A fetal ultrasound is the most accurate way to determine the rough date of your pregnancy's conception. Because there are variations in a woman's menstrual cycle and some women spot through early pregnancy, an ultrasound is usually more accurate than methods calculating pregnancy from the first day of your last menstrual period.
According to the American Pregnancy Association fetal ultrasound uses sound waves to scan a woman's pelvic area to view what is inside your womb, creating a picture called a sonogram. A radiologist is able to estimate the date of conception based on measurements of the foetus.
There are seven different types of ultrasounds including transvaginal, standard, doppler, 3-D, advanced, 4-D and fetal echocardiography. To date the pregnancy from conception, a transvaginal ultrasound may be used, which can see smaller details and is used earliest in the first trimester of pregnancy.
Ultrasounds are used to determine if the pregnancy is viable and then to track the baby's development. Ultrasounds may be done to date the pregnancy based on fetal measurements or to check for abnormalities.
Ultrasounds are useful in determining conception in early pregnancy, which then creates a time line for proper fetal growth and development. Some early problems can be determined via ultrasound and fixed during pregnancy.
There is scientific debate over whether the sound waves in ultrasounds cause harm to the foetus. Dating conception may be difficult in early pregnancy, before exact fetal measurements are easy to make. Although there is no evidence that the procedure is invasive, it should only be done when medically recommended.
Ultrasounds are used in conjunction with blood hCG levels and last menstrual period dating to determine when your baby was conceived. In early pregnancy an ultrasound can be as much as five to seven days off on the conception date, according to the American Pregnancy Association.