INTRODUCTION

Amniotic fluid is a clear fluid that surrounds the fetus, it is necessary for a healthy fetal development.¹ Reduction in the amniotic fluid volume to less than 500 ml is called oligohydramnios while increase in amniotic fluid volume greater than 2000 ml is called polyhydramnios. Oligohydramnios or polyhydramnios usually leads to complications in pregnancy. At first, amniotic fluid consists of water from the mother’s body but gradually a larger proportion is made up of the baby’s urine and secretions from the fetal lungs. By 20 weeks of gestation, the amniotic fluid is entirely replaced by fetal urine as the fetus swallows and excretes the fluid.¹ Amniotic fluid volume is an important marker of intrauterine fetal wellbeing and its quantification is also a means of assessing fetal status.² It is a component of an obstetric ultrasound scan and forms part of the obstetrician’s decision making in the management of pregnancy. The amniotic fluid index (AFI) technique is a rapid, readily reproducible, non-invasive method of determining the amniotic fluid volume. This was developed by Phelan et al,² it is calculated sonographically by the summation of the values of the maximum vertical heights of the amniotic fluid in four quadrants of the gravid uterus and measured in centimeters. Its validity has been demonstrated by Moore and Cayles.³ Establishing normal values of amniotic fluid volume for a given population will help in determining pregnant women with oligohydramnios and polyhydramnios and their complications. The aim of this study was to determine the amniotic fluid index (AFI) and relationship with some fetal biometrics in women during their routine antenatal visits in Umuahia Abia state.

MATERIALS AND METHODS

Study Design and Setting

This was a cross-sectional study of pregnant women who were on their routine antenatal ultrasound visit in Alpha Clinics and Radio-Diagnostic centre, Umuahia, Abia state, Nigeria. The study was carried out from January, 2022 to July, 2022. Umuahia is the capital of Abia state, in the South-east geopolitical zone and it is dominated by civil servants.

Eligibility Criteria

The inclusion criteria were all singleton healthy pregnant women with no underlining pathology, while the exclusion criteria were diabetes mellitus in pregnancy, hypertension in pregnancy, multiple gestation, grand-multiparity and fetus with congenital abnormalities.

Sample Size Determination

The sample size was calculated using the formula for estimating a population mean⁴;

Sample size, N = Z²δ² / ε²

N= Sample size

Z= the abscissa of the normal curve (1.96).

δ= Population standard deviation or variance (4.95).

ε = Error range (0.97)

N = (1.96)² (4.95)² / (0.97)²

N = 100

Procedure

Consent was obtained from the patients prior to inclusion in the study. Subjects were scanned transabdominally in supine position. A digital real time ultrasound scan with a 3.5 MHz convex transducer was used. To determine the AFI, the uterus was divided into four imaging quadrants with the linear nigra and a mediolateral line running through the umbilicus acting as the vertical and the horizontal axes respectively. Measurement of the pocket of amniotic fluid in the four quadrants was in centimeters, avoiding the placenta tissue and umbilical cord. The sum of the maximum vertical pool of amniotic fluid in all the four quadrants gave the AFI in cm.⁵

Data Analysis

Data was analysed using IBM Statistical Package for Social Science (IBM SPPS Inc., USA) Version 16.0. Qualitative variables like gender, fetal lie and presentation and placentation were expressed in frequencies and percentages, while quantitative variables like maternal age and fetal biometrics were expressed in mean and standard deviations. Chi-square was used to determine the relationship between AFI and fetal gender, fetal lie and presentation and placental localization, at a P-value of <0.05.