Background Vasa praevia (VP) is a rare phenomenon that is assumed to increase the risk of severe complications, including fetal death. Critical data on its incidence are lacking, so there is no rational basis for prenatal screening.Objectives To review the literature on the incidence and risk indicators for VP.Search strategy We searched OVID MEDLINE, OVID EMBASE, the Cochrane Library and PubMed for case-control and cohort studies on incidence and risk indicators for VP. Selection criteria Two reviewers selected studies and scored their methodological quality.Data collection and analysis We calculated the mean incidence of VP. We constructed 2 9 2 tables cross-classifying potential risk indicators against the incidence of VP to calculate common odds ratios and 95% confidence intervals, using the Mantel-Haenszel method.Main results We included 13 studies (two prospective cohort studies, ten retrospective cohort studies and one case-control study) reporting on 569 410 patients with 325 cases of VP. Based on ten included cohort studies providing information on the incidence, the mean incidence of VP was 0.60 per 1000 pregnancies. We identified five different risk indicators and markers for VP: second-trimester placenta praevia, conception by assisted reproductive technologies, a bilobed or succenturiate placenta, umbilical cord insertion in the lower third part of the uterus at first-trimester ultrasound and velamentous cord insertion. Almost 83% of the cases of VP had one or more risk indicators.Authors' conclusions In view of the low incidence, screening for VP in an unselected population is not advised. Targeted screening of women with one or more risk indicators as a part of routine mid-gestation scanning should be considered.

ABSTRACT

Psychological scientists have become increasingly concerned with issues related to methodology and replicability, and infancy researchers in particular face specific challenges related to replicability: For example, high-powered studies are difficult to conduct, testing conditions vary across labs, and different labs have access to different infant populations. Addressing these concerns, we report on a large-scale, multisite study aimed at (a) assessing the overall replicability of a single theoretically important phenomenon and (b) examining methodological, cultural, and developmental moderators. We focus on infants’ preference for infant-directed speech (IDS) over adult-directed speech (ADS). Stimuli of mothers speaking to their infants and to an adult in North American English were created using seminaturalistic laboratory-based audio recordings. Infants’ relative preference for IDS and ADS was assessed across 67 laboratories in North America, Europe, Australia, and Asia using the three common methods for measuring infants’ discrimination (head-turn preference, central fixation, and eye tracking). The overall meta-analytic effect size (Cohen’s d) was 0.35, 95% confidence interval = [0.29, 0.42], which was reliably above zero but smaller than the meta-analytic mean computed from previous literature (0.67). The IDS preference was significantly stronger in older children, in those children for whom the stimuli matched their native language and dialect, and in data from labs using the head-turn preference procedure. Together, these findings replicate the IDS preference but suggest that its magnitude is modulated by development, native-language experience, and testing procedure.

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