In utero ponderal index as a prognostic factor in the evaluation of intrauterine growth retardation

Prenatal exposure to multiple metals and birth outcomes: An observational study within the National Children's Study cohort

BACKGROUND

Prenatal exposure to metals may play an important role in fetal growth. However, the epidemiologic evidence for certain metals is sparse, and most of the existing research has focused on evaluating single metals in highly exposed target populations.

OBJECTIVES

We evaluated associations of cadmium, lead, manganese, selenium, and total mercury exposures during pregnancy with fetal growth using data from mother-infant pairs participating in the National Children's Study.

METHODS

Prenatal metal exposures were measured using maternal blood collected from 6 to 32 weeks of gestation. Birth outcomes, including gestational age, birthweight, birth length, head circumference, and ponderal index, were ascertained through physical measurement at birth or abstraction from medical records. Regression coefficients and their 95% confidence intervals were estimated from multivariable linear regression models in the overall study population as well as among male and female infants. We further evaluated pairwise metal-metal interactions.

RESULTS

Sex-specific associations were observed for lead, with inverse associations for birthweight, birth length, head circumference, and gestational age observed only among female infants. Sex-specific associations were also observed for selenium, with a positive association for birthweight observed among male infants; selenium was also positively associated with ponderal index and inversely associated with birth length among female infants. Overall, total mercury was inversely associated with birthweight and ponderal index, and the association with birthweight was stronger among female infants. No significant associations were observed with cadmium and manganese. In the metal-metal interaction analyses, we found evidence of a synergistic interaction between lead and total mercury and antagonistic interaction between selenium and total mercury with selected birth outcomes.

CONCLUSIONS

Our findings suggest that prenatal exposure to metals may be related to birth outcomes, and infant sex may modify these associations.

Association between prenatal arsenic exposure, birth outcomes, and pregnancy complications: An observational study within the National Children's Study cohort

BACKGROUND

Chronic arsenic exposure has been associated with pregnancy complications and reduced fetal growth in populations where total arsenic exposure exceeds 50 μg/L. However, the potential effect on pregnancy outcomes remains unclear at lower levels of arsenic exposure, such as those most commonly observed in the United States.

OBJECTIVES

We evaluated the associations between arsenic exposure during pregnancy with fetal growth and risk of pregnancy complications using data from mother-infant pairs participating in the National Children's Study.

METHODS

Prenatal arsenic exposure was measured using maternal urine collected during the third trimester. Information about pregnancy complications was abstracted from medical records. Fetal growth, including gestational age, birth weight, birth length, head circumference, and ponderal index, was ascertained through physical measurement at birth and extracted from medical records.

RESULTS

Medians [interquartile range (IQR)] of maternal urinary total arsenic and dimethylarsinic acid (DMA) were 7.77 μg/L (7.98) and 3.44 μg/L (3.13), respectively. Each increase in IQR of prenatal total arsenic level was associated with greater birth length (+0.28 cm; 95% CI: 0.14, 0.42), greater head circumference (+0.12 cm; 95% CI: 0.04, 0.21), and lower ponderal index (-0.37 kg/m³; 95% CI: -0.58, -0.17). Similar results were obtained for levels of prenatal DMA. Tests for multiplicative interaction indicate that prenatal urinary DMA was negatively associated with gestational age among female infants (-0.44 week decrease in gestational age estimated for each IQR increase in DMA; 95% CI: -0.84, -0.05), while no association was observed among male infants (p_interaction = 0.02). No significant associations were detected between arsenic and birth weight or pregnancy complications.

CONCLUSIONS

Higher prenatal arsenic exposure was associated with longer birth length, greater head circumference, and lower ponderal index. Associations between arsenic and gestational age may be modified by infant sex.

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.

Endocrine regulation in asymmetric intrauterine fetal growth retardation

OBJECTIVE

The ponderal index (PI) is a widely accepted measure of disproportionate growth or asymmetrical growth retardation by pediatricians worldwide. Identification of disproportionately grown small for gestational age (SGA) neonates by using the ponderal index as a measure of the nutritional status at birth, is important because they constitute a high-risk group among SGA neonates. Poor nutritional status of the mother could have a direct effect on the organs of the developing fetus and/or affect the endocrine milieu in the maternal feto-placental unit resulting in an increased incidence of intrauterine growth-retarded (IUGR)/SGA births. IUGR is a significant risk factor for adult disease. In this study, we have investigated the endocrine adaptation by the fetus to overcome the growth disadvantage caused due to poor nutritional status of the mother.

MATERIALS AND METHODS

We examined the quantitative variations in hormonal and growth factor profiles in paired maternal and cord blood samples obtained from mothers and their neonates who were classified based on their growth status into SGA and appropriate for gestational age (AGA).

RESULTS

(1) A total of 24.7% neonates had a PI < 2, indicating a high incidence of asymmetric IUGR in the population studied. (2) Anthropometric parameters measured in the mothers indicate that the mothers giving birth to neonates with a PI < 2 had poor nutritional status, both prior to and during pregnancy. (3) We observed increased levels of placental lactogen and prolactin and decreased levels of insulin in the cord blood of neonates with PI < 2, while lower levels of insulin-like growth factor 1 (IGF-1) and higher levels of epidermal growth factor (EGF) were observed in their mothers.

CONCLUSION

Poor maternal nutritional status results in fetal adaptation to a growth restricted environment via the modulation of the pituitary-thyroid axis thereby altering the endocrine milieu, thus affecting fetal growth.

Foetal size and body proportion at 17-19 weeks of gestation and neonatal size, proportion, and outcome

OBJECTIVE

To determine whether proportionate or disproportionate foetal smallness at 17 to 19 weeks of gestation in low-risk pregnancies was associated with size, body constitution, and adverse outcome at birth.

METHODS

We included ultrasound measurements at 17-19 weeks of gestation in 7285 uncomplicated pregnancies with reliable information on last menstrual period. We considered a foetus with both mean abdominal diameter (MAD) and biparietal diameter (BPD) below the 10th percentile for gestational age, gender, and parity as symmetrically small. Those who had MAD below the 10th percentile and BPD at or above the 10th percentile were asymmetrically small (thin and small).

RESULTS

The occurrence of small for gestational age (SGA) (birth weight below the 10th percentile) decreased with increasing second trimester MAD percentile (P<0.0001). The risk in foetuses which were both thin and extremely small (MAD below the 2.5th percentile) of having weight, ponderal index, crown-heel length, or head circumference below the 10th percentile at birth was 19-28%. The risk of perinatal composite outcome (prenatal death, Apgar score after 5 min < or =7, birth weight below the 10th percentile, or <1500 g, or preterm birth) was 37%. Apgar score of < or =7 at 5 min and explained foetal death both occurred in 7%, which was significantly higher than those with larger MAD.

CONCLUSION

Asymmetric as well as symmetric foetal smallness may start early in pregnancy. Symmetric and particularly asymmetric small foetuses at 17-19 weeks of gestation were generally lighter, shorter, and thinner at birth and had more often adverse perinatal outcome.

Fetal body composition

PURPOSE OF REVIEW

The purpose of this review is to highlight recent developments in the evaluation of fetal growth, focusing on the determination of fetal body composition. The ultimate goal of this area of investigation is to improve predictions of perinatal morbidity and mortality beyond that achieved employing estimated fetal weight as the primary discriminator of the risk associated with abnormal fetal growth.

RECENT FINDINGS

Several validated techniques have emerged which appear capable of quantifying fetal lean body mass and fat mass. Preliminary investigations suggest that these body composition parameters do distinguish, with a higher degree of precision than estimates of fetal weight alone, clinical influences that contribute to abnormal fetal growth. Studies linking estimates of fetal body composition to improved prediction of perinatal morbidity and mortality are currently limited.

SUMMARY

Quantitative estimates of fetal body composition can currently be achieved with recently developed and validated ultrasound tools. Their utility for the improved prediction of perinatal morbidity and mortality has not yet been rigorously examined.

The intrauterine ponderal index in relation to birth weight discordance in twin gestations

OBJECTIVE

To establish the relationship between the fetal ponderal index and birth weight discordance in twins.

METHOD

The fetal ponderal index (estimated fetal weight divided by femur length3) was calculated in 86 pairs of twins delivered within 2 weeks of the last sonography and analyzed in relation to birth weight discordance.

RESULTS

A weak but significant correlation between fetal ponderal index and birth weight (r = 0.26, P < 0.0007) but no correlation with gestational age (r = 0.035, P = 0.65) were found. Members of concordant pairs (< 15% birth weight difference) had a significantly higher fetal ponderal index compared with members of mildly (15-25%) discordant pairs (P < 0.02), but not as compared with members of severely discordant (> 25%) pairs.

CONCLUSION

The characteristics of the fetal ponderal index in twins are similar to those in singletons. Fetal size seems to be diminished in severe but not in mild discordants. However, in its present form, the fetal ponderal index is a poor predictor of discordant growth and therefore should be employed cautiously in twin gestations.

Weight-for-length model in newborn Swedish infants

A new methodology for evaluation of weight in relation to length normalized for sex and gestational age (leanness/fatness) in the newborn infant is presented. Using standard deviation scores (SDS) for weight and length in a linear regression model, a new continuous variable called LEANSDS has been constructed with intercept = zero, regression coefficient = 0.7152, SD = 0.6988 and r2 = 0.51, irrespective of gender and gestational age within the range 34-43 weeks' gestation. The model is based on the Swedish 1986 Medical Birth Register and was tested on the 1985 year cohort. The reference material consisted of live-born, singleton infants considered "healthy". This new variable is independent of length. A chart is presented which simplifies visual evaluation. Using -2 SD as the cut-off limit, approximately one-third of light-for-dates infants are also lean, while two-thirds of the lean infants are not light for dates. Proportions of "not healthy" live-born infants and still births are given. Using another method, based on weight and length, and with some approximations needed for calculation of a comparable BW/BLSDS, the correlation was 0.9974, but this calculation is more elaborate and the comparable chart more complex. This method reveals the influence of gestational age on the relationship between weight and length, indicating a "prenatal puberty". Empirically, the logarithmic relationship found between weight and length indicates a ponderal index exponent of 2.4-2.5 instead of 3. LEANSDS, with its continuous nature, also gives the degree of deviation in each individual and in groups of infants, and can be added together and further analysed with improved sensitivity.

Antenatal screening and risk factors for intrauterine growth retardation

Antenatal risk factors in combination with symphysis-fundus distance can identify pregnancies with small infants, who can be divided in genetically small, malformed, and malnourished infants. Only the last category benefit from fetal surveillance. Maternal diseases, pregnancy complications (hypertension), and environmental factors (smoking) are connected to malnourished small infants.

The differential neonatal morbidity of the intrauterine growth retardation syndrome

This is a prospective study of differential morbidity among subgroups of intrauterine growth retardation. Cases of intrauterine growth retardation (N = 3450) (greater than or equal to 37 weeks, less than 10th percentile birth weight for gestational age) were classified by their ponderal index (weight/length3) in four subgroups using the 10th, 25th, and 90th percentiles of the Lubchenco's ponderal index-gestational age distribution. There were 432 cases (12.5%) with low ponderal index or disproportionate intrauterine growth retardation, 936 (27.1%) with intermediate ponderal index, 2030 (58.8%) with adequate ponderal index or proportionate intrauterine growth retardation, and 52 (1.5%) with high ponderal index. The low ponderal index group or disproportionate intrauterine growth retardation group had a statistically significant higher risk (between 1.6 and 12.5 times) for low 1- and 5-minute Apgar scores, aspiration syndrome, hypoglycemia, and perinatal asphyxia than the adequate ponderal index group. The low ponderal index group also had an increased risk (relative risk = 2.0 [95% confidence interval, 1.0 to 3.8]) for hospital stay of more than 1 week. These differences persist after a stratified analysis by birth weight and in a multiple logistic regression analysis. Similarly, higher neonatal morbidity is observed among infants with normal birth weights but with low ponderal index. These data provide further evidence of the heterogeneity of the intrauterine growth retardation syndrome and of the independent effect of body disproportion on neonatal morbidity, even among infants with normal birth weights. Because there are significant clinical implications attributed to the low ponderal index group, this subgroup should be identified as early as possible.