Aspiration of meconium and amniotic fluid

Meconium aspiration is a type of respiratory distress syndrome, characterized by obstruction of the airways due to the entry of fetal amniotic fluid into the tracheobronchial tree.

Departure of meconium with head presentations has long attracted the attention of midwives. However, until now, the role of meconium as a sign of fetal suffering has not been finally established; the reasons and the mechanism of its departure are not fully elucidated, as well as the significance of the time of meconium withdrawal for the outcome of childbirth.

The frequency of meconium withdrawal ranges from 4.5 to 20% and on average is 10% of births with fetal presentation, even with optimal management of the pregnant. The discrepancy in the frequency of meconium detection is explained by different contingent of the examined pregnant and parturient women. A number of authors indicate that the presence of meconium in the amniotic fluid does not indicate hypoxia both at the time of the study and does not establish the period of its development, in connection with which it can not serve as an absolute criterion for assessing the state of the fetus in childbirth.

Other researchers attribute this fact to the reflex response of the intestine of the fetus to some irritations that could be noted long before the study.

[1], [2], [3], [4]

Meconium in the amniotic fluid

It is believed that the departure of meconium indicates a threatening condition of the fetus.

Most researchers testify that in the presence of meconium in the amniotic fluid the frequency of fetal hypoxia increases, perinatal mortality and morbidity of newborns increase. In cases where the amniotic fluid is transparent at the time of onset of labor, perinatal mortality is low, and when it is stained with meconium, it increases to 6%. In the presence of meconium in amniotic fluid, a severe complication of the neonatal period is meconium aspiration syndrome leading to high neonatal mortality. However, only 50% of the newborns, who had amniotic fluid stained with meconium during labor, had primary feces in the trachea; in the latter group, if measures were taken, respiratory disorders (respiratory distress) developed in% of cases. Thus, the average frequency of symptomatic meconium aspiration syndrome is 1-2%. Aspiration syndrome is observed in the born, born on time, but in a state of hypoxia, and in children with growth retardation in the intrauterine period. Meconium aspiration syndrome rarely occurs with normal fetal development if labor occurs before the 34th week of pregnancy.

It was found that the intrauterine fetus in the presence of meconium in the amniotic fluid has a lower oxygen tension in the umbilical vein than with the clear waters.

Some authors attributed the departure of meconium to a random defecation of a normal fetus with overgrown intestines, sometimes associated with the action of various drugs. However, in many cases, the coloring of amniotic fluid with meconium signals a threatening condition of the fetus, as indicated by monitoring data and biochemical changes in the blood.

Therefore, at the present time, most authors are inclined to regard the admixture of meconium in the amniotic fluid as a sign of the fetal hypoxia that has begun.

How does meconium aspiration develop?

Fetal hypoxia can cause mesenteric vasospasm, intestinal peristalsis, relaxation of the anal sphincter and meconium passage. The compression of the umbilical cord stimulates the vagal reaction leading to the meconium passage even in the normal state of the fetus. Convulsive respiratory movements both in utero (as a result of fetal hypoxia) and immediately after birth contribute to the aspiration of meconium into the trachea. The movement of meconium into the respiratory tract of small caliber occurs rapidly, within 1 h after birth.

The consequence of aspiration of meconium is the early mechanical obstruction of the airways with the gradual development of chemical pneumonitis after 48 hours. Complete blockage of small airways leads to subsegmental atelectasis. They are adjacent to the zones of increased aeration caused by the valve effect ("ball valve") with partial blockage and the formation of "air traps". As a result, the ventilation-perfusion ratio, the extensibility of the lungs decrease, their diffusion capacity decreases, intrapulmonary shunting and respiratory tract resistance increase. Against the background of increased breathing and uneven ventilation, an alveolar rupture can occur, leading to air leakage from the lungs.

Vascular spasm and impaired microcirculation in the lungs determine long-term pulmonary hypertension and the development of extrapulmonary shunts. 

With the help of amnioscopy, it is possible to detect an admixture of meconium in the amniotic fluid before delivery or in childbirth. The detection of staining of the amniotic fluid and the determination of its optical density can serve as a valuable method for diagnosing fetal abnormalities. There are isolated reports on the possibility of detecting the meconium admixture in the water through echography.

Meconium is a green-black viscous substance that fills the large intestine of the fetus. The chemical composition, its morphological and ultrastructural data are well studied.

It has been established that meconium particles with a size of 5-30 μm are a kind of glucoprotein containing sialomucopolysaccharide; with spectrophotometric evaluation, meconium has the highest adsorption at 400-450 μm. Studies have shown that an increase in the serotonin level in the water more than 2 times leads, apparently, to an increase in intestinal peristalsis. Predisposing factors are:

• hypertension;
• diabetes;
• isoimmunization;
• late toxicosis of pregnant women;
• Rhesus-conflict;
• the age of the mother;
• number of births and abortions;
• stillbirth in the anamnesis;
• collisions with umbilical cord.

When the umbilical cord is entangled, meconium withdrawal in labor is noted in 74%. Established a faster end of labor after rupture of the bladder and the outflow of green amniotic fluid, which may be associated with a high content of oxytocin in meconium. With the weakness of labor activity, meconium withdrawal was detected in every fifth woman in labor. The importance of fruit factors affecting the migration of meconium to the amniotic fluid has not been adequately studied. They include:

• hyaline membranes;
• pneumonia;
• chorioamnionites;
• erythroblastosis.

Meconium retreat is more common with a fetus mass of more than 3,500 g, and in children weighing less than 2,000 g, meconium is extremely rare, which may be due to its insignificant accumulation in the intestine of the fetus during preterm labor or a decreased sensitivity of preterm infants to a hypoxic condition.

Aspiration of the amniotic fluid

During childbirth it is possible to aspirate the fruit with a clean and containing microorganisms (even pus) and blood of the amniotic fluid. In this case, transient tachypnea or persistent pulmonary hypertension occurs. If the liquid is purulent, antibiotics are administered to prevent pneumonia.

[5], [6], [7]

Management of pregnancy and childbirth in the presence of meconium in the amniotic fluid

The tactics of managing pregnancy and childbirth in the presence of meconium in the waters are not completely solved. There are single reports on the significance of the time of meconium withdrawal and the degree of its coloring on the outcome of labor for the fetus and the newborn.

It is noted that the staining of the amniotic fluid after the departure of the meconium first of all appears in the bottom of the uterus at the head presentations of the fetus. Then, the whole mass of amniotic fluid, including the anterior ones, is stained. The staining of the meconium pigments with the nails and the skin of the fetus, as well as the casei oil flakes, is directly dependent on the time of meconium withdrawal: the fetal nails are painted after 4-6 h, the grease flakes after 12-15 h.

It is also suggested that meconium may appear in the second trimester of pregnancy and remain there until the onset of urgent labor, during which it is treated as a sign of impaired fertility. There is also evidence that the appearance of meconium in the waters is a sign of fetal death in the second trimester of pregnancy.

In labor, the early appearance of meconium in amniotic fluid is observed in 78.8%, later in 21.2%. Early minor meconium exposure to amniotic fluid, observed in 50% of pregnant women with meconium-stained water, was not accompanied by an increase in the incidence or mortality of fetuses and newborns. Massive hit of meconium was accompanied by increased morbidity and mortality of newborns during complicated pregnancy.

Concerning the diagnostic significance of the nature of meconium found in the amniotic fluid, there are conflicting opinions. Some authors believe that the uniform coloration of the amniotic fluid with meconium indicates a prolonged suffering of the fetus, suspended lumps and flakes - about the short-term reaction of the fetus. An increase in meconium content is an unfavorable prognostic sign.

Some authors describe light-green meconium as "old, liquid, weak" and more dangerous with respect to the fetus, and dark green - as "fresh, recent, dense" and less dangerous, since its connection with perinatal mortality has not been established. In contrast, Fenton and Steer (1962) indicated that at a fetal heart rate of 110 beats per minute and the presence of dense meconium, the perinatal mortality was 21.4%, with a slight staining of water 3.5%, with light water 1.2% . It was also established that in the presence of thick meconium in the waters and the opening of the uterine pharynx for 2-4 cm, the pH of the fetal blood decreases.

Moreover, a correlation was established between the nature of meconium, the pH of fetal blood and the state of newborns on the Apgar scale. So, according to the research, when the meconium waters were dense at the beginning of birth, the pH of the fetal blood was below 7.25 in 64%, and the Apgar score in 100% was 6 points or lower. At the same time, the presence of meconium in amniotic fluid without other symptoms (acidosis, deceleration of fetal heart rate) can not be regarded as evidence of impairment of the fetus and therefore there is no need to accelerate delivery. At the same time, whenever there are irregular heartbeats of the fetus in the presence of meconium in the water, the risk to the fetus increases compared to the clear waters. 

In order to reduce the risk of complications for the fetus and newborn associated with asphyxia, in the presence of meconium in the water, it is recommended to resort to an operative delivery at a pH of 7.20 or below. If there are violations of the fetal heart rate according to cardiotocography, the delivery is indicated with preacidosis (pH 7.24-7.20).

In connection with this, in labor during the staining of the water with meconium, most investigators roll about the advisability of monitoring the fetal condition. When performing a comprehensive assessment of the fetal status in labor, it is possible to reduce perinatal mortality in the presence of meconium in waters up to 0.46%.

The frequency of surgical interventions in the presence of meconium in the waters is 25.2% compared to 10.9% in light waters.

It is important to note that with caesarean section meconium can get into the abdominal cavity, as a result of which a granulomatous reaction to the foreign body can develop, resulting in spikes and abdominal pain.

One of the severe complications of the neonatal period in the presence of meconium in the water is meconium aspiration syndrome , the frequency of which varies from 1 to 3%. It is more often found in fruits in the early and abundant appearance of meconium than in the light and late withdrawal. When the amniotic fluid is dense, the aspiration of amniotic fluid in the initial stage of labor is 6.7%. It was noted that when meconium recedes in the amniotic fluid, respiratory disorders develop in different degrees in 10-30% of newborns. The syndrome of meconium aspiration is more often observed in term and delayed children in acute hypoxia. Hypoxic stress leads to an increase in respiratory movements of the fetus, and amniotic fluid colored with meconium, aspirated. Meconium particles penetrate deeply to the alveoli, causing chemical and morphological changes in the lung tissue. In some cases, aspiration of meconium may occur in a more chronic form, which can contribute to the development of acute intrauterine pneumonia.

Aspiration of meconium is an important cause of neonatal mortality, the indices of which, although lower, than with hyaline membrane disease, however constitute a large percentage - 19-34%. Therefore, meconium aspiration syndrome is an important clinical problem faced by neonatologists in the intensive care unit.

To prevent the development of respiratory pathology in newborns, most authors point to the need to minimize aspiration during labor. Aspirated meconium should be aspirated by a catheter for 2-3 hours. The need for careful management of labor and immediate suction of meconium from the upper respiratory tract is an important preventive measure to prevent neonatal mortality.

Thus, the data available in the literature indicate that the diagnostic and prognostic value of the meconium admixture in the amniotic fluid has not been fully established. However, most authors regard the presence of meconium in the amniotic fluid as a sign of fetal suffering.

Monitoring monitoring in childbirth with the use of modern diagnostic methods (cardiotocography, amnioscopy, determination of the acid-base state of the fetal blood, pH-metry of amniotic fluid) in maternity patients with meconium in the water makes it possible to clarify the condition of the fetus in childbirth and determine the further tactics of labor.

At the end of physiological pregnancy, in the absence of disturbances in the fetal condition, a characteristic amniascopic picture is a moderate amount of transparent (less often "dairy") water with a moderately large content of easy-moving flakes of caseous grease. Detection of the same meconium in the waters is regarded as a sign of the suffering of the fetus. Meconium pigments stain the water in green. This coloration persists for a long time and can be detected after several hours and days. Calculations by E. Zaling showed that with a live fruit, at least 4-6 days are required to eliminate meconium from the amniotic cavity. Therefore, when monitoring is carried out every 2 days, it is impossible not to notice the meconium. It was noted that asphyxia of newborns is observed in 1,5-2,4 times more often in the presence of meconium in waters than in light waters.

To improve the diagnosis of the fetal condition in childbirth in the presence of meconium in the amniotic fluid, a complex assessment of the fetal condition was carried out, including cardiotocography, amniography, determination of the acid-base state of fetal and maternal blood, monitor pH-metric amniotic fluid. A clinical analysis of the course of labor was performed in 700 women in labor, 300 of them having meconium in the amniotic fluid; 400 mothers (control group) - 150 women giving birth with timely water discharge and 250 women giving birth with untimely water withdrawal. Clinical and physiological study was conducted in 236 women in labor.

The received information array of 148 characteristics was statistically processed on a computer "EU-1060" using the American package of applied statistical programs.

As a result of the conducted studies it was established that the number of abortions and miscarriages in the anamnesis was 2-2.5 times higher in the group with the presence of meconium in the waters. Among the 50-60% recurrent females, the previous delivery had a complicated course (surgical interventions, intrapartum fetal death), which was not observed in the control group of parturient women. Almost every second mother of the main group had a complicated pregnancy. It should be emphasized that only the parturients of the main group suffered from nephropathy. Edemas and anemia of pregnant women were twice as common in women with meconium in the water.

Primary elderly people also prevailed in the main group, which confirms the opinion of the above authors on the significance of the age of the mother in the meconium.

Obviously, with severe accompanying diseases of the mother and complications of pregnancy, first of all, the conditions of nutrition and gas exchange of the fetus, caused by a violation of uteroplacental blood circulation, that can lead to the passage of meconium into the amniotic fluid. 

A definite relationship between the clinical course of pregnancy and childbirth and the state of the fetus and the newly born is revealed. Thus, a high relationship between nephropathy was revealed in both pregnancy and childbirth, weakness of labor, anomalies of the insertion of the head, cord rounding around the neck of the fetus and low estimates of newborns on the Apgar scale. Each third woman in labor, suffering from nephropathy (35.3%) and weakness of labor (36.1%), the newborns had an Apgar score of 6 and lower. Studies have shown that in nephropathy, the fetus experiences hypoxia only when meconium is removed; Asphyxia of the newborn increases 2.5 times in comparison with the control one. It should be noted that the departure of meconium depends not so much on the degree of toxicosis, but on its duration.

In maternity patients with meconium in the amniotic fluid, a longer duration of the birth act (13.6 ± 0.47 h) was noted in comparison with the control group (11.26 ± 0.61 h).

Each second newborn born in asphyxia had an umbilical cord around the neck of the fetus (50%), one in five (19.4%) had an anomaly in the insertion of the head.

Complications of the birth act caused a high percentage of operative delivery (14.33%), in the structure of which the operation of cesarean section was 7.66%, obstetric forceps and vacuum extraction of the fetus - 6.67%.

Despite the fact that there are reports of low correlation (22.3%) of surgical interventions and the coloring of amniotic fluid by meconium, there is a high correlation between the method of delivery and low Apgar scores. Thus, asphyxia of newborns with the application of cavitary obstetrical forceps was observed in 83.3%, with vacuum extraction of the fetus - in 40%, operations of cesarean section - in 34.7 %.

Acceleration of fetal birth by activation of labor (quinine, oxytocin), as well as the use of obstetric forceps and vacuum extractor aggravates the pathological condition of the fetus, which is on the verge of failure of compensatory possibilities. In the presence of meconium in the water and the phenomena of metabolic acidosis in the fetus, even a physiologically occurring birth act can be such a load that at any moment can lead to the failure of the compensatory mechanisms of the fetus.

Asphyxia of newborns, observed in 12% in the presence of meconium in the waters, caused a severe complication of the neonatal period - meconium aspiration syndrome (16.65%). Hypoxic stress leads to an increase in respiratory movements of the fetus and aspiration of the amniotic fluid. The syndrome of meconium aspiration is an important cause of neonatal mortality. According to our observations, the meconium aspiration syndrome in newborn asphyxia led to a lethal outcome of 5.5%, which is consistent with literature data indicating an increase in perinatal mortality in this pathology to 7.5%.

Thus, the data convincingly show that the admixture of meconium in waters should be regarded as a sign of fetal suffering. Clinico-physiological study showed that in the presence of meconium in the water, the fetal blood CBC values significantly differ with the control group. A significant decrease in blood pH (7.26 ± 0.004) and a deficiency in the base (-6.75 ± 0.46) already at the onset of labor in the presence of meconium in the water indicates the stress of the compensatory mechanisms of the fetus. On the depletion of reserve capabilities of the fetus in the presence of meconium in the waters, our observations indicate that it was possible to detect a pre-acidosis in his blood (pH 7.24-7.21) at the beginning of labor at 45.7%, at the end of the period of exposure - twice as often (80%), which is consistent with the data of Starks (1980), in studies of which in the fetuses that had meconium withdrawal, there was a significant acidosis in the blood.

In the group of newborns with an Apgar score of 6 points or lower, the fetal blood COS values reflect pathological acidosis: at the beginning of labor, the pH is 7.25 ± 0.07; BE - 7.22 ± 0.88; at the end of the pH-opening period, 7.21 ± 0.006; BE - 11.26 ± 1.52; an increase in pCO ₂, especially in the second stage of labor (54.70 ± 1.60), indicates the presence of respiratory acidosis.

The results of the studies revealed a correlation between fetal blood COS and low infant score on Apgar scale in the presence of meconium in amniotic fluid. The CBS of the mother's blood in these cases does not differ from the one-to-one in the control group and is within physiological limits. Delta pH does not carry additional diagnostic information, since this indicator changes practically only due to the fruit component. These data contradict the reports of some authors pointing to a change in the mother's blood COS associated with intrauterine fetal hypoxia.

A clear correlation was found between the pH of fetal blood and the pH of the amniotic fluid. The lower pH values of the amniotic fluid, stained with meconium (7.18 ± 0.08) at the onset of labor and 6.86 ± 0.04 at the end of the opening period, fit into the "pre-pathological" zone, a high-risk area for the fetus, and reflect exhaustion of compensatory resources of the fetus.

When the fetus is hypoxic, the pH of the water drops to 6.92, with light asphyxia it is 6.93, with a heavy asphyxia it is 6.66. With fetal hypoxia, the decrease in the pH of the water and fetal blood is due to the release of a large number of acidic metabolic products from the fetal organism into the amniotic fluid. The decrease in the pH of amniotic fluid (6.67 ± 0.11 at the onset of labor and 6.48 ± 0.14 at the end of the II stage of labor) in the neonatal group with low Apgar scores indicates marked acidosis, especially in period II, when the reaction of the amniotic fluid essentially shifts to the acidic side, and the more significantly, the heavier the condition of the fetus. Buffer capacity of amniotic fluid is half of the buffer capacity of fetal blood, so the depletion of its resources is faster and with fetal hypoxia, acidosis is much more pronounced. The decrease in the buffer capacity of water is manifested during hypoxia of the fetus and the presence of meconium manifests itself as an increase in intra-hour fluctuations in the pH of the waters to 0.04 ± 0.001 versus 0.02 ± 0.0007 in control in the presence of light amniotic fluid. In addition, an increase in the index of intra-hour fluctuations in the pH of amniotic fluid may occur earlier than a decrease in the absolute value of their pH, which makes it possible to reveal in a timely manner the initial signs of fetal suffering during labor. 

Cardiotocography in the presence of meconium in the water leads to a decrease in the oscillation amplitude (6.22 ± 0.27) and myocardial reflex (10.52 ± 0.88), which indicates a decrease in the reserve capacity of the fetus and agrees with the results of Krebs et al. (1980).

In the presence of meconium in the water, pathological declerations are registered four times more often (35.4 ± 4.69) than in clear waters (8.33 ± 3.56), indicating a violation of the fetal life. However, in our observations false-positive and false-negative results were noted. So, with normal fetal blood CBC parameters, pathological declerations were registered in 24% of cases, with the presence of acidosis in his blood, normal cardiotocography rates were registered in 60%.

The appearance of meconium at normal CTG and normal pH of fetal blood can be temporarily compensated for by the stage of disruption of its vital activity; However, whenever there are irregular heartbeats of the fetus in the presence of meconium in the waters, the risk for it is greater than with light waters.

To determine the diagnostic significance of various methods for assessing the fetal condition in the presence of meconium in the waters, for the first time we carried out a correlation analysis, which makes it possible to establish a relationship between different characteristics. Correlation matrices were compiled for each group separately and for each stage of the generic act.

In the presence of meconium in the amniotic fluid, the pH of the fetal blood was highly correlated with the pH of the water and its intra-hour fluctuations, late decelerations; The pH of waters stained with meconium entered into a correlation with the myocardial reflex, the amplitude of the oscillations, and the deceleration. The mean frequency correlated with the deceleration.

A high correlation with Apgar scores was the pH of the fetal blood, the pH of the water, the hourly fluctuations in the pH of the water, late de-icerations, pCO2 _of fetal blood. Correlation dependence between the pH of the fetal blood and the parturient child was not revealed.

The carried out research allowed us to develop a technique for a comprehensive assessment of the fetal condition in childbirth in the presence of meconium in the amniotic fluid:

• in all parturient women during the birth, cardiotocography is performed with the determination of the average fetal heart rate, the amplitude of the oscillations, the magnitude of the myocardial reflex, and pathological deceleration. Regardless of the CTG indices, amnioscopy is performed;
• when a meconium is found in the waters, a fetal bladder is opened and the acid-base state of fetal blood is examined according to the Zaling method;
• with the indices of the fetal blood CBC showing the intrauterine suffering of the fetus, an urgent delivery is performed;
• at stably satisfactory pH values of water, further monitoring of the fetal condition until the end of labor is carried out; with the increase of acidosis in the amniotic fluid - Zaling's repeated test.

The main complications of pregnancy in the presence of meconium in the waters are late toxicosis (28.9%) and anemia of pregnant women (12%), occurring in them twice as often as in the control group.

In maternity patients with meconium in the waters, the main complications of the birth act are abnormalities of labor (31.3%), nephropathy (19.3%), cord cord entanglement around the fetal neck (21%), head insertion anomalies (4.6%), observed twice as often as in the control group.

In the presence of meconium, a high incidence of surgical interventions (14.33%) is noted in the waters, in the structure of which the operation of caesarean section is 7%, the operation of obstetrical forceps is 2% (cavitary), cavity vacuum extractor - 1.67%.

In the presence of meconium in the water, asphyxia of the newborn occurs six times more often than in the comparison group. Severe complication of the neonatal period - meconium aspiration syndrome is the cause of death in 5.5 % of newborns.

Multifactorial discriminant analysis allowed predicting in maternity patients with meconium in the water an operative delivery in the interests of the fetus in 84%, and the condition of the newborn in 76%.

The high frequency of complications of pregnancy, labor, operative interventions, as well as complex monitoring monitoring of the fetus condition allows mothers with meconium in the amniotic fluid to be assigned to a high-risk group who need intensive supervision during childbirth.