Results were restricted to systematic reviews, randomized control trials/controlled clinical trials, and observational studies written in English. Searches were updated on a regular basis and incorporated in the guideline to July 31, 2013.Grey (unpublished) literature was identified through searching the websites of health technology assessment and health technology-related agencies, clinical practice guideline collections, clinical trial registries, and national and international medical specialty societies.It will usually take place at your local hospital ultrasound department.The person performing the scan is called a sonographer.But ultrasounds can also lift the lid on a few worries you might be having. The main reason for the ultrasound is to work out how many weeks pregnant you are, and to estimate your due date.The length of your pregnancy is calculated from the first day of your last menstrual period (LMP), even though you don't actually conceive until 14 days after your LMP, and later than this if your cycle is longer than 28 days.The scan will usually show that your pregnancy is less far along than suggested by your LMP.
You can ask your midwife or doctor before the scan if this is the case. Find out more about what happens during a pregnancy ultrasound scan.
To provide maternity health care providers and researchers with evidence-based guidelines for the assignment of gestational age.