhibits the bacteriostatic properties of amniotic fluid, and antagonizes host defense systems such as phagocytosis, thus explaining the association between MSAF and intrauterine infection. Other evidence suggests that the presence of intraamniotic infection may actually cause passage of meconium in utero by inducing fetal enteritis and gastrointestinal hypermotility. Prophylactic intravenous ampicillin-sulbactam has been shown to be effective in significantly decreasing the rate of chorioamnionitis in patients with MSAF. Additional investigation is necessary to determine the optimal prophylactic antibiotic(s) and method of drug administration in patients with MSAF.     

Meconium-stained amniotic fluid in term pregnancies-a clinical view.

The objective of this study was to explore details of the clinical relationship between meconium-stained amniotic fluid (MSAF) in labour, abnormal fetal heart pattern and meconium aspiration (MA). This was a prospective study carried out in Princess Badeea Teaching hospital during a 6-month period from March to September 1997. During the study period 344 (8.5%) of the deliveries had MSAF (344 women). Continuous fetal heart monitoring was routinely used and 36 women with MSAF (10.5%) needed to be delivered by caesarean section because of fetal distress (diagnosed by abnormal fetal heart pattern) in early labour, compared with 0.95% in those with clear amniotic fluid (CAF), (P <0.00001). Many infants in the MSAF group had a low Apgar score and required ventilation at birth. Nineteen infants (5.5%) developed MA, three of whom (15.8%) died. We conclude that there is an association between MSAF, abnormal fetal heart pattern in labour and a low Apgar score and that it should be considered a high risk situation. MA a problem that occurs with particulate meconium was significantly related to abnormal fetal heart pattern and longer length of labour.     

Meconium-stained amniotic fluid: a risk factor for microbial invasion of the amniotic cavity

The purpose of this study was to determine whether meconium-stained amniotic fluid is a marker for microbial invasion of the amniotic cavity. Amniocentesis was performed on 707 patients presenting with preterm labor and intact membranes. Meconium-stained amniotic fluid was present in 4.2% (30/707) of patients with preterm labor. The prevalence of positive amniotic fluid cultures was significantly higher in women with meconium-stained amniotic fluid than in women with clear fluid (33% [10/30] vs 11% [75/677]; p = 0.001; odds ratio = 4.01; 95% confidence interval = 1.6 to 9.4). Patients with meconium-stained amniotic fluid were also more likely to have failed tocolysis and delivered a preterm neonate more frequently than patients with clear fluid (83% [25/30] vs 38% (258/677); p = 0.0001; odds ratio = 8.1; 95% confidence interval = 2.9 to 24.4). We conclude that meconium-stained amniotic fluid is a risk factor for microbial invasion of the amniotic cavity and preterm delivery in women with preterm labor and intact membranes.     

Meconium-stained amniotic fluid exhibits chemotactic activity for polymorphonuclear leukocytes in vitro

We have studied whether meconium-stained, turbid amniotic fluid (turbid AF) obtained during term pregnancy possesses chemotactic activity for polymorphonuclear leukocytes (PMNs) in the absence of clinically apparent infection. Eight samples of turbid AF were obtained from eight women who underwent a cesarean section (four emergency and four elective cesarean sections) in the absence of signs of clinical infection or fetal distress. Samples of clear AF obtained from nine women during an elective cesarean section served as a control. We used also a negative control (medium only) and a positive control containing 10 nM N-formyl-methionyl-leucyl-phenylalanine. The control or turbid AF specimen was placed in the lower compartment of a blind well chamber, and the PMN suspension was placed in the upper compartment. Following incubation, the number of PMNs that had migrated and passed through the filter to the AF was counted. The number of control PMNs that migrated to the turbid AF (200+/-59) was comparable to that of the positive (162+/-24) but significantly exceeded that of the clear AF (17+/-11; P < 0.0001) and of the negative control (25+/-9; P < 0.0001). Checkerboard assay indicated that the turbid AF exhibited a dose-dependent chemotactic activity for PMNs. The turbid AF contained higher levels of TNFalpha, IL-1beta and IL-8 than the clear AF. The concentration of IL-8 in the AF was correlated positively with the chemotactic activity of the AF (r = 0.733, P = 0.0005). Anti-human IL-8 antibody added in the turbid AF dose-dependently abolished the chemotactic activity of the turbid AF. It is concluded that meconium-stained AF is a chemoattractant for PMNs and that cytokines such as an IL-8 may be involved in this phenomenon.     

Meconium-stained amniotic fluid and neonatal morbidity in near-term and term deliveries with acute histologic chorioamnionitis and/or funisitis.

OBJECTIVE: To determine the incidence of meconium-stained amniotic fluid (MSAF) and neonatal morbidity in near-term and term deliveries with histologic acute chorioamnionitis and/or funisitis compared to those with normal placental histology. STUDY DESIGN: In a retrospective case-control design, we compared the incidence of MSAF and neonatal outcome in 45 cases of acute histologic chorioamnionitis and/or funisitis with 89 cases of normal placental histology. We reviewed the obstetric and neonatal records for perinatal complications and neonatal morbidity. RESULTS: Mean birthweights (3372+/-473 vs 3287+/-518 g) were similar in infants born to mothers with histologic chorioamnionitis and/or funisitis compared to infants born to mothers with normal placental histology. The incidence of MSAF was significantly higher in the group with acute chorioamnionitis/funisitis (p<0.05). Similarly, the incidence of admissions to newborn intensive care unit, respiratory distress, meconium aspiration syndrome, and presumed sepsis was also significantly higher (p<0.05) in this group. CONCLUSION: The incidence of MSAF and neonatal morbidity is higher in the presence of acute inflammation of placental membranes. The presence of meconium in the amniotic fluid should alert the physician to the potential for infection and increased neonatal morbidity.     

Meconium-stained amniotic fluid in labor: a randomized trial of prophylactic amniofusion

OBJECTIVES: To investigate the effect of amnioinfusion in women with meconium-stained amniotic fluid on the rate of cesarian sections and on neonatal morbidity. STUDY DESIGN: A randomized controlled trial. A total of 206 women with meconium-stained amniotic fluid were assigned to receive amnioinfusion via two-way catheter or no amnioinfusion (control group). The catheter was inserted and other treatment was the same in both groups. RESULTS: Amnioinfusion decreased the rate of cesarian sections for fetal distress (RR 0.23, 95% CI 0.07-0.79) and increased mean pH at birth (7.24+/-0.1 versus 7.21+/-0.1, P<0.05). It also decreased the frequency of variable fetal heart rate decelerations (RR 0.74, 95% CI 0.59-0.92), and of meconium below the vocal cords in neonates (RR 0.37, 95% CI 0.19-0.69). CONCLUSIONS: Amnioinfusion improves the neonatal outcome and reduces the frequency of cesarian sections.     

Evaluation of fetal and neonatal acid-base status

Determination of fetal acid-base status, either at birth, intrapartum, or antepartum, is the gold standard for the diagnosis of fetal asphyxia. Indirect methods such as Apgar scores and fetal heart rate monitoring show at best only minimal correlation. It is evident that intrauterine hypoxia is a rare cause of central nervous system injury, and the finding of a normal acid-base status at birth should lead the clinician to search for other causes of central nervous system injury or birth depression. A combination of techniques including fetal acid-base assessment, electronic fetal heart rate monitoring, and thorough neonatal evaluation probably provides the best predictor of long-term outcome. Newer methods of umbilical cord sampling and acid-base determinations in the intrauterine growth retarded fetus hold some hope for the future.     

Research on predicting neonatal acid-base status

Intrapartum monitoring and umbilical arterial blood pH study were carried out in 103 cases of normal pregnancy from March 1987 to December 1987. A stepwise linear regression analysis was done on 23 factors concerning the status of the newborns and 5 significant umbilical arterial blood pH, related ones that is fetal scalp blood pH, duration of the second stage of labour. Maternal blood PCO2, BB and M/F delta BDHb5. It is considered that Fischer's FHR-monitoring scoring system M/F delta pH and status of amniotic fluid etc, bear no relation to umbilical arterial blood pH. From these 5 significant factors, a regression equation was obtained so that the acid-base status of newborns can be predicted.     

Detectability and pattern of immunoglobulins in normal amniotic fluid throughout gestation

Immunoglobulin (Ig) M, IgA, and IgD class and IgA, and IgA2 subclass levels were detected in normal amniotic fluid throughout gestation with a hemagglutination-inhibition assay: IgG was measured by single radial immunodiffusion. In 161 tested samples, IgA, IgA, IgA2, and IgG were measurable in all cases; IgM was measurable in 99.4 per cent and IgD, in 90.6 per cent of the fluids. IgA, IgG, and IgD concentrations increased toward midpregnancy and thereafter decreased to term in a pattern similar to that for amniotic fluid total protein. IgM, on the other hand, remained relatively constant through week 35 of gestation; thereafter, it increased to term. There was no correlation in this normal group between amniotic fluid and cord blood levels of Ig class or subclass at term. Mean IgA values were 2.2 times higher in amniotic fluid than in cord serum. This was in sharp contrast to IgM, which was 16 times higher, IgG, which was 66 times higher, and IgD, which was 2.4 times higher in cord serum than in amniotic fluid. The inverse data for IgA as compared to other Ig classes suggest that amniotic fluid IgA may be partially derived from IgA in fetal gastrointestinal and pulmonary secretions. Determination of the concentration of the different Ig classes (and eventually subclasses) in amniotic fluid may be useful in diagnosis of intrauterine infections, malformations, and immunodeficiencies.