Routine third trimester ultrasound in low risk pregnancy confers no benefit!: AGAINST: Arguments for a routine third trimester ultrasound: what the meta-analysis does not show!

Abstract

The Cochrane meta-analysis on third trimester scanning, updated in June 2015, reached no new conclusions: ‘Based on existing evidence, routine late pregnancy ultrasound in low-risk or unselected populations does not confer benefit on mother or baby’ (Bricker et al. Cochrane Database Syst Rev 2015;6:CD001451). Most of the studies included in this meta-analysis, however, took place during the 1970s and 1980s. In the light of advances in ultrasound technologies and medical knowledge and practices, we can legitimately question the validity of the implementation of current pregnancy management based on the findings of these relatively old studies. This meta-analysis does not consider the detection rate of fetal anomalies to be a pertinent result. Nonetheless, it appears that routine late pregnancy ultrasound significantly increases this rate: the largest trial (Ewigman et al. N Engl J Med 1993;329:821–7) found that 50% of fetal anomalies are diagnosed during the third trimester. Some anomalies, such as congenital heart defects, can be missed at an earlier stage of pregnancy. When great vessel transposition, for example, is diagnosed during the third trimester, women can be referred to specialists during pregnancy and, finally, give birth in a specialised maternity unit prepared to provide optimal neonatal management, thus decreasing the risk of neonatal mortality (Khoshnood et al. Pediatrics 2005;115:95–101). Other rare critical anomalies, such as a vein of Galen aneurysmal malformation or microcephaly, are not detectable before the third trimester. Antenatal management can be adapted appropriately or, when allowed by law, women can choose a late termination of pregnancy in the most severe situations. Finally, the diagnosis of less severe but more frequent anomalies, such as hydronephrosis or megaureter, may improve, thus enabling increased monitoring during the baby's first months of life, which may sometimes prevent the onset of renal dysplasia. The Cochrane meta-analysis found that the risk of birthweight below the 10th percentile did not decrease among women having a routine third trimester ultrasound scan. Three of the four trials which utilised this outcome were published before 1993. All three studies failed to show a reduction in the incidence of intrauterine growth restriction (IUGR) with routine third trimester ultrasound screening. On the contrary, the most recent trial published by McKenna et al. in 2003 (McKenna et al. Obstet Gynecol 2003;101:626–32) found a significantly decreased risk of IUGR in the group of women who had routine third trimester ultrasounds. When IUGR is diagnosed, labour can be induced without increasing the risk of adverse outcomes (Boers et al. BMJ 2010;341:c7087). Studies have unfortunately been underpowered to estimate the impact of induction on the perinatal mortality rate among infants with IUGR. It is thus possible that ultrasound might decrease mortality in this population. Although meta-analyses are deemed to provide the highest level of evidence, they require detailed analysis from a clinical perspective, especially when they include very old trials. We consider that routine third trimester ultrasound confers benefit on babies and thus also on mothers and couples. In developed countries, where advanced ultrasound technology is widely available, there is no reason not to offer this examination routinely to all women. None declared. Completed disclosure of interests form available to view online as supporting information. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.