An ultrasound is actually the most accurate way to date a pregnancy because all fetuses grow at a consistent rate during the first trimester and early second. In other words, if your baby measures 9 weeks 2 days when you have your ultrasound, thats how far along you are, no matter when your last period was.

How can I know my exact delivery date?

An estimated due date can be calculated by following steps 1 through 3: First, determine the first day of your last menstrual period. Next, count back 3 calendar months from that date. Lastly, add 1 year and 7 days to that date.

How does ultrasound predict due date?

An ultrasound allows your doctor to measure the crown-rump length (CRL) — the length of the fetus from one end to the other. During the first trimester, this measurement provides the most accurate estimation for the age of the baby. Your doctor may change your due date based on the ultrasound measurement.

Which due date is correct LMP or ultrasound?

LMP versus early ultrasound If the ultrasound date is within seven days of your LMP date, we would stick with your LMP date. Ultrasounds done later in the pregnancy are less accurate for dating, so if your due date is set in the first trimester, it shouldnt be changed.

Can my due date be wrong by a month?

In fact, only 6% of women deliver on their due date, Cackovic said. I tell patients that really, your due date is a date in the middle of almost a month-long period of time that you could have your baby. The reality is that about 70% of women will have their baby within 10 days of their due date, he said.

When is ultrasound most accurate for due date?

Ultrasound measurement of the embryo or fetus in the first trimester (up to and including 13 6/7 weeks of gestation) is the most accurate method to establish or confirm gestational age.

Why is due date based on last period?

If you were having regular periods before pregnancy, your doctor will calculate your due date based off of your last menstrual period. This goes back to the fact that in order to get pregnant, your body ovulated—or released an egg—roughly in the middle of your cycle and it was fertilized by sperm.

How do I calculate my due date?

An estimated due date can be calculated by following steps 1 through 3:First, determine the first day of your last menstrual period.Next, count back 3 calendar months from that date.Lastly, add 1 year and 7 days to that date.