Two trials reported fetal loss before 20 weeks of pregnancy evidence suggests that a first-trimester ultrasound scan may make little or no difference to miscarriage before 20 weeks of pregnancy (two trials, 1111 pregnancies RR 0.84, 95% CI 0.57–1.24 low-certainty evidence, downgraded due to study design limitations and imprecision). Stillbirth: This was reported in a single trial, and the evidence was very uncertain (463 pregnancies RR 2.96, 95% CI 0.12–72.32 very low-certainty evidence, downgraded due to study design limitations and serious imprecision). Perinatal mortality: First-trimester ultrasound scans may make little or no difference to perinatal mortality (two trials, 1472 newborns RR 0.73, 95% CI 0.23–2.31 low-certainty evidence, downgraded due to study design limitations and imprecision). The evidence suggests that women undergoing first-trimester ultrasound scans are probably less worried about their pregnancy after the scan (634 women RR 0.80, 95% CI 0.65–0.99 low-certainty evidence, downgraded due to study design limitations and indirectness). Positive pregnancy experience: Maternal anxiety was reported in one trial. Induction of labour: A first-trimester ultrasound scan may make little or no difference to induction of labour for post-term pregnancy (three trials, 1474 women RR 0.83, 95% CI 0.50–1.37 low-certainty evidence, downgraded due to study design limitations and imprecision) or to induction of labour for any reason (one trial, 463 women RR 0.73, 95% CI 0.49–1.09 low-certainty evidence, downgraded due to study design limitations and imprecision).ĭetection of multiple pregnancy: It is not known whether a first-trimester ultrasound scan improves the detection of multiple pregnancy before 24–26 weeks of gestation or before labour, as these outcomes were reported in a single trial and event rates were very low ( very low-certainty evidence, downgraded due to study design limitations and very serious imprecision). Maternal mortality: This outcome was not reported.Ĭaesarean section: A first-trimester ultrasound scan may make little or no difference to the number of women undergoing caesarean section (three trials, 1253 women risk ratio 1.27, 95% confidence interval 0.99–1.61 low-certainty evidence, downgraded due to study design limitations and imprecision). Thus, two comparisons evaluated in the 2021 review are relevant to this guideline: More details of the cluster trial can be found in the “Additional considerations” subsection under “Certainty of the evidence”. The cluster RCT ( 7) included in the 2021 review compared the effects of two ultrasounds in pregnancy – the first between 16 and 22 weeks of pregnancy, and the second between 32 and 36 weeks of pregnancy – and is therefore outside the scope of this guideline, which is focused on scans before 24 weeks of pregnancy only. No new individual RCTs were included in the 2021 review. The difference between the 2021 review and the 2015 review is that the 2021 review authors split the individual RCT data according to whether the ultrasound scan was done in the first or second trimester, whereas the 2015 review considered the data together irrespective of the timing of the ultrasound scans. The review included data from 12 individually randomized RCTs involving 37 719 women, along with a large cluster-randomized RCT including an additional 46 904 deliveries. The following evidence was derived from a 2021 systematic review ( 8).
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