Objective: To assess the influence of the test-to-delivery interval (TDI) on the performance of ultrasound (US) and magnetic resonance imaging (MRI) for predicting birthweight (BW). Design: Secondary analysis of a prospective cohort study. Setting: Belgium, 2016. Population: Women with singleton pregnancy and live birth who underwent estimated fetal weight (EFW) by US and MRI between 36 +0/7 and 36 +6/7 weeks of gestation (WG). Methods: The study population was grouped into three groups: TDI<2 weeks (group 1, n=313), TDI≥2 and <4 weeks (group 2, n=1440), and TDI≥4 weeks (group 3, n=625). Main outcome measures The correlation between EFW-US or EFW-MRI and BW as well as the performance of both tests in predicting BW>95 th, >90 th, <10 th, and <5 th percentiles according to TDI. Results: There was a strong positive correlation between MRI-EFW and BW percentiles in group 1 (R=0.934 [95%CI: 0.918-0.947]), it dropped significantly but remained strongly positive in groups 2 and 3 (p<0.001). In contrast, the correlation between US-EFW and BW percentiles was highly positive only in group 1, and significantly lower than that of MRI-EFW/BW percentiles among the three groups (p<0.001). At the upper extreme of BW percentiles, MRI had a higher sensitivity with higher threshold of EFW percentile at a fixed false positive rate of 5%, in comparison to US regardless of TDI. Conclusions: The performance of MRI in the prediction of BW is maximal when the delivery occurs within two weeks of the examination, declining slowly thereafter, in contrast to the performance of US which decreases drastically over time.

Background: Medical literature supports planned caesarean delivery (CD) for breech presentation at term, due to observed reductions in neonatal morbidity and mortality when compared to normal vaginal delivery (NVD). Objectives: We want to compare perinatal outcomes of singleton pregnancies with breech presentation at term in two University hospitals. One where the option of NVD is routinely offered (Protocol I), a second where these babies are routinely delivered by CD (Protocol II). Study design: A retrospective matched cohort-study was conducted between January 2015 and May 2021. We included singleton pregnancies with frank or complete breech presentations, delivered from 34+0 weeks gestation with known outcomes. Primary outcomes were a composite of adverse obstetrical outcomes (CAOO) and a composite of neonatal adverse outcomes (CANO). Results: 1079 women were eligible for analysis. After matching for possible confounding factors, the final analysis was conducted in 257 patients in each group. CAOO was similar in the two groups (24.1% versus 24.5%, p-value = 1.000), CANO was significantly higher in patients of Protocol I (17.9% versus 1.2%, p-value < 0.001). No neonatal death or birth trauma were reported in either group. The rates of NICU admission (4.3% vs 0.4%; p=0.004), respiratory distress at birth (17.5% vs 1.2%; p<0.001) and APGAR scores <7 after 5 minutes (5.8% vs 0.4%; p<0.001) were significantly higher for Protocol I. Conclusion: Short-term, non-severe adverse neonatal outcomes are significantly increased in the Protocol I group. These must be balanced against the possible negative impacts of caesarean birth on long-term infant and maternal health.