The proper measure of intrauterine growth retardation is function, not size

Fetal and neonatal outcomes of preterm infants born before 32 weeks of gestation according to antenatal vs postnatal assessments of restricted growth

BACKGROUND

Fetal growth restriction is defined using ultrasound parameters during pregnancy or as a low birthweight for gestational age after birth, but these definitions are not always concordant.

OBJECTIVE

The purpose of this study was to investigate fetal and neonatal outcomes based on antenatal vs postnatal assessments of growth restriction.

STUDY DESIGN

From the EPIPAGE 2 population-based prospective study of very preterm births in France in 2011, we included 2919 singleton nonanomalous infants 24-31 weeks gestational age. We constituted 4 groups based on whether the infant was suspected with fetal growth restriction during pregnancy and/or was small for gestational age with a birthweight <10th percentile of intrauterine norms by sex: 1) suspected with fetal growth restriction/small for gestational age 2) not suspected with fetal growth restriction/small for gestational age 3) suspected with fetal growth restriction/not small for gestational age and 4) not suspected with fetal growth restriction/not small for gestational age. We estimated relative risks of perinatal mortality and morbidity for these groups adjusting for maternal and neonatal characteristics.

RESULTS

We found that 22.2% of infants were suspected with fetal growth restriction/small for gestational age, that 11.4% infants were not suspected with fetal growth restriction/small for gestational age, that 3.0% infants were suspected with fetal growth restriction/not small for gestational age, and that 63.4% infants were not suspected with fetal growth restriction/not small for gestational age. Compared with infants who were not suspected with fetal growth restriction/not small-for-gestational-age infants, small-for-gestational-age infants suspected and not suspected with fetal growth restriction had higher risks of stillbirth or termination of pregnancy (adjusted relative risk, 2.0 [95% confidence interval, 1.6-2.5] and adjusted relative risk, 2.8 [95% confidence interval, 2.2-3.4], respectively), in-hospital death (adjusted relative risk, 2.8 [95% confidence interval, 2.0-3.7] and adjusted relative risk, 2.0 [95% confidence interval, 1.5-2.8], respectively), and bronchopulmonary dysplasia (adjusted relative risk, 1.3 [95% confidence interval, 1.2-1.4] and adjusted relative risk, 1.3 [95% confidence interval, 1.1-1.4], respectively), but not severe brain lesions. Risks were not increased for infants suspected with fetal growth restriction but not small-for-gestational-age.

CONCLUSION

Antenatal and postnatal assessments of fetal growth restriction were not concordant for 14% of very preterm infants. In these cases, birthweight appears to be the more relevant parameter for the identification of infants with higher risks of adverse short-term outcomes.

Normal and abnormal fetal growth

The fetal origins of adult disease hypothesis suggests that poor intrauterine growth is associated with an increased risk of cardiovascular disease. The hypothesis goes on to implicate different growth 'phenotypes', particularly disproportionate growth, in the determination of the type of cardiovascular disease that develops. Analysis of the antenatal growth of a low-risk pregnancy population does not identify such growth phenotypes within the general population. Rather, intrauterine growth is characterized by poor predictability of subsequent size, suggesting that centile crossing is a common feature of intrauterine growth. Furthermore, there is a sexually dimorphic pattern to this growth that needs to be considered in further work to test the fetal origins hypothesis.

The management of large and small for gestational age fetuses

The major influence on birth weight is gestational age. At any given week of gestation, however, size varies enormously. There is no specific cut-off that separates abnormally large or small babies for gestational age from normal. Instead, function alters as a continuum across the weight distribution. Small babies are prone to hypoxia, acidosis, and stillbirth. Large babies on the other hand are associated with prolonged labor and mechanical problems. The optimum size for fetal survival is 1 to 1.5 standard deviations above the mean, whereas cesarean section rates are lowest when the fetal weight is 0.5 to 1.5 standard deviations below the mean. Antenatal detection of both very small and very large babies is difficult and imprecise. Expectant management is therefore preferable unless there are very specific indications for emergency or operative delivery.

Intrauterine growth and its relationship to size and shape at birth

Birth size and shape are commonly used as indicators of fetal growth. Epidemiologic studies have suggested a relationship between birth size and the risk of developing cardiovascular disease in later life. Certain "growth phenotypes" have been linked to the development of certain components of cardiovascular disease, particularly babies who display disproportional growth in utero. These observations are based on retrospective analysis of historical data sets. If the "Fetal Origins of Adult Disease" hypothesis is to be generalisable to the present day, then it is essential to establish whether these "growth phenotypes" exist within the normal distribution of birth size. The UCL Fetal Growth Study is a prospective study of antenatal fetal growth assessed by ultrasound at 20 and 30 wk gestation in 1650 low risk, singleton, white pregnancies. Measures of birth size were obtained and analyzed by principal components to explain shape at birth. Birth measures were also related to antenatal growth measurements to determine the strength of ultrasound evaluation in determining subsequent growth. There was significant sexual dimorphism in all measures at birth, with males heavier, longer, and leaner than females. From 20 wk of gestation onwards, males had a significantly larger head size than females. Parity, maternal height, and body mass index were important determinants of birth weight (p < 0.001). Cigarette smoking influenced birth weight, length, and head circumference (p < 0.001) but had no effect on placental size. Principal component analysis revealed that proportionality was the predominant size/shape at birth (55% of variance explained). A further 18% of variance was explained by a contrast between weight, head circumference, and length versus three skinfolds. Anthropometric measures as assessed by ultrasound at 20 and 30 wk gestation were poor predictors of birth length, weight, and head circumference (adjusted R(2) 18, 40, and 28% at 30 wk gestation scan, respectively). These predictions were not improved by including growth patterns between 20 and 30 wk. There is sexual dimorphism in a number of anthropometric measures at birth and in utero. These sex differences are important determinants of body size and shape. In a low risk population delivering at term, body shape was largely determined by proportionality between anthropometric measures. The low correlations between antenatal measures and birth size suggest that it is unwise to ascribe birth shape phenotypes to adverse events at any particular stage of gestation. The weak relationship also suggests that routine antenatal scans around 30 wk of gestation to predict growth problems are unlikely to be of benefit in the majority of cases.

Identification of fetal growth abnormalities in diabetes mellitus

Gestational diabetes complicates 3% to 5% of all pregnancies. Shoulder dystocia and fetal injuries are associated with macrosomia, a complication often encountered in diabetic pregnancies. The route of delivery is often planned in advance and based on estimated fetal weight. Fetuses of diabetic mothers are prone to macrosomia due to increased subcutaneous adipose tissue deposits, and perinatal complications are more frequent in these fetuses. For this reason, particular effort should be directed toward the diagnosis of fetal growth abnormalities in fetuses of diabetic mothers. There are numerous formulas for estimating fetal weight, and they are all error prone. An effort should be made to follow these high-risk pregnancies in a longitudinal fashion to detect any developing growth abnormality as early as possible. Whether macrosomia or intrauterine growth restriction, early detection and careful planning of mode and time of delivery is the foundation of successful lowering of perinatal morbidity and mortality.

Fetal growth retardation and second trimester maternal serum human chorionic gonadotrophin levels

Second trimester maternal serum human chorionic gonadotrophin (hCG) levels in women who remained normotensive but delivered an unexplained growth retarded infant were compared with those from a control group and a group of women who developed pre-eclampsia in a retrospective observational study. Our hypothesis was that the similar placental pathological changes shared by unexplained normotensive IUGR and pre-eclampsia would be reflected by elevated maternal serum hCG levels in the second trimester. Normotensive women delivering unexplained singleton growth retarded infants were identified (n=43) and their second trimester hCG levels, taken as part of antenatal screening for Down's syndrome, were obtained. These were compared with a control group of 625 women, and a group of 48 women who subsequently developed pre-eclampsia. There was no significant difference in the hCG levels expressed as multiples of the median (MOM) between the women who delivered growth retarded fetuses (median MOM 0.96) and the control group (median MOM 0.97). The levels of hCG in the women who subsequently developed pre-eclampsia were significantly higher (median MOM 1.3, P=0.008). There were no significant differences in AFP levels in the three groups; however, the trend was towards a higher level of AFP in the fetal growth retardation group. Maternal serum hCG in the second trimester does not appear to be elevated in normotensive women who later produce a growth retarded fetus, although human chorionic gonadotrophin levels are significantly higher in women who subsequently develop pre-eclampsia.

Fetal size and growth velocity in the prediction of intrapartum caesarean section for fetal distress

OBJECTIVE

To evaluate and compare third trimester ultrasound measurements of fetal size and growth velocity in the prediction of intrapartum operative delivery for fetal distress and admission to the special care baby unit in a low risk antenatal population undergoing labour at term.

DESIGN

Retrospective analysis of prospectively collected ultrasound data.

SETTING

Ninewells Hospital, Dundee, Scotland.

POPULATION

Three hundred and ninety-eight women previously enrolled in a longitudinal study of intrauterine volume undergoing labour at a gestational age of > 37 weeks.

METHOD

Fetal abdominal area (FAA) standard deviation scores (Z scores) were calculated for size at 32 and 36 weeks of gestation together with the growth velocity Z scores between these two gestational ages. Receiver-operator characteristics were calculated for fetal abdominal area Z scores at 32, 36 weeks and velocity Z scores in the prediction of caesarean section for fetal distress and/or admission to the special care baby unit.

MAIN OUTCOME MEASURES

Intrapartum caesarean section for fetal distress and admission to the special care baby unit with a diagnosis of perinatal hypoxia.

RESULTS

Pregnancies ending in caesarean section for fetal distress or admission to the special care baby unit (n = 17) had significantly lower fetal abdominal area Z scores at 36 weeks of gestation (mean Z score -0.71 vs -0.18) and lower fetal abdominal area growth velocity (mean Z score - 1.31 vs -0.01). Taking a cutoff Z score of -1.2 derived from the receiver-operator characteristic curve, fetal abdominal area velocity has a sensitivity of 65% and specificity 75% for caesarean section for fetal distress and/or admission to the special care baby unit.

CONCLUSION

Growth velocity of the fetal abdominal area in the third trimester is superior to a single measurement of the fetal abdominal area at either a mean of 32 or 36 weeks of gestation in the prediction of caesarean section for fetal distress and admission to the special care baby unit in low-risk women labouring at term. These results support the hypothesis that in the third trimester at least, growth rate in utero is more relevant to intrapartum performance and immediate perinatal outcome than estimates of fetal size alone.

The biochemistry and clinical application of urinary oestriol measurement during late pregnancy in the 1990's

Part 1. The present disillusionment with oestriol measurement as a test of fetoplacental function could be explained by the use of poor methodology and inappropriate normal ranges rather than that the test has lost its usefulness. We have updated the Lever method for measuring oestriol in urine, and examined the automatic TDX system supplied by Abbott Laboratories. The precision of the methods and consistency of results between methods have been determined and normal ranges have been established for both methods. The overall accuracy of collection of 24-hour urine specimens in a routine laboratory setting has also been calculated. The normal ranges suggested as a guide for the TDX method by Abbott were based on those derived from the original method of Brown and were found to be too low and therefore unsuitable for clinical use. This study reports appropriate lower limits of normal for both the updated Lever and the TDX methods. Part 2. The results obtained using the updated Lever method since its introduction in 1991 have been compared with those obtained by the original Brown method during the years 1971-1989. The new, user-friendly Lever method of oestriol assay measurement used in 1991-1993 gave results of equivalent clinical value to the Brown method used in 1971-1989, although the perinatal mortality rates in the tested populations fell from 0.95% to 0.37%. During 1971-1989, low oestriol excretion on 1 or more occasions was associated with a 5.6-fold increase in the perinatal mortality rate (0.66% to 3.67%), whereas in 1991-1993, the factor was 4.4 (0.27% to 1.2%).(ABSTRACT TRUNCATED AT 250 WORDS)