When a doctor performs an ultrasound, they write a report on the findings and include two estimated due dates.
The first date is calculated using the date of the LMP.
In the second trimester, an ultrasound is less accurate and your doctor probably won’t adjust your date unless the estimates vary by more than two weeks.
The third trimester is the least accurate time to date a pregnancy.
Ultrasounds are not a necessary part of prenatal care.
Your doctor probably won’t change your due date unless its significantly different from your ultrasound date.Your doctor may change your due date based on the ultrasound measurement.This is most likely to occur in the first trimester, especially if the date estimated by the ultrasound differs by more than one week from the date estimated by your doctor based on your LMP.Your doctor may change your due date if your fetus is significantly smaller or larger than the average fetus at your particular stage of pregnancy.Generally, your doctor orders an ultrasound to determine the gestational age of your baby when there’s a history of irregular periods, when the date of your LMP is uncertain, or when conception occurred despite oral contraceptive use.