How to Figure Conception Date Using Ultrasound
An ultrasound is the most effective way to date a pregnancy. If the ultrasound is performed in the first trimester, then it is extremely accurate. It will provide an estimate of gestational age and date of delivery. Once a gestational age is obtained, there is a window of possible conception dates. In order to establish a conception date, your menstrual cycle must be predictable and occur every 28 to 30 days.
Other People Are Reading
Instructions
-
-
1
Have an ultrasound completed in the first trimester. After the first trimester, the accuracy is diminished, since there is quite a bit of variance in fetal growth.
-
2
Using the crown rump dating method, determine gestational age. This is where the sonographer measures the fetus from the crown of the head to the baby's bottom. The measurement will be in centimeters. Either on the ultrasound image itself or the report, a gestational age is noted. This is also how a due date is determined. Gestational age is the age of the fetus from the first day of the last menstrual cycle. This can be confusing, since conception occurred several days after the first day of the menstrual cycle.
-
-
3
Take the gestational age and subtract 14 days. This will give you how many days ago, counting backwards from the date of the ultrasound, that conception occurred. Then use a calendar to locate the date. This is an average, since not every woman ovulates at the same time of the month. Generally, ovulation occurs 10 to 14 days after the first day of the menstrual cycle. Conception occurs one to two days after ovulation. This is not an exact science, since a woman may ovulate very early or late.
-
1
