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Evidence summaries

Routine Ultrasound in Late Pregnancy (after 24 Weeks Gestation)

Routine late pregnancy ultrasound in low-risk or unselected populations does not confer benefits on mother or baby. Level of evidence: "A"

A Cochrane review [Abstract] 1 included 13 studies with a total of 34 980 subjects. There was no difference in antenatal, obstetric and neonatal intervention or morbidity in screened versus control groups T1. Routine late pregnancy ultrasound was not associated with improvements in overall perinatal mortality.

Table 1. Routine ultrasound over 24 weeks for pregnant women

OutcomeRelative effect (95% CI)Assumed risk -ControlCorresponding risk - Intervention=Routine ultrasound > 24 weeks (95% CI)Participants (studies)
Perinatal mortalityRR 1.01 (0.67 to 1.54)6/10006 /1000(4 to 9)30 675(8)
Preterm delivery< 37 weeks' gestationRR 0.96 (0.85 to 1.08)59/100057 /1000(50 to 64)17 151(2)
Induction of labourRR 0.93 (0.81 to 1.07)238/1000222/1000(193 to 255)22 663(6)
Caesarean sectionRR 1.02 (0.97 to 1.09)139/1000142 /1000(135 to 152)27461(6)

A nationwide, multicentre, cluster randomised trial 2 included 13 046 women with a low risk singleton pregnancy. 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% for the intervention strategy and 1.8% for usual care. After adjustment for confounders, the difference between the groups was not significant (odds ratio 0.88, 95% CI 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.

A systematic review and cost-effectiveness analysis 3 assessed diagnostic test accuracy reviews of 5 ultrasonic measurements in late pregnancy. Umbilical artery Doppler flow velocimetry, cerebroplacental ratio, severe oligohydramnios and borderline oligohydramnios were all either non-predictive or weakly predictive of the risk of neonatal morbidity (summary positive likelihood ratios between 1 and 2) and were all weakly predictive of the risk of delivering a small for gestational age infant (summary positive likelihood ratios between 2 and 4). Suspicion of fetal macrosomia is strongly predictive of the risk of delivering a large infant, but it is only weakly, albeit statistically significantly, predictive of the risk of shoulder dystocia. Health economic analysis indicated that universal ultrasound for fetal presentation only may be both clinically and economically justified on the basis of existing evidence.

    References

    • Bricker L, Medley N, Pratt JJ. Routine ultrasound in late pregnancy (after 24 weeks' gestation). Cochrane Database Syst Rev 2015;(6):CD001451. [PubMed]
    • Henrichs J, Verfaille V, Jellema P et al. 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. BMJ 2019;367():l5517. [PubMed]
    • Smith GC, Moraitis AA, Wastlund D, et al. Universal late pregnancy ultrasound screening to predict adverse outcomes in nulliparous women: a systematic review and cost-effectiveness analysis. Health Technol Assess 2021;25(15):1-190 [PubMed]

Primary/Secondary Keywords