The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) is a scientific organization that encourages sound clinical practice, teaching and research for diagnostic imaging in women's healthcare. The ISUOG Clinical Standards Committee (CSC) has a remit to develop Practice Guidelines and Consensus Statements as educational recommendations that provide healthcare practitioners with a consensus-based approach for diagnostic imaging. They are intended to reflect what is considered by ISUOG to be the best practices at the time at which they were issued. Although ISUOG has made every effort to ensure that guidelines are accurate when issued, neither the Society nor any of its employees or members accepts any liability for the consequences of any inaccurate or misleading data, opinions or statements issued by the CSC. They are not intended to establish a legal standard of care because interpretation of the evidence that underpins the guidelines may be influenced by individual circumstances and available resources. Approved guidelines can be distributed freely with the permission of ISUOG (

K E Y W O R D S: 35.5 (range, 30-38) weeks in controls, 35.4 (range, 16-38) weeks in Type I, 30.7 (range,[27][28][29][30][31][32][33][34][35][36][37][38][39][40] weeks in Type II (P < 0.0001) and 31.6 (range, 23-39)

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