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Low amniotic fluid index is associated with increased risks of cesarean delivery for fetal distress and low Apgar score
OB S T E TR ICS
Low amniotic fluid index is associated with increased risks of cesarean delivery for fetal distress and low Apgar score Chauhan SP, Sanderson M, Hendrix NW, Magann EF, Devoe LD. Perinatal outcome and amniotic fluid index in the antepartum and intrapartum periods: a meta-analysis. Am J Obstet Gynecol 1999; 181: 1473d1478
OBJECTIVE To determine if low antepartum or intrapartum amniotic fluid index (AFI) is associated with adverse peripartum outcomes. DESIGN Meta-analysis of cohort and case-control studies. DATA SOURCES MEDLINE search of English-language articles published between 1987 and 1997, using the key words amniotic fluid index, oligohydramnios, and amniotic fluid. STUDY SELECTION Studies in peer-reviewed journals which determined AFI by the method of Phelan et al during either the antepartum or intrapartum period, used AFI 45 cm as the definition of oligohydramnios, and reported peripartum outcomes in relation to AFI. DATA EXTRACTION Data were extracted into 2;2 tables for each of three adverse outcomes, according to AFI level below or above the threshold of 5 cm. MAIN OUTCOME MEASURES Relative risk (RR, 95% CI) for cesarean delivery for fetal distress, 5-minute Apgar score (7, and umbilical arterial pH (7.00 in cases with AFI 45 cm, compared to those with AFI'5 cm.
Commentary Oligohydramnios may be due to placental insufficiency, ruptured membranes or abnormal fetal kidneys. It can also cause umbilical cord compression. Can intervening upon the detection of low amounts of liquor improve perinatal morbidity? The intervention might involve induction of labour, cardiotocographic monitoring, neonatal support, cesarean section or supportive informed-choice counselling for women and their families. The aim of this meta-analysis was to investigate the association between oligohydramnios and perinatal morbidity. It had significant methodological limitations, many of which were acknowledged by the authors in their discussion. In particular, it could not distinguish between causal and casual associations. The selection of studies may have been biased by restricting the search to papers in English, and scanning only the MEDLINE database with three keywords. Two authors appraised each paper, but they were not blinded to investigator or institution. They gave no details of the objectivity and reproducibility of their appraisal nor was there a funnel plot to assess publication bias. Furthermore, they did not specify the importance of ethical criteria such as the informed consent. Thirteen studies were excluded because they did not define oligohydramnios as AFI (5. However, AFI is known to vary with gestation and the meta-analysis included preterm and postdate pregnancies. Also, there is no real-world consensus that AFI is better than measuring single pool depth or even ‘eyeballing’ the liquor volume. The pooled studies were highly heterogeneous, with the incidence of oligohydramnios ranging from 3 to 41%. The reasons for this variability require consideration: it could reflect differential training of the sonographers or their foreknowledge of the obstetrical history. Alternatively, it may reflect the different study populations that were pooled in the meta-analysis (e.g. three studies included women with diabetes, pre-eclampsia or postdate pregnancy, possibly skewing the outcomes).
62
Evidence-based Obstetrics and Gynecology (2000) 2, 62 doi:10.1054/ebog.2000.0167, available online at http://www.idealibrary.com on
MAIN RESULTS 17 cohort studies and one case-control study were included in the meta-analysis. Eight studies, involving 5962 cases, measured antepartum AFI in women with unruptured membranes, and reported an overall incidence of oligohydramnios of 15% (range 3–41%). Pooling seven studies, the RR for cesarean delivery for fetal distress was 2.2 (1.5–3.4) in the presence of oligohydramnios. From six studies, the RR for Apgar score (7 was 5.2 (2.4–11.3). No study reported umbilical arterial pH (7.00 as an outcome. Ten studies, involving 4589 cases, measured intrapartum AFI, and reported an overall incidence of oligohydramnios of 22% (range 4–38%). Pooling nine studies, the RR for cesarean delivery for fetal distress was 1.7 (1.1–2.6). From nine studies, the RR for Apgar score (7 was 1.8 (1.2–2.7). Only one study reported the outcome umbilical arterial pH (7.00, with a RR of 0.2 (0.03–1.3)*. CONCLUSION Oligohydramnios, defined as amniotic fluid index 45 cm, is associated with increased risks of cesarean delivery for fetal distress and Apgar score (7 at 5 minutes. * Calculated from numbers in article.
‘Cesarean section for fetal distress’ may be an imprecise outcome measure, because the readiness to perform a cesarean section varies with the obstetrician’s level of training and experience, the institution, and even the time of the day. Objective diagnosis of fetal distress requires a fetal scalp pH measurement, which should have been one of the entry criteria. This study confirmed that there is a significant association between oligohydramnios and subsequent cesarean section, but this relationship may merely represent diagnostic suspicion bias. The knowledge of the low AFI could have modified the management approach and influenced the decision to induce labour or perform a cesarean section. Decision-makers and outcome assessors should have been blinded to the AFI result and the obstetrical history. The results of this meta-analysis are certainly consistent with the notion that oligohydramnios predicts perinatal morbidity, but the only safe implication for clinical practice is to recognise that the incidence of a low AFI varies widely. To answer the research question posed in the first paragraph, we need a prospective, population-based trial with sufficient power to compare objective perinatal outcomes (such as fetal scalp pH) with caregivers being blinded to the AFI. If each method of liquor volume assessment was compared in this manner, and the results analysed by intention to treat and numbers needed to treat, the clinical utility of liquor volume assessment in influencing management could be rigorously established.1 Alex M. Pirie, MB, ChB, BSc, MRCP(UK), MRCOG City Hospital, Birmingham, UK
Literature cited 1. Alfirevic Z, Luckas M, Walkinshaw SA, et al. A randomized comparison between amniotic fluid index and maximum pool depth in the monitoring of postterm pregnancy. Br J Obstet Gynaecol 1997; 104: 207d211
^ 2000 Harcourt Publishers Ltd
Low amniotic fluid index is associated with increased risks of cesarean delivery for fetal distress and low Apgar score Chauhan SP, Sanderson M, Hendrix NW, Magann EF, Devoe LD. Perinatal outcome and amniotic fluid index in the antepartum and intrapartum periods: a meta-analysis. Am J Obstet Gynecol 1999; 181: 1473d1478
OBJECTIVE To determine if low antepartum or intrapartum amniotic fluid index (AFI) is associated with adverse peripartum outcomes. DESIGN Meta-analysis of cohort and case-control studies. DATA SOURCES MEDLINE search of English-language articles published between 1987 and 1997, using the key words amniotic fluid index, oligohydramnios, and amniotic fluid. STUDY SELECTION Studies in peer-reviewed journals which determined AFI by the method of Phelan et al during either the antepartum or intrapartum period, used AFI 45 cm as the definition of oligohydramnios, and reported peripartum outcomes in relation to AFI. DATA EXTRACTION Data were extracted into 2;2 tables for each of three adverse outcomes, according to AFI level below or above the threshold of 5 cm. MAIN OUTCOME MEASURES Relative risk (RR, 95% CI) for cesarean delivery for fetal distress, 5-minute Apgar score (7, and umbilical arterial pH (7.00 in cases with AFI 45 cm, compared to those with AFI'5 cm.
Commentary Oligohydramnios may be due to placental insufficiency, ruptured membranes or abnormal fetal kidneys. It can also cause umbilical cord compression. Can intervening upon the detection of low amounts of liquor improve perinatal morbidity? The intervention might involve induction of labour, cardiotocographic monitoring, neonatal support, cesarean section or supportive informed-choice counselling for women and their families. The aim of this meta-analysis was to investigate the association between oligohydramnios and perinatal morbidity. It had significant methodological limitations, many of which were acknowledged by the authors in their discussion. In particular, it could not distinguish between causal and casual associations. The selection of studies may have been biased by restricting the search to papers in English, and scanning only the MEDLINE database with three keywords. Two authors appraised each paper, but they were not blinded to investigator or institution. They gave no details of the objectivity and reproducibility of their appraisal nor was there a funnel plot to assess publication bias. Furthermore, they did not specify the importance of ethical criteria such as the informed consent. Thirteen studies were excluded because they did not define oligohydramnios as AFI (5. However, AFI is known to vary with gestation and the meta-analysis included preterm and postdate pregnancies. Also, there is no real-world consensus that AFI is better than measuring single pool depth or even ‘eyeballing’ the liquor volume. The pooled studies were highly heterogeneous, with the incidence of oligohydramnios ranging from 3 to 41%. The reasons for this variability require consideration: it could reflect differential training of the sonographers or their foreknowledge of the obstetrical history. Alternatively, it may reflect the different study populations that were pooled in the meta-analysis (e.g. three studies included women with diabetes, pre-eclampsia or postdate pregnancy, possibly skewing the outcomes).
62
Evidence-based Obstetrics and Gynecology (2000) 2, 62 doi:10.1054/ebog.2000.0167, available online at http://www.idealibrary.com on
MAIN RESULTS 17 cohort studies and one case-control study were included in the meta-analysis. Eight studies, involving 5962 cases, measured antepartum AFI in women with unruptured membranes, and reported an overall incidence of oligohydramnios of 15% (range 3–41%). Pooling seven studies, the RR for cesarean delivery for fetal distress was 2.2 (1.5–3.4) in the presence of oligohydramnios. From six studies, the RR for Apgar score (7 was 5.2 (2.4–11.3). No study reported umbilical arterial pH (7.00 as an outcome. Ten studies, involving 4589 cases, measured intrapartum AFI, and reported an overall incidence of oligohydramnios of 22% (range 4–38%). Pooling nine studies, the RR for cesarean delivery for fetal distress was 1.7 (1.1–2.6). From nine studies, the RR for Apgar score (7 was 1.8 (1.2–2.7). Only one study reported the outcome umbilical arterial pH (7.00, with a RR of 0.2 (0.03–1.3)*. CONCLUSION Oligohydramnios, defined as amniotic fluid index 45 cm, is associated with increased risks of cesarean delivery for fetal distress and Apgar score (7 at 5 minutes. * Calculated from numbers in article.
‘Cesarean section for fetal distress’ may be an imprecise outcome measure, because the readiness to perform a cesarean section varies with the obstetrician’s level of training and experience, the institution, and even the time of the day. Objective diagnosis of fetal distress requires a fetal scalp pH measurement, which should have been one of the entry criteria. This study confirmed that there is a significant association between oligohydramnios and subsequent cesarean section, but this relationship may merely represent diagnostic suspicion bias. The knowledge of the low AFI could have modified the management approach and influenced the decision to induce labour or perform a cesarean section. Decision-makers and outcome assessors should have been blinded to the AFI result and the obstetrical history. The results of this meta-analysis are certainly consistent with the notion that oligohydramnios predicts perinatal morbidity, but the only safe implication for clinical practice is to recognise that the incidence of a low AFI varies widely. To answer the research question posed in the first paragraph, we need a prospective, population-based trial with sufficient power to compare objective perinatal outcomes (such as fetal scalp pH) with caregivers being blinded to the AFI. If each method of liquor volume assessment was compared in this manner, and the results analysed by intention to treat and numbers needed to treat, the clinical utility of liquor volume assessment in influencing management could be rigorously established.1 Alex M. Pirie, MB, ChB, BSc, MRCP(UK), MRCOG City Hospital, Birmingham, UK
Literature cited 1. Alfirevic Z, Luckas M, Walkinshaw SA, et al. A randomized comparison between amniotic fluid index and maximum pool depth in the monitoring of postterm pregnancy. Br J Obstet Gynaecol 1997; 104: 207d211
^ 2000 Harcourt Publishers Ltd