Reduced fetal growth velocity and weight loss are associated with adverse perinatal outcome in fetuses at risk of growth restriction

BACKGROUND: Although fetal size is associated with adverse perinatal outcome, the relationship between fetal growth velocity and adverse perinatal outcome is unclear. OBJECTIVE: This study aimed to evaluate the relationship between fetal growth velocity and signs of cerebral blood ﬂow redistribution, and their association with birthweight and adverse perinatal outcome. STUDY DESIGN: This study was a secondary analysis of the TRUFFLE-2 multicenter observational prospective feasibility study of fetuses at risk of fetal growth restriction between 32 þ 0 and 36 þ 6 weeks of gestation (n ¼ 856), evaluated by ultrasound biometry and umbilical and middle cerebral artery Doppler. Individual fetal growth velocity was calculated from the difference of birthweight and estimated fetal weight at 3, 2, and 1 week before delivery, and by linear regression of all available estimated fetal weight measurements. Fetal estimated weight and birthweight were expressed as absolute value and as multiple of the median for statistical calculation. The coefﬁcients of the individual linear regression of estimated fetal weight measurements (growth velocity; g/wk) were plotted against the last umbilical-cerebral ratio with subclassiﬁcation for perinatal outcome. The association of these measurements with adverse perinatal outcome was assessed. The adverse perinatal outcome was a composite of abnormal condition at birth or major neonatal morbidity. RESULTS: Adverse perinatal outcome was more frequent among fetuses whose antenatal growth was < 100 g/wk, irrespective of signs of cerebral blood ﬂow redistribution. Infants with birthweight < 0.65 multiple of the median were enrolled earlier, had the lowest fetal growth velocity, higher umbilical-cerebral ratio, and were more likely to have adverse perinatal outcome. A decreasing fetal growth velocity was observed in 163 (19%) women in whom the estimated fetal weight multiple of the median regression coefﬁcient was < (cid:2) 0.025, and who had higher umbilical-cerebral ratio values and more frequent adverse perinatal outcome; 67 (41%; 8% of total group) of these women had negative growth velocity. Estimated fetal weight and umbilical-cerebral ratio at admission and fetal growth velocity combined by logistic regression had a higher association with adverse perinatal outcome than any of those parameters separately (relative risk, 3.3; 95% conﬁdence interval, 2.3 e 4.8). CONCLUSION: In fetuses at risk of late preterm fetal growth restriction, reduced growth velocity is associated with an increased risk of adverse perinatal outcome, irrespective of signs of cerebral blood ﬂow redistribution. Some fetuses showed negative growth velocity, suggesting catabolic metabolism.


Introduction
Birthweight (BW) for gestational age is a key risk factor for perinatal mortality, which is lowest for births between the 80th and 84th percentile and highest below the 2.3rd percentile. 1 The attainment of optimal fetal growth velocity, in contrast, is rarely studied in relation to mortality or perinatal outcome. 2e5 Determination of fetal growth velocity requires serial ultrasound biometric assessments, from which estimated fetal weight (EFW) is derived, which has a close, although imperfect, relationship with BW. 6 Differences are frequently ascribed to the derivation algorithm or inaccuracy in biometric measures, but may be also related to divergent growth between ultrasound estimation of fetal weight and birth. 6 Neonatal weight loss is common after birth because of a range of factors, primarily water loss during perinatal adaptation and slow establishment of nutritional intake. 7 In utero weight loss has recently been reported. 8,9 In a cohort of 885 term singletons with fetal biometry within 2 weeks of delivery, fetal weight gain, defined as a discrepancy between EFW and BW, ranged from À26 g/d for BW <10th percentile, through positive gain in all other groups, to þ48 g/d for those >90th percentile. 9 Apparent weight loss was associated with evidence of fetal compromise, namely cerebral blood flow redistribution, and may represent a fetal catabolic state. 9 Thus, fetal growth velocity estimation provides different information from that of a single EFW measurement.
To investigate this further, we performed an analysis of a large prospective cohort of fetuses at risk of late preterm fetal growth restriction (FGR) who had well characterized Doppler velocimetry. We evaluated fetal growth velocity in relation to umbilical and cerebral Doppler indices, BW, and adverse perinatal outcome. Original Research ajog.org

Study population
This was a secondary analysis from a prospective multicenter observational study conducted between April 1, 2017 and July 1, 2018 in 33 European perinatal centers with fetal medicine and specialized neonatal intensive care services, the TRUFFLE-2 Feasibility Study. 11 Briefly, women with singleton pregnancy at 32 þ0 to 36 þ6 weeks of gestation were eligible if the fetus was considered at risk for growth restriction. This was defined as EFW or abdominal circumference (AC) <10th percentile, an abnormal arterial Doppler, or an AC growth velocity drop from the 20-week scan of >40 percentile points, and an expected date of delivery verified by ultrasound before 20 weeks of gestation. The references for EFW, AC, and Doppler parameters were based on local charts. Fetuses with absent diastolic flow in the umbilical artery, an abnormal cardiotocography (CTG), an immediate indication for delivery, or structural abnormalities were not eligible. Delivery timing was based on the local protocol. The study protocol advised the use of computerized CTG or absent or reversed umbilical artery flow to decide if delivery was needed; although not specified as a criterion for delivery, the umbilical-tocerebral-artery (UCR) ratio was calculated for each fetus as part of the feasibility study.

Study endpoint
The primary adverse perinatal outcome was a composite of abnormal condition at birth or major neonatal morbidity or neonatal death. Abnormal condition at birth was defined as at least 1 of the following: Apgar score <7 at 5 minutes, umbilical artery pH <7.0 or vein pH <7.1, resuscitation with intubation, chest compressions or medication, or stillbirth. Major neonatal morbidity was defined as at least 1 of the following: neurologic abnormality (intracerebral hemorrhage grade 3 or 4, periventricular leukomalacia grade 2 or 3, encephalopathy, or seizures necessitating antiepileptic drug treatment); cardiovascular abnormality (hypotensive treatment, ductus arteriosus treatment, or disseminated coagulopathy); respiratory morbidity (respiratory support for >1 week, or mechanical ventilation, meconium aspiration, persistent pulmonary hypertension); or sepsis (clinical sepsis with positive blood culture, necrotizing enterocolitis [Bell's stage !2], or meningitis).

Data analysis
Preeclampsia was defined as hypertension and proteinuria, or hypertension and clinical signs of preeclampsia. 12 UCR was categorized as normal (<0.9) or abnormal (!0.9), corresponding to a cerebroplacental ratio (CPR) of 1.1. This threshold was used because it is most closely associated with adverse birth and neonatal outcome, 13 and a single threshold was used because reference charts of UCR or CPR show very little variation in the gestational age window of 32 to 37 weeks. 13 The association of abnormal UCR with fetal growth and composite adverse outcome was assessed by crosstab test. EFW was calculated using the Hadlock algorithm. 14 BW multiple of the median (MoM) and EFW MoM were calculated by dividing measured weight by the median expected weight for the gestational age derived from the Hadlock fetal growth chart. 15 We preferred MoM values over percentiles because these require a normal distribution, whereas MoM values do not. Moreover, the advantage of the MoM is that it expresses the measured weight to the expected median weight as a proportion and thereby gives an exact figure of the growth deficit. Perinatal details were specified for BW MoM <0.65, !0.65 to <0.75, and !0.75. These BW MoM categories represent the 10th and the 50th percentile of BW in the study population, and correspond to the 0.3rd percentile and the 3rd percentile of Hadlock fetal growth chart. 15 Fetal growth velocity was assessed by 3 methods: This study aimed to evaluate the growth velocity in fetuses at risk of growth restriction and assess the association of fetal growth velocity with adverse perinatal outcome and signs of cerebral blood flow redistribution.

Key findings
In the last week before delivery, the fetuses with lowest growth velocity showed no growth, and in some cases negative growth. Fetal growth velocity <100 g/wk was associated with adverse perinatal outcome, irrespective of signs of cerebral blood flow redistribution.

What does this add to what is known?
Fetal growth velocity is an important parameter that might identify fetuses at risk of adverse outcome irrespective of signs of cerebral blood flow redistribution, and might differentiate from constitutionally small fetuses. individual fetal growth velocity in g/ wk, and was plotted against the last UCR measured within 3 weeks (ie, 20 days) of delivery. The plot was divided in 4 quadrants separated at UCR !0.9 vs <0.9, and fetal growth !100 g/wk vs <100 g/wk, to determine differences in BW MoM, gestational age at delivery, and adverse perinatal outcome between these categories. In addition, the association of adverse perinatal outcome with fetal growth velocity, UCR, or both was assessed by logistic regression analysis. We chose a threshold of 100 g/wk, corresponding to growth below the 3rd percentile according to the Hadlock EFW growth charts in the period between 32 and 36 weeks, 15

Ethical approval
The study was observational and practice (monitoring, delivery, steroid administration) was based on existing local guidance. Data were recorded and anonymized after delivery outcomes were obtained. In 6 countries (19 centers), ethical approval was required and obtained, and participating women gave informed signed consent. In the remaining 5 countries this was not required.

Results
Complete delivery and outcome data were recorded for 873 women. Seventeen women were excluded because of major fetal congenital abnormality, leaving 856 women and their fetuses for the final cohort analysis. Demographic, obstetrical, and fetal Doppler velocimetry data are shown in Table 1 Table 2).
Evaluation of the relationship between BW and study parameters is shown in Table 3. Infants with the lowest BW MoM were enrolled at an earlier gestational age, and had lower EFW MoM at inclusion and lower fetal growth velocity than infants in higher BW MoM categories. This lowest-BW group also had higher UCR values, both at inclusion and at last measurement within 3 weeks of delivery. They were delivered at an earlier gestational age, more frequently by cesarean delivery, and had a higher proportion of adverse perinatal outcomes.
Fetal growth velocity was lowest in the category of BW MoM <0.65, and in this group the median fetal growth velocity was not different from 0 at 1 week before delivery (10 g/wk; IQR, À61 to 73; 1 sample Wilcoxon signed-rank test) ( Figure 1). In the 2 lowest BW categories, fetal growth velocity reduced from week 3 to week 1, whereas in the group with BW MoM !0.75, fetal growth velocity did not change. In the last group, fetal growth velocity was close to normal (152 g/wk [IQR, 95e203] vs 200 g/wk). 15 Compared with those with higher growth velocity, infants with fetal growth <100 g per week had a significantly lower BW MoM and gestational age at delivery, as a sign of more severe FGR ( Figure 2). Adverse perinatal outcomes were more frequent in infants with fetal growth <100 g/wk (20% vs 9%; P<.001). When specified for normal vs abnormal UCR, this difference reached statistical significance only in those with normal UCR. In both fetal growth categories (fetal growth <100 g/wk vs !100 g/wk), gestational age at delivery was lower when UCR was abnormal vs normal. When fetal growth was <100 g/ wk, BW MoM and adverse perinatal outcome were not associated with UCR. In those with higher growth velocity, BW MoM and gestational age at delivery were significantly lower following abnormal UCR (Figure 2). Fetal growth velocity was lower in infants with abnormal UCR (Table 4), either at any time or at the last measurement, and lower in those with adverse perinatal outcome. Among those with consistently normal UCR, growth was similar between those with adverse and those with normal outcomes.
For 612 (72%) women, the EFW MoM linear regression coefficient was between À0.025 and 0.025, indicating little change in growth velocity after study inclusion (Figure 3). Compared with these women, 163 (19%) women who had an EFW MoM regression coefficient <À0.025, indicating a reduction of fetal growth velocity, had higher UCR at inclusion, lower BW MoM, and more frequent adverse perinatal outcomes; 67 (41%; 8% of total group) of these women had negative growth velocity.

OBSTETRICS Original Research
The different thresholds that were discussed earlier (UCR !0.9, EFW <10th percentile, fetal growth <100 g/ wk and EFW MoM change <À0.025) were assessed for their association with adverse perinatal outcome, first by univariable analysis, and then combined with logistic regression analysis. Table 5 shows that the highest association with adverse perinatal outcome was by multivariable analysis, using UCR, EFW, and fetal growth (risk ratio, 3.3; 95% confidence interval, 2.3e4.8).

Principal findings
In this prospective study of closely monitored fetuses at risk of late preterm FGR, we observed that adverse perinatal outcomes were more prevalent with decreased fetal growth velocity (<100 g/ wk). Individual growth velocities varied greatly, and 67 (8%) fetuses showed negative growth. Those with reduced fetal growth velocity showed signs of cerebral blood flow redistribution more frequently than those with higher growth velocity. However, in the reduced growth velocity group, abnormal UCR on its own was not associated with adverse perinatal outcome. Importantly, although poor fetal growth and fetal smallness are to some extent related, fetal growth velocity was a better independent predictor of adverse perinatal outcome than EFW at inclusion. When both were combined with a raised UCR, the predictive value was further improved.

Results in the context of what is known
Fetal nutritional (growth) and oxidative metabolism depends on the balance between fetoplacental demands and maternoplacental availability of oxygen and nutritional substrates. Whenever there is a mismatch, irrespective of the underlying cause, compensatory fetal adaptive mechanisms are necessary to preserve fetal condition. 16 The oxygen and nutrient requirements for tissue growth are substantial and increase with higher fetal weight during the course of pregnancy. 16,17 The fetal response to impaired oxygen and nutrient delivery drives redistribution of fetal cardiac output in favor of brain, heart, and adrenal glands, the so-called "brainsparing" effect, 18 with subsequent growth restriction of the remaining parts of the body including the liver and limbs. 19,20 The association of lower fetal growth velocity with abnormal UCR reflects this process. 9 Using umbilical cord sampling in hypoxemic fetuses with FGR, plasma concentrations of essential amino acids were decreased and the ratio of nonessential to essential amino acids was increased compared with normally growing fetuses, suggesting that intrauterine starvation was occuring. 21 Alongside this there is an impaired process of gluconeogenesis. 21e23 Glucose is the major metabolic substrate capable of sustaining 50% to 70% of oxidative metabolism. 24 Thus, impaired gluconeogenesis, together with shortage of substrates, may explain the finding of reduced fetal growth velocity.
Reduced fetal growth velocity represents not only a consequence of a shortage of nutrient and oxygen substrates, but also an adaptive "saving" mechanism in an attempt to reduce substrate demands. 16,25 Indeed, an ovine model with prolonged oxygen starvation was associated with reduced total oxygen and substrate consumption. 26e28 In some cases, this reduction in fetal growth, and thus in fetal demands, will be sufficient to normalize the balance between demands and supply, and restore fetal normoxia. 16 However, the long-term impact of restricted growth, even in the absence of cerebral blood flow redistribution, on fetal organs and systems is still not well understood.

Clinical and research implications
Late preterm FGR is associated with poor neurodevelopmental outcome and school achievement. 29e32 Thus, a standardized definition of the condition is central to identifying pregnancies that are at highest risk. 3 In our cohort, fetuses with reduced fetal growth (<100 g/wk) more commonly had adverse perinatal outcome than those with normal fetal growth, irrespective of signs of cerebral blood flow redistribution. We selected growth <100 g/wk as "poor weight gain"  ajog.org OBSTETRICS Original Research on the basis of a very conservative weight gain (third percentile) from the Hadlock EFW model. This finding is of clinical importance because it suggests that decreased fetal growth velocity, even in the presence of normal Doppler findings, may be associated with short-term adverse outcome. Although it is not possible to infer that fetuses that grow most slowly or negatively are likely to suffer later developmental concerns, this hypothesis cannot be excluded on the basis of current data.
Detection of FGR during routine prenatal care is known to be low. 33 Prenatal differentiation between the constitutionally small but healthy fetus and true FGR poses further difficulties. 5 Ultrasound evaluation of EFW has been shown to be a poor predictor of BW in small-for-gestational-age neonates because of an apparent EFW overestimation in the context of reduced fetal growth velocity, 8,9 although other studies found EFW to be the only ultrasound parameter independently associated with adverse perinatal outcome in late FGR. 34 In 2021, Deter et al, 35 using data from the PORTO study, 36 observed a large heterogeneity in individual fetal growth velocity. Approximately 30% of infants with normal BW (>10th perecentile) had an abnormal growth pattern, whereas nearly 40% of infants with a BW <10th percentile had a normal growth pattern. As can be observed from the confidence intervals presented in the results section, individual variation in growth velocity was also large in our population. A small subgroup (17%) had BW >10th percentile with fetal growth velocity of 216 g/wk (IQR, 189e255); thus, 25% of these fetuses had fetal growth velocity <189 g/ wk. Conversely, in those with a BW <10th percentile, 15% had fetal growth velocity >189 g/wk (data not shown). Part of these inconsistencies might have been caused by measurement error.
A recent study that assessed the efficacy of biometry for the diagnosis of FGR concluded that AC growth was more effective than a single EFW measurement for the prediction of adverse  37 This supports our finding that measurement of fetal growth velocity is more relevant in this respect than a single measurement. During normal near-term growth, the fetal liver is large because of glycogen storage, which is necessary to maintain blood glucose levels during the first week when nutrient supply may be insufficient. 38 In FGR, liver volume may be reduced by the reduced deposit of glycogen owing to insufficient nutrients. This study supports the hypothesis that the growth pattern might differentiate between constitutionally small-forgestational-age newborns and those with growth restriction because of insufficient placental supply.

Strengths and limitations
A weakness of all studies of EFW, including our study, is the large interand intraobserver error of EFW estimation; a random error of AE15% is reported. 6 In this study we used the Hadlock formula for EFW calculation; this has the closest correlation to BW, especially between 1500 and 3500 g, 10 which mirrors that of our cohort. The Hadlock formula for EFW has also been shown to outperform that of INTERGROWTH-21st, particularly at the extreme percentiles. 39 Multiple measurements and calculation of fetal growth velocity may further improve detection of FGR. 40,41 In our study, biweekly biometry facilitated accurate prediction of low BW, using a combination of EFW MoM and gestational age at first measurement, and of fetal growth velocity. Our data also support the hypothesis that the prediction of BW by EFW might be affected by a progressive reduction in fetal growth in a proportion of fetuses, and not by systematic or random errors of ultrasound measurements or algorithm calculation issues. Indeed, in a randomized study of induction vs expectant management in term FGR, there were significantly more infants born with BW <third percentile in the expectant management group where there was delayed delivery (31% vs 13%), suggesting a falling of growth velocity after randomization. 42 Thus, an overestimation of EFW in FGR might be

UCR 3 weeks before delivery and fetal growth per week
Scatterplot of the last UCR measured within 3 weeks before delivery and fetal growth per week, calculated by individual linear regression analysis (n¼753). A linear regression line is shown for all measurements. The quadrants are divided by a line at fetal growth larger or less than 100 g/wk (bold vertical line) and UCR !0.9 vs <0.9 (intermittent line). The asterisk denotes significant difference between growth <100 g/wk vs !100 g/wk. The hashtag denotes significant difference between UCR !0.9 vs <0.9.  The study was performed in 33 centers in 10 different European countries, and although differences in management and definition might have affected results, this is unlikely. The results of a multilevel logistic regression analysis with an unconditional mean model, using the participating centers and composite adverse outcome, showed that 6% of the chance of having an abnormal composite endpoint was explained by differences between centers. 11 A characteristic of all observational studies, including this one, is that obstetrical management is frequently based on the parameters that are studied. The association between abnormal fetal growth or UCR and adverse perinatal outcome is clear, but whether perinatal outcome can be improved by using these parameters to determine delivery timing remains unproven. This can only be assessed by a randomized trial, and given the low incidence of adverse perinatal outcome after 32 weeks, such a trial would need a large sample size. 43

Conclusions
In fetuses at risk of late preterm FGR, reduced fetal growth velocity is associated with increased risk of adverse perinatal outcome. In a proportion of fetuses, it is plausible to consider that fetal growth is negative and associated with in utero catabolism. The clinical observation of reduced fetal growth velocity based on ultrasound findings should not be assumed to be because of ultrasound measurement error, but instead should warrant further assessment of fetal condition and whether delivery or additional monitoring is indicated. n