Current Issues in the Development of Foetal Growth References and Standards

Development and validation of an ultrasound-based estimated fetal weight reference for Chinese twin pregnancy: a retrospective cohort study

BACKGROUND

Fetal growth monitoring is important for twin pregnancies. However, there has been no clinically validated tool for monitoring fetal growth of twin pregnancies in China. This study aims to develop and validate a chorionicity-specific growth chart of ultrasound estimated fetal weight (EFW) for Chinese twin pregnancies.

METHODS

This retrospective cohort study included all twin pregnancies who delivered two live fetuses with gestational age ≥ 34 weeks without severe obstetric complications at a tertiary hospital from January 2007 to March 2021. The participants were divided into a development set (delivered in or before December 2017) and a validation set (delivered in or after January 2018). Chorionicity-specific growth charts were created using the generalized additive models for location, scale, and shape (GAMLSS) based on the development set. The fetuses from the validation set were classified into three groups based on the last EFW: small-for-gestational-age (SGA) indicated by both the newly established twin charts and the Hadlock singleton chart currently used for twin pregnancies in China, suspected SGA indicated by only the singleton chart, and no SGA indicated by either chart. The incidence of neonatal outcomes among the three groups was then compared accordingly, including intensive care unit (NICU) stay length, respiratory diseases, and neurological disorders.

RESULTS

The development set included 883 twin pregnancies and a total of 6374 EFW measurements between 16 and 38 weeks of gestation, and the validation set included 801 twin pregnancies and 7630 EFW measurements. In the development set, monochorionic diamniotic (MCDA) twins had a significantly lower EFW compared to dichorionic diamniotic (DCDA) twins beginning at 26 weeks, with the difference gradually increasing thereafter, supporting the establishment of chorionicity-specific growth charts. Of the 1,602 twin neonates in the validation set, 103 (6.4%) were classified into the SGA group, 164 (10.2%) into the suspected SGA group, and 1335 (83.3%) into the no SGA group. The incidence of respiratory diseases and neurological disorders was comparable between the suspected SGA group and the no SGA group, but apparently higher in the SGA group. Meanwhile, NICU stay lengths were consistently longer for twins in the SGA group compared to the no SGA group (difference: 0.57, 95% CI: 0.31-0.83), with no significant differences observed between the suspected SGA and no SGA groups.

CONCLUSIONS

The fetal growth trajectories differed by chorionicity, with a lower EFW for MCDA twins beginning at 26 weeks. The establishment of chorionicity-specific growth chart could reduce overdiagnosis of SGA and improve fetal growth monitoring of twin pregnancies.

Abnormal Maternal Body Mass Index and Customized Fetal Weight Charts: Improving the Identification of Small for Gestational Age Fetuses and Newborns

BACKGROUND

Obesity and thinness are serious diseases, but cases with abnormal maternal weight have not been excluded from the calculations in the construction of customized fetal growth curves (CCs).

METHOD

To determine if the new CCs, built excluding mothers with an abnormal weight, are better than standard CCs at identifying SGA. A total of 16,122 neonates were identified as SGA, LGA, or AGA, using the two models. Logistic regression and analysis of covariance were used to calculate the OR and CI for adverse outcomes by group. Gestational age was considered as a covariable.

RESULTS

The SGA rates by the new CCs and by the standard CCs were 11.8% and 9.7%, respectively. The SGA rate only by the new CCs was 18% and the SGA rate only by the standard CCs was 0.01%. Compared to AGA by both models, SGA by the new CCs had increased rates of cesarean section, (OR 1.53 (95% CI 1.19, 1.96)), prematurity (OR 2.84 (95% CI 2.09, 3.85)), NICU admission (OR 5.41 (95% CI 3.47, 8.43), and adverse outcomes (OR 1.76 (95% CI 1.06, 2.60). The strength of these associations decreased with gestational age.

CONCLUSION

The use of the new CCs allowed for a more accurate identification of SGA at risk of adverse perinatal outcomes as compared to the standard CCs.

Maternal Thinness and Obesity and Customized Fetal Weight Charts

OBJECTIVE

The aim of the study was to determine if customized fetal growth charts developed excluding obese and underweight mothers (CC(18.5-25)) are better than customized curves (CC) at identifying pregnancies at risk of perinatal morbidity.

MATERIAL AND METHODS

Data from 20,331 infants were used to construct CC and from 11,604 for CC(18.5-25), after excluding the cases with abnormal maternal BMI. The 2 models were applied to 27,507 newborns and the perinatal outcomes were compared between large for gestational age (LGA) or small for gestational age (SGA) according to each model. Logistic regression was used to calculate the OR of outcomes by the group, with gestational age (GA) as covariable. The confidence intervals of pH were calculated by analysis of covariance.

RESULTS

The rate of cesarean and cephalopelvic disproportion (CPD) were higher in LGAonly by CC(18.5-25) than in LGAonly by CC. In SGAonly by CC(18.5-25), neonatal intensive care unit (NICU) and perinatal mortality rates were higher than in SGAonly by CC. Adverse outcomes rate was higher in LGAonly by CC(18.5-25) than in LGAonly by CC (21.6%; OR = 1.61, [1.34-193]) vs. (13.5%; OR = 0.84, [0.66-1.07]), and in SGA only by CC(18.5-25) than in SGAonly by CC (9.6%; OR = 1.62, [1.25-2.10] vs. 6.3%; OR = 1.18, [0.85-1.66]).

CONCLUSION

The use of CC(18.5-25) allows a more accurate identification of LGA and SGA infants at risk of perinatal morbidity than conventional CC. This benefit increase and decrease, respectively, with GA.

Fetal growth standards for Chinese twin pregnancies

Background

The common use of singleton fetal growth standard to access twin growth might lead to over-monitoring and treatment. We aimed to develop fetal growth standards for Chinese twins based on ultrasound measurements, and compare it with Zhang’s and other twin fetal growth charts.

Methods

A cohort of uncomplicated twin pregnancies were prospectively followed in 2014–2017. Smoothed estimates of fetal growth percentiles for both monochorionic (MC) and dichorionic (DC) twins were obtained using a linear mixed model. We also created growth charts for twins using a model-based approach proposed by Zhang et al. Our twin standards were compared with Hadlock’s (singleton) in predicting adverse perinatal outcomes.

Results

A total of 398 twin pregnancies were included, with 214 MC and 582 DC live-born twins. The MC twins were slightly lighter than the DC twins, with small differences throughout the gestation. Our ultrasound-based fetal weight standards were comparable to that using Zhang’s method. Compared with previous references/standards from the US, Brazil, Italy and UK, our twins had very similar 50th percentiles, but narrower ranges between the 5th and 95th or 10th and 90th percentiles. Compared with the Hadlock’s standard, the risks of neonatal death and adverse perinatal outcomes for small for gestational age (SGA) versus non-SGA were substantially elevated using our standards.

Conclusions

A normal fetal growth standard for Chinese twins was created. The differences between MC and DC twins were clinically insignificant. The 50th weight percentiles of the Chinese twins were identical to those in other races/ethnicities but the ranges were markedly narrower. Our standard performed much better than the Hadlock’s in predicting low birth weight infants associated with adverse perinatal outcomes in twin pregnancies. The present study also indicated that Zhang’s method is applicable to Chinese twins, and other areas may use Zhang’s method to generate their own curves for twins if deemed necessary.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-021-03926-y.

Pregnancy-specific continuous reference intervals for haematology parameters from an Australian dataset: A step toward dynamic continuous reference intervals

BACKGROUND

Pregnancy is a time of dynamic physiological changes occurring as a continuous spectrum. Smoothed centile curves describe the distribution of measurements as a function of age. There has been no application of centile charts in pregnancy for haematological parameters.

AIMS

To derive gestational age-specific centile curves for six haematological parameters and compare these with published reference intervals.

MATERIALS AND METHODS

An LMS approach was used with haematology results from an obstetric hospital laboratory database. After application of exclusion criteria, smoothed centiles conditional on gestational age were obtained by a two-step process: (i) finding the best model within four response distributions using Bayesian information criteria, and (ii) selecting the best model among the response distributions based on test-dataset global deviance.

RESULTS

In total, 11 255 deliveries were extracted from 10 813 patients. There was little difference between distributions, and Box-Cox power exponential was selected overall. Red cell parameters showed similar trends: values fell until the second trimester and increased thereafter. Leukocyte and neutrophil counts rapidly increased and plateaued around 15 weeks. Platelets exhibited a gradual fall with advancing gestation.

CONCLUSIONS

This is the first study to use an LMS approach to model gestational age-dependent variations in haematological parameters. Proposed haemoglobin reference intervals were lower than those published but reflect our patient population. Serial monitoring of antenatal patients, as is the standard of care, in conjunction with these centile charts, may highlight trends in red cell changes with advancing gestation, allowing early identification of adverse pregnancy outcomes and evolving anaemia.

The development of an alternative growth chart for estimated fetal weight in the absence of ultrasound: Application in Indonesia

A fetal growth chart is a vital tool for assessing fetal risk during pregnancy. Since fetal weight cannot be directly measured, its reliable estimation at different stages of pregnancy has become an essential issue in obstetrics and gynecology and one of the critical elements in developing a fetal growth chart for estimated fetal weight. In Indonesia, however, a reliable model and data for fetal weight estimation remain challenging, and this causes the absence of a standard fetal growth chart in antenatal care practices. This study has reviewed and evaluated the efficacy of the prediction models used to develop the most prominent growth charts for estimated fetal weight. The study also has discussed the potential challenges when such surveillance tools are utilized in low resource settings. The study, then, has proposed an alternative model based only on maternal fundal height to estimate fetal weight. Finally, the study has developed an alternative growth chart and assessed its capability in detecting abnormal patterns of fetal growth during pregnancy. Prospective data from twenty selected primary health centers in South Kalimantan, Indonesia, were used for the proposed model validation, the comparison task, and the alternative growth chart development using both descriptive and inferential statistics. Results show that limited access to individual fetal biometric characteristics and low-quality data on personal maternal and neonatal characteristics make the existing fetal growth charts less applicable in the local setting. The proposed model based only on maternal fundal height has a comparable ability in predicting fetal weight with less error than the existing models. The results have shown that the developed chart based on the proposed model can effectively detect signs of abnormality, between 20 and 41 weeks, among low birth weight babies in the absence of ultrasound. Consequently, the developed chart would improve the quality of fetal risk assessment during pregnancy and reduce the risk of adverse neonatal outcomes.

Effectiveness of routine third trimester ultrasonography to reduce adverse perinatal outcomes in low risk pregnancy (the IRIS study): nationwide, pragmatic, multicentre, stepped wedge cluster randomised trial

OBJECTIVES

To investigate the effectiveness of routine ultrasonography in the third trimester in reducing adverse perinatal outcomes in low risk pregnancies compared with usual care and the effect of this policy on maternal outcomes and obstetric interventions.

DESIGN

Pragmatic, multicentre, stepped wedge cluster randomised trial.

SETTING

60 midwifery practices in the Netherlands.

PARTICIPANTS

13 046 women aged 16 years or older with a low risk singleton pregnancy.

INTERVENTIONS

60 midwifery practices offered usual care (serial fundal height measurements with clinically indicated ultrasonography). After 3, 7, and 10 months, a third of the practices were randomised to the intervention strategy. As well as receiving usual care, women in the intervention strategy were offered two routine biometry scans at 28-30 and 34-36 weeks' gestation. The same multidisciplinary protocol for detecting and managing fetal growth restriction was used in both strategies.

MAIN OUTCOME MEASURES

The primary outcome measure was a composite of severe adverse perinatal outcomes: perinatal death, Apgar score <4, impaired consciousness, asphyxia, seizures, assisted ventilation, septicaemia, meningitis, bronchopulmonary dysplasia, intraventricular haemorrhage, periventricular leucomalacia, or necrotising enterocolitis. Secondary outcomes were two composite measures of severe maternal morbidity, and spontaneous labour and birth.

RESULTS

Between 1 February 2015 and 29 February 2016, 60 midwifery practices enrolled 13 520 women in mid-pregnancy (mean 22.8 (SD 2.4) weeks' gestation). 13 046 women (intervention n=7067, usual care n=5979) with data based on the national Dutch perinatal registry or hospital records were included in the analyses. Small for gestational age at birth was significantly more often detected in the intervention group than in the usual care group (179 of 556 (32%) v 78 of 407 (19%), P<0.001). The incidence of severe adverse perinatal outcomes was 1.7% (n=118) for the intervention strategy and 1.8% (n=106) for usual care. After adjustment for confounders, the difference between the groups was not significant (odds ratio 0.88, 95% confidence interval 0.70 to 1.20). The intervention strategy showed a higher incidence of induction of labour (1.16, 1.04 to 1.30) and a lower incidence of augmentation of labour (0.78, 0.71 to 0.85). Maternal outcomes and other obstetric interventions did not differ between the strategies.

CONCLUSION

In low risk pregnancies, routine ultrasonography in the third trimester along with clinically indicated ultrasonography was associated with higher antenatal detection of small for gestational age fetuses but not with a reduced incidence of severe adverse perinatal outcomes compared with usual care alone. The findings do not support routine ultrasonography in the third trimester for low risk pregnancies.

TRIAL REGISTRATION

Netherlands Trial Register NTR4367.

The use of magnetic resonance imaging in the prediction of birthweight

Extremes of fetal growth can increase adverse pregnancy outcomes, and this is equally applicable to single and multiple gestations. Traditionally, these cases have been identified using simple two-dimensional ultrasound which is quite limited by its low precision. Magnetic resonance imaging (MRI) has now been used for many years in obstetrics, mainly as an adjunct to ultrasound for congenital abnormalities and increasingly as part of the post-mortem examination. However, MRI can also be used to accurately assess fetal weight as first demonstrated by Baker et al in 1994, using body volumes rather than standard biometric measurements. This publication was followed by several others, all of which confirmed the superiority of MRI; however, despite this initial promise, the technique has never been successfully integrated into clinical practice. In this review, we provide an overview of the literature, detail the various techniques and formulas currently available, discuss the applicability to specific high-risk groups and present our vision for the future of MRI within clinical obstetrics.