Detection and clinical outcome of small‐for‐gestational‐age fetuses in the third trimester—A comparison between routine ultrasound examination and examination on indication

Abstract

Introduction Fetal growth restriction is a major risk factor for adverse perinatal outcome. As most of the growth‐restricted fetuses are small for gestational age (SGA), an efficient antenatal screening method for SGA fetuses would have a major impact on perinatal health. The aim of this study was to compare the SGA prediction rate achieved with third‐trimester routine ultrasound estimation of fetal weight (EFW) with that obtained using ultrasound examination on indication. The secondary aim was to evaluate the clinical outcome in relation to the SGA screening method. Material and Methods During 1995–2009, two perinatal centers in southern Sweden offered routine ultrasound examination at 32–34 gestational weeks to 99 265 women with singleton pregnancies. Of these, 59 452 (60%) underwent the ultrasound examination. The other population, comprising 24 868 pregnancies, was cared for in another three centers that used a risk‐based method with ultrasound examinations on indication only. Of them, 5792 (23%) underwent ultrasound examination at 32–36 gestational weeks. The deviation in the EFW from the expected one was expressed as the EFW z‐score, SGA EFW being defined as the EFW z‐score less than −2. SGA prediction ability was assessed by receiver operating characteristic (ROC) curves. Crude and adjusted risk ratios were calculated for selected variables of perinatal outcome when comparing the populations. Results The SGA prediction ability for routine ultrasound was high, area under the ROC curve was 0.90 (95% CI 0.89–0.91). For an EFW z‐score of −1, the sensitivity was 67.3% and specificity was 90.5% among routinely screened pregnancies; corresponding numbers in the ultrasound on indication population were 34.3% and 96.6%. The screened population had a lower risk of preterm birth, birthweight z‐score less than −3, and Apgar score less than 7 at 5 min with adjusted risk ratios 0.87 (95% CI 0.82–0.92), 0.75 (95% CI 0.61–0.92), and 0.77 (95% CI 0.68–0.87), respectively. No difference in perinatal mortality was detected. There were no differences in perinatal outcome between the two subcohorts of infants born SGA. Conclusions Third‐trimester routine ultrasound improves the detection of SGA antenatally compared with ultrasound performed on indication, but no convincing improvement in perinatal outcome was identified.

The association between undetected small‐for‐gestational age and abnormal admission cardiotocography: A registry‐based study

“…Detecting SGA fetuses during pregnancy is difficult and most such fetuses are diagnosed with SGA only after birth, 11 Although the proportion of diagnosed SGA is slightly higher when late ultrasound biometry is used, many SGA fetuses are still missed 12 . Therefore, among presumed low‐risk pregnancies, there is a substantial group of SGA fetuses (10.3%) who are at a higher risk of intrapartum compromise.…”

“…Detection of small‐for‐gestational age (SGA) fetuses is poor. In one Swedish study, only 34% of SGA fetuses were identified before delivery with standard care including serial symphysis–fundus height and ultrasound if indicated 11 . Undetected SGA fetuses are more prone to hypoxic complications, especially during vaginal delivery 12 .…”

“…In one Swedish study, only 34% of SGA fetuses were identified before delivery with standard care including serial symphysis-fundus height and ultrasound if indicated. 11 Undetected SGA fetuses are more prone to hypoxic complications, especially during vaginal delivery. 12 One of the main objectives of admCTG is to identify pregnancies that have an increased risk of asphyxia complications, such as undetected SGA fetuses.…”

Investigation and Care of a Small‐for‐Gestational‐Age Fetus and a Growth Restricted Fetus (Green‐top Guideline No. 31)

“…186 In a pragmatic screening study in nulliparous women, SGA was detected in 57% with routine third trimester USS compared with 20% with USS by clinical indication, but it is only when fetal growth velocity was combined with fetal biometry that a subset of SGA fetuses at risk of increased neonatal morbidity was identified. 187 Studies published since the NICE review have similarly demonstrated an unclear effect on perinatal mortality, 188,189 and a systematic review of diagnostic performance concluded that for a fixed 10% false positive rate sensitivity was higher for AC than EFW and better performance when the scan was carried out near term and to detect FGR rather than SGA. 190 The NICE committee did note that the evidence in their review was overall moderate to low quality and that within their recommendation not to offer routine third trimester USS there is an inherent assumption that risk assessment and selective scanning is being appropriately applied.…”

Fetal growth restriction and stillbirth: Biomarkers for identifying at risk fetuses

“…Some evidence suggests that universal third trimester ultrasound tripled SGA infant detection, and combining this approach with Doppler velocimetry measures identified SGA infants at high risk of morbidity (Sovio and Smith, 2018). Worryingly, other studies have shown that diagnosis of FGR by third trimester ultrasound did not materially improve perinatal outcomes (Henrichs et al, 2019;Bonnevier et al, 2022). Some of this discrepancy may be due to different gestational ages at screening (Roma et al, 2015), which highlights the importance of timing in the interpretation of biomarkers.…”