We always recommend mums get a definitive dating scan closer to 12 weeks as this will be much more accurate. Experts say that the scan date can sometimes come out as less pregnant than suggested by your LMP. This early ultrasound can provide reassurance that everything is progressing normally. The heart rate of babies is much quicker than adults. Even average babies can differ by up to 2 to 3 "weeks of growth". By weeks gestation, the embryo is clearly recognisable as a baby with a body, head, arms and legs, as well as many other identifiable features.
As soon as data from the LMP, the first accurate ultrasound examination, or both are obtained, the gestational age and the EDD should be determined, discussed with the patient, and documented clearly in the medical record.
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Gestational age in pregnancies conceived after in vitro fertilization: Ultrasound dating at 12—14 weeks of gestation. For many women, especially after 8 weeks gestation, sufficient information about the baby may be obtained with transabdominal ultrasound only.