- Email: [email protected]
The critical period of non-reassuring fetal heart rate patterns in preterm gestation
European Journal of Obstetrics & Gynecology and Reproductive Biology 106 (2003) 36–39
The critical period of non-reassuring fetal heart rate patterns in preterm gestation Yoshio Matsudaa,b,*, Takatsugu Maedaa, Satoshi Kounoa a
Department of Obstetrics and Gynecology, Kagoshima City Hospital, Kagoshima, Japan Department of Obstetrics and Gynecology, Tokyo Women’s Medical University, Kawada-cho, 8-1 Shinjuku-ku, Tokyo 162-8666, Japan
b
Received 4 March 2002; received in revised form 21 May 2002; accepted 5 June 2002
Abstract Objective: Our purpose was to determine the critical period for non-reassuring fetal heart rate (FHR) patterns in preterm gestation in predicting fetal acidosis (umbilical arterial pH <7.1) at birth. Study design: A prospective descriptive study was performed. We reviewed the FHR pattern and umbilical blood gas level measurements, and investigated the correlations between non-reassuring FHR patterns and umbilical arterial pH. Results: There was a significant difference in the frequency of fetal acidosis between the neonatal death and survival groups (5/13 versus 30/759, P ¼ 0:0001). Umbilical pH values in fetuses with persistent late deceleration with loss of variability (7:15 0:11, P < 0:01) and in those with prolonged deceleration (7:17 0:16, P < 0:01) were significantly lower than in fetuses with reassuring FHR patterns (7:29 0:06). Fetal acidosis also occurred more often in these two groups. The critical periods for late deceleration with loss of variability and for prolonged deceleration were 60 and 30 min, respectively. Conclusion: These data indicate that a critical period for nonreassuring FHR patterns in preterm gestation exists. Prompt delivery is required within that short critical period. # 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Non-reassuring fetal heart rate (FHR) pattern; Preterm fetus; Umbilical pH
1. Introduction In spite of recent dramatic progress in neonatal care, the prognosis for preterm infants is still worse than that for term infants. The preterm fetus is more likely not only to be exposed to hypoxia, but also to develop and die from the most common and serious complications of prematurity if born acidemic and/or acidotic [1]. The diagnostic criteria for fetal heart rate (FHR) monitoring used in term fetuses [2] were previously considered inappropriate for preterm fetuses, although Parer stressed that they can also be used for preterm fetuses [3]. Although the Apgar scores of preterm infants may be significantly lower than those of term infants [4], the blood pH value and acid–base status are similar [5–7]. Important differences, however, are that the premature fetus can rapidly develop abnormal patterns and that these patterns tend to progress in severity much more rapidly than in the term fetus [3]. There are few data available on the correlation between the time from the detection of a non-reassuring FHR pattern to delivery and the development of fetal * Corresponding author. Tel.: þ81-3-3353-8111; fax: þ81-3-5269-7350. E-mail address: [email protected] (Y. Matsuda).
acidosis. We have investigated the critical period in preterm gestation to predict abnormal blood pH at birth when nonreassuring FHR patterns are observed.
2. Patients and methods The approval of the Institutional Review Board was obtained before the start of this prospective descriptive study. A review was conducted of the medical records of mothers and neonates from all live singleton births at between 26 and 36 weeks of gestation at the Perinatal Medical Center, Kagoshima City Hospital, between 1 January 1992 and 31 December 1999. Gestational age was determined based on the date of the last menstrual period and standard obstetric ultrasonography. Details of diagnosis and management were also recorded. There were no changes in either maternal or neonatal management protocols during this study period. FHR was monitored for at least 2 h before delivery using a Corometrics 116 Fetal Monitor (Atom Medical, Tokyo, Japan). FHR patterns were defined as non-reassuring when one of the following was detected: persistent late deceleration, recurrent severe variable deceleration, prolonged deceleration, or loss
0301-2115/02/$ – see front matter # 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S 0 3 0 1 - 2 1 1 5 ( 0 2 ) 0 0 2 1 2 - 9
Y. Matsuda et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 106 (2003) 36–39
37
Fig. 1. An example of persistent late deceleration with loss of variability in a fetus who was born from the mother with severe preeclampsia at 31 weeks of gestation. Apgar score was 4 and 8 at 1 and 5 min, respectively. Umbilical arterial pH was 7.03.
of variability [2]. Those patterns indicate non-reassuring status in full-term fetuses and are also used for the assessment of preterm fetuses [3]. The fetuses were delivered because of the onset of active labor, non-reassuring fetal status, maternal indications, etc. Cesarean delivery was performed based on standard indications [8]. At delivery, the umbilical cord was isolated by double clamping. Then 0.2 ml of arterial blood was collected on ice for blood gas analysis using a Radiometer ABL-2 blood gas analyzer (Radiometer Co., Copenhagen, Denmark) [9]. The
critical level of umbilical arterial pH (low pH) was defined as less than 7.1 [6,8]. The results are expressed as mean S:D. Statistical analysis was carried out using the Chi-square test, Fisher’s exact probability test, and the Mann–Whitney test. P values of less than 0.05 were considered significant. In order to clarify the critical period, the relationship between the time from the appearance of non-reassuring FHR patterns to delivery and pH at delivery was investigated. We have set the following four periods: 15, 30, 60, and 90 min.
Fig. 2. An example of prolonged deceleration in a fetus who was born from the mother with preterm premature rupture of the membranes at 28 weeks of gestation. Apgar score was 5 and 8 at 1 and 5 min, respectively. Umbilical arterial pH was 7.08.
38
Y. Matsuda et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 106 (2003) 36–39
Table 1 Umbilical cord blood pH and blood gas values in preterm gestation
Reassuring FHR Non-reassuring FHR L/D with LOV PD Severe V/D L/D
Cases
pH
pO2 (mmHg)
pCO2 (mmHg)
BE (meq./l)
pH <7.1 (%)
591
7.29 0.06
24.7 8.0
48.1 8.8
3.2 2.8
17 (2.9)
7.8 7.3 4.9 3.6
7 11 0 0
29 48 29 75
7.15 7.17 7.29 7.29
0.11 0.16 0.06 0.06
18.2 22.2 27.6 20.2
2.7 8.1 10.1 6.5
60.0 58.6 49.4 55.7
11.9 19.8 11.7 7.6
5.4 6.2 3.5 2.6
(24.1) (22.9) (0) (0)
L/D: late deceleration, LOV: loss of variability, PD: prolonged deceleration, V/D: variable deceleration.
Table 2 Prediction of fetal acidosis (pH <7.1) in late deceleration with loss of variability and prolonged deceleration Sensitivity n
Specificity %
Positive predictive value
Negative predictive value
n
%
n
%
Diagnostic efficacy
n
%
Late deceleration with loss of variability <15 mm 0 – <30 mm 2/7 28.6 <60 mm 6/7 85.7 <90 mm 7/7 100
0 19/22 15/22 10/22
– 86.4 68.2 45.5
0 2/5 6/13 7/19
– 40.0 46.2 36.8
0 19/24 15/16 10/10
– 79.2 93.8 100
– 0.25 0.58 0.45
Prolonged deceleration <15 mm 4/11 <30 mm 9/11 <60 mm 10/11 <90 mm 11/11
28/37 21/37 14/37 6/37
75.7 56.8 37.8 16.2
4/13 9/25 10/33 11/42
30.8 36.0 30.3 26.2
28/35 21/23 14/15 6/6
75.7 91.3 93.3 100
0.28 0.46 0.34 0.16
36.4 81.8 90.9 100
3. Results During the study period, there was a total of 772 preterm births. Low pH values were observed in 35 cases (4.5%). There was a significant difference in the frequency of fetal acidosis between the neonatal death and survival groups (5/13 versus 30/759, P ¼ 0:0001). Non-reassuring FHR patterns were observed in 181 cases (23.4%), consisting of persistent late deceleration with loss of variability (Fig. 1, n ¼ 29), prolonged deceleration (Fig. 2, n ¼ 48), recurrent severe variable deceleration (n ¼ 29), and persistent late deceleration (n ¼ 75) (Table 1). The umbilical arterial blood gas level and pH were compared in fetuses with reassuring and non-reassuring FHR patterns (Table 1). The relationship between non-reassuring FHR patterns and umbilical arterial pH was also investigated. Umbilical arterial pH values in persistent late deceleration with loss of variability (7:15 0:11, P < 0:01) and prolonged deceleration (7:17 0:16, P < 0:01) were significantly lower than in the reassuring FHR pattern group (7:29 0:06). Fetal acidosis developed more frequently in fetuses with persistent late deceleration with loss of variability (24.1%) and with prolonged deceleration (22.9%) than in those with other non-reassuring FHR patterns or with reassuring FHR patterns (2.9%). The critical period from the appearance of non-reassuring FHR to delivery in terms of low pH prediction was examined.
Table 2 shows the diagnostic efficacy of late deceleration with loss of variability and of prolonged deceleration in predicting abnormal umbilical arterial pH. Four periods were used to compare the sensitivity, specificity, positive predictive value, and negative predictive value of fetal acidemia. In terms of diagnostic efficacy (sensitivity specificity), 60 min was superior to 30 and 90 min in cases of late deceleration with loss of variability (P ¼ 0:026, 0.569, and 0.063, respectively). On the other hand, 30 min was superior to 15, 60, and 90 min in cases of prolonged deceleration (P ¼ 0:039, 0.458, 0.136, and 0.313, respectively).
4. Discussion There now seems little doubt that the same FHR monitoring criteria used for term fetuses can be used for premature fetuses [10,11]. Important differences, however, are that premature fetuses can quickly develop abnormal heart rate patterns and that these patterns tend to progress in severity much more rapidly than in term fetuses [12]. Some fetuses are unusually susceptible to the effects of antepartum/intrapartum hypoxemia, such as those delivered prematurely. In those circumstances, hypoxia tends to progress more rapidly and is more likely to cause or aggravate metabolic acidemia, which, in extreme cases, correlates with poor short-term, as
Y. Matsuda et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 106 (2003) 36–39
well as long-term outcome. In severe cases, hypoxia may lead to death [13]. Therefore, it is very important to intervene promptly when a premature fetus exhibits heart rate abnormalities in the antepartum/intrapartum period. Traditionally, fetal acidosis has been defined as an umbilical artery blood pH of less than 7.20 [14]. However, most newborns with acidosis at this pH value will be vigorous at birth, with normal Apgar scores, and manifest no obvious neurologic sequelae [15]. Therefore, some investigators have recommended that pH concentration of two standard deviations below the mean pH should be used to define significant fetal acidosis [16]. In the present study, focusing specifically on preterm infants, there was a strong correlation between neonatal death and pH of less than 7.10, as previously reported by Dickinson et al. [6]. It has been believed that intervention should be performed as soon as possible when non-reassuring FHR patterns appear in a preterm fetus. However, recommendations on the time interval were lacking. Our results show that critical period in cases of prolonged deceleration was shorter than that in cases of late deceleration. As cholinergic responses in the immature fetus are decreased [17], even minimal or transient bradycardia may represent a more ominous change in them. There are several limitations to consider in the correct interpretation of the present results. First, the major limitation of our study is that it was based on a relatively small number of patients. Although the incidence of fetal acidosis is very low, this result should be confirmed in a larger series using the same protocol. Second, differing from the classic study by Kubli et al. [18], the pH value of umbilical arterial blood at the time of appearance of non-reassuring FHR patterns was not known. They performed fetal scalp blood sampling and described the relationship between the pH value and several FHR patterns. In the present study, scalp sampling and percutaneous umbilical blood sampling were not performed, because these procedures were not routine clinical practice for the management of preterm fetuses in our institutions. In addition, the natural course of these nonreassuring FHR patterns was not observed, because several interventions were performed from the time of appearance to delivery, such as oxygen administration, discontinuation of drugs, etc. In spite of the limitations, it has been clarified that in the preterm fetus, the presence of acidemia is strongly correlated with non-reassuring FHR patterns as well as to neonatal prognosis. As in the term fetus, both persistent late deceleration with loss of variability and prolonged deceleration predict low blood pH. In addition, a critical time
39
exists from the appearance of abnormal FHR to delivery to predict abnormal blood pH. References [1] Freeman RK, Garite TJ, Nageotte MP. Diagnosis and management of fetal distress in premature gestation in fetal heart rate monitoring. 2nd ed. Baltimore: Williams & Wilkins, 1991. p. 143–55. [2] ACOG Technical Bulletin. Fetal heart rate patterns: monitoring, interpretation, and management. Number 207. Int J Gynaecol Obstet 1995;51(1):65–74. [3] Parer JT. Handbook of fetal heart rate monitoring. Philadelphia: Saunders, 1983. p. 85–123. [4] Goldenberg RL, Huddleston JF, Nelson KG. Apgar scores and umbilical artery pH in preterm infants. Am J Obstet Gynecol 1984;149:651–4. [5] Ramin SM, Gilstrap III LC, Hauth JC, Widmer K. Umbilical artery acid–base status in the preterm infant. Am J Obstet Gynecol 1994;170:1705–12. [6] Dickinson JE, Eriksen NL, Meyer BA, Parisi VM. The effect of preterm birth on umbilical cord blood gases. Obstet Gynecol 1992;79:575–8. [7] Riley RJ, Johnson JWC. Collecting and analyzing cord blood gases. Clin Obstet Gynecol 1993;36:13–23. [8] Matsuda Y, Kouno S, Hiroyama Y, et al. Intrauterine infection, magnesium sulfate exposure and cerebral palsy in infants born between 26 and 30 weeks of gestation. Eur J Obstet Gynecol Reprod Biol 2000;91:159–64. [9] Winkler CL, Hauth JC, Tucker JM, Owen J, Brumfield CG. Neonatal complications as term, as related to the degree of umbilical artery acidemia. Am J Obstet Gynecol 1991;164:637–41. [10] Bowes WA, Gabbe SG, Bowes C. Fetal heart rate monitoring in premature infants weighing 1500 grams or less. Am J Obstet Gynecol 1980;137:791. [11] Zanini B, Paul RH, Huey JR. Intrapartum fetal heart rate: correlation with scalp pH in the preterm fetus. Am J Obstet Gynecol 1980;136:43. [12] Parer JT. Fetal heart rate. In: Creasy RK, Resnik R, editors. Maternal–fetal medicine. 4th ed. Philadelphia: Saunders, 1999. p. 290. [13] Westgren LMR, Malcus P, Svenningsen NW. Intrauterine asphyxia and long-term outcome in preterm fetuses. Obstet Gynecol 1986;67:512–6. [14] Wible JL, Petrie RH, Koons A, Perez A. The clinical use of umbilical cord acid-base determinations in perinatal surveillance and management. Clin Perinatol 1982;9:387–97. [15] Winkler CL, Hauth JC, Tucker JM, Owen J, Brumfield CG. Neonatal complications at term as related to the degree of umbilical artery acidemia. Am J Obstet Gynecol 1991;164:637–41. [16] Thorp JA, Sampson JE, Parisi VM, Creasy RK. Routine umbilical cord blood gas determinations? Am J Obstet Gynecol 1989;161:600–5. [17] Assali N, Brinkman C, Woods J, Dandavino A, Nuwayhid B. Development of neurohormonal control of fetal, neonatal, and adult cardiovascular functions. Am J Obstet Gynecol 1977;129:748–59. [18] Kubli FW, Hon EH, Khazin AF, Takemura H. Observation on heart rate and pH in the human fetus during labor. Am J Obstet Gynecol 1969;104:1190–206.
The critical period of non-reassuring fetal heart rate patterns in preterm gestation Yoshio Matsudaa,b,*, Takatsugu Maedaa, Satoshi Kounoa a
Department of Obstetrics and Gynecology, Kagoshima City Hospital, Kagoshima, Japan Department of Obstetrics and Gynecology, Tokyo Women’s Medical University, Kawada-cho, 8-1 Shinjuku-ku, Tokyo 162-8666, Japan
b
Received 4 March 2002; received in revised form 21 May 2002; accepted 5 June 2002
Abstract Objective: Our purpose was to determine the critical period for non-reassuring fetal heart rate (FHR) patterns in preterm gestation in predicting fetal acidosis (umbilical arterial pH <7.1) at birth. Study design: A prospective descriptive study was performed. We reviewed the FHR pattern and umbilical blood gas level measurements, and investigated the correlations between non-reassuring FHR patterns and umbilical arterial pH. Results: There was a significant difference in the frequency of fetal acidosis between the neonatal death and survival groups (5/13 versus 30/759, P ¼ 0:0001). Umbilical pH values in fetuses with persistent late deceleration with loss of variability (7:15 0:11, P < 0:01) and in those with prolonged deceleration (7:17 0:16, P < 0:01) were significantly lower than in fetuses with reassuring FHR patterns (7:29 0:06). Fetal acidosis also occurred more often in these two groups. The critical periods for late deceleration with loss of variability and for prolonged deceleration were 60 and 30 min, respectively. Conclusion: These data indicate that a critical period for nonreassuring FHR patterns in preterm gestation exists. Prompt delivery is required within that short critical period. # 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Non-reassuring fetal heart rate (FHR) pattern; Preterm fetus; Umbilical pH
1. Introduction In spite of recent dramatic progress in neonatal care, the prognosis for preterm infants is still worse than that for term infants. The preterm fetus is more likely not only to be exposed to hypoxia, but also to develop and die from the most common and serious complications of prematurity if born acidemic and/or acidotic [1]. The diagnostic criteria for fetal heart rate (FHR) monitoring used in term fetuses [2] were previously considered inappropriate for preterm fetuses, although Parer stressed that they can also be used for preterm fetuses [3]. Although the Apgar scores of preterm infants may be significantly lower than those of term infants [4], the blood pH value and acid–base status are similar [5–7]. Important differences, however, are that the premature fetus can rapidly develop abnormal patterns and that these patterns tend to progress in severity much more rapidly than in the term fetus [3]. There are few data available on the correlation between the time from the detection of a non-reassuring FHR pattern to delivery and the development of fetal * Corresponding author. Tel.: þ81-3-3353-8111; fax: þ81-3-5269-7350. E-mail address: [email protected] (Y. Matsuda).
acidosis. We have investigated the critical period in preterm gestation to predict abnormal blood pH at birth when nonreassuring FHR patterns are observed.
2. Patients and methods The approval of the Institutional Review Board was obtained before the start of this prospective descriptive study. A review was conducted of the medical records of mothers and neonates from all live singleton births at between 26 and 36 weeks of gestation at the Perinatal Medical Center, Kagoshima City Hospital, between 1 January 1992 and 31 December 1999. Gestational age was determined based on the date of the last menstrual period and standard obstetric ultrasonography. Details of diagnosis and management were also recorded. There were no changes in either maternal or neonatal management protocols during this study period. FHR was monitored for at least 2 h before delivery using a Corometrics 116 Fetal Monitor (Atom Medical, Tokyo, Japan). FHR patterns were defined as non-reassuring when one of the following was detected: persistent late deceleration, recurrent severe variable deceleration, prolonged deceleration, or loss
0301-2115/02/$ – see front matter # 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S 0 3 0 1 - 2 1 1 5 ( 0 2 ) 0 0 2 1 2 - 9
Y. Matsuda et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 106 (2003) 36–39
37
Fig. 1. An example of persistent late deceleration with loss of variability in a fetus who was born from the mother with severe preeclampsia at 31 weeks of gestation. Apgar score was 4 and 8 at 1 and 5 min, respectively. Umbilical arterial pH was 7.03.
of variability [2]. Those patterns indicate non-reassuring status in full-term fetuses and are also used for the assessment of preterm fetuses [3]. The fetuses were delivered because of the onset of active labor, non-reassuring fetal status, maternal indications, etc. Cesarean delivery was performed based on standard indications [8]. At delivery, the umbilical cord was isolated by double clamping. Then 0.2 ml of arterial blood was collected on ice for blood gas analysis using a Radiometer ABL-2 blood gas analyzer (Radiometer Co., Copenhagen, Denmark) [9]. The
critical level of umbilical arterial pH (low pH) was defined as less than 7.1 [6,8]. The results are expressed as mean S:D. Statistical analysis was carried out using the Chi-square test, Fisher’s exact probability test, and the Mann–Whitney test. P values of less than 0.05 were considered significant. In order to clarify the critical period, the relationship between the time from the appearance of non-reassuring FHR patterns to delivery and pH at delivery was investigated. We have set the following four periods: 15, 30, 60, and 90 min.
Fig. 2. An example of prolonged deceleration in a fetus who was born from the mother with preterm premature rupture of the membranes at 28 weeks of gestation. Apgar score was 5 and 8 at 1 and 5 min, respectively. Umbilical arterial pH was 7.08.
38
Y. Matsuda et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 106 (2003) 36–39
Table 1 Umbilical cord blood pH and blood gas values in preterm gestation
Reassuring FHR Non-reassuring FHR L/D with LOV PD Severe V/D L/D
Cases
pH
pO2 (mmHg)
pCO2 (mmHg)
BE (meq./l)
pH <7.1 (%)
591
7.29 0.06
24.7 8.0
48.1 8.8
3.2 2.8
17 (2.9)
7.8 7.3 4.9 3.6
7 11 0 0
29 48 29 75
7.15 7.17 7.29 7.29
0.11 0.16 0.06 0.06
18.2 22.2 27.6 20.2
2.7 8.1 10.1 6.5
60.0 58.6 49.4 55.7
11.9 19.8 11.7 7.6
5.4 6.2 3.5 2.6
(24.1) (22.9) (0) (0)
L/D: late deceleration, LOV: loss of variability, PD: prolonged deceleration, V/D: variable deceleration.
Table 2 Prediction of fetal acidosis (pH <7.1) in late deceleration with loss of variability and prolonged deceleration Sensitivity n
Specificity %
Positive predictive value
Negative predictive value
n
%
n
%
Diagnostic efficacy
n
%
Late deceleration with loss of variability <15 mm 0 – <30 mm 2/7 28.6 <60 mm 6/7 85.7 <90 mm 7/7 100
0 19/22 15/22 10/22
– 86.4 68.2 45.5
0 2/5 6/13 7/19
– 40.0 46.2 36.8
0 19/24 15/16 10/10
– 79.2 93.8 100
– 0.25 0.58 0.45
Prolonged deceleration <15 mm 4/11 <30 mm 9/11 <60 mm 10/11 <90 mm 11/11
28/37 21/37 14/37 6/37
75.7 56.8 37.8 16.2
4/13 9/25 10/33 11/42
30.8 36.0 30.3 26.2
28/35 21/23 14/15 6/6
75.7 91.3 93.3 100
0.28 0.46 0.34 0.16
36.4 81.8 90.9 100
3. Results During the study period, there was a total of 772 preterm births. Low pH values were observed in 35 cases (4.5%). There was a significant difference in the frequency of fetal acidosis between the neonatal death and survival groups (5/13 versus 30/759, P ¼ 0:0001). Non-reassuring FHR patterns were observed in 181 cases (23.4%), consisting of persistent late deceleration with loss of variability (Fig. 1, n ¼ 29), prolonged deceleration (Fig. 2, n ¼ 48), recurrent severe variable deceleration (n ¼ 29), and persistent late deceleration (n ¼ 75) (Table 1). The umbilical arterial blood gas level and pH were compared in fetuses with reassuring and non-reassuring FHR patterns (Table 1). The relationship between non-reassuring FHR patterns and umbilical arterial pH was also investigated. Umbilical arterial pH values in persistent late deceleration with loss of variability (7:15 0:11, P < 0:01) and prolonged deceleration (7:17 0:16, P < 0:01) were significantly lower than in the reassuring FHR pattern group (7:29 0:06). Fetal acidosis developed more frequently in fetuses with persistent late deceleration with loss of variability (24.1%) and with prolonged deceleration (22.9%) than in those with other non-reassuring FHR patterns or with reassuring FHR patterns (2.9%). The critical period from the appearance of non-reassuring FHR to delivery in terms of low pH prediction was examined.
Table 2 shows the diagnostic efficacy of late deceleration with loss of variability and of prolonged deceleration in predicting abnormal umbilical arterial pH. Four periods were used to compare the sensitivity, specificity, positive predictive value, and negative predictive value of fetal acidemia. In terms of diagnostic efficacy (sensitivity specificity), 60 min was superior to 30 and 90 min in cases of late deceleration with loss of variability (P ¼ 0:026, 0.569, and 0.063, respectively). On the other hand, 30 min was superior to 15, 60, and 90 min in cases of prolonged deceleration (P ¼ 0:039, 0.458, 0.136, and 0.313, respectively).
4. Discussion There now seems little doubt that the same FHR monitoring criteria used for term fetuses can be used for premature fetuses [10,11]. Important differences, however, are that premature fetuses can quickly develop abnormal heart rate patterns and that these patterns tend to progress in severity much more rapidly than in term fetuses [12]. Some fetuses are unusually susceptible to the effects of antepartum/intrapartum hypoxemia, such as those delivered prematurely. In those circumstances, hypoxia tends to progress more rapidly and is more likely to cause or aggravate metabolic acidemia, which, in extreme cases, correlates with poor short-term, as
Y. Matsuda et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 106 (2003) 36–39
well as long-term outcome. In severe cases, hypoxia may lead to death [13]. Therefore, it is very important to intervene promptly when a premature fetus exhibits heart rate abnormalities in the antepartum/intrapartum period. Traditionally, fetal acidosis has been defined as an umbilical artery blood pH of less than 7.20 [14]. However, most newborns with acidosis at this pH value will be vigorous at birth, with normal Apgar scores, and manifest no obvious neurologic sequelae [15]. Therefore, some investigators have recommended that pH concentration of two standard deviations below the mean pH should be used to define significant fetal acidosis [16]. In the present study, focusing specifically on preterm infants, there was a strong correlation between neonatal death and pH of less than 7.10, as previously reported by Dickinson et al. [6]. It has been believed that intervention should be performed as soon as possible when non-reassuring FHR patterns appear in a preterm fetus. However, recommendations on the time interval were lacking. Our results show that critical period in cases of prolonged deceleration was shorter than that in cases of late deceleration. As cholinergic responses in the immature fetus are decreased [17], even minimal or transient bradycardia may represent a more ominous change in them. There are several limitations to consider in the correct interpretation of the present results. First, the major limitation of our study is that it was based on a relatively small number of patients. Although the incidence of fetal acidosis is very low, this result should be confirmed in a larger series using the same protocol. Second, differing from the classic study by Kubli et al. [18], the pH value of umbilical arterial blood at the time of appearance of non-reassuring FHR patterns was not known. They performed fetal scalp blood sampling and described the relationship between the pH value and several FHR patterns. In the present study, scalp sampling and percutaneous umbilical blood sampling were not performed, because these procedures were not routine clinical practice for the management of preterm fetuses in our institutions. In addition, the natural course of these nonreassuring FHR patterns was not observed, because several interventions were performed from the time of appearance to delivery, such as oxygen administration, discontinuation of drugs, etc. In spite of the limitations, it has been clarified that in the preterm fetus, the presence of acidemia is strongly correlated with non-reassuring FHR patterns as well as to neonatal prognosis. As in the term fetus, both persistent late deceleration with loss of variability and prolonged deceleration predict low blood pH. In addition, a critical time
39
exists from the appearance of abnormal FHR to delivery to predict abnormal blood pH. References [1] Freeman RK, Garite TJ, Nageotte MP. Diagnosis and management of fetal distress in premature gestation in fetal heart rate monitoring. 2nd ed. Baltimore: Williams & Wilkins, 1991. p. 143–55. [2] ACOG Technical Bulletin. Fetal heart rate patterns: monitoring, interpretation, and management. Number 207. Int J Gynaecol Obstet 1995;51(1):65–74. [3] Parer JT. Handbook of fetal heart rate monitoring. Philadelphia: Saunders, 1983. p. 85–123. [4] Goldenberg RL, Huddleston JF, Nelson KG. Apgar scores and umbilical artery pH in preterm infants. Am J Obstet Gynecol 1984;149:651–4. [5] Ramin SM, Gilstrap III LC, Hauth JC, Widmer K. Umbilical artery acid–base status in the preterm infant. Am J Obstet Gynecol 1994;170:1705–12. [6] Dickinson JE, Eriksen NL, Meyer BA, Parisi VM. The effect of preterm birth on umbilical cord blood gases. Obstet Gynecol 1992;79:575–8. [7] Riley RJ, Johnson JWC. Collecting and analyzing cord blood gases. Clin Obstet Gynecol 1993;36:13–23. [8] Matsuda Y, Kouno S, Hiroyama Y, et al. Intrauterine infection, magnesium sulfate exposure and cerebral palsy in infants born between 26 and 30 weeks of gestation. Eur J Obstet Gynecol Reprod Biol 2000;91:159–64. [9] Winkler CL, Hauth JC, Tucker JM, Owen J, Brumfield CG. Neonatal complications as term, as related to the degree of umbilical artery acidemia. Am J Obstet Gynecol 1991;164:637–41. [10] Bowes WA, Gabbe SG, Bowes C. Fetal heart rate monitoring in premature infants weighing 1500 grams or less. Am J Obstet Gynecol 1980;137:791. [11] Zanini B, Paul RH, Huey JR. Intrapartum fetal heart rate: correlation with scalp pH in the preterm fetus. Am J Obstet Gynecol 1980;136:43. [12] Parer JT. Fetal heart rate. In: Creasy RK, Resnik R, editors. Maternal–fetal medicine. 4th ed. Philadelphia: Saunders, 1999. p. 290. [13] Westgren LMR, Malcus P, Svenningsen NW. Intrauterine asphyxia and long-term outcome in preterm fetuses. Obstet Gynecol 1986;67:512–6. [14] Wible JL, Petrie RH, Koons A, Perez A. The clinical use of umbilical cord acid-base determinations in perinatal surveillance and management. Clin Perinatol 1982;9:387–97. [15] Winkler CL, Hauth JC, Tucker JM, Owen J, Brumfield CG. Neonatal complications at term as related to the degree of umbilical artery acidemia. Am J Obstet Gynecol 1991;164:637–41. [16] Thorp JA, Sampson JE, Parisi VM, Creasy RK. Routine umbilical cord blood gas determinations? Am J Obstet Gynecol 1989;161:600–5. [17] Assali N, Brinkman C, Woods J, Dandavino A, Nuwayhid B. Development of neurohormonal control of fetal, neonatal, and adult cardiovascular functions. Am J Obstet Gynecol 1977;129:748–59. [18] Kubli FW, Hon EH, Khazin AF, Takemura H. Observation on heart rate and pH in the human fetus during labor. Am J Obstet Gynecol 1969;104:1190–206.