Prematurity and fetal growth restriction

The customised growth potential: an international research tool to study the epidemiology of fetal growth

Customised centiles based on individual fetal growth potential enhance our ability to differentiate between physiological and pathological smallness. A series of studies in different maternity populations has found striking similarities in the way fetal growth varies with maternal and pregnancy related characteristics, and has established the clear advantages of this method over generic, population-based birthweight or fetal weight standards. The method opens up many new avenues for the retrospective study of risk factors and fetal growth. The findings quantify the strength of association between fetal growth restriction and perinatal outcome, and therefore also highlight the clinical imperative to improve antenatal detection of the at-risk fetus. Applied prospectively as customised charts, the concept improves the detection of fetal growth restriction and reduces the need for unnecessary investigations.

Site-specific IGFBP-1 hyper-phosphorylation in fetal growth restriction: clinical and functional relevance

Phosphorylation enhances IGFBP-1 binding to IGF-I, thereby limiting the bioavailability of IGF-I that may be important in fetal growth. Our goal in this study was to determine whether changes in site-specific IGFBP-1 phosphorylation were unique to fetal growth restriction. To establish a link, we compared IGFBP-1 phosphorylation (sites and degree) in amniotic fluid from FGR (N = 10) and controls (N = 12). The concentration of serine phosphorylated IGFBP-1 showed a negative correlation with birth weight in FGR (P = 0.049). LC-MS/MS analysis revealed all four previously identified phosphorylation sites (Ser98, Ser101, Ser119, and Ser169) to be common to FGR and control groups. Relative phosphopeptide intensities (LC-MS) between FGR and controls demonstrated 4-fold higher intensity for Ser101 (P = 0.026), 7-fold for Ser98/Ser101 (P = 0.02), and 23-fold for Ser169 (P = 0.002) in the FGR group. Preliminary BIAcore data revealed 4-fold higher association and 1.7-fold lower dissociation constants for IGFBP-1/IGF-I in FGR. A structural model of IGFBP-1 bound to IGF-I indicates that all the phosphorylation sites are on relatively mobile regions of the IGFBP-1 sequence. Residues Ser98, Ser101, and Ser169 are close to structured regions that are involved in IGF-I binding and, therefore, could potentially make direct contact with IGF-I. On the other hand, residue Ser119 is in the middle of the unstructured linker that connects the N- and C-terminal domains of IGFBP-1. The model is consistent with the assumption that residues Ser98, Ser101, and Ser169 could directly interact with IGF-I, and therefore phosphorylation at these sites could change IGF-I interactions. We suggest that site-specific increase in IGFBP-1 phosphorylation limits IGF-I bioavailability, which directly contributes to the development of FGR. This study delineates the potential role of higher phosphorylation of IGFBP-1 in FGR and provides the basis to substantiate these findings with larger sample size.

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.

Acute effect of cigarette smoking on placental circulation - a study by carbon-monoxide measurement and Doppler assessment

OBJECTIVE

Carbon-monoxide (CO) decreases placental vascular impedance. We assessed the consequences of smoking-induced temporary maternal CO-increase on fetal and placental circulation.

STUDY DESIGN

In a prospective study twenty-nine smoking pregnant women and their fetuses were evaluated. We determined the changes in maternal blood CO levels after smoking, and the concomitant changes in maternal and fetal circulation. Changes in fetal heart rate, uterine artery (UTA), middle cerebral artery (MCA), and descending aorta (DA) flow were measured by Doppler velocimetry. Changes in maternal CO level and umbilical flow value were assessed by paired t-test. The correlation between CO level and placental flow was assessed by partial correlation test.

RESULTS

CO level increased (mean +/-SD 1.7 +/- 0.065% vs. 2.36 +/- 0.89, p<0.0001). Nicotine-related maternal circulatory parameters changed significantly, but uterine flow values remained unchanged. Fetal heart rate increased, while flow in MCA and DA showed no change. CO-dependent umbilical artery impedance remained unchanged (Pulsatility Index: 0.956 +/- 0.18 vs. 0.948 +/- 0.21). Partial correlation between CO level and umbilical arterial impedance showed no significance (r:-0.324).

CONCLUSION

Despite significant CO elevation, the mainly CO-regulated placental flow remained unchanged.

The value of customised centiles in assessing perinatal mortality risk associated with parity and maternal size

OBJECTIVE

We wanted to compare customised and population standards for defining smallness for gestational age (SGA) in the assessment of perinatal mortality risk associated with parity and maternal size.

DESIGN

Population-based cohort study.

SETTING

Sweden.

POPULATION

Swedish Birth Registry database 1992-1995 with 354 205 complete records.

METHOD

Coefficients were derived and applied to determine SGA by the fully customised method, or by adjustment for fetal sex only, and using the same fetal weight standard.

MAIN OUTCOME MEASURE

Perinatal deaths and rates of small for gestational age (SGA) babies within subgroups stratified by parity, body mass index (BMI) and maternal size within the BMI range of 20.0-24.9.

RESULTS

Perinatal mortality rates (PMR) had a U-shaped distribution in parity groups, increased proportionately with maternal BMI, and had no association with maternal size within the normal BMI range. For each of these subgroups, SGA rates determined by the customised method showed strong association with the PMR. In contrast, SGA based on uncustomised, population-based centiles had poor correlation with perinatal mortality. The increased perinatal mortality risk in pregnancies of obese mothers was associated with an increased risk of SGA using customised centiles, and a decreased risk of SGA using population-based centiles.

CONCLUSION

The use of customised centiles to determine SGA improves the identification of pregnancies which are at increased risk of perinatal death.

A critical assessment of adverse pregnancy outcome and periodontal disease

BACKGROUND

Pre-term birth is a major cause of infant mortality and morbidity that has considerable societal, medical, and economic costs. The rate of pre-term birth appears to be increasing world-wide and efforts to prevent or reduce its prevalence have been largely unsuccessful.

AIM

To review the literature for studies investigating periodontal disease as a possible risk factor for pre-term birth and adverse pregnancy outcomes.

MAIN FINDINGS AND CONCLUSION

Variability among studies in definitions of periodontal disease and adverse pregnancy outcomes as well as widespread inadequate control for confounding factors and possible effect modification make it difficult to base meaningful conclusions on published data. However, while there are indications of an association between periodontal disease and increased risk of adverse pregnancy outcome in some populations, there is no conclusive evidence that treating periodontal disease improves birth outcome. Based on a critical qualitative review, available evidence from clinical trials indicates that, although non-surgical mechanical periodontal treatment in the second trimester of pregnancy is safe and effective in reducing signs of maternal periodontal disease, it does not reduce the rate of pre-term birth. Clinical trials currently underway will further clarify the potential role of periodontal therapy in preventing adverse birth outcomes. Regardless of the outcomes of these trials, it is recommended that large, prospective cohort studies be conducted to assess risk for adverse pregnancy outcome in populations with periodontal disease. It is critical that periodontal exposure and adverse birth outcomes be clearly defined and the many potential confounding factors and possible effect modifiers for adverse pregnancy outcome be controlled in these studies. If periodontal disease is associated with higher risk of adverse pregnancy outcome in these specific populations, large multicenter randomized-controlled trials will be needed to determine if prevention or treatment of periodontal disease, perhaps combined with other interventions, has an effect on adverse pregnancy outcome in these women.

Fetal growth and timing of parturition in humans

Animal studies indicate that either the fetus or the intrauterine environment, both of which set the pattern for fetal growth, may affect the timing of parturition. The authors examined the association between fetal growth and timing of spontaneous onset of labor in humans among low-risk white US women with singleton pregnancies (1987-1991). They restricted the data to pregnancies which had a reliable date of the last menstrual period, normal fetal growth in the first half of pregnancy, and no history of or current pregnancy complications that might have impaired fetal growth (n = 3,360). Subjects received ultrasound examinations at 15-22 and 31-35 weeks' gestation. Fetal growth was adjusted for parity, fetal sex, and maternal prepregnancy weight and height. Results showed that slower or faster fetal growth in the second half of pregnancy resulted in substantially lower or higher birth weight, respectively. However, fetal growth in the second half of pregnancy, even at extremes (2 standard deviations below or above the mean), did not have a meaningful impact on the timing of parturition; neither did fetal growth acceleration or deceleration in late pregnancy. Thus, in low-risk pregnancies where fetal growth is normal in early gestation, fetal growth in the second half of pregnancy does not affect the timing of normal parturition.

Cerebral palsy and restricted growth status at birth: population-based case-control study

OBJECTIVE

To evaluate the association between growth status at birth and subsequent development of cerebral palsy in preterm and term infants.

DESIGN

Population-based case-controlled study.

SETTING

Cerebral palsy register in Western Sweden. Subjects Cohort of 334 singletons born between 1983 and 1990, with cerebral palsy diagnosed from age 4, and 668 singletons matched for gestation, gender and delivery unit.

METHOD

Growth status at birth was determined using small for gestational age (SGA) categories, with customised birthweight percentiles (SGAcust) based on the Swedish population.

MAIN OUTCOME MEASURES

Proportion of babies that were SGAcust, comparing cases and controls in three gestational age categories: early preterm (24-33 weeks), late preterm (34-36 weeks) and term (37+ weeks).

RESULTS

Of the 334 children with cerebral palsy, 87 (26.6%) were born early preterm, 27 (8.1%) late preterm and 218 (66%) at term. Children who had been born at term were more likely to have been SGA <1st customised percentile (SGAcust1) than their matched controls (OR 6.6, 95% CI 2.3-18.6). In contrast, children with cerebral palsy born preterm were not more likely to have been SGAcust1 (OR 0.9, 95% CI 0.4-1.9), and this applied to early preterm as well as late preterm births. For less severely small babies (SGA between 1st and 5th customised percentiles), the association with cerebral palsy remained significant for term births (OR 5.2, 95% CI 2.7-10.1) but was again not significant for preterm births.

CONCLUSIONS

Term singletons with severely SGA birthweights had a five- to seven-fold risk of developing cerebral palsy compared with gestational age-matched infants with birthweights within normal limits. For children born preterm, SGA was not more likely to be present in cases than in controls. These findings support the concept of cerebral palsy as a multifactorial condition and highlight the importance of antenatal surveillance of fetal growth.

Twin-specific intrauterine 'growth' charts based on cross-sectional birthweight data

The assessment of fetal growth is an essential component of good antenatal care, especially for twins. The aims of this study are to develop twin-specific intrauterine 'growth' charts, based on cross-sectional birthweight data, for monochorionic and dichorionic twins according to sex and parity, and to detect twins at risk for neonatal death by comparing the use of twin-specific and singleton charts. The study sample consisted of 76,471 singletons and 8454 twins (4227 pairs) born in East Flanders (Belgium). Birthweights were analyzed using a nonlinear Gaussian regression. After 33 weeks of gestation, the birthweights of twins started to deviate from singletons (difference of 900 grams at 42 weeks). Birthweights of dichorionic twins continued to increase, whereas those of monochorionic twins decreased after week 40 (difference of more than 300 g at 42 weeks). After 31 weeks of gestation, neonatal mortality increased as centile decreased, and was especially high if birthweight was below the twin-specific third centile: .032 (below) versus .007 (above). Using singleton centiles, this was less obvious. In conclusion, twin-specific growth charts, taking chorionicity into account, are more accurate to detect twins at risk for neonatal death. Therefore the presented charts, based on cross-sectional birthweight data, enable an improved assessment of twin growth.

Newborn weight charts underestimate the incidence of low birthweight in preterm infants

OBJECTIVE

The objective of the study was to compare sonographic fetal weight estimates with newborn weight charts and analyze the predictive accuracy of the ponderal index (PI) in preterm infants.

STUDY DESIGN

We generated sonographic reference curves for fetal weight and PI estimates from a database of fetal biometric records from 12,589 term deliveries. We then plotted sonographic and newborn weight and PI of 2406 preterm newborns on these curves and compared them with published newborn weight charts.

RESULTS

The third centiles of sonographic and newborn weights diverged markedly between 25 and 36 weeks of gestation and by more than 400 g at 32-33 weeks. In contrast, sonographic and newborn PI values were similar despite uncertainties as to fetal length.

CONCLUSION

We suggest using sonographic reference fetal weights to screen preterm newborns for low birthweight. Uncertainties in fetal length threaten the reliability of the PI.

Fetal growth restriction: the etiology

Fetal growth restriction (FGR) is etiologically associated with various maternal, fetal and placental factors, although such an association may not be present in many cases. Maternal factors include hypertensive diseases, autoimmune disorders, certain medications, severe malnutrition, and maternal lifestyle including smoking, alcohol and cocaine use. Fetal etiologies include aneuploidy, malformations, syndromes related to abnormal genomic imprinting, perinatal viral or protozoan infections, preterm birth, and multiple gestation. Placental factors may involve many conditions including anatomical, vascular, chromosomal and morphological abnormalities. Better understanding of these etiologic conditions may lead to improved prediction, prevention and management of FGR.

The search for objective criteria at the limit of viability

BACKGROUND

Defining the limit of viability among very preterm infants remains a difficult issue. A recent study suggested severity of intrauterine growth retardation as a decisive criterion, reporting very poor survival for infants born at </=28 weeks with birth weight <2nd centile.

OBJECTIVE

To check whether the above criterion can be confirmed in a similar analysis of German data.

METHODS

Analyses were based on German population-based data from Lower Saxony, including preterm neonates (22-28 weeks) without severe congenital malformations (n = 3,453), born 1991-1999. For the definition of growth retardation postnatal (<3rd, <10th centile) and antenatal (<3rd centile) reference values were used.

RESULTS

Depending on the definition used, proportions of growth retarded infants varied considerably (4-16%). Survival rates increased from 0 to 64%, arguing against considering infants <28 weeks' GA as a homogenous group with regard to their odds for survival.

CONCLUSION

There is an association between severity of growth retardation and VLBW mortality in general, but overinterpreting results from single studies may lead to dangerous conclusions. Data from preterm infants should be stratified by week of gestation.

Clinical evidence of intrauterine disturbance in Prader-Willi syndrome, a genetically imprinted neurodevelopmental disorder

BACKGROUND

Imprinted genes are considered to play an important role in growth and early development but much of the research is based on animal studies.

AIM

This study reports clinical data from a French population concerning prenatal, perinatal and postnatal complications in Prader-Willi syndrome (PWS), a genetically imprinted neurodevelopmental disorder associated with growth retardation, intellectual impairment and obesity.

STUDY DESIGN

Data from family health records concerning prenatal, perinatal and postnatal complications were collected from 52 French people with the deletion form (DEL), and 34 French people with the maternal disomy form of PWS (UPD) and compared against national norms and between groups.

RESULTS

Significant findings include: a history of miscarriage, high rate of polyhydramnios (12/34 UPD, 11/52 DEL), a high rate of induced labour, a high rate of Caesarian section (20/34 UPD, 26/52 DEL), small gestational age (10/34 UPD, 22/52 DEL), hypotonia (34/34 UPD, 49/52 DEL), and suckling deficit (25/34 UPD, 46/52 DEL). Significant differences between genetic subtypes include a higher rate of induced labour in UPD (27/34 UPD, 25/52 DEL), an increased risk of premature term in UPD (9/34 UPD vs. 4/52 DEL), raised maternal age in UPD (36.4 years vs. 29.3 years), low birth weight for newborns with a deletion form of PWS (girls 2.8 kg, boys 2.7 kg), a positive correlation between parental weight and offspring birth weight only for patients with UPD (UPD maternal: r=0.62, paternal: r=0.51).

CONCLUSION

The results indicate significant intrauterine disturbance in PWS, particularly in PWS due to UPD, but a more significant weight disturbance for PWS due to deletion.

Customised birthweight standards accurately predict perinatal morbidity

OBJECTIVE

Fetal growth restriction is associated with adverse perinatal outcome but is often not recognised antenatally, and low birthweight centiles based on population norms are used as a proxy instead. This study compared the association between neonatal morbidity and fetal growth status at birth as determined by customised birthweight centiles and currently used centiles based on population standards.

DESIGN

Retrospective cohort study.

SETTING

Referral hospital, Barcelona, Spain.

PATIENTS

A cohort of 13 661 non-malformed singleton deliveries.

INTERVENTIONS

Both population-based and customised standards for birth weight were applied to the study cohort. Customised weight centiles were calculated by adjusting for maternal height, booking weight, parity, ethnic origin, gestational age at delivery and fetal sex.

MAIN OUTCOME MEASURES

Newborn morbidity and perinatal death.

RESULTS

The association between smallness for gestational age (SGA) and perinatal morbidity was stronger when birthweight limits were customised, and resulted in an additional 4.1% (n=565) neonates being classified as SGA. Compared with non-SGA neonates, this newly identified group had an increased risk of perinatal mortality (OR 3.2; 95% CI 1.6 to 6.2), neurological morbidity (OR 3.2; 95% CI 1.7 to 6.1) and non-neurological morbidity (OR 8; 95% CI 4.8 to 13.6).

CONCLUSION

Customised standards improve the prediction of adverse neonatal outcome. The association between SGA and adverse outcome is independent of the gestational age at delivery.

Twin birth weight standards

OBJECTIVE

The aim of this study was to present customized twin-specific birth weight standards. The relative contribution of gestational age, maternal factors, twin factors and placental factors to the birth weight was evaluated in a multivariate approach.

SUBJECTS AND METHODS

Perinatal data were obtained from 10,177 live-born twins from the East Flanders Prospective Twin Survey. Of 8,454 twins (4,227 pairs), of whom all data were available, the birth weights at different gestational ages were analyzed using a non-linear multivariate gaussian regression.

RESULTS

All considered covariates influenced birth weight of twins significantly, with the exception of sex of the co-twin and mode of conception and delivery. At 37 weeks of gestation, a difference of >1 kg existed between favourable and adverse prenatal environment. Up to 40 weeks, sex, site of the umbilical cord, parity, and birth order had a greater influence on birth weight than zygosity, chorionicity and fusion of the placentas. From 34 weeks on, the birth weight of the second-born twin deviated and after 40 weeks, birth weight of monozygotic monochorionic twins dropped, while the other twins continued to grow.

CONCLUSION

Customized twin-specific birth weight standards, which take these covariates into account, offer the opportunity for a better assessment of the influence of birth weight of the twin on neonatal health in future research. Already the Developmental Origins of Health and Disease hypothesis showed that these prenatal conditions might also be important for the follow-up of the twin.

Fetal growth risk curves: defining levels of fetal growth restriction by neonatal death risk

OBJECTIVE

We developed a fetal growth risk curve that delineates the birth weight values for gestational age that reflect a 2-, 2.5-, and 3-fold neonatal death risk relative to infants with normal fetal growth.

STUDY DESIGN

We analyzed 18,085,052 single gestation infants (25-42 weeks) who were born to US resident mothers from 1996 to 2000. Multivariate models were used to predict the relationship between neonatal death and birth weight percentile. Fetal risk curves were derived on the basis of birth weight percentile-specific neonatal mortality rates that were relative to an average rate of neonatal death for a comparison group that was representative of typical growth (ie, infants between 45th-55th birth weight percentiles for gestational age).

RESULTS

The 10th percentile of birth weight for gestational age is associated with an increased but variable risk of neonatal death relative to the comparison group across the spectrum of gestational ages. At 26 weeks of gestation, infants at the 10th percentile experienced a 3-fold risk of dying within the first 28 days of life (relative to the comparison group); whereas at 40 weeks, the risk was 1.13.

CONCLUSION

Fetal growth risk curves facilitate the identification of populations of infants whose risk of death are deemed excessive compared with that of infants at the norm of fetal growth and may be useful for counseling pregnant women.

New Definition of Small for Gestational Age Based on Fetal Growth Potential

Accurate definition of small for gestational age (SGA) is essential for antenatal as well as postnatal care. SGA is associated with significant antenatal and postnatal pathology. The term, however, includes constitutional smallness, and it is essential to adjust for physiological variation in order to identify those babies who are pathologically small. Maternal height, weight, parity, ethnic origin and the baby's gender have all been found to be significantly associated with normal variation in birth weight. These variables need to be adjusted for to calculate the true growth potential, which can be represented as individually customized fetal growth curves and birth weight percentiles (www.gestation.net). This method for calculating growth potential has been validated in a number of international studies. 'Customized SGA' defines neonates with intrauterine growth restriction, while 'small-normal' does not represent increased risk. Currently, coefficients are being developed for more ethnic groups, to broaden the international applicability of individualized standards. Work is also underway to incorporate the customized birth weight percentile as the starting point of infant growth curves.