A longitudinal study of fetal weight growth

Fetal Growth Curves: Is There a Universal Reference?

Three modern cohort studies have an advantage over historical fetal growth references because they included diverse populations. Despite similar inclusion criteria, estimated fetal weight percentiles for gestational age varied among studies, which result in different proportions of fetuses as being classified below or above a cutoff point. A universal reference would make comparison of fetal growth simpler for clinical use and for comparison across populations but may misclassify small-for-gestational-age or large-for-gestational-age fetuses. It is important to know how a growth reference performs in a local population in relation to fetal morbidity and mortality when implementing in clinical practice.

Fetal growth standards for Somali population

BACKGROUND

Accurate assessment of fetal size is essential in providing optimal prenatal care. National Institute of Child Health and Human Development (NICHD) study from 2015 demonstrated that estimated fetal weight (EFW) differed significantly by race/ethnicity after 20 weeks. There is a large Somali population residing in Minnesota, many of whom are cared for at our maternal fetal medicine practice at the University of Minnesota. Anecdotally, we noticed an increased proportion of small-for-gestational age diagnoses within this population. We sought to use our ultrasound data to create a reference standard specific for this population and compare to currently applied references.

PURPOSE

We aimed to model fetal growth standards within a healthy Somali population between 16 and 40 weeks gestation, and address possible differences in the growth patterns compared with standards for non-Hispanic White, non-Hispanic Black, Hispanic, and Asian singleton fetuses published by the NICHD in the Fetal Growth Study.

MATERIALS AND METHODS

This is a retrospective cohort study using ultrasound data from 527 low risk pregnancies of Somali ethnicity at single tertiary care center between 2011 and 2017. A total of 1107 scans were identified for these pregnancies and maternal and obstetrical data were reviewed. Women 18-40 years of age with low-risk pregnancies and established dating consistent with first trimester ultrasound scan were included. Exclusion criteria were any maternal, fetal or obstetrical conditions known to affect fetal growth.

RESULTS

Estimated fetal weight among Somali pregnancies differed significantly at some time points from the NICHD four ethnic groups, but generally the EFW graph curves crossed over at most time points between the study groups. At week 18, EFW was significantly larger than all other four ethnic groups (all p<.001), it was also significantly larger from the Hispanic, Black, and Asian ethnic groups at some time points between 18 and 27 weeks gestation (p < .05). Additionally, EFW among Somali pregnancies was significantly smaller than the Black and Asian ethnicity at 32 and 35-36 weeks and smaller than the White ethnicity at 30 and 38-39 weeks (p < .05). Abdominal circumference (AC) for the Somali population was significantly smaller than the other ethnic groups, especially than the White ethnicity at various time points across 16-40 weeks (p < .05). Femur and humerus length were significantly longer when compared to all other ethnic groups at most time points from 16 to 40 weeks of gestation (p < .05). Biparietal diameter (BPD) was significantly smaller than all other ethnic groups specifically at time of fetal survey (18 weeks) and at time of fetal growth assessment (32 weeks) (p < .05).

CONCLUSIONS

Significant differences in fetal growth standards were found between the Somali ethnicity and other ethnic groups (White, Black, Asian, and Hispanic) at various time points from 16 to 40 weeks of gestation. Racial/ethnic-specific standards improve the precision for evaluating fetal growth and may decrease the proportion of fetuses of Somali ethnicity labeled as small-for-gestational age.

A new customized fetal growth standard for African American women: the PRB/NICHD Detroit study

BACKGROUND

The assessment of fetal growth disorders requires a standard. Current nomograms for the assessment of fetal growth in African American women have been derived either from neonatal (rather than fetal) biometry data or have not been customized for maternal ethnicity, weight, height, and parity and fetal sex.

OBJECTIVE

We sought to (1) develop a new customized fetal growth standard for African American mothers; and (2) compare such a standard to 3 existing standards for the classification of fetuses as small (SGA) or large (LGA) for gestational age.

STUDY DESIGN

A retrospective cohort study included 4183 women (4001 African American and 182 Caucasian) from the Detroit metropolitan area who underwent ultrasound examinations between 14-40 weeks of gestation (the median number of scans per pregnancy was 5, interquartile range 3-7) and for whom relevant covariate data were available. Longitudinal quantile regression was used to build models defining the "normal" estimated fetal weight (EFW) centiles for gestational age in African American women, adjusted for maternal height, weight, and parity and fetal sex, and excluding pathologic factors with a significant effect on fetal weight. The resulting Perinatology Research Branch/Eunice Kennedy Shriver National Institute of Child Health and Human Development (hereinafter, PRB/NICHD) growth standard was compared to 3 other existing standards--the customized gestation-related optimal weight (GROW) standard; the Eunice Kennedy Shriver National Institute of Child Health and Human Development (hereinafter, NICHD) African American standard; and the multinational World Health Organization (WHO) standard--utilized to screen fetuses for SGA (<10th centile) or LGA (>90th centile) based on the last available ultrasound examination for each pregnancy.

RESULTS

First, the mean birthweight at 40 weeks was 133 g higher for neonates born to Caucasian than to African American mothers and 150 g higher for male than female neonates; maternal weight, height, and parity had a positive effect on birthweight. Second, analysis of longitudinal EFW revealed the following features of fetal growth: (1) all weight centiles were about 2% higher for male than for female fetuses; (2) maternal height had a positive effect on EFW, with larger fetuses being affected more (2% increase in the 95th centile of weight for each 10-cm increase in height); and (3) maternal weight and parity had a positive effect on EFW that increased with gestation and varied among the weight centiles. Third, the screen-positive rate for SGA was 7.2% for the NICHD African American standard, 12.3% for the GROW standard, 13% for the WHO standard customized by fetal sex, and 14.4% for the PRB/NICHD customized standard. For all standards, the screen-positive rate for SGA was at least 2-fold higher among fetuses delivered preterm than at term. Fourth, the screen-positive rate for LGA was 8.7% for the GROW standard, 9.2% for the PRB/NICHD customized standard, 10.8% for the WHO standard customized by fetal sex, and 12.3% for the NICHD African American standard. Finally, the highest overall agreement among standards was between the GROW and PRB/NICHD customized standards (Cohen's interrater agreement, kappa = 0.85).

CONCLUSION

We developed a novel customized PRB/NICHD fetal growth standard from fetal data in an African American population without assuming proportionality of the effects of covariates, and without assuming that these effects are equal on all centiles of weight; we also provide an easy-to-use centile calculator. This standard classified more fetuses as being at risk for SGA compared to existing standards, especially among fetuses delivered preterm, but classified about the same number of LGA. The comparison among the 4 growth standards also revealed that the most important factor determining agreement among standards is whether they account for the same factors known to affect fetal growth.

Individualized growth assessment: conceptual framework and practical implementation for the evaluation of fetal growth and neonatal growth outcome

Fetal growth abnormalities can pose significant consequences on perinatal morbidity and mortality of nonanomalous fetuses. The most widely accepted definition of fetal growth restriction is an estimated fetal weight less than the 10th percentile for gestational age according to population-based criteria. However, these criteria do not account for the growth potential of an individual fetus, nor do they effectively separate constitutionally small fetuses from ones that are malnourished. Furthermore, conventional approaches typically evaluate estimated fetal weight at a single time point, rather than using serial scans, to evaluate growth. This article provides a conceptual framework for the individualized growth assessment of a fetus/neonate based on measuring second-trimester growth velocity of fetal size parameters to estimate growth potential. These estimates specify size models that generate individualized third-trimester size trajectories and predict birth characteristics. Comparisons of measured and predicted values are used to separate normally growing fetuses from those with growth abnormalities. This can be accomplished with individual anatomical parameters or sets of parameters. A practical and freely available software (Individualized Growth Assessment Program) has been developed to allow implementation of this approach for clinical and research purposes.

The use of angiogenic biomarkers in maternal blood to identify which SGA fetuses will require a preterm delivery and mothers who will develop pre-eclampsia

OBJECTIVE

To determine (1) whether maternal plasma concentrations of angiogenic and anti-angiogenic factors can predict which mothers diagnosed with "suspected small for gestational age fetuses (sSGA)" will develop pre-eclampsia (PE) or require an indicated early preterm delivery (≤ 34 weeks of gestation); and (2) whether risk assessment performance is improved using these proteins in addition to clinical factors and Doppler parameters.

METHODS

This prospective cohort study included women with singleton pregnancies diagnosed with sSGA (estimated fetal weight <10th percentile) between 24 and 34 weeks of gestation (n = 314). Plasma concentrations of soluble vascular endothelial growth factor receptor-1 (sVEGFR-1), soluble endoglin (sEng) and placental growth factor (PlGF) were determined in maternal blood obtained at the time of diagnosis. Doppler velocimetry of the umbilical (Umb) and uterine (UT) arteries was performed. The outcomes were (1) subsequent development of PE; and (2) indicated preterm delivery at ≤ 34 weeks of gestation (excluding deliveries as a result of spontaneous preterm labor, preterm pre-labor rupture of membranes or chorioamnionitis).

RESULTS

(1) The prevalence of PE and indicated preterm delivery was 9.2% (n = 29/314) and 7.3% (n = 23/314), respectively; (2) the area under the receiver operating characteristic curve (AUC) for the identification of patients who developed PE and/or required indicated preterm delivery was greater than 80% for the UT artery pulsatility index (PI) z-score and each biochemical marker (including their ratios) except sVEGFR-1 MoM; (3) using cutoffs at a false positive rate of 15%, women with abnormal plasma concentrations of angiogenic/anti-angiogenic factors were 7-13 times more likely to develop PE, and 12-22 times more likely to require preterm delivery than those with normal plasma MoM concentrations of these factors; (4) sEng, PlGF, PIGF/sEng and PIGF/sVEGFR-1 ratios MoM, each contributed significant information about the risk of PE beyond that provided by clinical factors and/or Doppler parameters: women who had low MoM values for these biomarkers were at 5-9 times greater risk of developing PE than women who had normal values, adjusting for clinical factors and Doppler parameters (adjusted odds ratio for PlGF: 9.1, PlGF/sEng: 5.6); (5) the concentrations of sVEGFR-1 and PlGF/sVEGFR-1 ratio MoM, each contributed significant information about the risk of indicated preterm delivery beyond that provided by clinical factors and/or Doppler parameters: women who had abnormal values were at 8-9 times greater risk for indicated preterm delivery, adjusting for clinical factors and Doppler parameters; and (6) for a two-stage risk assessment (Umb artery Doppler followed by Ut artery Doppler plus biochemical markers), among women who had normal Umb artery Doppler velocimetry (n = 279), 21 (7.5%) developed PE and 11 (52%) of these women were identified by an abnormal UT artery Doppler mean PI z-score (>2SD): a combination of PlGF/sEng ratio MoM concentration and abnormal UT artery Doppler velocimetry increased the sensitivity of abnormal UT artery Doppler velocimetry to 76% (16/21) at a fixed false-positive rate of 10% (p = 0.06).

CONCLUSION

Angiogenic and anti-angiogenic factors measured in maternal blood between 24 and 34 weeks of gestation can identify the majority of mothers diagnosed with "suspected SGA" who subsequently developed PE or those who later required preterm delivery ≤ 34 weeks of gestation. Moreover, incorporation of these biochemical markers significantly improves risk assessment performance for these outcomes beyond that of clinical factors and uterine and umbilical artery Doppler velocimetry.

Estimating fetal weight for best clinical outcome

Clinical decisions are often based on the results of third trimester sonograms, particularly with small or large babies and so accuracy of estimating fetal weight (EFW) is essential. There are numerous EFW formula available and yet in Australia no one formula has been recommended for use due to the lack of clinical evidence as to their accuracy. Objectives: 1 To assess inter/intra observer error for fetal parameter measurements with multiple observers. 2 To compare six of the most commonly used EFW formulae and analyse inter/intra formulae variations for different weight range. Method: EFW of 121 pregnancies assessed within 7 days of birth by measuring the BPD, OFD, HC, AC, FL and comparing to actual birth weight. Results: Inter-observer error: 1.3 to 3.1%. Intra-observer error: 1.1 to 1.9% depending on fetal parameter. Accuracy of each EFW formula changed with different weight ranges. For all formulae the highest random error occurred in the macrosomic group. The lowest random error in all weight groups was the Hadlock B formula incorporating the HC/AC/FL (7.7%). Conclusion: Considering the possible problems of head moulding this study suggests the use of: Hadlock FP et al (1982) - Formula B - incorporating HC/AC/FL.

A modified prenatal growth assessment score for the evaluation of fetal growth in the third trimester using single and composite biometric parameters

OBJECTIVE

To define modified Prenatal Growth Assessment Scores (mPGAS) for single and composite biometric parameters and determine their reference ranges in normal fetuses.

METHODS

Nine anatomical parameters (ap) were measured and the weight estimated (EWTa, EWTb) in a longitudinal study of 119 fetuses with normal neonatal growth outcomes. Expected third trimester size trajectories, obtained from second trimester Rossavik size models, were used in calculating Percent Deviations (% Dev's) and their age-specific reference ranges in each fetus. The components of individual % Dev's values outside their reference ranges, designated +iapPGAS, -iapPGAS, were averaged to give +apPGAS and -apPGAS values for the 3rd trimester. The +iapPGAS and -iapPGAS values for different combinations of ap (c1a (HC, AC, FDL, ThC, EWTa), c1b (HC, AC, FDL, ThC, EWTb), c2 (ThC, ArmC, AVol, TVol), c3 (HC, AC, FDL, EWTa)) were then averaged to give +icPGAS and -icPGAS values at different time points or at the end of the third trimester (+cPGAS, -cPGAS). Values for iapPGAS, ic1bPGAS, and ic2PGAS were compared to their respective apPGAS or cPGAS reference ranges.

RESULTS

All mPGAS values had one 95% range boundary at 0.0%. Upper boundaries of 1D +apPGAS values ranged from 0.0% (HC) to +0.49% (ThC) and were +0.06%, +2.3% and +1.8% for EWT, AVol and TVol, respectively. Comparable values for -apPGAS were 0.0% (BPD, FDL, HDL), to -0.58% (ArmC), -0.13% (EWT), -0.8% (AVol), and 0.0% (TVol). The +cPGAS, 95% reference range upper boundaries varied from +0.36% (c1b) to +0.89% (c2). Comparable values for -cPGAS lower boundaries were -0.17% (c1b) to -0.43% (c2).

CONCLUSIONS

The original PGAS concept has now been extended to individual biometric parameters and their combinations. With the standards provided, mPGAS values can now be tested to see if detection of different types of third trimester growth problems is improved.

Establishment of fetal biometric charts using quantile regression analysis

OBJECTIVES

Fetal growth evaluation is an essential component of pregnancy surveillance. There have been several methods used to construct growth charts. The conventional charts used in current daily practice are based on small numbers and traditional statistical methods. The purpose of this study was to improve fetal biometric charts based on a much larger number of observations with an alternative statistical method: quantile regression analysis. A comparison between the charts is presented.

METHODS

During the 12 years of study, 17,708 sonographic examinations of pregnant women from the north of Israel, between 12 and 42 weeks of pregnancy, were performed. Fetal measurements were obtained by several operators using various equipment and included head circumference, abdominal circumference, and femur length.

RESULTS

Growth charts were established based on these measurements.

CONCLUSIONS

In this study, we constructed biometric growth charts using a large cohort of pregnant women. These charts offer the advantages of specific estimated regression parameters for each specified percentile, thus better defining the normal range. We suggest using these new charts in routine daily obstetric practice.

Stillbirth and fetal growth restriction

The association between stillbirth and fetal growth restriction is strong and supported by a large body of evidence and clinically employed for the stillbirth prediction. However, although assessment of fetal growth is a basis of clinical practice, it is not trivial. Essentially, fetal growth is a result of the genetic growth potential of the fetus and placental function. The growth potential is the driving force of fetal growth, whereas the placenta as the sole source of nutrients and oxygen might become the rate limiting element of fetal growth if its function is impaired. Thus, placental dysfunction may prevent the fetus from reaching its full genetically determined growth potential. In this sense fetal growth and its aberration provides an insight into placental function. Fetal growth is a proxy for the test of the effectiveness of placenta, whose function is otherwise obscured during pregnancy.

Defining normal and abnormal fetal growth: promises and challenges

Normal fetal growth is a critical component of a healthy pregnancy and influences the long-term health of the offspring. However, defining normal and abnormal fetal growth has been a long-standing challenge in clinical practice and research. We review various references and standards that are used widely to evaluate fetal growth and discuss common pitfalls of current definitions of abnormal fetal growth. Pros and cons of different approaches to customize fetal growth standards are described. We further discuss recent advances toward an integrated definition for fetal growth restriction. Such a definition may incorporate fetal size with the status of placental health that is measured by maternal and fetal Doppler velocimetry and biomarkers, biophysical findings, and genetics. Although the concept of an integrated definition appears promising, further development and testing are required. An improved definition of abnormal fetal growth should benefit both research and clinical practice.

Ultrasound-derived fetal size nomogram for a sub-Saharan African population: a longitudinal study

OBJECTIVES

To create a fetal size nomogram for use in sub-Saharan Africa and compare the derived centiles with reference intervals from developed countries.

METHODS

Fetal biometric measurements were obtained at entry to antenatal care (11-22 weeks' gestation) and thereafter at 4-week intervals from pregnant women enrolled in a longitudinal ultrasound study in Kinshasa, Democratic Republic of Congo. The study population comprised 144 singleton gestations with ultrasound-derived gestational age within 14 days of the menstrual estimate. A total of 755 monthly ultrasound scans were included with a mean +/- SD of 5 +/- 1 (range, 2-8) scans per woman. Estimated fetal weight (EFW) was calculated at each ultrasound examination using the Hadlock algorithm. A general mixed-effects linear regression model that incorporated random effects for both the intercept and slope was fitted to log-transformed EFW to account for both mean growth and within-fetus variability in growth. Reference centiles (5(th), 10(th), 50(th), 90(th) and 95(th) centiles) were derived from this model.

RESULTS

Nomograms derived from developed populations consistently overestimated the 50(th) centile EFW value for Congolese fetuses by roughly 5-12%. Differences observed in the 10(th) and 90(th) centiles were inconsistent between nomograms, but generally followed a pattern of overestimation that decreased with advancing gestational age.

CONCLUSIONS

In low-resource settings, endemic malaria and maternal nutritional factors, including low prepregnancy weight and pregnancy weight gain, probably lead to lower fetal weight and utilization of nomograms derived from developed populations is not appropriate. This customized nomogram could provide more applicable reference intervals for diagnosis of intrauterine growth restriction in sub-Saharan African populations.

Individualized norms of optimal fetal growth: fetal growth potential

OBJECTIVE

To demonstrate that individualized optimal fetal growth norms, accounting for physiologic and pathologic determinants of fetal growth, better identify normal and abnormal outcomes of pregnancy than existing methods.

METHODS

In a prospective cohort of 38,033 singleton pregnancies, we identified 9,818 women with a completely normal outcome of pregnancy and characterized the physiologic factors affecting birth weight using multivariable regression. We used those physiologic factors to individually predict optimal growth trajectory and its variation, growth potential, for each fetus in the entire cohort. By comparing actual birth weight with growth potential, population, ultrasound, and customized norms, we calculated for each fetus achieved percentiles, by each norm. We then compared proportions of pregnancies classified as normally grown, between 10th and 90th percentile, or aberrantly grown, outside this interval, by growth potential and traditional norms, in 14,229 complicated pregnancies, 1,518 pregnancies with diabetes or hypertensive disorders, and 1,347 pregnancies with neonatal complications.

RESULTS

Nineteen physiologic factors, associated with maternal characteristics and early placental function, were identified. Growth potential norms correctly classified significantly more pregnancies than population, ultrasound, or customized norms in complicated pregnancies (26.4% compared with 18.3%, 18.7%, 22.8%, respectively, all P<.05), pregnancies with diabetes or hypertensive disorders (37.3% compared with 23.0%, 28.0%, 34.0%, respectively, all P<.05) and neonatal complications (33.3% compared with 19.7%, 24.9%, 29.8%, respectively, all P<.05).

CONCLUSION

Growth potential norms based on the physiologic determinants of birth weight are a better discriminator of aberrations of fetal growth than traditional norms.

LEVEL OF EVIDENCE

II.

Predicting fetal growth restriction with liver volume by three-dimensional ultrasound: efficacy evaluation

It is well-documented that fetal growth restriction (FGR) may have increased risks of perinatal morbidity and mortality. Early detection of FGR is crucial in prenatal care and daily practice. We undertook a prospective and cross-sectional study using quantitative 3-D ultrasound (US) to assess the efficacy of fetal liver volume (LV) in predicting FGR. During the study period, 42 fetuses with FGR and 375 fetuses without FGR were included for the LV assessment in utero by 3-D US. All the fetuses were singletons and had follow-up to delivery to ensure whether they were complicated with FGR or not. Our results revealed that fetal LV assessed by 3-D US can differentiate well fetuses with FGR from those without FGR. The sensitivity of fetal LV in predicting FGR was 97.6%, with specificity 93.6%, predictive value of positive test 63%, predictive value of negative test 99.7% and accuracy 94%. In conclusion, fetal LV assessed by quantitative 3-D US can be used to predict fetuses with FGR antenatally. Our data support that fetal LV assessment by 3-D US would be a useful test in detecting fetuses with FGR.

Timing is everything: a reconsideration of fetal growth velocity patterns identifies the importance of individual and sex differences

Fetal growth has been posited to follow a "timing hypothesis" sequence in which the second trimester favors a single growth velocity peak in body length and the third trimester accommodates a single growth velocity peak in weight accrual. To our knowledge, this proposition has never been tested with high-frequency longitudinal ultrasound data from normally growing human fetuses. The present study examined whether fetal growth in leg length had its peak velocity at or about 20-26 gestational weeks and declined subsequently and whether estimated fetal weight velocity was maximal at or about 33 weeks and declined subsequently; if the greatest acquisition of leg length occurred in the second trimester and weight in the third trimester; and if birth outcomes reflected these relationships. The data in this study included approximately weekly longitudinal ultrasound data collected from 44 maternal/fetal pairs in Brussels, Belgium. Diaphyseal lengths of the femur and tibia provided information on leg growth and estimated fetal weight was assessed from the biparietal and occipital-frontal head diameters and transverse and anterior-posterior diameters of the abdomen. Growth patterns were investigated from individual growth curves derived from daily growth velocity z-scores. Paired t-tests compared individuals' trimestral increments in leg length and fetal weight. Least-squares regression models employing the robust procedure for repeated measurements were used to test for relationships between trimester, size, growth rates, and birth outcome, controlling for day of measurement, sex, maternal smoking, and gestational age at birth. The normal fetuses in this study grew by pulsatile patterns of leg and estimated weight acquisition, not a single peak and decline process. Greater incremental growth in estimated fetal weight occurred during the second trimester and leg length in the third trimester. Individual and sex effects were significant in growth velocity patterns. Girls grew with greater synchrony between leg and weight growth and were accelerated by comparison with boys, with faster leg growth predicting lower ponderal index by the second trimester. Birth outcomes were sex-specific in timing effects and predictive variables. These results support the importance of sex-specific analyses, reemphasize the common notion that girls grow faster than boys, and direct attention to cross-talk between energy resources and growth.

The assessment of normal fetal liver volume by three-dimensional ultrasound

Liver volume (LIVV) is very important in determining the status of fetal growth. However, to measure human fetal LIVV in utero precisely and noninvasively is not an easy task. With the recent advancement of three-dimensional (3-D) ultrasound (US), the limitation in assessing fetal LIVV by 2-D US can be overcome. The purpose of this study was to establish a normal reference chart of fetal LIVV for clinical use. A prospective and cross-sectional study using 3-D US was undertaken to assess the fetal LIVV in normal pregnancy. In total, 226 singleton fetuses ranging between 20 and 40 weeks of gestation and fitting the criteria of normal pregnancies were enrolled in this study. Our results showed that fetal LIVV is highly correlated with the gestational age (GA). Furthermore, using GA as the independent variable and fetal LIVV as the dependent variable, the best-fit regression equation was LIVV (mL) = -398.26 + 46.199 xGA - 1.7567 x GA(2) + 0.0236 x GA(3) (r = 0.97, n = 226, p < 0.0001), with SD of LIVV (mL) = 1.2533 x (0.77956 + 0.17267 x GA). These common indexes of fetal biometry, such as biparietal diameter (BPD), occipitofrontal diameter (OFD), head circumference (HCi), abdominal circumference (ACi), femur length (FL), and estimated fetal weight (EFW), were all highly correlated with fetal LIVV (all p < 0.0001). In conclusion, our data of fetal LIVV assessed by 3-D US can serve as a useful reference in evaluating fetal growth status during normal gestation.

Nutrient requirements for preterm infant formulas

Achieving appropriate growth and nutrient accretion of preterm and low birth weight (LBW) infants is often difficult during hospitalization because of metabolic and gastrointestinal immaturity and other complicating medical conditions. Advances in the care of preterm-LBW infants, including improved nutrition, have reduced mortality rates for these infants from 9.6 to 6.2% from 1983 to 1997. The Food and Drug Administration (FDA) has responsibility for ensuring the safety and nutritional quality of infant formulas based on current scientific knowledge. Consequently, under FDA contract, an ad hoc Expert Panel was convened by the Life Sciences Research Office of the American Society for Nutritional Sciences to make recommendations for the nutrient content of formulas for preterm-LBW infants based on current scientific knowledge and expert opinion. Recommendations were developed from different criteria than that used for recommendations for term infant formula. To ensure nutrient adequacy, the Panel considered intrauterine accretion rate, organ development, factorial estimates of requirements, nutrient interactions and supplemental feeding studies. Consideration was also given to long-term developmental outcome. Some recommendations were based on current use in domestic preterm formula. Included were recommendations for nutrients not required in formula for term infants such as lactose and arginine. Recommendations, examples, and sample calculations were based on a 1000 g preterm infant consuming 120 kcal/kg and 150 mL/d of an 810 kcal/L formula. A summary of recommendations for energy and 45 nutrient components of enteral formulas for preterm-LBW infants are presented. Recommendations for five nutrient:nutrient ratios are also presented. In addition, critical areas for future research on the nutritional requirements specific for preterm-LBW infants are identified.

Utilizing sonography to follow fetal growth

In utero diagnosis of fetal growth abnormalities continues to pose a clinical dilemma. Although significant advances have been made in the understanding of growth disturbances and their clinical importance, false-positive and false-negative diagnoses of IUGR and excessive fetal growth continue to affect the accuracy of antenatal diagnosis. Until more accurate methods are developed to aid in diagnosis, multiple biometric parameters should be assessed in patients either at risk for or with a suspected growth disturbance. Serial measurements obtained every 2 to 3 weeks may enhance diagnostic capabilities. Although antenatal diagnosis of IUGR has been shown to be of benefit in improving outcome, more study is needed to determine whether there is a benefit in antenatal diagnosis of macrosomia or LGA.

Nutrition management in a pregnant comatose patient

Major intracranial injury or disease during pregnancy resulting in a comatose state presents unique and complex management challenges. Our patient is a 34-year-old woman who suffered a closed-head injury associated with spousal abuse at 22 weeks' gestation. This injury resulted in a large right frontoparietal hematoma that was subsequently evacuated via a right frontotemporal craniotomy 5 days after the injury. She remained in a vegetative state postoperatively. Aggressive nutrition support was provided with enteral feedings through a nasoduodenal feeding tube. Mild oligohydramnios was detected at 30 weeks' gestation and was subsequently determined to be due to preterm premature rupture of membranes. She was managed until 33 weeks' gestation, when signs of chorioamnionitis were noted. She then underwent a primary cesarean delivery and was delivered of an appropriate-for-gestational-age 2150-g viable male infant. The patient had progressive improvement in her mental status with occupational and physical therapy and was discharged on the 29th postpartum day. This case presents the nutrition and medical challenges of maintaining adequate maternal and fetal health in a pregnant comatose patient.

Is obstetric and neonatal outcome worse in fetuses who fail to reach their own growth potential?

OBJECTIVES

To determine the perinatal outcome of fetuses who had birthweights less than that expected from early third trimester ultrasound scanning.

DESIGN

Retrospective estimation of centile fetal weight at early third trimester ultrasound scanning compared with actual centile birthweight corrected for gestational age, parity and sex.

SETTING

Teaching Hospital Obstetric Unit, London.

SUBJECTS

197 unselected women with singleton cephalic pregnancies who were delivered at term in our unit between October 1989 and May 1990.

MAIN OUTCOME MEASURES

CTG abnormality, need for fetal blood sampling in labour, meconium-staining of the amniotic fluid, mode of delivery, Apgar scores at 1 and 5 min, need for transfer of baby to neonatal unit, and need for neonatal intubation of the neonate at delivery.

RESULTS

An actual birthweight greater than 5% less than the birthweight estimated from ultrasound scanning identified 44 babies (22%) with an increased risk of CTG abnormalities (chi 2 = 8.38, P less than 0.0025; Odds ratio (OR) = 2.54; 95% CI 1.36 to 4.78) and need for operative delivery (chi 2 = 5.81, P less than 0.0125; OR = 1.94; 95% CI 1.15 to 3.27), when compared with the remainder of the sample. Overall 14 (32%) of this group had birthweights above the 50th centile. A group of 44 babies selected as being the smallest for gestational age, without reference to growth pattern, had a similar excess morbidity. (All this group had birthweights below the 39th centile).

CONCLUSIONS

This study supports the hypothesis that in-utero fetal growth pattern is as important for perinatal outcome as being small for gestational age per se.

Normal fetal growth evaluated by longitudinal ultrasound examinations

Fetal weight estimation was evaluated using the equations of Warsof, Shepard and Hadlock in 192 patients, less than 3 days before delivery. Warsof's and Hadlock's equations resulted in significantly better weight estimates compared to Shepard's equation. No systematic error was found below 2500 g by use of Warsof's equation, whereas Shepard's and Hadlocks's equations resulted in significant over-estimation in the low weight group. In a study of 5 fetuses, of 27-38 weeks gestational age, the intra-observer variation was calculated to 4.6%, whereas the coefficient of variation among observer means was 2.9%. The mixed intra- and inter-observer coefficient of variation was 6.5%. Thirty-five low-risk, uncomplicated pregnancies with reliable last menstrual dates were investigated longitudinally with ultrasound measurements of fetal weight. Population growth curves of fetal weight, fetal femur length, abdominal circumference and biparietal diameter were constructed by weighted polynomial regression. After 27 weeks of gestational age the weight growth curve showed only insignificant non-linearity. Compared to a Danish growth curve based on birth weights, significant higher mean weight was found, especially before 31 weeks of gestational age. The 10th and 90th percentiles for the individual percentage deviation change was +/- 4.4% per 28 days.

The predictability of the small-for-gestational-age infant by real-time ultrasound-derived measurements combined with pulsed Doppler umbilical artery velocimetry

During a 15-month period 373 level II ultrasound examinations were performed in 256 high-risk patients. In addition, pulsed Doppler spectral recordings of blood flow in the fetal umbilical arteries were made. A systolic/diastolic ratio was then calculated for each fetus. Real-time ultrasound-derived estimated fetal weight with the use of biparietal diameter and abdominal circumference was also calculated. The estimated fetal weights were categorized by placing them in a percentile for gestational age according to published nomograms. Complete birth data and outcomes were obtained in all patients. Both the systolic/diastolic ratio and ultrasound-estimated fetal weight grouped by percentile ranking for gestational age were highly predictive (p = 0.001) of babies who were subsequently born small for gestational age. Seventy-nine percent of the infants small for gestational age had umbilical artery systolic/diastolic ratios greater than or equal to 4, whereas only 21% had normal systolic/diastolic ratios. Forty-three percent of the infants who were small for gestational age had ultrasound-estimated fetal weights less than or equal to 10th percentile for the gestational age at which it was measured. Umbilical artery systolic/diastolic ratios, which reflect an increase in peripheral resistance in the placental circulation, showed a highly predictive and discriminatory index for the evaluation of the fetus suspected of having growth retardation.