Routine Third Trimester Ultrasound in Low-Risk Pregnancies and Perinatal Death: A Systematic Review and Meta-Analysis

ABSTRACT Objective To determine if routine third trimester ultrasounds in low-risk pregnancies decrease the rate of perinatal death compared to regular antenatal care of serial fundal height. Study Design This was a systematic review and meta-analysis of randomized control trials (RCT) to identify relevant studies published from inception until October 2019. Databases used were OVID, PubMed, SCOPUS, ClinicalTrials.gov and the Cochrane Central Register of Controlled Trials using a combination of keywords related to “third trimester ultrasound” and “low-risk”. Study eligibility criteria We included all RCTs of singleton, non-anomalous low-risk pregnancies that were randomized to either one or more third trimester ultrasounds (US group) or serial fundal height (FH group). Exclusion criteria were patients with multiple gestations, maternal medical complications, or fetal abnormalities requiring a third trimester ultrasound. Study appraisal and synthesis methods The primary outcome was the rate of perinatal death. The secondary outcomes were rates of FGR, suspected LGA, polyhydramnios, oligohydramnios, fetal anomalies, antenatal interventions, stillbirth, neonatal death, rates of cesarean delivery (CD) and induction of labor (IOL), and other neonatal outcomes. This meta-analysis was performed with the use of the random effects model of DerSimonian and Laird to produce relative risk (RR) or mean difference (MD) with a corresponding 95% confidence interval (CI). Results Seven RCTs with a total of 23,643 participants (12,343 US group vs 11,300 FH group) were included. The total rate of perinatal death was similar between the groups 41/11322 (0.4%) vs 34/10285 (0.3%), RR 1.14 (0.68 – 1.89). The rate of FGR was higher in the US group, 763/10388 (7%) vs 337/9021 (4%), RR 2.11 (1.86-2.39) as well as the rate of suspected LGA, 1060/3513 (30%) vs 375/3558 (11%) RR 2.84 (95% CI 2.6 – 3.2). Polyhydramnios was also significantly higher in the US group vs FH, 18/323 (6%) vs 4/322 (1%) RR 3.93 (95% CI 1.4 – 11). The rates of the remainder of the secondary outcomes were similar between the groups. Conclusion Routine third trimester ultrasounds do not decrease the rate of perinatal death compared to serial fundal height in low-risk pregnancies. Ideally, an adequately powered trial is warranted to determine if perinatal mortality in the FH group can be reduced by one-third with third trimester US.