Comparison of fetal growth estimates based on birth weight and ultrasound references

Fetal size in a rural melanesian population with minimal risk factors for growth restriction: an observational ultrasound study from Papua New Guinea

We conducted a prospective longitudinal study of fetal size in rural Papua New Guinea (PNG) involving 439 ultrasound-dated singleton pregnancies with no obvious risk factors for growth restriction. Sonographically estimated fetal weights (EFWs; N = 788) and birth weights (N = 376) were included in a second-order polynomial regression model (optimal fit) to generate fetal weight centiles. Means for specific fetal biometric measurements were also estimated. Fetal weight centiles from a healthy PNG cohort were consistently lower than those derived from Caucasian and Congolese populations, which overestimated the proportion of fetuses measuring small for gestational age (SGA; < 10th centile). Tanzanian and global reference centiles (Caucasian weight reference adapted to our PNG cohort) were more similar to those observed in our cohort, but the global reference underestimated SGA. Individual biometric measurements did not differ significantly from other cohorts. In rural PNG, a locally derived nomogram may be most appropriate for detection of SGA fetuses.

Somatic growth trajectory in the fetus with hypoplastic left heart syndrome

BACKGROUND

Fetal growth abnormalities in hypoplastic left heart syndrome (HLHS) have been documented primarily by birth measurements. Fetal growth trajectory has not been described. We hypothesized that fetal growth trajectory declines across late gestation in this population.

METHODS

Infants with a prenatal diagnosis of HLHS and no history of prematurity or a genetic syndrome were identified. Fetal ultrasound measurements and birth anthropometrics were obtained from clinical records. z-Scores for estimated fetal weight (EFWz) and birth weight (BWTz) were compared. BWTz for three neonatal standards were compared.

RESULTS

Paired fetal and neonatal data were identified in 33 cases of HLHS. Mean gestational age at ultrasound and birth were 27 and 38 wk, respectively. BWTz was lower than EFWz by a mean of 0.82 (SD: 0.72, P < 0.0001), with 64% of subjects demonstrating a decrease in z-score of >0.5. Umbilical artery (UA) Doppler found no evidence of significant placental insufficiency. Modest differences in BWTz were seen across BWT standards in this cohort.

CONCLUSION

The majority of fetuses with HLHS demonstrate decreased growth velocity during later pregnancy, suggesting growth abnormalities manifest in utero. The potential relationship to future clinical outcomes warrants further study.

Development of a fetal weight chart using serial trans-abdominal ultrasound in an East African population: a longitudinal observational study

Objective

To produce a fetal weight chart representative of a Tanzanian population, and compare it to weight charts from Sub-Saharan Africa and the developed world.

Methods

A longitudinal observational study in Northeastern Tanzania. Pregnant women were followed throughout pregnancy with serial trans-abdominal ultrasound. All pregnancies with pathology were excluded and a chart representing the optimal growth potential was developed using fetal weights and birth weights. The weight chart was compared to a chart from Congo, a chart representing a white population, and a chart representing a white population but adapted to the study population. The prevalence of SGA was assessed using all four charts.

Results

A total of 2193 weight measurements from 583 fetuses/newborns were included in the fetal weight chart. Our chart had lower percentiles than all the other charts. Most importantly, in the end of pregnancy, the 10^th percentiles deviated substantially causing an overestimation of the true prevalence of SGA newborns if our chart had not been used.

Conclusions

We developed a weight chart representative for a Tanzanian population and provide evidence for the necessity of developing regional specific weight charts for correct identification of SGA. Our weight chart is an important tool that can be used for clinical risk assessments of newborns and for evaluating the effect of intrauterine exposures on fetal and newborn weight.

Customized versus population-based growth curves: prediction of low body fat percent at term corrected gestational age following preterm birth

OBJECTIVE

Compare customized versus population-based growth curves for identification of small-for-gestational-age (SGA) and body fat percent (BF%) among preterm infants.

METHODS

Prospective cohort study of 204 preterm infants classified as SGA or appropriate-for-gestational-age (AGA) by population-based and customized growth curves. BF% was determined by air-displacement plethysmography. Differences between groups were compared using bivariable and multivariable linear and logistic regression analyses.

RESULTS

Customized curves reclassified 30% of the preterm infants as SGA. SGA infants identified by customized method only had significantly lower BF% (13.8 ± 6.0) than the AGA (16.2 ± 6.3, p = 0.02) infants and similar to the SGA infants classified by both methods (14.6 ± 6.7, p = 0.51). Customized growth curves were a significant predictor of BF% (p = 0.02), whereas population-based growth curves were not a significant independent predictor of BF% (p = 0.50) at term corrected gestational age.

CONCLUSION

Customized growth potential improves the differentiation of SGA infants and low BF% compared with a standard population-based growth curve among a cohort of preterm infants.

Modeling fetal weight for gestational age: a comparison of a flexible multi-level spline-based model with other approaches

We present a model for longitudinal measures of fetal weight as a function of gestational age. We use a linear mixed model, with a Box-Cox transformation of fetal weight values, and restricted cubic splines, in order to flexibly but parsimoniously model median fetal weight. We systematically compare our model to other proposed approaches. All proposed methods are shown to yield similar median estimates, as evidenced by overlapping pointwise confidence bands, except after 40 completed weeks, where our method seems to produce estimates more consistent with observed data. Sex-based stratification affects the estimates of the random effects variance-covariance structure, without significantly changing sex-specific fitted median values. We illustrate the benefits of including sex-gestational age interaction terms in the model over stratification. The comparison leads to the conclusion that the selection of a model for fetal weight for gestational age can be based on the specific goals and configuration of a given study without affecting the precision or value of median estimates for most gestational ages of interest.

Maternal hemoglobin concentration and its association with birth weight in newborns of mothers with preeclampsia

OBJECTIVE

Maternal hemoglobin concentration is inversely related to newborn size presumably through plasma volume constriction. We sought to determine whether birth weight would show an inverse relationship to hemoglobin concentration in a group of infants whose mothers had preeclampsia, where plasma volume constriction is common.

METHODS

Electronic and paper chart review identified 142 nulliparous women with preeclampsia (excluding hemolysis, elevated liver enzymes, low platelets syndrome). Birth weight percentile was determined based on cross-sectional hybrid growth curves. Maximal third trimester maternal hemoglobin concentrations were obtained and standardised to z-scores based on gestational age matched normative data. Birth weight percentile was examined as a function of hemoglobin z-score using appropriate statistics.

RESULTS

Average gestational age at delivery was 35.9 +/- 1.9 weeks. Mean birth weight percentile for infants of preeclamptic mothers was 34 +/- 32. Mean hemoglobin z-score for mothers with preeclampsia was 0.3 +/- 1.5, significantly higher than a control population (p = 0.04). Maternal hemoglobin z-score was inversely associated with birth weight percentile (r = -0.18, p = 0.03).

CONCLUSION

Maternal hemoglobin concentrations are significantly elevated prior to delivery in women with preeclampsia. There is a statistically significant inverse correlation of maternal hemoglobin concentration to birth weight percentile.

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.

Optimal growth modeling

Abnormal fetal growth is associated with preterm birth, stillbirth, neonatal death, respiratory distress syndrome, and necrotizing enterocolitis. An optimal fetal growth standard would be one that most correctly identifies the fetus at risk for poor perinatal outcome. A growth standard that is created using population-specific data is more applicable than generalized growth curves since there is evidence that optimal neonatal outcome is achieved at different birth weights in different populations. The development of fetal growth standards based exclusively on neonatal birth weights is flawed as fetal growth restriction is associated with preterm delivery. Likewise, employing clinically derived ultrasound standards for term gestations would include a population that is more likely to have abnormal growth. Novel approaches to defining normal intrauterine growth combine birth weights at term and fetal growth patterns in-utero to create growth curves useful in defining the normal intrauterine growth experience. This review examines the performance of a variety of the growth characterizing standards that have been employed to define abnormal growth and examines their performance in the prediction of adverse perinatal outcome.

Maternal Smoking and Its Association With Birth Weight

OBJECTIVE

Maternal smoking has been associated with a reduction in newborn birth weight. We sought to estimate how the pattern of maternal smoking throughout pregnancy influences newborn size.

METHODS

One hundred sixty pregnant smoking women were enrolled in a prospective study. We collected data on maternal age, education, prepregnancy body mass index, and parity, as well as alcohol and illicit drug use. Cigarette use was defined as self-reported consumption before pregnancy, at the time of study enrollment, and in the third trimester. Statistical analyses were performed based on bivariate correlations and multiple linear regression.

RESULTS

Of the smoking parameters examined, maternal third-trimester cigarette consumption was the strongest predictor of birth weight percentile (partial r = -0.23, P < .001). For each additional cigarette per day that a participant smoked in the third trimester, there was an estimated 27 g reduction in birth weight. Prepregnancy smoking volume was not significantly associated with birth weight percentile in bivariate (r = -0.06, P = .47) or multivariable analyses. Additional factors contributing to birth weight include gestational age (partial r = 0.69, P < .001), maternal body mass index (partial r = 0.23, P < .001), and parity (partial r = 0.16, P < .004). In total, these 4 variables explain 61% of the variance in newborn birth weight.

CONCLUSION

Maternal third-trimester cigarette consumption is a strong and independent predictor of birth weight percentile. This supports the hypothesis that reductions in maternal cigarette consumption during pregnancy will result in improved birth weight, regardless of the prepregnancy consumption levels.

LEVEL OF EVIDENCE

III.

The Influence of Pregnancy on Arterial Compliance

OBJECTIVE

To examine the effect of pregnancy and the interval between pregnancies on arterial compliance as measured by mean arterial pressure (MAP) and pulse pressure.

METHODS

We conducted a 3-month chart review of deliveries at a tertiary care hospital (index pregnancies). Data collected included demographics, obstetric history, blood pressures, prepregnancy weight, weight gain, and neonatal outcome. If a subject's first delivery occurred at our institution, these records were reviewed in a similar fashion. Mean antepartum MAP and pulse pressure were calculated and compared for each trimester between index and first pregnancies. Statistical methods employed included repeated measures analysis of variance, repeated measures analysis of covariance, and correlation analysis.

RESULTS

Two hundred eighty-five charts were reviewed. Forty-seven women had complete data covering both index and first pregnancy. Mean arterial pressure was significantly higher in all trimesters of first compared with index pregnancies (first pregnancy-first trimester 82.0 +/- 8.1 mm Hg, index pregnancy-first trimester 79.4 +/- 7.6 mm Hg, P = .032; first-second trimester 81.6 +/- 6.7 mm Hg, index-second trimester 78.7 +/- 6.6 mm Hg, P = .016; first-third trimester 83.9 +/- 6.9 mm Hg, index-third trimester 81.6 +/- 6.9 mm Hg, P = .047). Repeated measures analysis of covariance confirmed that pregnancy order contributed independently to differences in MAP. The interval between pregnancies was found to be inversely related to the difference in MAP from first to index pregnancies by trimester (r = -0.41, P = .004) and the change in MAP within pregnancy from first to third trimester (r = -0.31, P = .046).

CONCLUSION

Mean arterial pressure is reduced in subsequent pregnancies compared with first pregnancies. This raises the possibility that pregnancy plays a role in modifying cardiovascular compliance. Consistent with this, the effect has temporal limitations in that the shorter the interval between pregnancies, the greater the reduction in MAP.

Birth weight references for triplets

OBJECTIVE

The purpose of this study was to formulate growth references that reflect triplet fetal and neonatal populations at each gestational age by combining serial ultrasonographic estimates of fetal weights and measured birth weights.

STUDY DESIGN

This historical cohort study was based on 188 pregnancies of live-born triplets of > or =23 weeks' gestation. Ultrasonographic fetal weight measures were modeled as a function of gestational age for each infant. Linear regression models were used to fit the data, and weight percentiles were generated.

RESULTS

Well-grown triplets fell substantially below singletons by 30 weeks and twins after 34 weeks. Trichorionic vs monochorionic or dichorionic placentation resulted in 27% higher growth at the 10th %ile, 5% higher growth at the 50th %ile, and 4% higher growth at the 90th %ile by 34 weeks.

CONCLUSION

The overall pattern of fetal growth for well-grown triplets does not differ from that of singletons and twins until late gestation, confirming that, in utero, well-grown children have similar growth potentials, regardless of plurality.