sonographic estimation of fetal weight ( fw ) , especially in late pregnancy is an important guide in obstetric care . armed with this information informed decisions about delivery can be taken , thereby minimizing perinatal morbidity and mortality . amniotic fluid cushions the fetus from traumatic forces , cord compression , and pathogens , as well as playing an essential role in fetal lung development . in late pregnancy , amniotic fluid production is largely dependent on fetal micturition and renal size in the newborn has been shown to bear a significant relationship to birth weight . it is therefore , reasonable to postulate a relationship between sonographically determined amniotic fluid index ( afi ) and estimated fw . previous reports have investigated possible relationships between sonographically attained fluid index , and estimated fetal weight ( efw ) including the influence of afi on the accuracy of sonographically efw , among caucasians . however , such studies are rare among africans , especially nigerians . this study was carried out to find out if any significant relationships exist between afi and efw in a nigerian cohort of healthy pregnant women . two hundred and fifty - eight low - risk pregnant subjects referred for routine ultrasound scans to the radiology department of the university of benin teaching hospital , nigeria were randomly selected over a 12-month period . those with unsure dates , diabetes mellitus , and hypertensive disorders were excluded . only those whose menstrual dates sonography was performed with a 3.5 mhz transducer ( fukuda denshi ; fukuda co ltd , japan ) . fetal biometrics including biparietal diameter ( bpd ) , using the cavum septum pellucidum as landmark , as depicted in figure 1 ; fetal trunk cross sectional area ( fta ) using the four chamber view of the heart , as illustrated in figure 2 ; and the femur length ( fl ) , with the  hook from the greater trochanter to the distal metaphysis included , as illustrated in figure 3 , were measured . the fw was automatically estimated by the scanner using a combination of the bpd , fta , and fl , based on the in - built osaka university system 's formula . ultrasound scan shows how to measure fetal trunk cross sectional area , using the four chamber view of the heart . sample report 1 shows estimated fetal weight calculated by the osaka university system 's formula . sample report 2 shows estimated fetal weight calculated by the osaka university system 's formula . data was entered into a microsoft spreadsheet and analysed using the statistical package for the social sciences ( spss version 16 ) . measurements were stratified into pairs of afi and efw as follows ; 27 - 29 weeks , 30 - 32 weeks , 33 - 35 weeks , 36 - 38 weeks , and 39 - 41 weeks . spearman 's correlation was used to test possible relationship between the afi and efw pairs . the mean age of the subjects was 29.1  4.9 years , and parity ranged from 0 to 7 , with a mean of 1.5 . the mean maternal weight was 71.4  13.6 kg , and height was 1.6  0.5 m. the number of subjects in each gestational group were distributed as follows ; 64 ( 24.8% ) in the 27 - 29 weeks , 56 ( 21.7% ) in the 30 - 32 weeks ; 48 ( 18.6% ) in the 33 - 35 weeks ; 50 ( 19.4% ) in the 36 - 38 weeks , and 40 ( 15.5% ) in the 39 - 41 weeks ; as outlined in table 1 . amniotic fluid index and estimated fetal weight values for the gestational age ranges table 1 also shows that the mean afi and efw values for 27 - 29 weeks gestation were 172.1 mm and 1250.19 g respectively ; 30 - 32 weeks were 170.3 mm and 1,648.04 g ; 33 - 35 weeks were 162.3 mm and 2,273.54 g ; 36 - 38 weeks were 144.0 mm and 2,906.12 g ; and 39 - 41 weeks were 125.0 mm and 3,222.65 g. spearman 's correlation values between afi and efw were 0.123 , 0.472 , 0.179 , 0.210 , and 0.221 for 27 - 29 weeks , 30 - 32 weeks , 33 - 35 weeks , 36 - 38 weeks , and 39 - 41 weeks respectively . there was no significant association between afi and efw for all subdivisions of gestation age , except in the 30 - 32 weeks group ( p < 0.05 ; r = 0.472 ) . overall , there was no statistically significant relationship between afi and efw ( p > 0.05 ; r = 0.241 ) . figure 6 shows the scatter plot diagram for all pairs of afi and efw , with r value of 0.241 . amniotic fluid disorders , oligo - hydramnios , and poly - hydramnios have been associated with intrauterine growth restriction and abnormal fetal growth , but this relationship across the entire range of fws is unclear . however , when used alone , amniotic fluid measurement has been found to perform poorly in predicting fetal distress , fetal growth restriction or low apgar scores , among others . polyhydramnios and oligohydramnios could overestimate or underestimate sonographic fw assessment . while there are reports of afi measurements and ultrasound efws , as separate parameters , both in the nigerian and international literature,[810 ] there are few reports that assessed the possible relationship between afi and estimated weight , for both normal ( non - diabetic ) and diabetic pregnancies . this study found a decrease in mean afi values from 172.1 mm in early third trimester ( 27 - 29 weeks ) , to a value of 144.0 mm at 36 - 38 weeks , before a sharp drop to 125.0 mm at 39 - 40 weeks , as observed in previous studies . as expected increase in fw was noticed throughout pregnancy , but there was no significant association between afi and efw when all the afi and efw pairs were considered ( p > 0.05 ; r = 0.241 ) . only the afi and efw pair for gestation age 30 - 32 weeks showed any significant relationship ; ( p < 0.05 ) . this lack of significant relationship between afi and efw across all gestational age strata is supported by the works of perni et al . , and owen et al . possible reasons adduced for this are that swallowing and urinating mechanisms , rather than fetal size , are more involved in regulation of amniotic fluid volume . the implication of this is that fetal size may not need to be considered in variations of amniotic fluid volume across the gestational ages . it is interesting to note that kofinas and kofinas in 2012 , found a significant relationship between afi and efw for both diabetic and non - diabetic pregnancies . while no explanation was offered for the former , it was postulated that fetuses of diabetic pregnancies spend more time breathing than swallowing ; since swallowing and breathing are mutually exclusive , the fetuses do not swallow as much amniotic fluid as expected ; thus in diabetic pregnancies , it may be necessary to consider fetal size when interpreting amniotic fluid variations across gestational ages . this present report on relationship between amniotic fluid and estimated fetal weight is probably the first among pregnant women in nigeria and therefore , raises the need for more studies on the subject , especially with larger sample sizes . it has nonetheless supported the majority of the views of similar works in the foreign literature that reported the non - dependence of amniotic fluid measurements on ultrasound estimated fetal size . this study has produced a range of values of afi and efw among nigerian africans . however , no significant relationship exists between these parameters . the probable implication of this is neither parameter merits consideration when variations in the other are considered .
introduction : fetal weight ( fw ) estimation in late pregnancy is an important guide in obstetric care . 
 amniotic fluid protects the fetus against traumatic and infective insults . 
 there possibly exists a relationship between fw and amniotic fluid index ( afi ) that can be estimated by ultrasonography.materials and methods : two hundred and fifty - eight low - risk pregnancies were prospectively studied by means of ultrasound over a 12-month period . 
 fw was estimated using a combination of fetal parameters ; bi - parietal diameter , fetal trunk cross sectional area , and femur length . 
 afi was assessed using the 4-quadrant method . 
 spearman 's correlation was used to test possible relationship between amniotic fluid indices and estimated fw pairs . 
 the level of statistical significance was set at p  0.05.results:the mean af1 and estimated fetal weight ( efw ) pairs were as follows : at 27 - 29 weeks the values were 172.1 mm and 1,250.2 g ; at 30 - 32 weeks af1 and efw values were 170.3 mm and 1,648.0 g ; at 33 - 35 weeks values were 162.3 mm and 2,273.5 g ; at 36 - 38 weeks values were 144.09 mm and 2,906.1 g ; at 39 - 40 weeks af1 and efw values were 125.0 mm and 3,222.6 g. overall , there was no statistically significant relationship between afi and efw ( p > 0.05 ; r = 0.241).conclusion : while fw calculations and amniotic index showed variations in value in late pregnancy , there does not appear to be a linear relationship between ultrasound estimate of fw and amniotic index . 
 the implication of this is that fetal size need not be taken into cognizance when alterations in amniotic fluid values are noted .