FETUS,PLACENTA, ANDNEWBORN Significance of meconium during labor FRANK
C.
MILLER,
DAVID
A.
SACKS,
SZE-YA
YEH,
RICHARD BARRY EDWARD Los
Angeles,
B. H.
MC,
USA
M.D.
PAUL,
M.D.
SCHIFRIN,
CHESTER
COLONEL,
M.D.
H. S.
LIEUTENANT
M.D.
MARTIN, HON,
JR.,
M.D.
M.D.
California
Continuous fetal heart rate (FHR) monitoring and routine fetal scalp blood sampling was utilized in the evaluations of 366 fetuses during labor. One hundred and six patients had meconium in the amniotic fluid at some time during labor, A total of 26,110 uterine contractions were monitored during these 366 labors. The incidence of FHR patterns as a percentage of uterine contractions was calculated for the meconium and nonmeconium groups. Although there was a 3%-fold increase in the incidence of low five-minute Apgar scores (less than 7) in the meconium group, si 0.01). Aspiration of thick meconium and subsequent difficulty with newborn resuscitation could well be the causative factor. Several investigators have reported a good correlation between FHR patterns and fetal pH with
+
of meconium
Repetitive
passage.
the newborn condition as reflected by the Apgar score.7, ’ Kubli and associates8 found that the FHR pattern of late decelerations was the pattern most commonly associated with low fetal scalp blood pH. HobeP found a good correlation between fetal scalp blood pH of less than 7.25 and a one-minute Apgar of less than 7 when signs of fetal distress were present. The occurrence of late decelerations (ten, 15, and 20 per cent) and fetal scalp pH values (+ 7.25 and 7.20) in late labor was evaluated to determine the value of these parameters in the prediction of outcome as determined by the five-minute Apgar. The combination that was the most predictive of a low five-minute score was greater than 10 per cent late decelerations and pH of less than 7.25. Fifty-seven per cent of patients with meconium had greater than ten per cent late decelerations as compared with 52 per cent of the nonmeconium group. With the use of the chi square analysis, there was no statistical difference in the incidence of low Apgar scores between the two groups if there were less than ten per cent late decelerations. However, with greater than ten per cent late decelerations, the increased incidence of low Apgar scores in the meconium group was highly significant (p < 0.01) . When the parameter of pH was introduced in the greater than ten per cent late deceleration category, there was again no significant difference ( p < 0.1) between the meconium and nonmeconium groups. These data indicate that without signs of fetal distress (late decelerations), meconium in the amniotic fluid does not prejudice outcome. When distress occurs in the presence of meconium, the chances for newborn depression are greater than if meconium was not present. As expected, when both late deceleration and acidosis are present, there is an increased incidence of low Apgar scores
Volumr Number
122 5
Significance
in both the meconium and nonmeconium groups. There are many instances of fetal distress and asphyxia in which no meconium passage occurs. Conversely, meconium is often present in the amniotic fluid without any evidence of fetal distress or asphyxia. Passage of meconium in utero may result from various stimuli. Walker3 found that fetuses with meconium passage had lower umbilical vein oxygen saturation than did normal term infants. Salingll postulated that fetal hypoxia precipitates vasoconstriction in the fetal gut which causes hyperperistalsis and sphincter relaxation with passage of meconium. Honl” has suggested that vagal activation from cord compression will result in meconium passage, especially in a mature fetus. Fenton and Steer’ considered the passage of meconium to be a normal physiologic function; in which case, meconium passage may be a sign only of increasing fetal maturity. The passage of meconium is probably due to one or a combination of the above causes, as shown in Fig. 2. Pneumonitis secondary to meconium aspiration in the newborn period is well known to contribute to the morbidity and mortality rate. Since the majority of fetuses with meconium passage do well, why do some aspirate meconium and others do not? AdamsI and Dawes and co-workers’4 have shown a net outflow of fluid from the lungs of fetal lambs in utero. The factors affecting the rate of formation of pulmonary fluid are not known; however, pulmonary and bronchial blood flow must be considered as a factor. Asphyxia in the fetal lamb has been shown to cause both pulmonary vasoconstriction and a reduction in pulmonary blood flow.‘” When fetal distress occurs in the presence of meconium, the following series of events may occur which result in meconium aspiration : Fetal asphyxia may cause pulmonary vasoconstriction and reduced pulmonary blood flow. Fetal gasping occurs secondary to asphyxial insult with aspiration of meconium into the trachea. With the reduction of pulmonary fluids, the self-cleansing action of the tracheobronchial tree is lost and the meconium remains in the trachea with the potential for aspiration (Fig. 3). From the foregoing, we conclude that meconium passage per se does not indicate fetal distress. The
Steer, C. Hellman,
M.: L.
N. Y. State M., Schiffer,
Med. J. 57: 1925, 1957. M. A., Kohl, S. G., and
meconium
during
labor
579
Hvoox~c bowel
Normal breathing movementr, glottis clod (?I
Gasping in labor glottis open (?)
1 Net outflow
I Decreased pulmonary blood flow decrsased tracheal fluid (7)
of fluid
L No aspiration
L Retention I
Fig.
3. Possible
etiology
of meconium
in lungs
aspiration.
occurrence of fetal asphyxia when meconium is present enhances the potential for meconium aspiration and a poor neonatal outcome. The presence of meconium should serve to alert the physician to a high-risk fetal condition. All patients with meconium in the amniotic fluid should be primarily managed in labor with continuous FHR monitoring. If any “abnormal” FHR changes are noted, fetal blood sampling for acid-base state is indicated for additional commentary. Special care must be taken to avoid conditions which would cause fetal asphyxia, such as that caused by uterine hyperstimulation and maternal hypotension, either positional or secondary to conduction anesthesia and/or other medication. Every attempt should be made to avoid difficult and/or traumatic delivery with the inherent increase in fetal compromise and asphyxia. At delivery, the trachea and pharynx should be aspirated carefully in an attempt to remove the meconium in order to avoid aspiration. Positive pressure respiration should be avoided until adequate tracheal toilet, under direct vision, has been accomplished to prevent forcing meconium deeper into the fetal lungs. Although unanswered questions remain regarding the significance of meconium passage, a more rational approach is now possible for the management of labor with meconium in the amniotic fluid.
REFERENCES
1. 2.
of
3.
Tolles, 1958. Walker,
W. J.:
E.: AM.
AM.
J.
OBSTET.
J. OBSTET.
76:
GYNECOL.
GYNECOL.
77:
94,
998, 1959.
4.
Fenton,
A.
N., and Steer, C. M.: AM. J. OBSTET. 83: 354, 1962. Resnick, L.: S. Afr. Med. J. 29: 857, 1955. Drage, J., Kennedy, C., Berendes, H., et al.: Dev. Med. Child Neurol. 8: 141, 1964. Wood, C., Newman, W., Lumley, J., and Hammond, J.: AM. J. OBSTET. GYNECOL. 105: 942, 1969. MGndez-Bauer, C., Arnt, I. C., Gulin, L., Escarcena, L., and Caldeyro-Barcia, R.: AM. J. OBSTET. GYNECOL. 97: 530, 1967. Kubli, F. W., Hon, E. H., Khazin, A. F., and Takemura, H.: AM. J. OBSTET. GYNECOL. 104: 1190, 1969. Hobel, C. J.: AM. J. OBSTET. GYNECOL. 110: 336, 1971.
11.
GYNECOL.
5. 6. 7. 8.
9.
10.
12.
13. 14. 15.
Saling, E.: Foetal and Neonatal Hypoxia in Relation to Clinical Obstetric Practice, London, 1968, Edward Arnold, Ltd., p. 117. Hon, E. H. : The foetal heart rate, chap. 16, in Carey, H. M., editor: Modern Trends in Human Rrproductive Physiology, London, 1963, Butterworth & Co., Ltd., p. 245. Adams, F. H.: J. Pediatr. 68: 794, 1966. Dawes, G. S., Fox, H. E., Leduc, B. M., et al. : J. Physiol. 220: 119, 1972. Cassin, S., Dawes, G. S., Mott, J. C., et al.: J. Physiol. 171: 61, 1964.
C.
MILLER,
DAVID
A.
SACKS,
SZE-YA
YEH,
RICHARD BARRY EDWARD Los
Angeles,
B. H.
MC,
USA
M.D.
PAUL,
M.D.
SCHIFRIN,
CHESTER
COLONEL,
M.D.
H. S.
LIEUTENANT
M.D.
MARTIN, HON,
JR.,
M.D.
M.D.
California
Continuous fetal heart rate (FHR) monitoring and routine fetal scalp blood sampling was utilized in the evaluations of 366 fetuses during labor. One hundred and six patients had meconium in the amniotic fluid at some time during labor, A total of 26,110 uterine contractions were monitored during these 366 labors. The incidence of FHR patterns as a percentage of uterine contractions was calculated for the meconium and nonmeconium groups. Although there was a 3%-fold increase in the incidence of low five-minute Apgar scores (less than 7) in the meconium group, si 0.01). Aspiration of thick meconium and subsequent difficulty with newborn resuscitation could well be the causative factor. Several investigators have reported a good correlation between FHR patterns and fetal pH with
+
of meconium
Repetitive
passage.
the newborn condition as reflected by the Apgar score.7, ’ Kubli and associates8 found that the FHR pattern of late decelerations was the pattern most commonly associated with low fetal scalp blood pH. HobeP found a good correlation between fetal scalp blood pH of less than 7.25 and a one-minute Apgar of less than 7 when signs of fetal distress were present. The occurrence of late decelerations (ten, 15, and 20 per cent) and fetal scalp pH values (+ 7.25 and 7.20) in late labor was evaluated to determine the value of these parameters in the prediction of outcome as determined by the five-minute Apgar. The combination that was the most predictive of a low five-minute score was greater than 10 per cent late decelerations and pH of less than 7.25. Fifty-seven per cent of patients with meconium had greater than ten per cent late decelerations as compared with 52 per cent of the nonmeconium group. With the use of the chi square analysis, there was no statistical difference in the incidence of low Apgar scores between the two groups if there were less than ten per cent late decelerations. However, with greater than ten per cent late decelerations, the increased incidence of low Apgar scores in the meconium group was highly significant (p < 0.01) . When the parameter of pH was introduced in the greater than ten per cent late deceleration category, there was again no significant difference ( p < 0.1) between the meconium and nonmeconium groups. These data indicate that without signs of fetal distress (late decelerations), meconium in the amniotic fluid does not prejudice outcome. When distress occurs in the presence of meconium, the chances for newborn depression are greater than if meconium was not present. As expected, when both late deceleration and acidosis are present, there is an increased incidence of low Apgar scores
Volumr Number
122 5
Significance
in both the meconium and nonmeconium groups. There are many instances of fetal distress and asphyxia in which no meconium passage occurs. Conversely, meconium is often present in the amniotic fluid without any evidence of fetal distress or asphyxia. Passage of meconium in utero may result from various stimuli. Walker3 found that fetuses with meconium passage had lower umbilical vein oxygen saturation than did normal term infants. Salingll postulated that fetal hypoxia precipitates vasoconstriction in the fetal gut which causes hyperperistalsis and sphincter relaxation with passage of meconium. Honl” has suggested that vagal activation from cord compression will result in meconium passage, especially in a mature fetus. Fenton and Steer’ considered the passage of meconium to be a normal physiologic function; in which case, meconium passage may be a sign only of increasing fetal maturity. The passage of meconium is probably due to one or a combination of the above causes, as shown in Fig. 2. Pneumonitis secondary to meconium aspiration in the newborn period is well known to contribute to the morbidity and mortality rate. Since the majority of fetuses with meconium passage do well, why do some aspirate meconium and others do not? AdamsI and Dawes and co-workers’4 have shown a net outflow of fluid from the lungs of fetal lambs in utero. The factors affecting the rate of formation of pulmonary fluid are not known; however, pulmonary and bronchial blood flow must be considered as a factor. Asphyxia in the fetal lamb has been shown to cause both pulmonary vasoconstriction and a reduction in pulmonary blood flow.‘” When fetal distress occurs in the presence of meconium, the following series of events may occur which result in meconium aspiration : Fetal asphyxia may cause pulmonary vasoconstriction and reduced pulmonary blood flow. Fetal gasping occurs secondary to asphyxial insult with aspiration of meconium into the trachea. With the reduction of pulmonary fluids, the self-cleansing action of the tracheobronchial tree is lost and the meconium remains in the trachea with the potential for aspiration (Fig. 3). From the foregoing, we conclude that meconium passage per se does not indicate fetal distress. The
Steer, C. Hellman,
M.: L.
N. Y. State M., Schiffer,
Med. J. 57: 1925, 1957. M. A., Kohl, S. G., and
meconium
during
labor
579
Hvoox~c bowel
Normal breathing movementr, glottis clod (?I
Gasping in labor glottis open (?)
1 Net outflow
I Decreased pulmonary blood flow decrsased tracheal fluid (7)
of fluid
L No aspiration
L Retention I
Fig.
3. Possible
etiology
of meconium
in lungs
aspiration.
occurrence of fetal asphyxia when meconium is present enhances the potential for meconium aspiration and a poor neonatal outcome. The presence of meconium should serve to alert the physician to a high-risk fetal condition. All patients with meconium in the amniotic fluid should be primarily managed in labor with continuous FHR monitoring. If any “abnormal” FHR changes are noted, fetal blood sampling for acid-base state is indicated for additional commentary. Special care must be taken to avoid conditions which would cause fetal asphyxia, such as that caused by uterine hyperstimulation and maternal hypotension, either positional or secondary to conduction anesthesia and/or other medication. Every attempt should be made to avoid difficult and/or traumatic delivery with the inherent increase in fetal compromise and asphyxia. At delivery, the trachea and pharynx should be aspirated carefully in an attempt to remove the meconium in order to avoid aspiration. Positive pressure respiration should be avoided until adequate tracheal toilet, under direct vision, has been accomplished to prevent forcing meconium deeper into the fetal lungs. Although unanswered questions remain regarding the significance of meconium passage, a more rational approach is now possible for the management of labor with meconium in the amniotic fluid.
REFERENCES
1. 2.
of
3.
Tolles, 1958. Walker,
W. J.:
E.: AM.
AM.
J.
OBSTET.
J. OBSTET.
76:
GYNECOL.
GYNECOL.
77:
94,
998, 1959.
4.
Fenton,
A.
N., and Steer, C. M.: AM. J. OBSTET. 83: 354, 1962. Resnick, L.: S. Afr. Med. J. 29: 857, 1955. Drage, J., Kennedy, C., Berendes, H., et al.: Dev. Med. Child Neurol. 8: 141, 1964. Wood, C., Newman, W., Lumley, J., and Hammond, J.: AM. J. OBSTET. GYNECOL. 105: 942, 1969. MGndez-Bauer, C., Arnt, I. C., Gulin, L., Escarcena, L., and Caldeyro-Barcia, R.: AM. J. OBSTET. GYNECOL. 97: 530, 1967. Kubli, F. W., Hon, E. H., Khazin, A. F., and Takemura, H.: AM. J. OBSTET. GYNECOL. 104: 1190, 1969. Hobel, C. J.: AM. J. OBSTET. GYNECOL. 110: 336, 1971.
11.
GYNECOL.
5. 6. 7. 8.
9.
10.
12.
13. 14. 15.
Saling, E.: Foetal and Neonatal Hypoxia in Relation to Clinical Obstetric Practice, London, 1968, Edward Arnold, Ltd., p. 117. Hon, E. H. : The foetal heart rate, chap. 16, in Carey, H. M., editor: Modern Trends in Human Rrproductive Physiology, London, 1963, Butterworth & Co., Ltd., p. 245. Adams, F. H.: J. Pediatr. 68: 794, 1966. Dawes, G. S., Fox, H. E., Leduc, B. M., et al. : J. Physiol. 220: 119, 1972. Cassin, S., Dawes, G. S., Mott, J. C., et al.: J. Physiol. 171: 61, 1964.
