Perinatal Outcome in Pregnancies Complicated by Isolated Oligohydramnios at Term

Patients and Methods: During this study 500 patients with singleton pregnancy were selected and Amniotic Fluid Index (AFI) was evaluated within 4 days of delivery in these patients with technique of Phelan et al. All selected outcome variables of these pregnancies were recorded on printed proformas. On the bases of AFI measurements patients were divided in two groups. Those who have AFI > 50 mm and < 50 mm. The significance of difference or comparison of means was measured by Chai square test (by Yats corrections). Perinatal outcomes in pregnancies with oligohydramnios were compared with those with normal amniotic fluid volume.


INTRODUCTION
Oligohydramnios defined as an AFI ≤ 5 th centile for the gestational age, AFI ≤ 50 mm or maximum vertical pocket devoid of umbilical cord or fetal limbs measure < 30 mm, in the presence of intact membranes is a common obstetric complication, occurring in 3-5% of pregnancies at term.Some authors [1][2][3][4] state that such pregnancies are at an increased risk of adverse perinatal outcome such as fetal distress in labor, induction of labor, cesarean delivery for fetal distress, meconium passage, low Apgar score and neonatal resuscitation or neonatal intensive care unit admission.But others [5][6][7][8] have not confirmed the association of adverse perinatal outcome with oligohydramnios; Instead they state that isolated oligohydramnios is not associated with adverse perinatal outcome.The objective of this study was to determine the association of isolated oligohydramnios at term with adverse perinatal outcome.

Aims and Objectives
To determine the perinatal outcome in pregnancies complicated by isolated oligohydramnios at term.

Patients & Methods
This study was carried-out in the Department of Obstetrics and Gynecology Unit III, Sir Ganga Ram Hospital Lahore during one year period from 14.05.2002 to 15.06.2003.During this study 500 patients were selected, booked or unbooked attending antenatal clinic or labor room of Unit III in Sir Ganga Ram Hospital Lahore.Inclusion criteria for the study population was: women with singleton pregnancy with well established dates, at 40.0-42.0weeks gestational age (GA), fetus with no anomalies, amniotic fluid volume evaluated within 4 days of delivery in these patients, and determination of amniotic fluid volume with technique of Phelan et al (9) .Following patients were excluded from the study: Patients with less than 40 weeks and unsure gestational age, patients with multiple pregnancy, patients with history of preterm rupture of membranes, patients with preeclampsia and uncontrolled gestational diabetes, and delivery after 4 days of evaluation of amniotic fluid volume.Amniotic fluid measurements were performed by ultrasound on targeted patients.Equipment used in this study included Acuson model machine which was equipped with 3.5 and 5.0-MHz curvilinear transducers.
Estimates of amniotic fluid volume were recorded by means of AFI described by Phelan et al 9 .AFI values of ≤ 50 mm were interpreted to represent oligohydramnios.All selected outcome variables of these pregnancies were recorded on printed proformas in the hospital, which were shifted to computer for analysis.Selected outcome variables included: spontaneous vaginal delivery, abnormal non-stress testeither with decelerations or non-reactive, instrumental The data analysis was computer based using SPSS statistical package.On the basis of division of patients with AFI ≤ 50 mm and the particular outcome, tables were constructed and the relative risk for each calculated.Oligohydramnios was defined as an amniotic fluid index ≤ 50mm.Perinatal outcomes in pregnancies with oligohydramnios were compared with those with an amniotic fluid index of > 50 mm.

Results
Patients were divided in 2 groups on the basis of AFI measurements, those who have AFI > 50 mm and ≤ 50 mm; nearly 70% of patients showed values of AFI above 50 mm and 29% of patients showed AFI ≤ 50 mm (Oligohydramnios).
The results are favoured by a study by Rutherford et' al, 15 who observed an association between adverse perinatal outcome and oligohydramnios indicating that non-reactive non-stress tests (NST), FHR decelerations, meconium staining of amniotic fluid, cesarean section for fetal distress, and low Apgar scores are more common in patients with oligohydramnios.Similarly Sarno et al 16 found that intrapartum oligohydramnios was associated with an increased risk of cesarean delivery for fetal distress, an Apgar score < 7 at 1'minute and abnormal fetal heart rate patterns.
However Grubb and Paul 17 did not observe such asso-ciation (no significant increase in intervention for fetal distress, either cesarean or operative vaginal delivery, in patients with oligohydramnios (AFIs of 20 to 49 mm) when compared to those with normal amniotic fluid volume (AFI of 50 mm or more).Similarly Chauhan et al 18,19 failed to find an increased risk for cesarean delivery for fetal distress or low Apgar scores in patients with oligohydramnios.However, although the study results analysis demonstrate that oligohydramnios is associated with increased chances of induction of labor, non reassuring fetal heart rate, decelerations of fetal heart rate, caesarean delivery, Apgar score < 6 at 1 min, Apgar score < 7 at 5 min, neonatal resuscitation and neonatal ICU admission, yet the statistical significance was only present between advanced gestational age, presence of meconium, deceleration of fetal heart rate and chances of caesarean delivery.
The most important constrain to influence the decision to proceed with caesarean delivery is objective interpretation of fetal heart rate tracing.Similarly, the caesarean delivery for fetal distress would be preferable only after a fetal scalp pH value is obtained. 18However, because of non trained personnel, non-availability of the machine, cervical dilatation, or other constraints, the fetal pH may not be attainable before emergency caesarean delivery.Similarly a low Apgar score may be the result of use of narcotics in labor, pre-term birth, or vigorous suctioning of the neonate.Similar results have been shown by Elizabeth et al (20) and Morrris et al. 21Further studies are required to determine the association of isolated oligohydramnios at term with adverse perinatal outcome.

Conclusion
Oligohydramnios (AFI < 50 mm) is associated with an increased risk of caesarean delivery for fetal distress and poor Apgar scores.

Table 1 :
Selected Outcomes in Women with < 50 mm (Oligohydramnios) and Women with AFI > 50 mm.