Ultrasonographic estimate of birth weight at 24 to 34 weeks: a multicenter study

The clinical significance of an estimated fetal weight below the 10th percentile: a comparison of outcomes of <5th vs 5th-9th percentile

BACKGROUND

The association between small-for-gestational-age (birthweight <10th percentile for gestational age) and neonatal morbidity is well established. Yet, there is a paucity of data on the relationship between suspected small for gestational age (sonographic-estimated fetal weight <10th percentile) at 2 thresholds and subsequent neonatal morbidity.

OBJECTIVE

The objective of this study was to determine the relationship between sonographic-estimated fetal weight <5th percentile vs 5-9th percentile and neonatal morbidity.

STUDY DESIGN

This retrospective study involved 5 centers and included nonanomalous, singletons with sonographic-estimated fetal weight <10th percentile for gestational age who delivered from 2009-2012. Composite neonatal morbidity included respiratory distress syndrome, proven sepsis, intraventricular hemorrhage grade III or IV, necrotizing enterocolitis, thrombocytopenia, seizures, or death. Odd ratios were adjusted for center, maternal age, race, body mass index at first visit, smoking status, use of alcohol, use of drugs, and neonatal gender.

RESULTS

Of 834 women with suspected small-for-gestational-age fetuses, 513 (62%) had sonographic-estimated fetal weight <5th percentile, and 321 (38%) had sonographic-estimated fetal weight of 5-9th percentile for gestational age. At delivery, 81% of women with a suspected small-for-gestational-age fetus had a confirmed small-for-gestational-age fetus. In the group with a sonographic-estimated fetal weight <5th percentile, 59% of neonates had birthweight <5th percentile; in the group with a sonographic-estimated fetal weight 5-9th percentile, 41% had birthweight <5th percentile, and 36% had birthweight at 5-9th percentile. Neonatal intensive care unit admission differed significantly for those fetuses at <5th percentile (29%) compared with those fetuses at 5-9th percentile (15%; P<.001). The composite neonatal morbidity among the sonographic-estimated fetal weight <5th percentile group was higher than the sonographic-estimated fetal weight of 5-9th percentile group (31% vs 13%; adjusted odds ratio, 2.41; 95% confidence interval, 1.53-3.80). Similar findings were noted when the analysis was limited to sonographic-estimated fetal weight within 28 days of delivery (adjusted odds ratio, 2.22; 95% confidence interval, 1.34-3.67).

CONCLUSION

Eight of 10 suspected small-for-gestational-age fetuses had birthweight <10th percentile for gestational age; the prediction of actual birthweight was more accurate in the <5th percentile group. Neonates with sonographic-estimated fetal weight of <5th percentile were more likely to be admitted to the neonatal intensive care unit and have complications than were those neonates with sonographic-estimated fetal weight of 5-9th percentile.

MANAGEMENT OF ENDOCRINE DISEASE: Growth and growth hormone therapy in short children born preterm

Approximately 15 million babies are born preterm across the world every year, with less than 37 completed weeks of gestation. Survival rates increased during the last decades with the improvement of neonatal care. With premature birth, babies are deprived of the intense intrauterine growth phase, and postnatal growth failure might occur. Some children born prematurely will remain short at later ages and adult life. The risk of short stature increases if the child is also born small for gestational age. In this review, the effects of being born preterm on childhood growth and adult height and the hormonal abnormalities possibly associated with growth restriction are discussed, followed by a review of current information on growth hormone treatment for those who remain with short stature during infancy and childhood.

Optimal risk assessment of small-for-gestational-age fetuses using 31-34-week biometry in a low-risk population

OBJECTIVE

To compare the performance of traditional growth charts for estimated fetal weight (EFW) and a validated pragmatic probabilistic approach using biometry at 31-34 weeks' gestation to screen for late pregnancy small-for-gestational age (SGA) fetuses in a low-risk population.

METHODS

Records of ultrasound biometry at 31-34 weeks were reviewed in 7755 consecutive low-risk women between 2002 and 2011. Fetal malformations, Doppler anomalies and preterm delivery before 37 weeks were excluded. SGA was defined by various percentile cut-offs of birth weight. The probability of SGA was modeled as a function of Z-scores of femur length, abdominal circumference and head circumference. The model was validated on a second independent dataset of 1725 pregnancies from a different screening unit. The screening performance of this probabilistic approach was compared with those of traditional EFW growth charts. The additional value of factoring in maternal characteristics was also ascertained.

RESULTS

Using national birth-weight charts, the proportions of newborns at 37-42 weeks with birth weight<3(rd) , <5(th) and<10(th) centiles were 3%, 6% and 12%, respectively, and there was a 2% rate of birth weight<2500 g. For a 10% false-positive rate, a direct probabilistic approach yielded a 51% detection rate of neonates with birth weight<10(th) centile, compared to the 32% and 48% detection rates given by the 10(th) centile cut-off of two reference charts for EFW. Adding maternal characteristics significantly improved detection rate by 2% to 53%.

CONCLUSIONS

The suggested validated approach to screening for late SGA fetuses outperforms traditional approaches using growth charts. By adding maternal characteristics, this screening method offers a favorable alternative to customized charts.

A review of sonographic estimate of fetal weight: Vagaries of accuracy

PURPOSE

To determine the factors that might influence the accuracy of sonographic estimated fetal weight.

STUDY DESIGN

A PubMed search (Jan 1975 to Jan 2003) of articles published in the English language was carried out and the inclusion criterion was that estimates were within 10% of birth weight. A Chi-square test for trend was used and odds ratio (OR) with 95% confidence intervals (CI) was calculated.

RESULTS

Over 28 years, 175 articles were identified but only 54 (31%) met the inclusion criterion. Overall 62% (8895/14 384) of the predictions were within 10% of the actual weight. The accuracy was significantly different in articles where <7 vs. >7 days were allowed to lapse between examination and delivery (OR 2.17, 95% CI 1.93, 2.45); where examinations were done by registered diagnostic medical sonographers (RDMS; 65%) versus physicians (59%) or residents (57%; p < 0.0001); in term vs. preterm patients (OR 1.97, 95% CI 1.67, 2.13); and in studies with >1000 vs. <1000 cohorts (OR 1.62; 95% CI 1.51, 1.74).

CONCLUSIONS

If feasible the sonographic examination should be done by RDMS and within a week of delivery.

Detection of fetal growth restriction in patients with chronic hypertension: is it feasible?

OBJECTIVE

To determine the utility of sonographic estimated fetal weight (EFW) in diagnosing intrauterine growth restriction (IUGR, birth weight < 10% for gestational age) in patients with chronic hypertension.

METHODS

All pregnant patients with hypertension delivered during a 5-year period at three centers were identified retrospectively. Patients with gestational hypertension, pre-eclampsia, diabetes mellitus, fetal anomalies and absence of a sonographic examination within 3 weeks of delivery were excluded. Likelihood ratio (LR) and guidelines established by the Evidence-Based Medicine Working Group were used to determine whether sonographic EFW is a reliable diagnostic test to detect IUGR.

RESULTS

At the three centers, there were 264 patients with chronic hypertension (122, 77 and 65 at centers I, II and III, respectively). The incidence of IUGR ranged from 13% to 27% but was similar at the three locations (p = 0.064). The LR (with 95% confidence interval (CI)) of detecting IUGR was 4.4 (95% CI 2.5, 7.7), 2.3 (95% CI 1.4, 3.7) and 6.1 (95% CI 2.7, 13.7) at centers I, II and III, respectively. Based on the proportions of abnormal growth, we required 253 and 71 newborns with fetal growth restriction at centers I and II, respectively, to have narrow confidence intervals around the clinically important LR of 10. The extremely low incidence of IUGR at center III (13%) precluded the estimation of required sample size.

CONCLUSION

Use of Evidence-Based Medicine Working Group guidelines indicates that sonographic EFW is slightly to moderately useful in detecting fetal growth restriction in patients with chronic hypertension.

Birthweight percentiles by gestational age and gender for children in the North of Mexico

The objective of this study was to determine the 10th, 50th and 90th percentiles of birthweight, by gestational age and sex, for newborns covered by the Mexican Institute of Social Security (IMSS) in the State of Chihuahua. To generate the database, we used IMSS hospitals' records in the State of Chihuahua, covering the period between 1 January 2000 and 31 December 2004. We included singleton live births only, and excluded babies with congenital malformations. The birthweights of 88,368 children born at 21-44 weeks of gestation comprised our data. From these data, we calculated the 10th, 50th and 90th percentiles for each sex, at 32-44 weeks of gestation. The observed cutoffs for the 10th percentile in our population were 40-250 g higher than those reported in other references with Mexican populations. These results constitute an updated birthweight reference that will allow the identification of newborns in the North region of the country with low birthweight-for-gestational age. Such information can be a useful instrument for preventing or diminishing associated risks.

Estimation of fetal weight: reference range at 20-36 weeks' gestation and comparison with actual birth-weight reference range

OBJECTIVES

To formulate reference charts and equations for estimated fetal weight (EFW) from a large sample of fetuses and to compare these charts and equations with those obtained for birth weight during the same study period and in the same single health authority.

METHODS

Biometric data were obtained at 20-36 weeks' gestation from routine screening examinations spanning 4 years. Exclusion criteria were a known abnormal karyotype or congenital malformation and multiple pregnancy. No data were excluded on the basis of abnormal biometry. EFW was calculated based on Hadlock's formula. We used a polynomial regression approach (mean and SD model) to compute a new reference chart for EFW. This chart was compared with that of birth weight at 25-36 weeks' gestation during the same study period and in the same health authority.

RESULTS

18,959 fetuses were included in the study. New charts and equations for Z-score calculations at 20-36 weeks' gestation are reported. Comparison with the birth-weight chart showed that the EFW was noticeably larger at 25-36 weeks' gestation. At 28-32 weeks' gestation, the 50th centile for birth weight compared approximately with the 10th centile for EFW.

CONCLUSION

We present new reference charts and equations for EFW. EFW is computed throughout gestation based on measurements in healthy fetuses. However, before full term, birth-weight charts reflect a significant proportion of growth-restricted fetuses that deliver prematurely. We provide additional evidence that comparing EFW with birth-weight charts is misleading.

Sonographic estimate of birth weight among high-risk patients: feasibility and factors influencing accuracy

OBJECTIVE

This study was undertaken to determine the feasibility of detecting abnormal fetal growth among patients undergoing biophysical profile (BPP) and to identify the factors those influence the accuracy.

STUDY DESIGN

Retrospectively singletons with reliable gestational age (GA) having a BPP were identified. Fetal growth restriction (FGR) and large-for-gestational age (LGA) were based on estimated or actual birth weight 10% or less or 90% or greater for GA, respectively. Likelihood ratio (LR), odds ratio (OR) and 95% CIs were calculated and multivariate predictive models used.

RESULTS

Among the 1934 consecutive patients that met the inclusion criteria, the LR of detecting FGR was 10.9 and of LGA, 17.4. Multivariate analysis indicates that accurate classification of fetal growth is significantly better with hydramnios (OR 1.78, 95% CI 2.68), if the GA is less than 32 weeks (OR 3.71, 95% CI 1.50-9.16) or GA is between 32.1 and 36.9 weeks (OR 1.43, 95% CI 1.05-1.96).

CONCLUSION

It is feasible to accurately identify abnormal growth among high-risk patients and to delineate factors that influence the correct classification of fetal growth.

Bone, lean and fat mass of newborn twins versus singletons

AIM

Twin gestations are associated with disturbed fetal growth. The aim of this study was to compare body composition measurements of twins to those of singletons.

METHODS

Anthropometric and dual energy X-ray absorptiometry (DXA) measurements were performed in twins and in matched singleton neonates. There were 48 pairs of twins in which 76 infants were appropriate for gestational age (AGA) with birth weights between the 10th and 90th percentile and 20 were small for gestational age (SGA) with birth weights <10th percentiles. Each AGA twin was matched as closely as possible for birth weight to an AGA singleton. Each SGA twin was matched with two cohorts of AGA singletons: one with similar birth weight and one with similar gestation.

RESULTS

For AGA twins and their singleton cohort matched for birth weights, profile analysis using repeated measure analysis of variance showed that there were no significant differences in bone, fat and lean mass either as absolute values or as percentage of total weight. This was also the case for body composition of SGA twins compared to singletons matched for birth weight. In contrast, SGA twins have significantly lower absolute amounts of lean with tendency to lower fat and bone mass.

CONCLUSION

For clinically normally grown neonates, with comparable weight, the body composition with respect to bone, fat and lean mass components are similar regardless whether they are products of singleton or twin pregnancies.

Suspicion and treatment of the macrosomic fetus: a review

OBJECTIVE

To review the prevalence of and our ability to identify macrosomic (birthweight >4000 g) fetuses. Additionally, based on the current evidence, propose an algorithm for treatment of suspected macrosomia.

STUDY DESIGN

A review.

RESULTS

According to the National Vital Statistics, in the United States, the prevalence of newborns weighing at least 4000 g has decreased by 10% in seven years (10.2% in 1996 and 9.2% in 2002) and 19% for newborns with weights >5000 g (0.16% and 0.13%, respectively). Bayesian calculations indicates that the posttest probability of detecting a macrosomic fetus in an uncomplicated pregnancy is variable, ranging from 15% to 79% with sonographic estimates of birth weight, and 40 to 52% with clinical estimates. Among diabetic patients the post-test probability of identifying a newborn weighing >4000 g clinically and sonographically is over 60%. Among uncomplicated pregnancies, there is sufficient evidence that suspected macrosomia is not an indication for induction or for primary cesarean delivery. For pregnancies complicated by diabetes, with a prior cesarean delivery or shoulder dystocia, delivery of a macrosomic fetus increases the rate of complications, but there is insufficient evidence about the threshold of estimated fetal weight that should prompt cesarean delivery.

CONCLUSION

Due to the inaccuracies, among uncomplicated pregnancies suspicion of macrosomia is not an indication for induction or for primary cesarean delivery.

A new growth chart for preterm babies: Babson and Benda's chart updated with recent data and a new format

BACKGROUND

The Babson and Benda 1976 "fetal-infant growth graph" for preterm infants is commonly used in neonatal intensive care. Its limits include the small sample size which provides low confidence in the extremes of the data, the 26 weeks start and the 500 gram graph increments. The purpose of this study was to develop an updated growth chart beginning at 22 weeks based on a meta-analysis of published reference studies.

METHODS

The literature was searched from 1980 to 2002 for more recent data to complete the pre and post term sections of the chart. Data were selected from population studies with large sample sizes. Comparisons were made between the new chart and the Babson and Benda graph. To validate the growth chart the growth results from the National Institute of Child Health and Human Development Neonatal Research Network (NICHD) were superimposed on the new chart.

RESULTS

The new data produced curves that generally followed patterns similar to the old growth graph. Mean differences between the curves of the two charts reached statistical significance after term. Babson's 10th percentiles fell between the new data percentiles: the 5th to 17th for weight, the 5th and 15th for head circumference, and the 6th and 16th for length. The growth patterns of the NICHD infants deviated away from the curves of the chart in the first weeks after birth. When the infants reached an average weight of 2 kilograms, those with a birthweight in the range of 700 to 1000 grams had achieved greater than the 10th percentile on average for head growth, but remained below the 3rd percentile for weight and length.

CONCLUSION

The updated growth chart allows a comparison of an infant's growth first with the fetus as early as 22 weeks and then with the term infant to 10 weeks. Comparison of the size of the NICHD infants at a weight of 2 kilograms provides evidence that on average preterm infants are growth retarded with respect to weight and length while their head size has caught up to birth percentiles. As with all meta-analyses, the validity of this growth chart is limited by the heterogeneity of the data sources. Further validation is needed to illustrate the growth patterns of preterm infants to older ages.

Ultrasonic fetal weight estimation and tolerance to measurement error: A comparative analysis

The objective of the present study was to test the hypothesis that volumetric formulae for fetal weight estimation are more tolerant to measurement error than exponential models. A mathematical model of normal fetal growth was constructed, using published British reference standards for biometric variables. Observed measurements were computer-generated by contaminating reference measurements with error terms according to their published coefficients of variation. The error in weight estimation was computed as the percentage difference between weight estimates derived from the observed biometric variables and the true measurements. A total of nine weight estimation formulae were tested. Campbell's formula appeared to be most affected by observational errors, especially before 38 weeks. In this range, they varied up to 9%. The most tolerant was Shepard's formula, with errors of only approximately 2.8%. Other formulae showed errors of approximately 5-6%. With the exception of Campbell's formula, the effect of gestational age was minimal. There was no correlation between percentage error and fetal size. Combining ultrasound biometric variables into a fetal weight estimate does not always exaggerate the errors of the original measurements. There were no significant differences between volumetric and exponential formulae.

Perinatal factors affecting survival and survival without disability of extreme premature infants at two years of age

OBJECTIVE

To study obstetrical factors leading to very preterm delivery (between 24 and 28 weeks) and to relate these factors to neonatal outcome and psychomotor development at two years.

STUDY DESIGN

Among 144 infants born alive before 28 weeks of gestation at a single perinatal center between January 1993 and December 1996, we analyzed the influence on neonatal outcome and on psychomotor development at 24 months of a variety of perinatal and neonatal factors. Psychomotor development at two years was classified as: normal, borderline, or moderately or severely handicapped.

RESULTS

During the study period, 114 women delivered live infants before 28 weeks' gestation: 87 singletons, 25 sets of twins, 1 set of triplets and 1 set of quadruplets. All 144 live-born infants received neonatal resuscitation: 50 died before discharge. At two years of age, 6 of the 94 survivors were lost to follow-up. Assessments of the psychomotor development of the other 88 was normal for 52%; borderline for 20%, moderately handicapped for 20%, and severely handicapped for 8%. Multivariate analysis found that two factors affected survival: birthweight and fetal heart rate. (The 42% of infants with a birthweight below 700 g survived versus 83% above 900 g, P<0.001, OR=5.2, 95% CI (confidence interval) [2.4-11.2].)

CONCLUSION

These data show the influence of perinatal factors on the outcome of very preterm infants; birthweight and fetal heart rate are strongly correlated with survival. Gestational age is a good predictor of psychomotor development at two years.

Fetal heart rate and survival of the very premature newborn

OBJECTIVE

Our purpose was to study the likelihood of survival of infants who are born before 28 weeks of gestation and to examine the influence of fetal heart rate findings on neonatal death.

STUDY DESIGN

In this retrospective study, we analyzed the mortality rate of infants at 2 months of age as a function of various obstetric and prenatal indicators.

RESULTS

At 2 months, 207 of 325 children were still alive. The survival rate was also a function of gestational age, birth weight, the administration of corticosteroids, multiple pregnancies, and fetal heart rate. Fetal heart rate had the greatest effect on the mortality rate. Children with a reactive rate were 4 times more likely to survive than children with a flat tracing (P =.003; odd ratio, 4; 95% CI, 12.1; 39.8).

CONCLUSION

The results in our study lead us to think that recording the fetal heart rate before and during labor may be useful in the prediction of perinatal death and may help obstetric decision-making.

Menstrual age-dependent systematic error in sonographic fetal weight estimation: a mathematical model

PURPOSE

We used computer modeling techniques to evaluate the accuracy of different types of sonographic formulas for estimating fetal weight across the full range of clinically important menstrual ages.

METHODS

Input data for the computer modeling techniques were derived from published British standards for normal distributions of sonographic biometric growth parameters and their correlation coefficients; these standards had been derived from fetal populations whose ages were determined using sonography. The accuracy of each of 10 formulas for estimating fetal weight was calculated by comparing the weight estimates obtained with these formulas in simulated populations with the weight estimates expected from birth weight data, from 24 weeks' menstrual age to term. Preterm weights were estimated by interpolation from term birth weights using sonographic growth curves. With an ideal formula, the median weight estimates at term should not differ from the population birth weight median.

RESULTS

The simulated output sonographic values closely matched those of the original population. The accuracy of the fetal weight estimation differed by menstrual age and between various formulas. Most methods tended to overestimate fetal weight at term. Shepard's formula progressively overestimated weights from about 2% at 32 weeks to more than 15% at term. The accuracy of Combs's and Shinozuka's volumetric formulas varied least by menstrual age. Hadlock's formula underestimated preterm fetal weight by up to 7% and overestimated fetal weight at term by up to 5%.

CONCLUSIONS

The accuracy of sonographic fetal weight estimation based on volumetric formulas is more consistent across menstrual ages than are other methods.

Neurodevelopment of neonates in neonatal intensive care units and growth of surviving infants at age 2 years

SUMMARY

The presence of development disorders in neonates attended in a Neonatal Intensive Care Unit (NICU) is highly variable; the aim of this study, therefore, was to determine the evolution of somatic and neurosensory development in a group of neonates requiring treatment in the NICU and to analyse the perinatal and developmental aspects of children presenting abnormalities.

PATIENTS AND METHODS

A total of 492 neonates (275 premature, 106 with birthweight < or =1500 g), who were treated in the NICU between January 1994 and December 1997, were followed-up until the age of 2 years. Data were obtained concerning birthweight, body length, head circumference, gestational age, normality of weight for gestational age, single/multiple birth, duration of stay in the NICU and the hospital, duration of mechanically assisted respiration and evolutive somatometry, neurological examination and the Brunet-Lezine development test, adjusted for the gestational age of the neonates, at 6, 12, 18 and 24 months. When abnormal results were detected, Early Attention (EA) programmes were applied.

RESULTS

Somatometry at birth in relation to gestational age revealed a weekly weight gain of 8.6%, an increase in body length of 1% and in head circumference of 1% (p<0.001). The evolution of somatic development to the age of 2 years showed that neonates with a birthweight < or =1500 g did not reach the values of neonates with a greater birthweight. The prevalence of cerebral palsy among all neonates was 6.8%, 14.6% among those weighing < or =1500 g, 4% among those weighing 1501-2500 g and 5% among those weighing >2500 g. The overall rate of neurosensory injury was 10.5%. These neonates presented less somatic development than those did with no neurologic disorder. To sum up, most of the neonates attended in the NICU during the 1990s presented a normal pattern of development. Nevertheless, they should be the object of special attention during the first years of life, particularly those neonates with a birthweight < or =1500 g and those presenting neurosensory risk.

A new and improved population-based Canadian reference for birth weight for gestational age

BACKGROUND

Existing fetal growth references all suffer from 1 or more major methodologic problems, including errors in reported gestational age, biologically implausible birth weight for gestational age, insufficient sample sizes at low gestational age, single-hospital or other non-population-based samples, and inadequate statistical modeling techniques.

METHODS

We used the newly developed Canadian national linked file of singleton births and infant deaths for births between 1994 and 1996, for which gestational age is largely based on early ultrasound estimates. Assuming a normal distribution for birth weight at each gestational age, we used the expectation-maximization algorithm to exclude infants with gestational ages that were more consistent with 40-week births than with the observed gestational age. Distributions of birth weight at the corrected gestational ages were then statistically smoothed.

RESULTS

The resulting male and female curves provide smooth and biologically plausible means, standard deviations, and percentile cutoffs for defining small- and large-for-gestational-age births. Large-for-gestational age cutoffs (90th percentile) at low gestational ages are considerably lower than those of existing references, whereas small-for-gestational-age cutoffs (10th percentile) postterm are higher. For example, compared with the current World Health Organization reference from California (Williams et al, 1982) and a recently proposed US national reference (Alexander et al, 1996), the 90th percentiles for singleton males at 30 weeks are 1837 versus 2159 and 2710 g. The corresponding 10th percentiles at 42 weeks are 3233 versus 3086 and 2998 g.

CONCLUSIONS

This new sex-specific, population-based reference should improve clinical assessment of growth in individual newborns, population-based surveillance of geographic and temporal trends in birth weight for gestational age, and evaluation of clinical or public health interventions to enhance fetal growth. fetal growth, birth weight, gestational age, preterm birth, postterm birth.

Receiver operating characteristic curves of ultrasonographic estimates of fetal weight for prediction of fetal growth restriction in prolonged pregnancies

OBJECTIVE

Recent studies have documented increased perinatal morbidity and mortality rates in the growth-restricted postterm fetus. Our purpose was to evaluate the receiver operating characteristic curve of ultrasonographically estimated fetal weight as a predictor of fetal growth restriction in prolonged pregnancies.

STUDY DESIGN

Fetal weight was estimated ultrasonographically within 9 days of delivery (mode 1 day) in members of a cohort of 410 patients with prolonged pregnancies (>41 weeks). Estimated fetal weights were compared with birth weights in receiver operating characteristic curve analysis.

RESULTS

The areas under the receiver operating characteristic curves for predicting birth weights <10th percentile (3125 g in this population) and <5th percentile (2930 g in this population) were 0.89 and 0.96, respectively. Both areas were significantly different from an area indicating a useless test. The estimated fetal weight values corresponding to the inflection points for the receiver operating characteristic curves predicting birth weights <10th percentile and <5th percentile were 3370 and 3200 g, respectively. With estimated fetal weight at less than these test cutoff values, the relative risks for a fetus to have a birth weight <10th percentile or <5th percentile were 14.6 (95% confidence interval, 6.25-33.8) and 89.8 (95% confidence interval, 12.1-665), respectively. Analysis of the receiver operating characteristic curves resulted in improved test characteristics relative to using the actual 10th and 5th birth weight percentiles as cutoff values for estimated fetal weight (relative risk of 14.6 vs 9.5 and 89.8 vs 26.0, respectively).

CONCLUSIONS

Ultrasonographic estimation of fetal weight is a useful test for predicting fetal growth restriction in prolonged pregnancies. Future studies should evaluate whether intervention on the basis of this identification results in improved perinatal outcome.