Umbilical blood flow and neonatal morphometry: a multivariate analysis

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Abstract

Objective: To study the relation between the state of umbilical blood flow and neonatal morphometry. Study design: We have recorded data from 460 pregnant women. Umbilical systolic to diastolic ratio was measured within the 3 days prior to the birth. Weight, height, head and chest circumferences, ponderal and head to chest circumferences ratio were considered for the study. Results: In a univariate analysis, the best correlated variable to S/D ratio was the weight (r=−0.35). However, a forward stepwise multiple regression analysis demonstrated that the best predictors of S/D ratio were height and ponderal index. Small-for-gestational-age fetuses with placental insufficiency (n=20) had a significant more pronounced decrease of weight, height, head circumference and chest circumference than those with normal placental perfusion (n=31). The degree of decrease of ponderal index and HC/TC was similar in both groups. Conclusions: Umbilical blood flow is one important factor determining newborn morphometry. If only one growth variable is considered, the best correlation with umbilical S/D ratio is found to be the weight. The multivariate regression analysis concluded that the two most influential factors by umbilical blood flow are height and ponderal index and the rest of the morphometric parameters lost their significant correlations when adjusted by these variables. The impairment on neonatal morphometry in small-for-gestational-age fetuses associated to placental insufficiency is more severe than that with normal placental perfusion. However, it does not have a more pronounced decrease of ponderal index than the rest of causes of small-for-gestational-age fetuses.

Introduction

Several parameters have been considered more representative of fetal nutrition than weight. Many authors have used ponderal index to distinguish between asymmetric growth retardation (low ponderal index: weight more affected than length) and those with symmetric growth retardation (normal ponderal index: weight and length affected together). Asymmetric retardation is believed to arise as a result of placental insufficiency and in most of the cases this is caused by an impaired placental perfusion, which can be demonstrated by Doppler ultrasound 1, 2, 3. However, when one wishes to study the influence of placental perfusion on fetal growth, several problems are found.

Firstly, the majority of the studies that have evaluated and found significant relationships between umbilical blood flow and fetal growth have used ultrasonographic prenatal parameters. Although it was believed that fetal biometry could really estimate fetal growth and nutrition, there is now a considerable doubt about this. For instance, it has been demonstrated that it is very difficult to do the separation between the two types of growth retardation (symmetric and asymmetric) using ultrasonographic parameters (ratio of head and abdominal circumference) [4].

Secondly, in most of these studies, pathologic conditions are not separated from normal ones. We know that an impaired umbilical blood flow caused a fetal growth restriction, but we do not know how slight differences in placental perfusion could affect fetal growth and nutrition.

Thirdly, there is a very significant interrelation between all variables measuring neonatal morphometry. For example, it was believed that there was no reason why the ponderal index should be any different in infants with different weights, unless a specific disease altered it. Nevertheless, a continuous relation between ponderal index and weight throughout the entire range of normal birthweight has recently been demonstrated [5]. Therefore, the relation of one of these variables to umbilical Doppler ultrasound may be due to its relation to another one, which is strongly correlated with umbilical blood flow. We thought that a multivariate analysis among the different measured parameters should be done to avoid this source of errors.

In this way, we have studied the influence of the state of umbilical blood flow on fetal growth, taking into account these considerations. Firstly, we have used neonatal more than ultrasonographic prenatal parameters. Secondly, we have evaluated separately pathologic and normal conditions. Thirdly, we have employed multivariate analysis to study the real relation of umbilical blood flow to each morphometric parameter.

Section snippets

Materials and methods

We have recorded data from 460 pregnant women who were evaluated in the Division of Maternal–Fetal Medicine, University Hospital of Puerto Real. The mean age was 27.32 years (S.D., 11.25) and in 275 cases (59.78%) were nulliparous women. The mean gestational age was 39.44 weeks (S.D.: 2.39). The main diagnoses of these pregnant women were the following: 127 prolonged pregnancies, 46 hypertension, 39 small-for-gestational-age fetuses, 30 preterm labour, 31 diabetes, 28 maternal disease, 12 prior

Results

Four hundred and sixty newborns were studied. Two hundred and fifty four of them (55.22%) were female and 206 (44.78%) were male. One hundred and twenty two were delivered by a cesarean section (26.52%) and in 19 of these cases the operation was due to fetal distress. In 9 cases (1.96%) the Apgar score at 5 min was below 7. Fifty-eight newborns were admitted in Neonatal Unit. In 45 of these, the cause was a weight below 2500 g. There was no perinatal death and all infants were chromosomally and

Discussion

Only a few studies have reported data on the correlation between umbilical Doppler waveform indices and neonatal morphometry. Trudinger et al. [6]evaluated this relation in high risk pregnancies and reported a significantly reduced neonatal ponderal index in fetuses with an abnormal systolic/diastolic ratio compared with those with normal Doppler ratios. In infants with normal birth weight and without placental insufficiency, an inverse close relationship between birth weight and placental

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