Meconium-stained amniotic fluid—Perinatal outcome and obstetrical management in a low-risk suburban population

European Journal of Obstetrics & Gynecology and Reproductive Biology 132 (2007) 46–50 www.elsevier.com/locate/ejogrb

Meconium-stained amniotic fluid—Perinatal outcome and obstetrical management in a low-risk suburban population Sven Becker *, Erich Solomayer, Cemal Dogan, Diethelm Wallwiener, Tanja Fehm Universita¨tsfrauenklinik Tu¨bingen, Tu¨bingen University Medical Center, Calwerstr. 7, 72076 Tu¨bingen, Germany Received 7 December 2005; received in revised form 3 May 2006; accepted 24 May 2006

Abstract Objective: To determine whether amniotic fluid (MSAF) affects obstetrical interventions and immediate perinatal outcome in a low-risk suburban population. Study design: A retrospective cohort study examined 11,226 deliveries at Tu¨bingen University Hospital (1998–2003). Thousand one hundred and twenty-three women (10%) had MSAF during labor. A control group of matched pairs was created, assigning to each patient the next woman that gave birth without MSAF. Exclusion criteria were: gestational age less than 37 + 0 weeks, primary Cesarean (C-)section, multiple gestation, severe maternal disease, preeclampsia and fetal malformations. Results: Only small differences were noted between the meconium and non-meconium groups with regard to arterial pH and Apgar scores: mean arterial-pH was 7.26 (0.7) for both. Five minutes Apgar scores <6 occurred in 0.9% versus 0.4%. Obstetrical interventions were more common in the meconium group: C-section rates were 17.4% versus 9.6%, vaginal operative delivery rates 13.9% versus 6.2% and scalp pH rates 9.5% versus 3.7%, respectively. Conclusions: In a low-risk suburban population the effect of MSAF on the newborn during the immediate postpartum period was small. However, obstetrical management was significantly effected by the presence of MSAF, possibly reflecting a combination of more difficult labor and a lower threshold for obstetric intervention. # 2006 Elsevier Ireland Ltd. All rights reserved. Keywords: Meconium; Suburban population; Perinatal outcome; Obstetrical management

1. Introduction Over the past 30 years, the introduction and widespread availability of fetal surveillance technologies such as ultrasound, Doppler-ultrasound, fetal heart rate monitoring, fetal scalp pH and the biophysical profile have fundamentally altered peripartum obstetrical management [1–4]. Prior to this period the clinician was limited to direct auscultation of the fetal heart rate and evaluation of the amniotic fluid [5]. The presence of meconium-stained amniotic fluid (MSAF) was generally considered an important negative indicator of fetal status [6]. Based on observational and experimental evidence, the hypoxia theory of MSAF was created: acute hypoxic events would lead to parasympathetic stimulation of * Corresponding author. Tel.: +49 7071 2982211; fax: +49 7071 295381. E-mail address: [email protected] (S. Becker).

the fetal bowel, followed by premature, ‘‘stress’’-related bowel movements into the amniotic fluid [7,8]. Despite this pathophysiologically plausible explanation, it has always been noted that the vast majority of infants born with MSAF showed neither short-term nor long-term impairments [9]. The literature offers different views on short-term perinatal outcome with MSAF, with most studies showing a link with low Apgar-scores and decreased arterial cord pH values [10– 12] and some studies showing no correlation [13]. However, many of the studies were conducted over a decade ago or looked at populations from very specific ethnic and socioeconomic backgrounds [14,15]. Both with regard to their risk-status and to the peripartum management, these groups might not reflect today’s typical suburban population that makes up the majority of North American and European maternity patients. MSAF today continues to pose two unresolved problems: What is its significance for the

0301-2115/$ – see front matter # 2006 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ejogrb.2006.05.032

S. Becker et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 132 (2007) 46–50

obstetrician managing the laboring patient and how should the infant be managed in the immediate postpartum period. Looking at a typical low-risk suburban population, we wanted to revisit the first of these questions.

2. Materials and methods A retrospective cohort study was conducted looking at 11226 women who gave birth at the Tu¨bingen University Hospital between 1998 and 2003. Using the in-house perinatal data base, 1123 patients (10.0%) with the diagnosis of MSAF were identified that fullfilled inclusion and exclusion criteria. Inclusion criteria were singleton pregnancy, cephalic presentation, gestational age <36 + 6 weeks (term) and trial of vaginal birth. Exclusion criteria were twin or triplet gestations, non-cephalic presentation, primary C-section, severe maternal disease, preeclampsia, fetal malformations and gestational age <37 + 0 weeks. For the control group, the next women giving birth following the index patient who satisfied the same set of ex- and inclusion criteria and did not have MSAF was selected. A total of 2246 patients were available for analysis. Data obtained included maternal age, parity, gestational age, mode of delivery, use of peridural analgesia, augmentation of labor with oxytocin and fetal scalp pH as well as data regarding fetal sex, weight, Apgar values and arterial and venous cordpH. All patients received the same standardized in-house obstetrical care which included fetal heart rate monitoring at admission, intermittently in early labor and continuously after cervical dilatation beyond 5 cm and during the second stage. Peridural anesthesia was available at request and was neither encouraged nor discouraged. Fetal scalp pHdetermination is available at all times. C-section can be performed with a minimal delay of 10–15 min if necessary and vaginal operative deliveries were performed as indicated by fetal heart rate tracings or failure to progress with the head at a minimum of +2 station. The presence of meconium was noted but did not prompt special intrapartum intervention such as amnioinfusion. The literature regarding this procedure remains controversial [16,17]. All deliveries with MSAF were attended by a pediatrician. Standard treatment includes suctioning of the infant’s nose and mouth on the perineum if possible and immediate transfer to the pediatrician, who performs oropharyngeal suctioning and laryngoscopy to determine meconiumpresence at or below the cords. Chi-square test and Fisher’s exact test were used to examine the relationship between the presence of MSAF and categorical parameters. The binary logistic regression method was used to identify independent predictors for poor clinical outcome based on pH < 7.2. The variables were entered stepwise forward. Statistical analysis was performed by SPSS (Version 11.5). P-values less than 0.05 were considered statistically significant. Differences of non-categorical variables were evaluated by the Mann–Whitney test.

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Table 1 Maternal and basic obstetric data, MSAF group vs. control group (mean, standard deviation (S.D.)) MSAF

Control

Total Maternal age Parity Nulliparity Gestational age

1123 29.9 (5) 1.7 51% 40.3 (1.0)

1123 29.9 (5) 1.8 42% 39.9 (1.1)

P-value

<0.01 <0.01

Peridural anesthesia Labor augmentation Scalp pH

34.7% 39.4% 9.5%

19.5% 29.7% 3.7%

<0.01 <0.01 <0.01

Vaginal operative C-section

13.9% 17.4%

6.2% 9.6%

<0.01 <0.01

n.s.

3. Results Basic patient characteristics of the 1123 women with MSAF and the matched 1123 women of the control group, including data on obstetrical interventions are shown in Table 1. The total rate of women with MSAF was 10.0%. Statistically significant differences were noted with regard to gestational age and parity: MSAF is more common in nulliparous women and its frequency increases with advanced gestational age. All forms of obstetrical intervention occurred more frequently in the MSAF group, including scalp pH-sampling. Looking at the operative delivery groups (C-section/vaginal operative delivery), we find that 16% of the MSAF-infants that subsequently underwent an operative delivery had had scalp pH-sampling, compared with only 9% of those that had an operative delivery in the in the clearfluid group. Immediate perinatal fetal outcome is shown in Table 2. We noted no difference in overall mean arterial pH. Furthermore, no statistically relevant difference was noted looking at defined subgroups of categorized Apgar-values (0–3, 4–6, 7–10) and pH-values (<7.0, 7.0–7.19, <7.20). We also calculated p-values for non-categorized pH-values and non-categorizes Apgar-values. There was no statistical difference between pH-values (P = 0.328), however a Pvalue of 0.001 was found for Apgar-scores. This means, while the categories of 5-min Apgar scores 1–3, 4–6 and 7– 10 are no different in the MSAF group versus the clear fluid group, within for instance the 7–10 category, there are more Table 2 Perinatal fetal outcome MSAF

Control

P-value

Birth weight

3500 g (462 g)

3447 g (456 g)

<0.01

Apgar 5 min 0–3 4–6 7–10

– 10 (0.9%) 1113 (99.1%)

– 4 (0.4%) 1119 (99.6%)

0.108

Arterial chord pH <7.00 7.0–7.19 <7.20

7.26 (0.7) 2 (0.2%) 165 (14.8%) 942 (84.9%)

7.26 (0.07) 1 (0.1%) 150 (13.6%) 952 (86.3%)

0.328

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Table 3 Subgroup-analysis ‘post-term’: 40 + 0–42 + 0 weeks of gestation MSAF (N = 789)

Control (n = 623)

P-value

Birth weight

3565 g (453 g)

3581 (437)

0.356

Apgar 5 min 0–3 4–6 7–10

– 7 (0.9%) 782 (99.1)

– 2 (0.3%) 621 (99.7)

0.184

– 85 (13.8%) 529 (86.2%)

0.517

Arterial chord pH <7.0 1 (0.1%) 7.0–7.19 119 (15.2%) <7.20 661 (84.6%)

infants with Apgars 7 or 8 in the MSAF group and more infants with Apgars 9 or 10 in the clear fluid group. Due to technical difficulties, arterial pH-values were not available for 34/2246 patients (1.5%, 14 from meconium group, 20 from control group). The 5 min Apgar-values of these 34 patients were all in the 7–10 groups. Infants in the MSAF group were heavier, however, this mostly reflects more advanced gestational age. Table 3 looks at the perinatal data of pregnancies that went beyond 39 + 6 weeks. In this subgroup, differences between the two groups are again small. Lower values occur more often in the meconium group, however, in both groups more than 99% of infants did well. We were particularly interested in the lower end of Apgar-scores and pH-values as defined by arterial cord pH less than 7.10 and 5 min Apgar scores less than 5. These are shown for both groups and separated by gestational ages in Table 4. While there appears a statistically non-significant trend, again, the number of affected infants is small. Furthermore, we separately looked at the subgroups of infants delivered spontaneously versus those delivered by C-section, to see, whether the high obstetrical intervention rate corresponds to a more depressed fetal status after birth. Results are shown in Table 5. Both MSAF and clear fluid groups are similar, with slightly better pH-values and Apgar scores in the C-section groups,

irrespective of the meconium status. Values within the vaginal delivery group are also very similar, with a slight trend – as seen above – towards lower values in the meconium group. To answer the question whether obstetric interventions such as C-sections have by themselves an effect on short term fetal outcome as defined by pH- and Apgar-values, we performed a multivariate analysis looking at C-section, MSAF, parity, gestational age, infant weight, maternal age, the use of peridural analgesia and oxytocin augmentation: We find that obstetric interventions such as Csections have a statistically significant protective effect independent of the presence of meconium.

4. Comment Meconium continues to be considered a soft marker of fetal distress, based on its historical role before modern perinatal management. Furthermore, the presence of MSAF is generally associated with the perceived danger of meconium aspiration syndrome (MAS), a much feared pulmonary complication [18]. The causal relationship between MSAF – a common event – and MAS – a rare event – is not clear [19]. There is evidence, that the incidence of MSAF has remained fairly stable at 9–12% while the incidence of MAS has been declining over recent years [20]. Over the past decade, evidence has been accumulating that questions the causal relationship [21,22], findings that are confirmed clinically by failure to prevent MAS with naso- and oropharyngeal postpartum suction [23] and lack of correlation between tracheal meconium and MAS [24]. ‘‘Soft’’ markers such as MSAF can be important in influencing obstetrical decisions without directly causing such decision and most obstetricians would confirm that the same obstetrical situation is viewed differently in the presence of MSAF [25]. Not only do such soft markers influence obstetrical decision-making, they can be – unfairly and unduly – emphasized in forensic and legal situations. We wanted to provide an up to date assessment of the true significance of MSAF for the immediate postpartum

Table 4 Extremes of Apgar-scores and pH-values Gestational age Meconium Patients pH < 7.0 pH 7.0–7.10 Apgar 5 min <5

<40 + 0 Yes 327 1 (0.3) 13 (3.9%) 3 (0.9%)

No 488 1 (0.2) 6 (1.2%) 2 (0.4%)

40 + 0–40 + 6 Yes 489 1 (0.2%) 7 (1.4%) 7 (1.4%)

No 443 0 7 (1.6%) 2 (0.4%)

<41 + 0 Yes 287 0 7 (2.4%) 0

No 174 0 4 (2.4%) 0

Table 5 Subgroup analysis: C-section vs. spontaneous vaginal delivery MSAF Mode of delivery Apgar 5 mina Art. chord pH a

Median (range).

Vaginal 9 (6–10) 7.24 (0.07)

Clear AF C-section 9 (6–10) 7.28 (0.07)

Vaginal 10 (4–10) 7.25 (0.06)

C-section 10 (8–10) 7.28 (0.5)

S. Becker et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 132 (2007) 46–50

fetal well-being and the meaning of its presence for the managing obstetrician. Our study confirms that MSAF is associated with the duration of pregnancy and post-dates pregnancies [26,27]. Undiagnosed post-dates pregnancies were more common even in the 1970s’ and 1980s’, before the widespread use of ultrasound confirmed dating of pregnancies. Postdatism beyond 42 weeks of gestation is now a rarity. This could explain the historically ominous interpretation of MSAF: If MSAF is a concurring event of prolonged and post-date pregnancies [8,9], a concept also known as the ‘‘maturational theory of meconium passage’’ [28,29], the historical association ‘‘MSAF—depressed baby’’ might more truly reflect the association ‘‘post-dates pregnancy—depressed baby’’. Based on our large patient sample we find only a very small difference in the immediate peripartum fetal outcome between the MSAF and the control group as reflected by Apgar-scores and pH-values. Specifically, we find a trend towards slightly lower Apgar-values in the MSAF group. While this is most likely due to an observed clinical difference, we cannot entirely rule out the possibility of a physician bias when according Apgar-values to meconiumstained infants. Once we categorize the Apgar-values into clinically relevant groups [1–10], the differences between MSAF-infants and clear fluid infants disappear (Table 2). The more objective pH-values are almost identical in all groups and subgroups, both as non-categorical and as categorical variables, a finding that is confirmed by other studies [8]. Is the incidence of ‘‘extremely’’ depressed babies higher in the MSAF group? We defined as extremely depressed a 5 min Apgar of less than 5 and a cord-pH of less than 7.10. The data shows that both in the MSAF and in the control group, such events occurred rarely. At this level, we find slightly more infants with MSFA in the group of depressed babies. Underlining the rarity of such events even in the presence of MSAF, these numbers are too small to allow for statistical analysis. Our data show that obstetrical interventions such as fetal scalp pH measurements, peridural, vaginal operative delivery and C-section are more common with MSAF. To answer, whether this reflects physician bias [29] or an objectively worse fetal situation we compared the ‘‘intervention’’ groups with the non-intervention groups both within and between the MSAF and control groups with regard to C-section. We find that consistently, the infants delivered by C-section have slightly better pHvalues and Apgar-values than those delivered vaginally, irrespective of the status of the amniotic fluid. There are several potential limitations of our study. Retrospective studies can show associations but not causes. We find that in our low-risk suburban population, the association between MSAF and short-term adverse perinatal outcome is weaker to the point of non-significance than in previous studies. This does not exclude the possibility of a long-term effect [30,31]. It is becoming clearer that Apgar and pH-values correctly reflect the immediate peripartum situation but say little about antepartum adverse events and

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the development of postpartum long-term problems such as cerebral palsy. In legal situations, the obstetrician is most often judged based on his/her peripartum management and our study underlines that MSAF is not a relevant marker reflecting the quality of that care or influencing its outcome. Possibly MSAF is associated with chronic, antepartum fetal injury [8,32], creating a situation that is not altered by perinatal management, but that could explain the increased rates of labor complicated by C-section and vaginal operative deliveries, beyond our explanation of physician bias. Our data indicate, that in a low-risk suburban population and with the technical and logistic support of a modern obstetrical unit, the presence of MSAF has only a very small effect on the immediate perinatal outcome.

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