Dating pregnancy ultrasound vs lmp

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With the introduction of US in Sweden, the practice was changed to estimate the EDD from second-trimester US biometry irrespective of the LMP date [1].

Estimates are more precise when they are based on first-trimester rather than second-trimester biometry [3, 4].Early differences in fetal growth do exist [5–7], but it has been assumed that individual variation is too small to have any clinical significance [8]. For example, second-trimester US dating underestimates GA and overestimates preterm delivery rates in infants born small for gestational age (SGA) [12].Furthermore, postponing the date of estimated delivery by 7 days by US is associated with birth of SGA infants [11], increased risk of stillbirth, low Apgar score, and neonatal death [10].Our hypothesis was that a change in the method of dating pregnancy might have led to an increased risk for prematurity-related adverse outcomes among male infants in relation to female infants by introducing a misclassification bias due to sex differences in early growth.The aim of this study was to compare rates of adverse prematurity-related outcomes in early term and late preterm male infants in relation to their female counterparts, between a time period, when pregnancy dating was based on the LMP, and a time period when ultrasound was used for pregnancy dating, in order to assess the dating method’s influence on prematurity-related adverse outcomes by fetal sex.

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