Measuring the baby using ultrasound is most accurate in early pregnancy. The best time to estimate gestational age using ultrasound is between the 8th and 18th weeks of pregnancy.
The most accurate way to determine gestational age is using the first day of the woman’s last menstrual period and confirming this gestational age with the measurement from an ultrasound exam.
Note that if you want to calculate what date your baby is due to be born on, please visit the Pregnancy Due Date Predictor -- which also includes How to Calculate Due Date based on Naegele's Rule.
I would like to know the accuracy of ultrasounds in the first trimester. On Feb 2 I went off birth control for good & had withdrawal bleed on Feb 5-8.
He used a condom, I believe I was on birth control (but cant remember for sure), and took Plan B 55 hours later.
There are various ways to estimate the day of ovulation.
You can estimate your date of ovulation and conception from the length of your menstrual cycle if this is fairly regular.
The day of conception depends on: An obvious fact is you cannot conceive until you ovulate; therefore, the most likely date of conception is on the day of ovulation, if there is sperm around.
If you can determine that day, you will come close to identifying your date conception.Other ultrasounds at 19, 21, and 27 weeks all gave EDD of 11/12. Totally 6 ultrasounds have all given you the same EDD - 11/12.Given this information, would it be possible that all of my ultrasounds were a month off and I conceived Jan 18? Based on this EDD, the last date of your period would have been 5th of February.Could the birth control not have worked in Jan, the embryo lived through the withdrawal bleeding, and the fetus has continued to measure small throughout the pregnancy? According to this period date, the most likely date of conception would be around 14 days after the period, that is around the 19th of February.Ultrasound has intrinsic error of upto maximum 5 - 7 days, so the probable dates of sex would have been a week before or after the 19th of February, but in NO WAY as early as January 18th.Want to know what date and day of the week you were likely conceived on?