The earlier the ultrasound is done, the more accurate it is at estimating the babys due date. Ultrasounds performed during the first 12 weeks of pregnancy are generally within 3 - 5 days of accuracy. The most accurate time is between 8 and 11 weeks gestation.

Can an ultrasound tell when you conceived?

Fetuses grow quickly, and they also follow the same pattern of growth in virtually every case. That means that by measuring the size of the fetus and looking for certain distinguishing characteristics, an ultrasound can give an accurate estimate of when you conceived.

How accurate are ultrasound pregnancy dates?

As pregnancy progresses, the accuracy of an ultrasound for predicting due dates decreases. Between 18 and 28 weeks of gestation, the margin of error increases to plus or minus two weeks. After 28 weeks, the ultrasound may be off by three weeks or more in predicting a due date.

How do you know conception has taken place?

Some women do notice signs and symptoms that implantation has occurred. Signs may include light bleeding, cramping, nausea, bloating, sore breasts, headaches, mood swings, and possibly a change in basal body temperature.