Clinical characteristics of pregnancies complicated by intrapartum fetal asphyxia J.
M.D. M.D. M.D.
The clinical characteristics of 124 pregnancies complicated by intrapartum fetal asphyxia have been reviewed. The evidence of fetal asphyxia tends to appear earlier in patients with maternal medical and obstetric complications than in those with labor complications. Evidence of clinical fetal distress was present in 36 per cent and was not related to the severity of the asphyxia, Low Apgar scores occurred in 40 per cent of infants with moderate asphyxia and in 80 per cent of infants with severe asphyxia at delivery. In the newborn infants, clinical evidence of cerebral abnormality was observed in 3 per cent, and evidence of the respiratory distress syndrome was seen in 3 per cent of the study group.
A N U M B E R o F relevant maternal, fetal, and newborn infant clinical characteristics have been reviewed in 124 pregnancies complicated by intrapartum fetal asphyxia. The criteria for intrapartum fetal asphyxia and the acid-base and biochemical characteristics of this study group have been rep0rted.l The maternal medical, obstetric, labor, and delivery complications and the presence of clinical fetal distress have been recorded. The characteristics of the newborn infant in respect to maturity, developmental anomalies, intrauterine growth retardation, association with maternal diabetes, and blood group incompatibility have been identified. Apgar score has been assessed and recorded by independent observors. The neonatal course of each infant has been carefully reviewed in regard to morbidity.
Maternal complications. Most obstetric patients in this study had one or more medical, obstetric, or labor complication. Thus, the interpretation of the relationship of these complication categories and the severity of fetal asphyxia is complicated by the frequent overlap of complications in individual patients. A medical complication such as hypertension, cardiac disease, or diabetes was present in 22 patients, of whom 18 had a second complication. A major obstetric complication such as toxemia or antepartum hemorrhage was present in 62 patients, of whom 42 had a second complication. A labor complication such as abnormal uterine action or cephalopelvic disproportion occurred in 32 patients, of whom 18 had a second complication. The pH and buffer base during labor and at delivery in patients of the three complication categories are compared in Fig. 1. There is no significant difference between the three complication categories in respect to the severity of fetal asphyxia as expressed by pH and buffer base at delivery. The change of pH and buffer base is apparent earlier, 2 hours prior to delivery, in those patients with medical and obstetric complications in relation to those with labor complications. Clinical fetal distress. Clinical fetal distress, that
From the Department of Obstetrics and Gynaecology and the Department of Pediatrics, Queen’s University. Presented at the Thirtieth Annual Meeting of the Society of Obstetricians and Gynaecologists of Canada, Murray Bay, Quebec, Canada, June 20-23, 1974. Reprint requests: Dr. ]. A. Low, Department Obstetrics and Gynecology, Queen’s University, Kingston, Ontario, Canada.
Fig. 1. The obstetric,
pH and buffer base during and labor complications.
is, meconium-stained amniotic fluid and/or fetal heart rate abnormality, occurred in 45 patients (36 per cent). The fetal pH and buffer base during labor and at delivery in patients with and without evidence of clinical fetal distress are compared in Fig. 2. The fetus in patients with signs of clinical fetal distress had a slightly but not significantly lower buffer base and pH in relation to those without evidence of clinical fetal distress at delivery. The pattern of developing fetal asphyxia during labor is essentially the same in the two groups. Apgar score. The Apgar scores of the newborn infants of the asphyxia group are outlined in Table I. A normal Apgar score, that is, greater than 7 at one minute, was observed in 54 newborn infants (44 per cent). An abnormal Apgar score, that is 7 7 at one minute, was observed in 68 newborn infants (56 per cent), of whom 18 infants or 15 per cent had a persisting low Apgar score at 5 minutes. The relationship between Apgar scores and the severity of fetal asphyxia is outlined in Table II. The study group was subdivided into two groups, moderate and severe asphyxia, on the basis of the umbilical artery lactate-pyruvate ratio. The severe asphyxia group includes the quartile of the study group with the highest lactate-pyruvate ratio. An abnormal Apgar score occurred in 40 per cent of the moderate asphyxia and in 80 per cent of the severe asphyxia group. The relationship between Apgar score and maternal clinical complication
and at delivery
Table I. The Apgar score of the newborn of the asphyxia group Afqar > 7 4-7 1-3 < 7
at at at at
1 min. 1 min. > 1 min. > 5 min.
SCOTC 7 at 5 min. 7 at 5 min.
NO. 54 28 ‘9’)
%o 44 "3 18 15
categories is outlined in Table II. An abnormal Apgar score occurred in 30 per cent of patients with no major clinical complication, in 45 per cent of patients with a medical complication, 55 per cent of patients with an obstetric complication, and 74 per cent of patients with a labor and delivery complication. Neonatal complications. The variations other than asphyxia present in the newborn infants of the asphyxia group which may influence neonatal behavior are outlined in Table III. There were 76 mature, 32 preterm, and 16 postterm infants. There were 7 with congenital anomalies, 16 with intrauterine growth retardation, and 7 infants of diabetic mothers. Clinical evidence of cerebral abnormality was observed in 4 newborn infants, 3 per cent of the asphyxia group. The 4 infants were all large (3,390 to 4,600 grams, seventy-fifth to ninetieth percenmature (39 to 43 weeks) with a marked tile), metabolic acidosis (umbilical artery buffer base, 25 to 32 mEq. per liter) and corresponding low umbilical
February Am. J. Obstet.
15, 1975 Cynecol.
Fig. 2. The pH and buffer base evidence of clinical fetal distress.
Table II. The maternal
Normal > 7 at I min.
NO CLINICAL FETAL DISTRESS CLlNlCAL FETAL DISTRESS
< 7 at 1 min.
and the presence
1 < 7 at 5 min.
Fetal asphyxia Moderate Severe
Clinical complications None Medical Obstetric Labor and delivery
7 12 27 9
70 55 45 26
3 5 27 15
0 5 8 8
30 45 55 74
artery pH (6.680 to 7.125) at delivery. Two infants demonstrated transient hypotonia or hypertonia, which resolved, for several hours following delivery. One infant experienced marked hypertonia, reflex irritability with seizures, which cleared during the first week. The final infant had marked anemia caused by bleeding from a vasa previa and died 42 hours following delivery with evidence of severe cerebral depression. Neonatal respiratory complications occurred in 7 infants. Four preterm infants developed the respiratory distress syndrome (RDS). Two infants at 25 and 31 weeks, respectively, developed severe RDS and died during the neonatal period; Two infants, an infant of a diabetic mother at 36 weeks and an infant from a mother with eclamptic toxemia at 35 weeks, developed moderately severe RDS and survived. One preterm (27 weeks) infant survived a protracted Wilson-Mikity syndrome.
Two mature infants developed resolved satisfactorily.
Comment Some indication of the relative significance of the 3 clinical complication categories in the obstetric patient in respect to the occurrence of intrap&turn fetal asphyxia can be derived from this review. Fig. 1 suggests that the fetal asphyxia developed more gradually and was less severe during the last half of labor in those patients with labor complications than in those patients with medical and obstetric complications, although the severity of the metabolic acidosis at delivery was essentially the same in the three clinical categories. The classical criteria of clinical fetal distress, meconium-stained amniotic fluid, and clinicaIly observed fetal heart rate abnormality occurred in only 36 per cent of the asphyxia group. Fig. 2 indicates
that the pattern of development during labor and the severity at delivery of fetal asphyxia was the same in the patients with no evidence of clinical fetal distress as in those with these clinical signs. Although newborn Apgar scores have undoubtedly been influenced by the fetal asphyxia, it is noteworthy that 44 per cent of the newborn infants in this study group had normal Apgar scores. The Apgar score is influenced by the degree of asphyxia, 80 per cent with severe asphyxia in relation to 40 per cent with moderate asphyxia have an abnormal Apgar score. The relevance of other factors upon the Apgar score is indicated by the high incidence of abnormal Apgar scores in those infants delivered of patients with labor complications (74 per cent) who, as previously noted, had evidence of less severe fetal asphyxia during the last half of labor. Cerebral depression and damage have been well documented in animal model studies of total and partial asphyxia.?-” Myers6 has described the effect on fetal monkeys of a spectrum of fetal asphyxia of increasing severity. Mild partial asphyxia with a pH above 7.10 and oxygen content above 2.0 vol. per cent resulted in no evidence of brain injury on clinical or pathologic examination. Intermediate degrees of partial asphyxia for longer periods or short-lived severe asphyxia may permit survival but with evidence of permanent brain damage. Severe partial asphyxia with a pH below 7.0 and oxygen content less than 0.5 vol. per cent for several hours leads to fetal death. In the current study the umbilical artery pH was 7.109 with a range from 6.5 to 7.3; the umbilical artery buffer base was 32.4 mEq. per liter with a range from 15.4 to 36.0 mEq. per liter, and the umbilical artery oxygen saturation was 10 per cent, indicating that the oxygen content was less than 2.0 vol. per cent in many cases. Thus, it is apparent that the fetal asphyxia characteristics of these infants was approximating the critical levels noted in monkeys (Fig. 3). There were 4 infants in the present study with evidence of cerebral effects. The 3 infants with transient clinical evidence of cerebral injury occurred in large mature infants in whom the
2. 3. 4.
Low, J. A., Pancham, S. R., Worthington, D., and Boston, R. W.: AM. J. OBSTET. GYNECOL. 120: 862, 1974. Windle, W. F.: Science 140: 1186, 1963. Windle, W. F.: J. A. M. -4. 206: 1967, 1968. Myers, R. R.: In Goldsmith, E. J., and Moor-Jan-
O2 content Vol %
0,content Vol. %
Fig. 3. The severity of fetal asphyxia at delivery presence study is compared to the spectrum asphyxia in monkeys as described by Myers.G
in the fetal
Characteristics of the newborn asphyxia group
Maturity Congenital anomaly Intrauterine growth retardation Infant of diabetic mother
role of mechanical stress must be considered. The neonatal death occurred in an infant whose course was further complicated by severe anemia resulting from blood loss. The key is the combination of degree and duration of fetal asphyxia, and from the available data the duration of severe fetal asphyxia has been short in the infants of the present study. The importance of an accurate measure of the degree of fetal asphyxia in the management of individual clinical problems is apparent. Intrapartum fetal asphyxia has been identified as a relevant factor to the subsequent occurrence of the neonatal respiratory disress syndrome7 but was not a frequent occurrence in the present study. Respiratory distress syndrome occurred in 4 newborn infants, representing 3 per cent of the total asphyxia group and 12 per cent of the preterm infants.
kowski, J., editors: Medical Perinatology 1970, Basel, 1971, S. Karger AG, pp. 394-425. Myers, R. E.: In Perinatal Factors Affecting Human Development, Washington, 1969, Pan American Health Organization Scientific Publication No. 185, p. 205. Myers, R. E.: AM. J. OBSTET. GYNECOL. 112: 246, 1972.