Estimated Due Date Calculation: The Breakdown

Estimated Due Date Calculation: The Breakdown

So you go to the doctor because you think that you’re knocked up. Ahem [cough], Excuse Me. I mean you believe that you are expecting or shall I say, “with child.” However you say it, you likely are anxious to know when to expect the arrival of your little one or your estimated due date (EDD).

Of course! How else will you know when to do important stuff like the gender reveal party and the baby shower. Oh, and what about getting the pool ready for that home birth (if you are planning on going that route or even thought this far out yet).

The point is, the EDD is important. Not just for the fun stuff but also for getting the proper healthcare during the pregnancy. The EDD sets the tone for how and what to expect at different time points of the pregnancy for you and your doctor. Any errors made in this phase can definitely have a snowball effect on the rest of the pregnancy. So making sure that the estimated due date is as accurate as possible can help to detect things like growth-related issues and to avoid things like early inductions.

Your doctor will definitely want to confirm your pregnancy by urine test or blood test first before discussing your EDD with you. That is, unless you decide to go to the doctor after Mother Nature has revealed your pregnant belly to the world already…LOL (Laugh Out Loud).

The EDD is generally decided based on two methods; both are discussed in this post.

Method 1: Estimated Due Date by Last Menstrual Period (EDD by LMP)

As a woman, every single time we go to the doctor, we get the “when was the last menstrual period question.” It virtually does not matter why we are at the doctor’s office. It could be for a broken big toe and before you even see a doctor, you must answer, when was your LMP? Sometimes, I just want to scream and be like Why????? Is this really necessary? For crying out loud, It’s My Big Toe!!!!

But… I digress.

EDD by LMP is one of the times that the answer to the LMP question actually matters. Of course, it goes without saying that you are actually expected to be keeping track of your menstrual period (this should be relatively easy these days with so many apps available).

So after you give the doctor the date of your LMP, what happens next? Well, let me tell you.

Thanks to Naegele’s rule, your doctor takes the first day of your last period and adds 279 days to get the baby’s due date. That’s a total of 280 days (40 weeks), as in 6,720 hours or a whopping 403, 200 minutes that you are expected to carry a child but who’s counting…LOL (laugh out loud).

Actually, you will be, and so will your doctor, and your neighbor, oh, and don’t forget the random lady that stops you at the grocery store, she will be counting also. Literally, EVERYONE You Meet Will Be Counting!

The EDD by LMP is generally looked at as a rough estimate. Most providers are not comfortable with just using this method alone; in fact, it is recommended by a committee consisting of women health care physicians, that the EDD by LMP be confirmed by ultrasound (method 2).

Assumptions of EDD by LMP

This method assumes a few things about you that may not always be true.

  1. The date you give for your LMP is correct.
  2. Your period is regular, and you have every month
  3. Your cycle is a 28-day cycle, and you ovulate (release an egg) 14 days from the start of it.

So you see, confirmation may not just be a matter of opinion but may totally be necessary.

Method 2: EDD by Ultrasound also known as Ultrasonography

Since we are in the age of technology, of course technology (ultrasound) is used to determine the gestational age of the baby and to confirm the baby’s estimated due date (EDD). The ultrasound allows you and your doctor to visualize what’s going on in your belly. Albeit the images created using this technique usually looks like a random spread of black and white spots to an untrained eye until somebody (the sonographer) says, this area of black and white spot is the baby’s head…lol.

So, how does the ultrasound really work? I’m glad you asked.

A very general explanation is that an ultrasound machine uses sound waves to create an image of the developing baby in real-time. That means if the baby has fingers and is wriggling it, You… Can… See… It!

Creepy or Cool? I’ll leave that up to you.

When is the ultrasound usually performed?

The recommended best time for a dating ultrasound is in the first trimester and before 14 weeks of pregnancy. Apparently, during this time frame, the growth of all humans is basically the same and a measurement of the crown to rump length is good enough to tell them what they need to know. This means that it doesn’t matter if the child is going to grow up to big as tall as Shaquille O’Neal or just clearing the average height for “American” women like myself. Well, I’m a little taller than average but too short for runway modeling, which apparently wasn’t written in the books for me. Anywho, the point is, we all start off around the same size during these early stages of development and the results can be used to adjust the EDD by LMP if the are too far apart from each other (about a week or so). Remember 1 day makes a huge difference in the life of a developing baby, so you can imagine what a difference a week or so would make. Ultrasound measurements after the 14-week mark is a bit trickier and a bit more involving.

With that being said, there are two different ultrasound techniques that could potentially be used for the due date estimation. The first is the transvaginal ultrasound. This one caught me totally by surprise. It is typically used early in the pregnancy (1st trimester) and like the name says, it is performed inside the vagina with a magic wand because of the smaller size of everything at this early stage. The second technique, the traditional over the stomach ultrasound works better when everything is bigger and easier to see. It is typically used from the second trimester on and for all follow-up visits requiring an ultrasound.

Assumptions of EDD by Ultrasound

There are a few assumptions when using this method:

  1. Every ultrasound technician or sonographer is equally well trained to capture the images and to perform the measurements.
  2. Everything is reproducible and you should be able to switch doctors without much variance in the measurements.

One can only hope that the assumptions are true.

With that being said…. I’m done with this topic. No, really, I’m Finished. Seriously…Nexxxtttt!

Feel free to share your thoughts in the comment section. Also, I’m curious to see how many of my ladies get as annoyed by the LMP question as much I do but are happy to finally see how it is put to use for your benefit.

Looking forward to reading your feedback/responses. I’ll catch up with you soon on the next post of the What They Forgot To Tell About Pregnancy Series.

Dr. U
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[…] create a tiny human, the birds and the bees get together and then boom, out come a human child 40 weeks later. Oh Come On, you got “The Talk,” from your parents or guardian, you know how these things […]

Dr. U

Hola! I'm Utibe also known as Dr. U. I am sharing my experiences as a wife and mother, as well as a woman starting her career. My goal is to live a more holistic life, Join Me!