Adjustment of birth weight standards for maternal and infant characteristics improves the prediction of outcome in the small-for-gestational-age infant

A prenatal standard for fetal weight improves the prenatal diagnosis of small for gestational age fetuses in pregnancies at increased risk

Objective

Our aim was to assess diagnostic accuracy in the prediction of small for gestational age (SGA <10th centile) and fetal growth restricted (FGR) (SGA <3rd centile) fetuses using three different sonographic methods in pregnancies at increased risk of fetal growth restriction: 1) fetal abdominal circumference (AC) z-scores, 2) estimated fetal weight (EFW) z-scores according to postnatal reference standard; 3) EFW z-scores according to a prenatal reference standard.

Methods

Singleton pregnancies at increased risk of fetal growth restriction seen in two university hospitals between 2014 and 2015 were studied retrospectively. EFW was calculated using formulas proposed by the INTERGROWTH-21st project and Hadlock; data derived from publications by the INTEGROWTH-twenty-first century project and Hadlock were used to calculate z-scores (AC and EFW). The accuracy of different methods was calculated and compared.

Results

The study group included 406 patients. Prenatal standard EFW z-scores derived from INTERGROWTH-21st project and Hadlock and co-workers performed similarly and were more accurate in identifying SGA infants than using AC z-scores or a postnatal reference standard. The subgroups analysis demonstrated that EFW prenatal standard was more or similarly accurate compared to other methods across all subgroups, defined by gestational age and birth weight.

Conclusions

Prenatal standard EFW z-scores derived from either INTERGROWTH-21 st project or Hadlock and co-workers publications demonstrated a statistically significant advantage over other biometric methods in the diagnosis of SGA fetuses.

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.

[Fetus, small for gestational age]

A small for gestational age foetus is defined by the foetal weight below the 10th centile for the corresponding gestational age. However, the vast majority of these cases has no apparent underlying abnormality, while in other cases a serious causative pathological condition can be identified. The detection, follow-up and treatment of an intrauterine growth retarded, compromised foetus has great obstetric and neonatologic relevance. In this review, the causes, clinical aspects and screening methods of intrauterine growth retardation are summarized based on the most recent international guidelines. Furthermore, recommendations regarding the monitoring and the optimal timing of the labour induction of pregnancies complicated with intrauterine growth retardation are discussed.

Low birth weight in the offspring of women with anorexia nervosa

A growing body of literature has investigated the association between maternal anorexia nervosa and pregnancy outcomes. Infant low birth weight is associated with a number of neurodevelopmental and physical sequelae; however, consistent results on its association with maternal anorexia nervosa are scant. Therefore, a systematic review and meta-analysis of the existing literature were undertaken. PubMed, Embase, and PsychInfo were searched for studies comparing the mean birth weight of babies delivered by mothers with (a history of) anorexia nervosa against those of healthy mothers. Studies were excluded from the meta-analysis if not presenting data from an unexposed comparison group and if using multiple eating disorders as exposure without presenting individual results. Fourteen studies were included in the systematic review and 9 in the meta-analysis, undertaken between 1999 and 2012 in Denmark, the Netherlands, New Zealand, Norway, Sweden, and the United Kingdom. Birth weights were standardized by dividing the difference in mean birth weight by the pooled standard deviation (equivalent to Cohen's d). Results showed a standardized mean difference of -0.19 kg (95% confidence interval: -0.25, -0.15; P = 0.01) in the birth weight of children of mothers with anorexia nervosa, and some bias in favor of papers presenting lower birth weight results for exposed mothers was detected. However, the small power of the analysis due to the small number of available studies and, thus, chance could partially account for this result. Our results confirm that maternal anorexia nervosa predicts lower birth weight and, despite some limitations, they have important clinical implications for prevention of adverse child outcomes.

Intrauterine growth restriction: effects of physiological fetal growth determinants on diagnosis

The growth of the fetus, which is strongly associated with the outcome of pregnancy, reflects interplay of several physiological and pathological factors. The assessment of fetal growth is based on comparison of birthweight (BW) or estimated fetal weight (EFW) to standards which define reference ranges at a spectrum of gestational ages. Most birthweight standards do not take into account effects of physiological determinants of fetal growth. Additionally, gestational age in many standards is based on the menstrual history and is often inaccurate. Fetal growth norms should be based on an early ultrasound estimate of gestational age. Customized standards, which have included only ultrasound-dated pregnancies, seem to be superior to population-based birthweight norms in predicting perinatal mortality and morbidity. Adjustment for individual variation in customized growth curves reduces false-positive diagnosis of IUGR and may lead to a very significant reduction in intervention for suspected IUGR. Customized growth potential identifies better the risk for adverse outcome than the currently used national standards, but customized charts may fail in detecting growth-restricted stillbirth. An individual's birthweight is the sum of physiological and pathological influences operating during pregnancy. Growth potential norms are a better discriminator of aberrations of fetal growth than population, ultrasound, and customized norms.

Population versus customized fetal growth norms and adverse outcomes in an intrapartum cohort

OBJECTIVE

To compare population versus customized fetal growth norms in identifying neonates at risk for adverse outcomes (APO) associated with small for gestational age (SGA).

STUDY DESIGN

Secondary analysis of an intrapartum fetal pulse oximetry trial in nulliparous women at term. Birth weight percentiles were calculated using ethnicity- and gender-specific population norms and customized norms (Gardosi).

RESULTS

Of the studied neonates, 508 (9.9%) and 584 (11.3%) were SGA by population (SGApop) and customized (SGAcust) norms, respectively. SGApop infants were significantly associated with a composite adverse neonatal outcome, neonatal intensive care admission, low fetal oxygen saturation, and reduced risk of cesarean delivery; both SGApop and SGAcust infants were associated with a 5-minute Apgar score < 4. The ability of customized and population birth weight percentiles in predicting APO was poor (12 of 14 APOs had area under the curve of <0.6).

CONCLUSION

In this intrapartum cohort, neither customized nor normalized population norms adequately identified neonates at risk of APO related to SGA.

A test of agreement of customised birthweight models

BACKGROUND

The objective of this study was to determine whether the physiological effects on birthweight as described by customised birthweight models (CBMs) from various populations and locations are consistent when applied to a single sample.

METHODS

The predicted birthweight was calculated for 52 826 White-European singleton term births between 1997 and 2008 from a large Australian hospital using the same set of variables from 12 published CBMs. The accuracy of prediction was tested against both the actual birthweight and a reference model. Intraclass correlation coefficients (ICCs) along with 95% confidence intervals of the measurements, paired differences (predicted-actual birthweight) and absolute values of the paired differences are reported.

RESULTS

The average difference in predicted and actual birthweight was <200 g for all CBMs, with ICCs for all but one model indicating fair agreement (between 0.3 and 0.5). When compared with the reference model, eight of the 11 models had a difference in predicted birthweight of <220 g, and the ICCs indicated that the majority of models had strong agreement.

CONCLUSION

All published CBMs demonstrated ability to predict birthweight with reasonable accuracy. The effects of maternal and fetal characteristics on birthweight appear to be consistent across birthweight models. This finding is a further step in validating the CBM, and provides greater evidence for the creation of a global model.

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.

Prediction of adverse perinatal outcome at term in small-for-gestational age fetuses: comparison of growth velocity vs. customized assessment

OBJECTIVE

To explore the ability of growth velocity and customized standards of fetal weight to predict adverse outcomes in small fetuses delivered at term.

METHODS

We evaluated a cohort of 86 consecutive singletons suspected to be small for gestational age during the third trimester (estimated fetal weight <10(th) centile), who had normal umbilical artery Doppler and ultimately delivered at term. Conditional growth velocity and customized fetal growth were compared for the prediction of adverse outcome.

RESULTS

Overall, customized growth assessment showed better sensitivity than growth velocity assessment (57.1% vs. 42.9% for a 10(th) centile cut-off) for the prediction of adverse outcome, but with comparable specificity. The odds of having an adverse outcome for women with a positive test compared with women with a negative test were 1.54 and 3.22 for the 10(th) centile growth velocity and customized definitions, respectively. The area under the curve for the prediction of adverse outcome was larger for customized than for growth velocity standards (0.65 vs. 0.59), albeit without statistical significance.

CONCLUSIONS

Our study suggests that customized growth assessment may have better accuracy in predicting adverse perinatal outcome than growth velocity in small fetuses with normal umbilical Doppler delivered at term.

Customized birthweight standards for a Spanish population

OBJECTIVE

To analyse the biological factors affecting birthweight and to derive customized birthweight standards for a Spanish population.

METHODS

A retrospective cohort was created with all the singleton pregnancies delivered at term and free of pathology in our Institution. Birthweight was modeled by multiple linear regression from maternal (ethnic origin, maternal height, booking weight, smoking, and parity), and fetal (gender, gestational age) characteristics.

RESULTS

In addition to gestational age and sex, height, booking weight, ethnic origin, parity, and smoking all have significant and independent effects on birthweight. Women from East-Asia, Morocco and South-America had newborns on average 83 g, 74 g and 95 g heavier than White-European Spanish women. The effect of smoking was found to be dose-related.

CONCLUSION

We found the relative effect of the maternal and fetal characteristics to be very similar to that reported in previous studies. We report coefficients for ethnic groups that account for a sizeable proportion of the population composition of several European countries.

Reduced maternal corticosteroid-binding globulin and cortisol levels in pre-eclampsia and gamete recipient pregnancies

OBJECTIVE

To measure and contrast maternal cortisol and corticosteroid-binding globulin (CBG) levels in pregnancies with normal outcomes, pre-eclampsia, intrauterine growth restriction (IUGR) and in gamete recipients.

STUDY DESIGN

Prospective study of 93 women at high risk of pre-eclampsia, including gamete recipients (n = 22) and 33 controls. Plasma total and free cortisol and CBG were measured every 2 weeks from 16 weeks' gestation until delivery.

RESULTS

Forty-two per cent of the high-risk group had complications, including pre-eclampsia (n = 11), gestational hypertension (n = 16) and small-for-gestational-age (SGA) neonates (n = 12). There were no complications in the controls. In all groups, plasma CBG concentrations increased progressively across gestation (P < 0.05), in parallel to total cortisol, but fell significantly from 36 weeks' gestation onwards, with a corresponding rise in free cortisol concentrations. In pre-eclampsia and gestational hypertension, plasma CBG, and total and free cortisol concentrations were lower from 36 weeks onwards (P < 0.05). In IUGR, plasma CBG concentrations were suppressed from 28 weeks' gestation until delivery (P < 0.05), but with no significant difference in plasma total and free cortisol. Gamete recipients had significantly lower plasma CBG from 20 weeks' gestation onwards, and plasma total and free cortisol were reduced at 24 and 32 weeks onwards, respectively.

CONCLUSIONS

Maternal plasma CBG, total and free cortisol concentrations are reduced in pre-eclampsia/gestational hypertension, and markedly reduced in gamete recipients. Low CBG may be due to reduced synthesis or enhanced inflammation-driven degradation. Low maternal cortisol may be due to a lack of placental corticotropin-releasing hormone or reduced maternal ACTH, driving cortisol production. Low maternal cortisol may influence the foetal hypothalamic-pituitary-adrenal axis and disease patterns later in life following complicated pregnancy.

Individualized growth charts for ultrasound measurements can significantly improve fetal monitoring

OBJECTIVE

For monitoring pregnancies it is useful to reduce unnecessary examinations due to wrongfully assumed growth retardation in cases with a small fetal growth potential. It also makes sense to improve the detection of objectively retardated children in order to a disproportionately high growth potential. It was the aim of this study to modify the standard growth charts for ultrasound parameters according to parental influences to better display the individual growth potential.

MATERIAL AND METHODS

In a prospective trial 1,390 ultrasound measurements of 174 completed pregnancies were observed. For all patients a standard questionnaire was conducted in which possible predictors for fetal growth were collected. Customizing the growth charts had been achieved by (1) calculating the general impact of parental factors on the ultrasound measurement values, (2) plotting the individual growth charts for each pregnancy and (3) analyzing the difference of every observed measurement from either unchanged normal values or customized growth charts.

RESULTS

The obtained biparietal diameter measurements all in all are 291 mm closer to the individualized charts than to the unmodified charts. The total improvement of all thoracal diameter measurements was found to be 294 mm, the summarized advancement of all abdomen circumference values was 1,005 mm and the femur length measurements are 296 mm nearer to customized charts. All results were statistically significant.

DISCUSSION

This is the first time the impact of several predictors on ultrasound growth charts had been analyzed. While other working groups have demonstrated the benefit of customizing the fetal weight and length, this concept had never been carried forward onto the growth charts for ultrasound values. The method to adjust the common mean values by so called 'modifiers' is derived from the mathematical concept of the sequential first-trimester screening for Down's syndrome. For customizing growth charts this approach seems to be useful as well. The feasability and the statistical benefit of customizing ultrasound growth charts has been demonstrated in this work. A larger study seems to be promising and should be performed. Further improvements could be obtained by using normal growth charts which were derived from the examined cohort.

Customized birthweight centiles predict SGA pregnancies with perinatal morbidity

OBJECTIVES

To determine the following: (1) the proportion of babies reclassified as small or appropriately grown using customized and population centiles; and (2) the relative risks of perinatal morbidity, including abnormal umbilical Doppler studies, in babies classified as small for gestational age (SGA) and appropriate for gestational age (non-SGA) using the two centile calculations.

DESIGN

Cohort study in SGA and general hospital populations.

SETTING

National Women's Hospital, Auckland, NZ.

POPULATION

A cohort of SGA pregnancies (n= 374) and a general obstetric population (n= 12,879).

METHODS

Pregnancy outcomes were compared between 'non-SGA both' (> or =10th% by population and customized centiles) and those who were 'SGA both' (<10th% by population and customized centiles), 'SGA customized only' (SGA by customized but non-SGA by population centiles) and 'SGA population only' (SGA by population but non-SGA by customized centiles).

MAIN OUTCOME MEASURES

Maternal and newborn morbidity and perinatal death.

RESULTS

In the SGA cohort 271 (72%) babies were 'SGA both', 27 (7%) were 'SGA customized only', 32 (9%) were 'population SGA only' and 44 (12%) were 'non-SGA both'. In the general obstetric population 863 (6.7%) babies were 'SGA both', 445 (3.5%) were 'customized SGA only', 285 (2.2%) were 'population SGA only' and 11,286 (88%) were 'non-SGA both'. Perinatal death and newborn morbidity including nursery admission and long hospital stay were increased and comparable between 'SGA both' and 'customized SGA only' in both study populations. Newborn morbidity was low and comparable between 'population SGA only' and 'non-SGA both'. No perinatal deaths occurred in 'population SGA only' babies. Abnormal Doppler studies were more common in 'SGA both' or 'customized SGA only' but not in 'population SGA only' groups compared with 'non-SGA both'.

CONCLUSIONS

Customized birthweight centiles identified small babies at risk of morbidity and mortality. Use of customized centiles is likely to detect more babies at risk of perinatal morbidity and mortality than would be detected by population centiles.

Prenatal diagnosis of fetal growth restriction

Fetal growth restriction is one of the most challenging obstetric problems. Due to confusing terminology, there is an obvious lack of uniform diagnostic criteria. At present, most authors do not distinguish between the terms 'small for gestational age' (SGA) and 'intra-uterine growth restriction' (IUGR). These two clinical entities are not the same. The term 'SGA' should be used for an infant who has failed to achieve a weight threshold (usually defined as the 10th percentile). Conversely, an IUGR infant has, by definition, not reached his/her genetic growth potential due to an insult that has occurred in utero. An IUGR fetus may or may not be SGA but it always implies a pathological process. Clinicians tend to manage both conditions in the same way by delivering affected cases, often by elective Caesarean section and often prematurely. This strategy obviously represents an overtreatment. This chapter will discuss the various aetiologies of small fetuses and will provide the reader with diagnostic tools to distinguish between subtypes.

Methodologic issues in epidemiologic studies of congenital microcephaly

In this methodological paper, we explore a number of issues that pose problems for those who seek the antecedents of congenital microcephaly. We pay particular attention to three concerns: Who is a case? How should cases be classified? To whom should cases be compared?

Predictive value of hormone measurements in maternal and fetal complications of pregnancy

Intrauterine tissues (placenta, amnion, chorion, decidua) express hormones and cytokines that play a decisive role in maternal-fetal physiological interactions. The excessive or deficient release of some placental hormones in association with gestational diseases may reflect an abnormal differentiation of the placenta, an impaired fetal metabolism, or an adaptive response of the feto-placental unit to adverse conditions. This review is focused on the applicability of hormone measurements in the risk assessment, early diagnosis, and management of pregnancies complicated by Down's syndrome, fetal growth restriction, preeclampsia, preterm delivery, and diabetes mellitus. Combined hormonal tests or the combination of hormones and ultrasound may achieve reasonable sensitivity, but research continues to simplify the screening programs without sacrificing their accuracy. Only in a few instances is there sufficient evidence to firmly recommend the routine use of hormone tests to predict maternal and fetal complications, but the judicious use of selected tests may enhance the sensitivity of the risk assessment based solely on clinical and ultrasound examination.

Prenatal detection of a high-risk group for intrauterine growth restriction based on sonographic fetal biometry

OBJECTIVE

This study was performed to evaluate the significance of sonographic fetal biometry in predicting low birth weight.

METHOD

Five hundred and sixty-eight single-term pregnancies were analyzed. They were stratified into seven subgroups by birth weight deviation (BWD). Among the 568 pregnancies, 115 were revealed to be small-for-gestational-age (SGA) (birth weight less than mean -1.5 S. D.). When IUGR was suspected by routine sonographic fetal biometry, 'IUGR work-up' was carried out. The diagnostic performance of our screening method for the detection of SGA pregnancies in the general population was calculated.

RESULT

The sensitivity, specificity, positive predictive value, negative predictive value and odds ratio of our screening method for the detection of SGA pregnancies in the general population were 73.0, 96.6, 83.2, 98.0% and 131.0, respectively.

CONCLUSION

These data suggest that sonographic biometry is useful for the prenatal detection of high-risk cases of fetal growth restriction.

Customized fetal weight limits for antenatal detection of fetal growth restriction

OBJECTIVE

To define cut-off limits for individually adjustable fetal weight standards for the detection of intrauterine growth restriction.

DESIGN

Retrospective study, with the outcome measures small-for-gestational age (SGA) birth weight, operative delivery for fetal distress, umbilical artery pH < 7.15, and admission to the neonatal intensive care unit.

SUBJECTS AND METHODS

Two hundred and fifteen women considered to be at increased risk of uteroplacental insufficiency were recruited to a study of serial ultrasound scans. Fetal weights were derived using standard formulae and, retrospectively, weight percentiles were calculated after individual adjustment for maternal height, weight in early pregnancy, ethnic group, parity and fetal sex.

INTRODUCTION

One or more antenatal scans indicative of fetal weight below the 10th customized percentile were predictive for a SGA neonate at birth (P < 0.001), operative delivery for fetal distress (P < 0.01) and admission to neonatal intensive care (P < 0.01) but not for a low umbilical artery pH (P = 0.6). Receiver-operator curves showed the optimal customized fetal weight percentile limit for predicting an SGA neonate to be the 18th percentile (sensitivity 83%, specificity 79%, positive predictive value 63% and negative predictive value 92%). For the prediction of operative delivery for fetal distress and admission to neonatal intensive care, the optional customized cut-off value was the 8th percentile.

CONCLUSIONS

The assessment of fetal weight using ultrasound and an individually-adjusted standard is predictive of growth restriction and perinatal events associated with hypoxia or diminished reserve. The optimal cut-off value for predicting operative delivery for fetal distress or admission to the neonatal intensive care unit suggests that the 10th customized percentile is a good limit for clinical use.

Newborn shoulder width: a prospective study of 2222 consecutive measurements

OBJECTIVES

To relate maternal and infant characteristics to newborn shoulder width and to evaluate the predictive value of newborn shoulder width measurement in cases of shoulder dystocia.

DESIGN

Newborn shoulder width was systematically measured at birth during a period of 18 months.

SETTING

Department of Obstetrics and Gynaecology of Saint-Antoine University Hospital, Paris, France.

POPULATION

A total of 2222 newborn shoulder width measurements were performed and 22 cases of true shoulder dystocia occurred during the study period.

METHODS

Newborn shoulder width measurements were reviewed and correlated with maternal age, parity, nonpregnant weight, weight gain during pregnancy, height, race, fasting glucose and one hour glucose levels, gestational age, birthweight and sex of the neonate. A receiver-operating characteristics curve was constructed to evaluate newborn shoulder width as a test for predicting shoulder dystocia.

RESULTS

The mean newborn shoulder width was 122.06 mm (10.50 SD). Stepwise multiple regression showed that newborn shoulder width was significantly associated with birthweight (P < 0.001), parity (P = 0.04), and nonpregnant weight (P = 0.04). We estimated that the best cut off for shoulder dystocia prediction was a newborn shoulder width measurement with a low false positive rate (< 10%) in association with a high sensitivity rate. Therefore, newborn shoulder width measurement > or = 140 mm was selected. This measurement should have a low sensitivity of 27.27%, a specificity of 91.82%, a positive predictive value of 4.02%, and a negative predictive value of 99.01% for shoulder dystocia prediction. Nevertheless, birthweight > or = 4000 g should have a better predictive value retrospectively for shoulder dystocia.

CONCLUSIONS

Newborn shoulder width measurement, which is strongly correlated with birthweight, still remains a poor predictor for shoulder dystocia, even when this evaluation is correct antenatally.

Foetal nutrition, foetal growth restriction and health later in life

Retarded intrauterine growth has been linked to increased risk of perinatal mortality and morbidity, sudden infant death and poorer health later in life. The independent variables used in these studies are mainly neonatal size parameters, such as weight, ponderal index and ratios of head and abdominal measures. These are, in terms of foetal development and growth, crude parameters. This paper discusses the concepts of growth retardation used in most clinical and epidemiological studies. It is again emphasized that small for gestational age (SGA) and intrauterine growth retardation (IUGR) are different concepts. SGA is a size parameter that may or may not reflect restricted foetal growth and is therefore of limited value. Even IUGR, defined as retarded foetal growth rate, may be a too crude a criterion to select foetuses with short- and long-term health risks. Other biophysical measurements, such as foetal blood flow patterns and biochemical parameters, may be helpful in a better selection of these foetuses and infants. Furthermore, different causes of IUGR, e.g. poor maternal nutrition versus insufficient placental function, may not have the same effects on the foetus. The discrepancies in the results of studies on the relationship between IUGR or foetal malnutrition and short- and long-term health risks may be explained by the crudeness of the independent variables used. In the future, research on the biology of the developing human foetus should be more focused in the studies of the relationship between the intrauterine environment and nutrition and risk of poor health later in life.

The application of individualised fetal growth curves

Individually adjusted or 'customised' growth charts aim to optimise the assessment of fetal growth by taking individual variation into account, and by projecting an optimal curve which delineates the potential weight gain in each pregnancy. This results in an increased detection rate of true growth restriction and a reduction in false positive diagnoses for IUGR. An adjustable standard can apply across geographical boundaries, as individual variation exceeds that between different maternity populations.

The application of individualised fetal growth curves

Individually adjusted or 'customised' growth charts aim to optimise the assessment of fetal growth by taking individual variation into account, and by projecting an optimal curve which delineates the potential weight gain in each pregnancy. This results in an increased detection rate of true growth restriction and a reduction in false positive diagnoses for IUGR. An adjustable standard can apply across geographical boundaries, as individual variation exceeds that between different maternity populations.

Differences in late fetal death rates in association with determinants of small for gestational age fetuses: population based cohort study

OBJECTIVE

To examine differences in late fetal death rates in association with determinants of small for gestational age fetuses.

DESIGN

Population based cohort study.

SUBJECTS

1 026 249 pregnancies without congenital malformations.

SETTING

Sweden 1983-92.

MAIN OUTCOME MEASURE

Late fetal death rate.

RESULTS

Depending on underlying determinants late fetal death rates were greatly increased in extremely small for gestational age fetuses (range 16 to 45 per 1000) compared with non-small for gestational age fetuses (1.4 to 4.6). In extremely small for gestational age fetuses late fetal death rates were increased from 31 per 1000 in mothers aged less than 35 years to 45 per 1000 in older mothers, and from 22 per 1000 in women <155 cm in height to 33 per 1000 in women >=175 cm tall. Late fetal death rates were also higher in extremely small for gestational age fetuses in singleton compared with twin pregnancies and in non-hypertensive pregnancies compared with pregnancies complicated by severe pre-eclampsia or other hypertensive disorders. Slightly higher late fetal death rates were observed in nulliparous compared with parous women and in non-smokers compared with smokers.

CONCLUSIONS

Although the risk of late fetal death is greatly increased in fetuses that are extremely small for gestational age the risk is strongly modified by underlying determinants-for example, there is a lower risk of late fetal death in a small for gestational age fetus if the mother is of short stature, has a twin pregnancy, or has hypertension.

Consequences of fetal growth restriction

An increasing number of diseases in child and adult life are now thought to have their origins in the fetal period. Central to this predisposition is restriction of fetal growth. During the period reviewed in this article, the associations between adult hypertension and low birthweight were confirmed, and numerous studies have investigated possible mechanisms by which the metabolism of an individual may be programmed by an adverse intrauterine environment. The consequences in adult life of intrauterine undernutrition now highlight prenatal care as one of the most crucial issues in medicine and challenge many aspects of current obstetric decision-making. Research targeting fetal growth and development can be expected to result in improved health at all ages.

The new obstetrics: its integration into neonatal clinical practise, teaching and research

Most neonatologists have not yet incorporated into their teaching, clinical service and research the advances in high risk obstetrics particularly as it relates to fetal surveillance. This brief review emphasizes some of the "new obstetrics" from the viewpoint of perinatal medicine, particularly in terms of neonatal teaching and the design of future neonatal research. The information that can be obtained about an infant prenatally by the use of ultrasound. power doppler, computerized fetal heart rate monitoring, cordocentesis, etc is extensive and yet, has rarely been utilized in the design of neonatal research protocols. It is becoming imperative that the "new obstetrics" be recognized and utilized in modern neonatal thinking if a truly "perinatal medicine" is to be practised.