If that’s the case, your doctor or midwife will likely recommend what’s known as a dating ultrasound to help determine how far along you are. (This is often part of the quad screen.) While high levels of AFP sometimes indicate a potential genetic abnormality, the number one reason is simply your due date was miscalculated.As I share in “ The Motherly Guide to Becoming Mama” it’s common for women not to know when their LMP was. Between weeks 14 and 22, your physician will likely order a blood test to screen for AFP - short for Alpha fetoprotein, a protein that’s normally produced by the liver and yolk sac of your baby-to-be levels vary widely throughout pregnancy.

And if the measurements are off by three weeks or more, in many cases your due date is moved to reflect this. It could be that your uterus size doesn’t sync up with the standard growth charts (i.e. At each appointment, you’ll have a fundal measurement, which is the distance from the top of your pubic bone to the top of your uterus, and this number closely correlates to how far along you are. Trusted Source American College of Obstetricians and Gynecologists Methods for Estimating the Due Date See All Sources Ultrasounds performed during the first trimester (not the second) give the most accurate due date predictions, according the American College of Obstetrics and Gynecology (ACOG). Did you get your very first ultrasound in your second trimester? If so, this is another reason why your due date has shifted. Your first ultrasound was in the second trimester.(An early ultrasound, usually done at about 6 to 9 weeks, can give the most accurate due date estimation by measuring the size of the embryo or fetus.) If this was you, it could be why your doctor’s original timing was off. Many pregnancies are first confirmed by a Doppler heartbeat monitor, not an ultrasound. Does your monthly go MIA from time to time? It can be pretty difficult to determine a due date using the date-of-last-period method for women with irregular cycles - which is why an ultrasound exam is often required to determine gestational age. Here are some of the more common reasons your baby’s arrival day might have to change: Your pregnancy will be filled with appointments, tests, measurements and more, which means there’s lots of time for your practitioner to check on your progress and possibly revise your due date. Every pregnancy is different, with some babies jumping the gun and arriving early and others taking their own sweet time and showing up late.ĭue Date Calculator Why might your due date change? Regardless of how you conceived, remember that your due date is ultimately just an estimate. If you conceived using IVF, your due date will be calculated using your date of transfer, taking into account whether a three- or five-day embryo was used. And since most pregnancies last an average of 280 days, or 40 weeks, your due date is counted forward with this timespan. But because this practice assumes you have a regular menstrual cycle of 28 days with ovulation occurring on the 14th day, it is not an exact science - it doesn't account for an irregular cycle or variability in the timing of your ovulation, for example. How are due dates usually calculated?Īs mentioned, your due date is calculated from the first day of your LMP. Here’s more about why it happens so you can be prepared for a possible change in your delivery plans. Sometimes, however, your due date may be revised. And from that day, 40-weeks of pregnancy is counted, and your doctor will bust out the red pen to mark your due date on the calendar -and you’ll likely commit this day to memory. Because of this, pregnancy is calculated from the first day of your last menstrual period (or LMP).

Conception date to due date