The day you find out that you’re expecting a newborn is the day you begin the countdown to your baby’s arrival. You’re overwhelmed and already can’t wait to hold your baby(or babies) in your arms.

During the course of your pregnancy, you’ll be attending a lot of natal care and paying regular visits to the gynecologist especially to get the ultrasound done. Some of the information you can get from the ultrasound is the gender of the baby, the growth, and also, the due date.

And we both know the one info you’re truly interested in is the date you get to hold your baby in your motherly arms. But what happens when you get a different due date every time you get the ultrasound done? Can be quite annoying because how can you really tell if your date is wrong or not?

Knowing How Your Due Date Calculation Works

Based on studies and records, the normal calculation for every due date involves your last menstrual period. Basically, 40 weeks are added and the resulting date is marked on the calendar and etched in your memory.

But, you discover that this date has been changed after your next ultrasound, what gives. There are some inaccuracies in the calculations and here are the reasons why:

1. Irregular Menstrual Periods

Like we mentioned earlier, your last menstrual cycle is used to determine the time of your baby’s arrival. And this is calculated based on the assumption that every cycle lasts 28 days and ovulation occurs on day 14.

But as we know, not everyone goes through the same cycle and not everyone has the same length of the cycle. This irregularity in the menstrual cycles can result in miscalculation of the due date.

2. Ultrasound Scan

Every due date calculation is done immediately after the first ultrasound scan has been carried out. Therefore, the timing of the first ultrasound is vital for checking the proper due date. The best time to conduct the first ultrasound is in the first trimester or early stages of the second.

Anything later than that and the accuracy of the conclusions decrease and the later your first ultrasound scan, the lower your chances of getting an accurate estimate of when your baby is due for delivery.

3. Doppler

Another way to tell if your due date is wrong is to check if your date was checked through the use of a Doppler heartbeat monitor. If this is the case then the original timing by your doctor will be off since it wasn’t carried out by ultrasound.

4. Fundal Height

Firstly, what’s the fundal height? Don’t worry, this isn’t one of those complicated medical terms. Your fundal height is a measurement of the distance between the top of your pubic bone and the top of your uterus.

What this does is determine how far along you are into your pregnancy. The height should be just average for an accurate due date determination. If you’re measured as “above average”, it means that you’re out of sync with the normal growth chart.

This is checked periodically and if you’re off by a few weeks, then your date is moved.


The due date is important for many reasons. It allows you to plan ahead for when your baby will arrive and helps the doctor know when certain prenatal tests should be performed to make sure the fetus is developing healthily.

With so much being based on the expected due date, it’s important for it to be as accurate as possible. However, there is some imprecision involved with how due dates are measured.

What effects does this change in due date have on your pregnancy? Is it a thing of huge concern?

The above questions are bound to pop up once you encounter periodic changes in your due date. But here’s a refreshing fact, due dates are rarely accurate. In as much as there are methods of determining the date, they only provide a close estimate and not the actual date.

In fact, the percentage of accurate due dates is less than 5 so a change in due date shouldn’t give you serious headaches as they’re completely normal.

Regardless of the date your baby arrives, he or she will still be welcomed with joy and happiness. At this point, the date no longer matters, only the tiny creature in your hands.