During your dating scan, your consultant will calculate your estimated date of delivery using the size of your baby. This process is the most accurate way to determine your due date. If you use your period to calculate your due date, you may believe your baby is further along than he or she really is. An accurate due date minimises the risk of unnecessary labour induction or late pregnancy disappointment. Please keep in mind that if you conceived your baby with in vitro fertilisation (IVF), your dating ultrasound will not change the estimated date of delivery.