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

High-altitude population neonatal and maternal phenotypes associated with birthweight protection

BACKGROUND

States which reduce foetal oxygen delivery are associated with impaired intrauterine growth. Hypoxia results when barometric pressure falls with ascent to altitude, and with it the partial pressure of inspired oxygen ('hypobaric hypoxia'). birthweight is reduced when native lowlanders gestate at such high altitude (HA)-an effect mitigated in native (millennia) HA populations. Studying HA populations offer a route to explore the mechanisms by which hypoxia impacts foetal growth.

METHODS

Between February 2017 and January 2019, we prospectively studied 316 pregnant women, in Leh, Ladakh (altitude 3524 m, where oxygen partial pressure is reduced by 1/3) and 101 pregnant women living in Delhi (low altitude, 216 m above sea level).

RESULTS

Of Ladakhi HA newborns, 14% were small for gestational age (<10th birthweight centile) vs 19% of newborn at low altitude. At HA, increased maternal body mass index, age, and uterine artery (UtA) diameter were positively associated with growth >10th weight centile.

CONCLUSIONS

This study showed that Ladakhi offspring birthweight is relatively spared from the expected adverse HA effects. Furthermore, maternal body composition and greater UtA size may be physiological HA adaptations and warrant further study, as they offer potential mechanisms to overcome hypoxia-related growth issues.

IMPACT

Reduced foetal oxygen delivery seen in native lowlanders who gestate at HA causes foetal growth restriction-an effect thought to be mitigated in native HA populations. We found that greater maternal body mass and UtA diameter were associated with increased offspring birthweight in a (Ladakh) HA population. This supports a role for them as physiological mediators of adaptation and provides insights into potential mechanisms that may treat hypoxia-related growth issues.

Customized versus Population Growth Standards for Morbidity and Mortality Risk Stratification Using Ultrasonographic Fetal Growth Assessment at 22 to 29 Weeks' Gestation

OBJECTIVE

The aim of study is to compare the performance of ultrasonographic customized and population fetal growth standards for prediction adverse perinatal outcomes.

STUDY DESIGN

This was a secondary analysis of the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-Be, in which l data were collected at visits throughout pregnancy and after delivery. Percentiles were assigned to estimated fetal weights (EFWs) measured at 22 to 29 weeks using the Hadlock population standard and a customized standard (www.gestation.net). Areas under the curve were compared for the prediction of composite and severe composite perinatal morbidity using EFW percentile.

RESULTS

Among 8,701 eligible study participants, the population standard diagnosed more fetuses with fetal growth restriction (FGR) than the customized standard (5.5 vs. 3.5%, p < 0.001). Neither standard performed better than chance to predict composite perinatal morbidity. Although the customized performed better than the population standard to predict severe perinatal morbidity (areas under the curve: 0.56 vs. 0.54, p = 0.003), both were poor. Fetuses considered FGR by the population standard but normal by the customized standard had morbidity rates similar to fetuses considered normally grown by both standards.The population standard diagnosed FGR among black women and Hispanic women at nearly double the rate it did among white women (p < 0.001 for both comparisons), even though morbidity was not different across racial/ethnic groups. The customized standard diagnosed FGR at similar rates across groups. Using the population standard, 77% of FGR cases were diagnosed among female fetuses even though morbidity among females was lower (p < 0.001). The customized model diagnosed FGR at similar rates in male and female fetuses.

CONCLUSION

At 22 to 29 weeks' gestation, EFW percentile alone poorly predicts perinatal morbidity whether using customized or population fetal growth standards. The population standard diagnoses FGR at increased rates in subgroups not at increased risk of morbidity and at lower rates in subgroups at increased risk of morbidity, whereas the customized standard does not.

Prediction of adverse perinatal outcome by fetal biometry: comparison of customized and population-based standards

OBJECTIVE

To compare the predictive performance of estimated fetal weight (EFW) percentiles, according to eight growth standards, to detect fetuses at risk for adverse perinatal outcome.

METHODS

This was a retrospective cohort study of 3437 African-American women. Population-based (Hadlock, INTERGROWTH-21^st , World Health Organization (WHO), Fetal Medicine Foundation (FMF)), ethnicity-specific (Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD)), customized (Gestation-Related Optimal Weight (GROW)) and African-American customized (Perinatology Research Branch (PRB)/NICHD) growth standards were used to calculate EFW percentiles from the last available scan prior to delivery. Prediction performance indices and relative risk (RR) were calculated for EFW < 10^th and > 90^th percentiles, according to each standard, for individual and composite adverse perinatal outcomes. Sensitivity at a fixed (10%) false-positive rate (FPR) and partial (FPR < 10%) and full areas under the receiver-operating-characteristics curves (AUC) were compared between the standards.

RESULTS

Ten percent (341/3437) of neonates were classified as small-for-gestational age (SGA) at birth, and of these 16.4% (56/341) had at least one adverse perinatal outcome. SGA neonates had a 1.5-fold increased risk of any adverse perinatal outcome (P < 0.05). The screen-positive rate of EFW < 10^th percentile varied from 6.8% (NICHD) to 24.4% (FMF). EFW < 10^th percentile, according to all standards, was associated with an increased risk for each of the adverse perinatal outcomes considered (P < 0.05 for all). The highest RRs associated with EFW < 10^th percentile for each adverse outcome were 5.1 (95% CI, 2.1-12.3) for perinatal mortality (WHO); 5.0 (95% CI, 3.2-7.8) for perinatal hypoglycemia (NICHD); 3.4 (95% CI, 2.4-4.7) for mechanical ventilation (NICHD); 2.9 (95% CI, 1.8-4.6) for 5-min Apgar score < 7 (GROW); 2.7 (95% CI, 2.0-3.6) for neonatal intensive care unit (NICU) admission (NICHD); and 2.5 (95% CI, 1.9-3.1) for composite adverse perinatal outcome (NICHD). Although the RR CIs overlapped among all standards for each individual outcome, the RR of composite adverse perinatal outcome in pregnancies with EFW < 10^th percentile was higher according to the NICHD (2.46; 95% CI, 1.9-3.1) than the FMF (1.47; 95% CI, 1.2-1.8) standard. The sensitivity for composite adverse perinatal outcome varied substantially between standards, ranging from 15% for NICHD to 32% for FMF, due mostly to differences in FPR; this variation subsided when the FPR was set to the same value (10%). Analysis of AUC revealed significantly better performance for the prediction of perinatal mortality by the PRB/NICHD standard (AUC = 0.70) compared with the Hadlock (AUC = 0.66) and FMF (AUC = 0.64) standards. Evaluation of partial AUC (FPR < 10%) demonstrated that the INTERGROWTH-21^st standard performed better than the Hadlock standard for the prediction of NICU admission and mechanical ventilation (P < 0.05 for both). Although fetuses with EFW > 90^th percentile were also at risk for any adverse perinatal outcome according to the INTERGROWTH-21^st (RR = 1.4; 95% CI, 1.0-1.9) and Hadlock (RR = 1.7; 95% CI, 1.1-2.6) standards, many times fewer cases (2-5-fold lower sensitivity) were detected by using EFW > 90^th percentile, rather than EFW < 10^th percentile, in screening by these standards.

CONCLUSIONS

Fetuses with EFW < 10^th percentile or EFW > 90^th percentile were at increased risk of adverse perinatal outcomes according to all or some of the eight growth standards, respectively. The RR of a composite adverse perinatal outcome in pregnancies with EFW < 10^th percentile was higher for the most-stringent (NICHD) compared with the least-stringent (FMF) standard. The results of the complementary analysis of AUC suggest slightly improved detection of adverse perinatal outcome by more recent population-based (INTERGROWTH-21^st ) and customized (PRB/NICHD) standards compared with the Hadlock and FMF standards. Published 2019. This article is a U.S. Government work and is in the public domain in the USA.

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

BACKGROUND

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

OBJECTIVE

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

STUDY DESIGN

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

RESULTS

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

CONCLUSION

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

Review: Systematic review of the utility of the fetal cerebroplacental ratio measured at term for the prediction of adverse perinatal outcome

AIM

This systematic review evaluates the utility of the fetal cerebroplacental ratio (CPR) when assessed at term (from 37 + 0 weeks gestation) as a predictor of adverse obstetric and perinatal outcomes.

DATA SOURCES AND SEARCH STRATEGY

An electronic search of Pubmed and Embase using variations of 'cerebroplacental ratio' and 'cerebroumbilical ratio' was conducted by two independent reviewers. Full text studies written in English that reported on low CPR and its correlation with relevant obstetric and perinatal outcomes were included.

RESULTS

Twenty one studies satisfied inclusion with 13 prospective and eight retrospective analyses. Fetal CPR was predictive of caesarean section for intrapartum fetal compromise, small for gestational age and fetal growth restriction and neonatal intensive care unit admission. Low CPR was also significantly associated with abnormal fetal heart rate pattern, meconium stained liquor, low Apgar score, acidosis at birth and composite adverse perinatal outcome scores. The CPR when taken at term had comparable if not better predictive value than that when taken at preterm. Most studies included small for gestational age fetuses and postdate pregnancies. Subtle variation existed in the threshold for low CPR.

CONCLUSION

The CPR at term has a strong association with adverse obstetric and perinatal outcomes. This review suggests the predictive utility of CPR at term is promising however there is insufficient evidence to demonstrate its value as a stand-alone test. Inclusion of CPR as a component of clinical care may help better identify fetuses at risk of adverse outcome, and this should be tested with randomised control trials.

Polymorphisms of CYP51A1 from cholesterol synthesis: associations with birth weight and maternal lipid levels and impact on CYP51 protein structure

We investigated the housekeeping cytochrome P450 CYP51A1 encoding lanosterol 14α-demethylase from cholesterol synthesis that was so far not directly linked to human disorders. By direct sequencing of CYP51A1 in 188 women with spontaneous preterm delivery and 188 unrelated preterm infants (gestational age <37 weeks) we identified 22 variants where 10 are novel and rare. In infants there were two novel CYP51A1 variants where damaging effects of p.Tyr145Asp from the substrate recognition region, but not p.Asn193Asp, were predicted by PolyPhen2 and SIFT. This was confirmed by molecular modeling showing that Tyr145Asp substitution results in changed electrostatic potential of the CYP51 protein surface and lengthened distance to the heme which prevents hydrogen bonding. The CYP51 Tyr145Asp mutation is rare and thus very interesting for further structure/function relationship studies. From the 12 identified known variants rs6465348 was chosen for family based association studies due to its high minor allele frequency. Interestingly, this CYP51A1 common variant associates with small for gestational age weight in newborns (p = 0.028) and lower blood total cholesterol and low density lipoprotein cholesterol levels in mothers in 2nd trimester of pregnancy (p = 0.042 and p = 0.046 respectively). Our results indicate a new link between a cholesterol synthesis gene CYP51A1 and pregnancy pathologies.