Martín-Palumbo Giovanna, Atanasova Vangeliya Blagoeva, Rego Tejeda María Teresa, Antolín Alvarado Eugenia, Bartha José Luis
Department of Obstetrics and Gynecology, Division of Maternal and Fetal Medicine, University Hospital La Paz, Madrid, Spain.
J Matern Fetal Neonatal Med. 2022 Dec;35(25):6721-6726. doi: 10.1080/14767058.2021.1920915. Epub 2021 May 23.
The early detection of small-for-gestational age (SGA) fetuses and newborns is pivotal in the prevention of perinatal mortality.
To compare the predictive capability of performing ultrasound-based estimated fetal weight (EFW) at 32 versus 36 weeks' gestation on the detection rate of SGA fetuses and SGA newborns at delivery, and to find a better cutoff level to consider a fetus at risk of being born small.
Nine hundred fifteen low-risk pregnant women were assessed at both 32 and 36 weeks' gestation. EFW centile was calculated in both occasions. The rate of SGA fetuses was compared. SGA fetuses were considered when both abdominal circumference (AC) and EFW were below the 10th centile from a total of 488 delivered at our Hospital. Paired comparisons between ultrasound at 32 and 36 weeks' gestation were done to predict SGA at delivery. Percentages of SGA fetuses were compared by chi-squared test. ANOVA test was used for comparing centiles among groups. Receiver operating characteristic (ROC) curve was used to find the best cutoff ultrasound centile to predict SGA at delivery. Statistical significance was previously set at 95% level ( < .05).
Ultrasound-based EFW at 32 weeks showed 23 cases of SGA (2.5%) while at 36 weeks this rate increased up to 4% (37/915) ( < .000001). When comparing both outcomes, 2.8% of those catalogued as adequate-for-gestational age (AGA) at 32 weeks were cases of SGA at 36 weeks. In addition, 47.8% of those diagnosed as SGA were not confirmed at 36 weeks. Only 12.3% of SGA neonates were identified at 32 weeks' gestation ultrasound, while using the 36 weeks' gestation approach this rate increased up to 30.9%. So, only a low proportion of SGA neonates were SGA fetuses at any of these two gestational ages. However, the area under the curve (AUC) at 36 weeks was as high as 0.86. Being a matter of cutoff rather than a matter of choosing the correct variable, ROC analysis showed that the best cutoff for prediction having the best sensitivity (0.80) with the best specificity (0.77) was 28th centile of EFW. This represents 24.9% of the studied women (228/915).
In general, ultrasound at 36 weeks has better performance detecting SGA fetuses than ultrasound at 32 weeks and we suggest to definitively change from 32 to 36 weeks in order to increase the detection rate of SGA fetuses. Moreover, in order to detect those fetuses who will grow below the lower level of the normal range in the last month of pregnancy, we suggest that those with EFW below the 28th centile at 36 weeks should be rescanned later in pregnancy to identify prenatally as many cases as we can of SGA newborns.
早期发现小于胎龄（SGA）胎儿和新生儿对于预防围产期死亡率至关重要。
比较在妊娠32周与36周时进行基于超声的估计胎儿体重（EFW）对分娩时SGA胎儿和SGA新生儿检出率的预测能力，并找到一个更好的临界值来判断有出生体重小风险的胎儿。
对915名低风险孕妇在妊娠32周和36周时均进行评估。在两个时间点均计算EFW百分位数。比较SGA胎儿的发生率。当我院共488例分娩中腹围（AC）和EFW均低于第10百分位数时，将胎儿视为SGA。对妊娠32周和36周时的超声检查进行配对比较以预测分娩时的SGA。通过卡方检验比较SGA胎儿的百分比。使用方差分析检验比较各组间的百分位数。采用受试者工作特征（ROC）曲线来找到预测分娩时SGA的最佳超声百分位数临界值。统计学显著性预先设定为95%水平（<0.05）。
妊娠32周时基于超声的EFW显示23例SGA（2.5%），而在36周时该比例增至4%（37/915）（<0.000001）。比较两个结果时，在32周时被归类为适于胎龄（AGA）的胎儿中，2.8%在36周时为SGA。此外，47.8%被诊断为SGA的胎儿在36周时未得到确认。在妊娠32周超声检查时仅识别出12.3%的SGA新生儿，而采用妊娠36周的方法时该比例增至30.9%。因此，在这两个孕周中的任何一个孕周，只有一小部分SGA新生儿在相应孕周时就是SGA胎儿。然而，36周时曲线下面积（AUC）高达0.86。由于这是一个临界值的问题而非选择正确变量的问题，ROC分析表明，预测时具有最佳敏感性（0.80）和最佳特异性（0.77）的最佳临界值是EFW的第28百分位数。这占所研究女性的24.9%（228/915）。
总体而言，妊娠36周时的超声检查在检测SGA胎儿方面比妊娠32周时的超声检查表现更好，我们建议明确从32周改为36周以提高SGA胎儿的检出率。此外，为了检测那些在妊娠最后一个月生长低于正常范围下限的胎儿，我们建议对在36周时EFW低于第28百分位数的胎儿在妊娠后期进行再次扫描，以便尽可能在产前识别出更多SGA新生儿病例。
