| Sumario: | The Norwegian Knowledge Centre for the Health Services was asked to evaluate the clinical effects and diagnostic value of routine ultrasound in the first, second and third trimesters of pregnancy. Today all women are offered an ultrasound in the 17th to 19th week of pregnancy. This routine ultrasound offers information on estimation of term, number of fetuses, detection of placenta previa and detection of structural abnormalities and fetal development. Based on the research literature we found no additional evidence in favour of introducing additional routine ultrasound in the first trimester (week 11 to 14) or in the third trimester (week 32 to 34) of pregnancy. However, an effect of introducing an early ultrasound is the information it gives for identifying fetuses at increased risk of chromosome abnormalities. If this is the aim, the early ultrasound combined with serum markers is the most effective test. Combined ultrasound and serum markers early in pregnancy give better indication for finding fetuses at increased risk for chromosome abnormalitites (and therefore fewer miscarriages due to amniocentesis) than testing based on mothers' age. Based on our review of the included literature, there does not seem to be important differences between ultrasound in the first or second trimester with respect to term estimation. When it comes to twin pregnancies, ultrasound in the first trimester will provide added information about mono- or dichorionic placentas. Ultrasound with measurement of nuchal translucency (NT) in week 11+0 to 13+6 supplied with maternal blood tests (CUB) is an effective means of identifying fetuses at increased risk of Down's syndrome and is sensitivity more sensitive method than ultrasound in the second trimester or risk assessment based on maternal age. Severe structural abnormalities (with normal chromosomes) are more effectively detected in the second trimester. There does not seem to be any evidence in favour of routine ultrasound in the third trimester of pregnancy as an addition to ultrasound in the first and/or second trimester on health outcomes. Ultrasound is offered to all pregnant women in weeks 17 to 19 of pregnancy and has a high uptake which indicates that women are in favour of it. Based on the literature included, there screening programmes in the first or second trimester does not seem to increase levels of anxiety or worries. For women who experience positive findings (increased risk for abnormalities) the level of anxiety increases. Although further investigations or diagnostic tests indicate that a finding was "false positive", these women will continue to suffer from higher levels of anxiety than other pregnant women throughout the pregnancy. Recent studies indicate that women are well informed about routine ultrasound in pregnancy, but there are challenges related to informing about nuchal translucency (NT) and serum markers. Ultrasound is part of routine antenatal care in Norway and is offered from the 17th to the 19th week of pregnancy. Norwegian clinicians do not define the routine ultrasound as a screening test (Consensus report of 1995). In international literature, however, it is often defined as such. When clinicians and health authorities discuss whether to introduce more ultrasound scans in routine practice they might consider requirements that are commonly seen as important in population screening programmes. These include documentation of diagnostic precision, effect of interventions, as well as information about the screening test and how findings are handled.
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