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

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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 Tübingen 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.

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], [2], [3], [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 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], [11], [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 socio-economic 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 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.

Section snippets

Materials and methods

A retrospective cohort study was conducted looking at 11226 women who gave birth at the Tübingen 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

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,

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

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