Methods. A prospective survey was performed, in which a sample of 3000 low-risk pregnant adult females were studied utilizing everyday ultrasound, including foetal biometrics and measuring of AFI, and SDP. Data were analysed utilizing multiple additive arrested development, and building a curve for both the AFI, and SDP measurings, harmonizing to gestational age, the foetal places and attitudes, in add-on to the appraisal of the concluding perinatal result.
Consequences. The fiftieth percentile remained practically changeless at about 150 millimeters between the 20th and 33rd hebdomad, after which there was a diminution in volume, which became apparent after the 38th hebdomad. At the fortieth hebdomad, the 10th percentile was around 62 millimeter and the 2.5th percentile about 33 millimeters. Among the group with integral membranes, no important differences in perinatal result could be seen in relationship to the AFI and SDP, although a 50 % addition in exigency operations for foetal hurt was seen in adult females with oligohydramnios. Fetal place had significantly affected the AFI, which was unusually lower in rear of barrel gestations, but without similar consequence on SDP. There was no important difference for either SDP ( P = 0.8 ) or AFI ( P = 0.3 ) between foetuss lying on the right or the left side of the maternal venters.
Decisions. The percentiles incidence of amnionic fluid measurings in low-risk pregnant adult females showed important lessening with gestational age, particularly after the 33rd hebdomad gestation. Fetal place and lateralization had affected significantly the AFI, but non the SDP.
Cardinal words: Amniotic fluid index, low-risk gestation, obstetric echography
Abbreviations: AFI: amnionic fluid index, AFV: amnionic fluid volume, GA: gestational age, P: percentile
The importance of fluctuations in volume of amnionic fluid to foetal wellbeing has been peculiarly well-established, and are closely correlated to an addition in perinatal mortality and morbidity rates ( 1, 2 ) , although some uncertainties have late been raised ( 3 ) . Fetal wellbeing is an of import inquiry that can, nevertheless, remain unreciprocated in many state of affairss, but advancement in diagnostic techniques has resulted in better perinatal results, and has besides contributed to understanding the complex physiological and pathological interaction between foetus and female parent ( 4, 5 ) .
AFI and SDP are the sonographic parametric quantities most normally used to gauge amnionic fluid volume. Both use a planar measuring to gauge a three- dimensional parametric quantity and are hence capable to mistake. Amniotic fluid index ( AFI ) , a semiquantitative ultrasound step used to denote the volume of amnionic fluid, was first described in 1987 by Phelan et Al. ( 6, 7 ) .
Since AFI involves measurings in four quarter-circles and SDP merely measures the deepest pocket, it is possible that foetal place would impact these two indices otherwise. The comparative truth of SDP and AFI is still controversial. Using invasive methods, some surveies have shown these methods to be comparable, while others have shown that one index might be better than the other. However, none of these surveies took into history the possible consequence of foetal place on the amnionic fluid volume indices ( 8 ) .
Many surveies have shown an increased hazard of intrapartal foetal hurt in parturient adult females with oligohydramnios, as identified by ultrasound scrutiny. The exact pathophysiologic mechanism of olighydramnios has non been defined, but one likely account is an increased hazard of umbilical cord compaction during uterine contractions ( 7,9 ) . However, uncertainties remain refering normal values of AFI for each gestational age.
The mention curves established some old ages ago are still in usage in current obstetrical pattern, but there is a demand for new informations, utilizing a dependable mention low-risk pregnant adult females sample, to set up the bounds of AFI that would bespeak perinatal hazard ( 9 ) . Some bing curves ( 10 – 13 ) , were based on comparatively little sample sizes, and normal AFI for each gestational age was non yet decidedly established.
The intent of this survey was to gauge the curve for the amnionic fluid volume in low hazard gestation, utilizing a set of obstetric echograms of adult females between the 20th and 42nd hebdomad, utilizing two constituted parametric quantities, the AFI and SDP, and to measure the effects of those measurings on the concluding perinatal result, in add-on to analyzing the effects of different foetal places and attitudes on those measured parametric quantities.
Material and methods
A prospective survey was carried out to gauge and measure the mention curve of AFI values in low-risk pregnant adult females, and to follow its effects on the concluding perinatal result. The survey was performed at the Feto-maternal Unit, Department of Obstetrics and Gynecology at El-Minya University, Egypt. Inclusion standards were: gestational age clearly established by last catamenial period, and confirmed by early ultrasound scrutiny performed in first trimester of gestation ; and gestational age between 20 and 42 hebdomads.
Womans excluded were those with pregnancy-induced high blood pressure, diabetes mellitus, chronic high blood pressure, gestational diabetes, foetal macrosomia, ruptured membranes, placental aging, duplicate gestation, foetal growing limitation, foetal abnormalcies, foetal decease, foetal isoimmunisation, or other conditions, such as metabolic upsets, kidney and bosom upsets, and hypo- and thyrotoxicosis. Amniotic fluid volume was measured utilizing a 3.5 MHz additive transducer linked to a ALOKA SS 280. A scanner utilizing the 4-quadrant technique for the appraisal of AFV, described by Phelan et Al. ( 6, 7, 9 ) , with a alteration proposed by Jeng et Al. ( 11 ) .
A sum of 3000 adult females between the 20th and 42nd hebdomad of gestation were evaluated in this survey, between August 2008 and December 2010. In order to avoid any possible prejudice due to repeat of scrutinies in adult females with some undetected job, an independent sample was chosen. Therefore, merely the first ultrasonographic scrutiny of each adult female was included in the survey, and different sample populations were used for each gestational age, in a cross-sectional design. A formal consent had been taken form the adult females included in the survey, after full account and guidance, and blessing of the regional ethical commission.
The womb was imaginarily divided into right and left halves along the linea nigger on the surface of the maternal venters. Using the mid-point between the fundus womb and the pubic symphysis, the womb was besides divided into upper and lower halves. With the transducer caput perpendicular to the land, the largest amnionic fluid pocket in each quarter-circle was identified. The perpendicular diameter of this largest pocket of each one of the four quarter-circles was so measured. The AFI was defined as the amount of the measurings of each quarter-circle in millimetres. All scrutinies were performed by merely one professional in order to avoid inter-observer variableness. The intra-observer variableness of the steps performed with this technique was estimated to be high ( correlativity coefficient 0.92 ) ( 14-18 ) .
Both AFI and SDP were measured at the same clip during the scrutiny. SDP was obtained by mensurating the deepness of the individual deepest perpendicular amnionic fluid pocket that was clear of umbilical cord or foetal parts ( 19,20 ) . AFI was calculated as the amount of the deepnesss of the deepest pockets from each of the four quarter-circles of the womb. The place of the foetal bole was characterized by three parametric quantities. Initially, the ultrasound investigation was placed transversally on the maternal abdominal wall, with the center of the investigation over the sagittal midplane of the maternal venters, at the degree of the foetal abdominal perimeter ( Figure 1 ) .
A perpendicular line ( Line Y ) was drawn downwards from the centre of the ultrasound investigation. A horizontal line ( Line X ) was drawn across the maximal diameter of the foetal abdominal perimeter. Line X was therefore divided by Line Y into a shorter portion ( S ) and a longer portion ( L ) . The first parametric quantity to be determined was the place of the foetal bole. This was assigned as either foetal bole left or foetal bole right depending on whether L was on the left or the right side, severally, of the maternal venters ( 21-24 ) .
Following, we determined by how much the foetal bole lay to one side of the womb, by ciphering the lateralization mark, defined as S/ ( S + L ) . This mark ranged from 0 to 0.5 ; a mark of precisely 0.5 meant that the foetal bole was on the sagittal midplane of the maternal venters, and a mark of 0 meant that the foetal bole was to the side and did non traverse over Line Y. The usage of the lateralization mark has non been reported antecedently.
Finally, we determined the orientation of the ventral portion of the foetal venters: a line ( Line Z ) was drawn from the foetal hepatic vena to the foetal spinal column, and the angle ( A ) between Lines Z and Y was determined. Fetuss were classified into one of three groups: ventral front tooth ( A = 300.1 – 360- or0-60- ) , ventral lateral ( A = 60.1 – 120- or 240.1 – 300- ) and ventral buttocks ( A= 120.1 – 240- ) . Figure I.
The survey population was categorized into different groups harmonizing to the foetal place, and AFI and SDP in the different groups were compared. Pearson ‘s correlativity coefficient between lateralization mark and AFI was considered the primary outcome step. For an R of 0.25, a lower limit of 62 instances was needed at a Type I error of 0.05. Based on the curve of Jeng et Al. ( 25 ) , and following a average AFI measuring of 140 millimeters at 40 hebdomads, and a standard divergence of 48 millimeters, a sample size of at least 120 measurings for each hebdomad of gestation was estimated, presuming an ? mistake of 0.05 and a maximal difference of 10 millimeter between population and sample measurings.
The AFI was correlated to perinatal result based on the Apgar mark, umbilical cord blood pH, birthweight, frequence of cesarian subdivision for foetal hurt, operative bringing for foetal hurt, including both cesarian subdivision, vaginal forceps, and ventous extractions, and referral to the neonatal intensive attention unit ( NICU ) . Fisher ‘s exact trial was used for statistical rating. P & A ; lt ; 0.05 was considered statistically important. The computing machine plan ‘nQuary Advisor Release 3 ‘ ( Statistical Solutions Ltd, Cork, Ireland ) was used to cipher the sample size needed in order to obtain significance degrees at P & A ; lt ; 0.05 and 0.01 with 90 % assurance intervals ( CI ) .
Datas were analysed utilizing multiple additive arrested development, and by building a curve of the 2.5th, 10th, 50th, 90th and 97.5th percentiles of the amnionic fluid measurings harmonizing to gestational age. All statistical analyses were performed utilizing the Statistical Package for Social Sciences for Windows version 10.0 ( SPSS Inc, Chicago, IL, USA ) . Student ‘s t- trial, Pearson ‘s correlativity coefficient, additive arrested development and ANOVA were used as appropriate. A P-value of & A ; lt ; 0.05 was considered statistically important.
The 3000 pregnant adult females included in the survey had a average age of 25.9 old ages ( scope 13 – 46 ) , with low para ( 45 % were primigravida ) . The sample was fundamentally from a low hazard population because of the exclusion standards used. The values of the 2.5th, 10th, 50th, 90th and 97.5th percentiles of the AFI, and SDP harmonizing to gestational age are shown in Figure II, III and IV show the information after being submitted to a smoothing procedure utilizing quadratic multinomial accommodations.
Analysis of the fiftieth percentile measurings of the AFI, and SDP curve at different gestational ages revealed that these values remained practically changeless, at around 150 millimeter, between the 20th and 33rd hebdomad of gestation. At this point, values began to diminish, and this diminution became peculiarly apparent after the 38th hebdomad, making 130 millimeter at the 39th hebdomad, 120 millimeter at the 41st hebdomad and 116 millimeter at the 42nd hebdomad of gestation. Table I, and II
The average gestational age at the clip of scrutiny was 33.3 ± 2.8 hebdomads. The average SDP and AFI were 5.5 ( scope, 2.8 – 9.3 ) centimeter and 14.5 ( scope, 6.7 – 29.3 ) centimeter, severally. There were no important differences in average AFI measurings when these informations were controlled for age, race, literacy, para or old cesarean cicatrix ( informations already published elsewhere ) ( 18 ) . Measurements of the tenth percentile remained 100 millimeter until the 33rd hebdomad, when an accentuated lessening started, worsening even more aggressively after the 38th hebdomad of gestation, making values 80 millimeters and 40 millimeter at the 42nd hebdomad.
Harmonizing to the published normal scopes, six instances had polyhydramnios ( AFI = 29.3 centimeter at 29 hebdomads ‘ gestation, SDP = 9.1 centimeter at 37 hebdomads and SDP = 9.3 centimeter at 33 hebdomads ‘ gestation ) and two instances had oligohydramnios ( AFI = 6.7 centimeter at 36 hebdomads ‘ gestation ) . Twelve 100s and five ( 42 % ) instances were foetal bole right and 1663 ( 58 % ) were foetal bole left. There were no important differences between these groups with regard to gestational age ( 33.1 ± 2.4 vs. 33.4 ± 2.7 hebdomads, P = 0.7 ) , average SDP ( 5.4 ± 1.3 vs. 5.5 ± 1.4 centimeter, P = 0.3 ) and average AFI ( 15.1 ± 5.1 vs. 14.1 ± 4.0 centimeter, P = 0.8 ) .Table Three
In fact, our consequences showed that foetal place had a important consequence on AFI but non on SDP ; the more the foetus was positioned to one side of the womb, the lower was the AFI. Both methods show good correlativity between the measurings and the existent volume of amnionic fluid. The consequence of lateralization mark on amnionic fluid volume indices was assessed by Pearson ‘s correlativity coefficient and additive arrested development. It had no important consequence on SDP ( r = 0.13, ? = 1.1, standard mistake = 0.9, P = 0.23 ) . However, it did significantly influence AFI ( r = 0.31, ? = Transverse subdivision of maternal bole degree of foetal abdomen8.7, standard mistake = 3.0, P = 0.005 ) .
The arrested development line is shown in Figure III. In other words, when the lateralization mark increased, the AFI increased proportionally. When the lateralization mark was 0.5 ( foetal bole positioned at the midplane of the maternal venters ) , the AFI was, on norm, 4.35 centimeter higher than it was when the lateralization mark was 0 ( foetal bole ballad on the side and did non traverse the midplane of the maternal sagittal plane ) . Figure III, IV.
There were two instance of high AFI ( 29.3 centimeter ) in the survey population. In order to except the possibility that the consequences were influenced by this individual instance, we repeated the analysis quarter-circles of the ipsilateral side, the perpendicular deepness of these two quarter-circles being be much shallower compared with those on the contralateral side.
Although amnionic fluid should be displaced to the contralateral side, this may non be reflected wholly in a planar measuring of the deepness of the other two pockets. Therefore, it is non surprising to happen that AFI measuring is lower when the foetus lies on one side of the uterus alternatively of centrally. The difference was statistically important and is clinically of import. When the foetus lay on one side of the womb, the AFI was, on norm, 4.35 centimeter lower compared with the AFI for a foetus lying centrally. On the contrary, SDP is seemingly instead ‘inert ‘ to foetal place. Since SDP merely measures the deepest pocket, it is apprehensible that the consequence of foetal place on its measuring is less.
Based on the consequences of this survey, SDP may be a better index for appraisal of amnionic fluid volume than is AFI, because the association between SDP and lateralization mark remained non-significant ( P = 0.4, ? = 0.8, standard mistake = 0.9 ) . Further analysis was besides performed with additive arrested development to command for the consequence of gestational age. These consequences showed that the lateralization mark had a important consequence on AFI ( ? = 9.6, standard mistake = 3.0, P = 0.002 ) that was independent of gestational age ( ? = ?0.4, standard mistake = 0.2, P = 0.019 ) .
AFI was significantly higher in cephalic foetal place, more than with breech 1s. This consequence had been clearly evident after 32 hebdomads gestation, and with less AFI with the ventral foetal bole attitude with the rear of barrel place, than other. SDP had non demo the same image in different foetal places, either rear of barrel or cephalic, so SDP as an AFV parametric quantity had non been affected with the different foetal places. Of the 3000 foetuss, 345 were ventral anterior, 1720 were ventral sidelong and 803 were ventral buttocks. The several gestational ages of these groups were 33.5 ± 2.7, 32.8 ± 2.7 and 34.2 ± 2.8 hebdomads, the SDPs were 5.5 ± 1.4, 5.5 ± 1.3 and 5.5 ± 1.4 centimeter, and the AFIs were 14.5 ± 5.3, 14.4 ± 4.4 and 14.8 ± 4.4 centimeter. None of these was significantly different between the three groups ( P = 1.0, P = 0.14 and P = 0.9, severally ) .
The 3000 pregnant adult females were divided into two subgroups harmonizing to the position of the foetal membranes. The membranes were found to be ruptured at the clip of the scrutiny in 1400 ( 44 % ) adult females ; 750 ( 25 % ) had oligohydramnios. The membranes were integral in 1600 ( 55 ) ; 350 ( 15 % ) had hydramnios. Table I shows the maternal variables of the two groups. The average interval between the ultrasound scrutiny and bringing was 4 H ( range 0-24 H ) in the group with ruptured membranes and 6 H ( range 0-70 H ) in those with integral membranes.
In the group with ruptured membranes there was a important difference in the frequence of operative bringing due to feta hurt between the parturients with oligohydramnios and those with a normal volume of amnionic fluid [ 10.6 % and 3.0 % , severally, P & A ; lt ; 0.02, OR 3.86 ( run 1.34-1.11 ) ] . No important differences were found sing the other variables of perinatal result ( Table II ) . In the group with integral membranes, there was a 50 % increased hazard of operative intercession due to foetal hurt ( OR 1.5 ) , though non important ( CI 0.48-4.63 ) ( Table III ) .
There is a fluctuation in AFI measurings harmonizing to gestational age. Valuess in the current survey remain comparatively changeless until the 33rd hebdomad of gestation when a progressive lessening starts, going peculiarly apparent after the 38th hebdomad of gestation. The normal lower and upper bound values of the AFI normally used up to now, which vary between 50 and 200 millimeter, are similar to those found in the nowadays study up to the fortieth hebdomad of gestation. When following mention values between 80 and 180 millimeter for every hebdomad of gestation ( 19,20 ) , wrong diagnosing are likely to happen.
Our findings, suggested a strong influence of foetal place on sonographic indices of amnionic fluid volume. Furthermore, we recruited adult females with seemingly normal gestations and hence most likely with normal amnionic fluid volumes. Further surveies should look at the relationship between foetal place and amnionic fluid volume indices in instances of oligohydramnios and polyhydramnios. Pregnant adult females, who are classified as holding oligohydramnios by these standards, may perchance be considered normal if a mention curve of AFI specific to gestational age were used, particularly in term and post-term gestations.
The adoptive bound values bespeaking an change in the AFV are variable. For the foetal biophysical profile, the measuring of merely one pocket is adopted, changing from 1 to 3 centimeter, and considered the lower normal bound by some writers ( 21,22 ) ; nevertheless, in this instance, entire volume would be considered reduced if the AFI were used. In fact, a RCT comparing both techniques showed an overestimate of unnatural consequences with AFI in post term gestations, increasing the figure of obstetric intercessions ( 23 ) .
These fluctuations in sorting oligohydramnios reflect uncertainties sing which percentiles best express the correlativity between the lessening in AFV and hapless foetal result. When the 50th percentile AFI was compared with that reported in a old survey ( 14 ) , measurings were ever higher in our survey at all gestational ages by about 50 mm up to 28 hebdomads, and by 30 – 40 millimeter between 32 and 40 hebdomads of gestation. On the other manus, the current fiftieth percentile showed fewer fluctuations, around 10 millimeters at all gestational Ges, compared to the consequences of the Indian survey population ( 15 ) .
The importance of a curve that includes the tenth and 90th percentiles is reflected in its greater capacity to place unnatural instances. Therefore, if the 10th percentile is used as the lower normal bound, there would be less likeliness of losing a instance of existent oligohydramnios. A curve that included the 2.5th and 97.5th percentiles would name fewer instances of unnatural AFI, and this could ensue in more instances of oligohydramnios or polyhydramnios being included within the normal scope.
By following the 10th percentile of AFI as the diagnosing for oligohydramnios in our population, the values are higher than those found for the Chinese analyze up to 36 hebdomads, but similar around 40 hebdomads of gestation ( 14 ) . When we compare the consequences of this survey to old published curves ( 10-17 ) , similarities can be seen for the fiftieth percentile of AFT at all gestational ages. However, when comparing the 2.5th percentile, it is apparent that the measurings in Moore and Cayle ‘s curve are lower up to the thirty-fifth hebdomad of gestation, after which they are higher than the values found in our survey curve. The 97.5th percentile of the Moore and Cayle curve is somewhat higher at all gestational ages except for the 41st and 42nd hebdomads.
The lower bound of 2 standard-deviations and the average values of the Jeng et Al. ( 11 ) curve are somewhat lower in relation to the present curve at matching gestational ages, except from the 37th to the 42nd hebdomad, when values remain higher than those in the present curve. The definition of normal AFI can non, in itself, guarantee good perinatal result. For case, a 42-week gestation with an AFI of 45 millimeters would be considered normal, but how physiological this value is and what existent hazard it represents are inquiries that still need to be to the full answered.
If the correlativity between AFV and perinatal result can be established, this curve may hold a broader clinical application in antenatal diagnosing and attention. Furthermore, the curve of the 2.5th, 10th, 50th, 90th and 97.5th percentiles of the AFI measurings shows a important lessening harmonizing to gestational age, particularly after the 32nd hebdomad.
This measuring could, hence, considered a normal mention curve for the rating of AFI. The consequences of the present survey suggest that oligohydramnios after rupture of the membranes in low-risk gestations is associated with a about four-fold increased hazard of operative bringing due to foetal hurt. An ultrasound scrutiny of AFI could therefore place those who may necessitate intensified foetal surveillance during labour.
The present survey was performed on a selected group of adult females with low-risk gestation. As AFI is one of the parametric quantities checked in bad gestations at our infirmary, these parturients were excluded in order to do the survey ‘blind ‘ . By adding bad gestations, a much smaller sample size would be needed. The frequence of oligohydramnios in instances with integral membranes was out of the blue high: 15 % alternatively of 5 % in the controls.
Although our gestations were low-risk, a few showed marks of gestation complications on admittance to the labour ward ( Table I ) , which might explicate the higher frequence of oligohydramnios in this group. Although there was a important correlativity between operative bringing due to foetal hurt and oligohydramnios in instances of ruptured membrane ( Table II ) , sensitiveness was low ( 11 % ) , and false-positive and negative rates were 46 % and 23 % , severally. Thus the cognition of oligohydramnios in these low-risk gestations did non do any immediate action, merely more intense surveillance during labour.
In the present survey there was a 50 % increased hazard of operative foetal bringing due to foetal hurt in parturients with oligohydramnios and integral membranes. Teoh et Al. studied 120 gestations as an admittance survey in early labour with integral membranes. The frequence of oligohydramnios ( AFI & A ; lt ; 5 centimeter ) in their survey was 22 % , and operative bringing due to foetal distress frequence among these was 27 % . Based on these informations, a sample size of 100 would be sufficient. We chose, nevertheless, three times that size, as the low-risk position of their population was unsure ( 9, 11 ) .
The pathophysiology of oligohydramnios before membrane rupture is ill-defined. One theory is that a decreased perfusion of the placenta causes hypovolaemia in the foetus, and/or an automatic redistribution of foetal blood volume to critical variety meats with a end point reduced blood supply to the kidneys. This in bend could take to decreased production of piss, and therefore cut down the volume of amnionic fluid. Bar- Hava et Al. studied marks of redistribution, nephritic blood flow, and marks of oligohydramnios, but could happen no correlativity. There was no alteration in the nephritic arteria pulsatility index ( 12, 14, 19 ) .
Oligohydramnios in labour after the rupture of membranes in a low-risk gestation is likely non caused by a decreased perfusion of the placenta, but is more likely caused by the loss of big sums of amnionic fluid at the clip of the rupture. One account for the significantly increased hazard of operative bringing due to foetal hurt in the group with ruptured membranes might be that there is an increased hazard of the umbilical cord going trapped in an ad- poetry place, at the clip of the rupture, if a big sum of amnionic fluid is lost. Amnioinfusion may be a manner to handle such instances in order to reconstruct the volume of amnionic fluid and cut down the hazard of compaction of the umbilical cord, therefore debaring the demand for operative bringing ( 11, 21, 23 ) .
As a decision of the current survey, appraisal of the AFV during gestation utilizing the SDP appears to be more accurate than the AFI, particularly the SDP rating has non been affected significantly with either different foetal places or attitudes, but still we are in demand for farther controlled surveies to compare the truth of the two manners of AFV appraisal. Another decision drawn from our survey is that an ultrasound scrutiny, including measuring of AFI as an admittance trial for adult females showing at the labour ward with ruptured membranes after an uneventful gestation, could assist place those with an increased hazard of intrapartum foetal hurt, viz. those with oligohydramnios.
Furthermore Measuring AFI in low-risk gestations on admittance to the labour ward might observe instances necessitating particular surveillance. We are presently fixing a new ongoing survey, as an extension to the current survey, comparing the old two parametric quantities of AFV appraisal in high hazard gestations, and the preliminary consequences could corroborate the antecedently mentioned consequences, but it is excessively early to acquire to a concluding decision.