Newborn Weight Predictor

Kimbarbour08 · December 2015

Hi there! So I was just curious to see what was out there for newborn weight predictors and I found this one which seemed pretty neat! I have no idea if it's actually at all accurate, but it is fun to try

You have to plug in the data yourself in the equation, but I'm a total math nerd so that's fine with me! I got 6.96 lb as the estimate, I'm curious what other mamas will get from this, or from other estimations (your healthcare provider, your own guesses, friends, old wive's tales, apps, random strangers who feel the need to tell you what they thing, whatever!)

Here's the link to what I used:

https://www.webmd.com/baby/news/20020926/you-can-predict-your-newborns-weight

Monkeybutt80 · December 2015

Using this gave me 8lbs 2 oz for my last one. He was born 8lbs 11 oz. I am still a little skeptical on how they can predict the weight but the calculation is closer than I thought!

SarahChristine12 · December 2015

Had to try this. It comes up with 8lbs 12oz. I guess we will have to wait and see, but he has been measuring 2-3 weeks ahead.

DrillSergeantCat · December 2015

It says Harrison here will weigh 8.5 pounds. It will be interesting to see what it really is because the ultrasound's estimated weight on the 2nd at 28 weeks was 3lbs 9oz. If he grows at the expected rate of half a pound per week he'll be a 9.5 pound baby.

ohbaby714 · December 2015

I tried this for my daughter and it came up with 5lbs and 8oz and she was born at 5lbs 9oz. Crazy!!

twinmom1121 · December 2015

That equation was way too much math for my brain at this time of night ha! I'll have to try it in the morning. I would see if it is correct with my twins but I think it said it only works with a singleton.
Edit: I decided to sit down and try to figure it out. So if I did it right, it estimates this baby will be 7.2 lbs! We'll see if that is close. My twins were 6lbs2oz and 6lbs3oz so it'll be interesting to see how big this baby is.

robinj716 · December 2015

Yikes- my head hurts! Pretty sure I did mine all wrong. I did try though!

Edit: I tried it again and got 6 pounds 6 ounces! SO was almost 11 and I was about 6.5, so that would be nice if this was accurate, because I surely have been hoping he isn't a 10 pounder like his daddy.

robinj716 · December 2015

I found a woman who broke the formula down a little and it helped me to figure out what to add and multiply with what- may be useful for others

I copied her thread and posted it below- have fun!
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Birth weight (g) = gestational age (days) x (9.38 + 0.264 x fetal sex + 0.000233 x maternal height [cm] x maternal weight at 26.0 weeks [kg] + 4.62 x 3rd-trimester maternal weight gain rate [kg/d]] x [number of previous births + 1]).

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And here's my simplified how to guide to calculate...

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Step 1:

If baby is a boy then A = 0.264

If baby is a girl then A = -0.264

If you don't know the gender then A = 0

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Step 2:

B = 0.000233 x (maternal height in cms) x (maternal weight at 26.0 weeks in kgs)

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To get maternal height from feet and inches to cms... First multiply #feet by 12, then add extra inches. I'm 5 foot 8 so my total inches are (5x12)+8 = 68 inches. Then go to this url www.nickpvb.com/projects/calculator/ where you can enter your inches, hit enter and get your height in cms.

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To get maternal weight at 26 weeks (try to think back to when you hit your third trimester, how many pounds had you gained so far?) from pounds to kilograms go to this url www.dhl-usa.com/lbs-2-kilo and enter your weight in pounds at 26 weeks then hit convert, and it will give you your weight at 26 weeks in kilograms.

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Step 3:

C = 3rd-trimester maternal weight gain rate = (# of kilograms you've gained since you hit 26 weeks) divided by (# days since you hit 26 weeks)

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Go to this url to change the # of pounds you've gained since 26 weeks to kilograms:

www.dhl-usa.com/lbs-2-kilo

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Now for how many days have gone by. I am 38 weeks, 2 days along. So I hit 26 weeks 12 weeks and 2 days ago which is 12x7 + 2 = 86. So I've been in my third trimester for 86 days.

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So again, C = (# of kgs you've gained since 26 weeks) divided by (# of days you've been in your third trimester)

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Step 4:

D = C x 4.62 x (number of previous births + 1)

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Step 5:

E = A + B + D + 9.38

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Step 6:

F = E x (gestational age in days)

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Your gestational age in days is the number of days since the onset of your last normal menstrual period minus 14.

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F should be a huge number, this is your baby's estimated weight in grams. But you probably want that in pounds and ounces, so now what you do is get that number and move the decimal point three spaces to the left to turn it into kilograms. I got 3671.9 grams, so I changed that to 3.6719 kilograms. Then I entered 3.6719 in the handy dandy pound converter at this url www.dhl-usa.com/lbs-2-kilo to get pounds and ounces. My 3671.9 ounces = 8.08 pounds.

DrillSergeantCat · December 2015

I made a spreadsheet. I hope this works.

https://docs.google.com/a/my.macu.edu/spreadsheets/d/1VTqwSMrtGPfQvcLQ2wB40s5VOLrk_JoB1_oMGeUgLX8/edit?usp=sharing

SgtLou2 · December 2015

For DD, the dr and I had slightly different EDDs. So the range of weight using this equation would have been 7lb5oz to 7lb11oz... She was 7lb9oz (I had to guess on my 26w weight from memory). Pretty darn crazy how accurate this is!! If DS arrives right on time, this estimates that he will be 8lb4oz. Yikes!

brushesnbrunch · December 2015

Just tried this and got 6lb2oz. We shall see!

egraves4 · December 2015

I swear I'm doing it wrong, just can't figure out what... I'm getting like 5lbs 11oz, and I think there's no way! Maybe because I've only gained 6 pounds since 26 weeks? Or maybe I'm doing the gestational age wrong?? I got 209 days out of 266 days!

strlitemiss · December 2015

egraves4 said:
I swear I'm doing it wrong, just can't figure out what... I'm getting like 5lbs 11oz, and I think there's no way! Maybe because I've only gained 6 pounds since 26 weeks? Or maybe I'm doing the gestational age wrong?? I got 209 days out of 266 days!

I emailed the link to my midwife and she says slow weight gainers like me (I'm only up 2 pounds) present a variable probably not taken I to account when making this formula. She tacted 2 pound tk make her predictions. I'm curious to see if what I got (6 pounds 7 oz) or what she thinks is closer.

egraves4 · December 2015

@strlitemiss Makes complete sense. I screwed up the first time and got like 13 pounds lol... I'm thinking this baby is going to be more like 8 pounds. My only thought was that they tell you to go off of 26 weeks because maybe from that point on is usually when babies start to really put the fat on, hence why not gaining as much in that time would result in a skewed output?

AdventureMama · December 2015

I'll have to calculate mine but according to all the numbers from my growth scan last week and my OB's formula, baby will weight 9lbs 6oz at 40 weeks. He could be way off, but I doubt it. My son was 9lbs 9oz. I have big babies! And I've been measuring ahead this pregnancy.

strlitemiss · December 2015

egraves4 said:
@strlitemiss Makes complete sense. I screwed up the first time and got like 13 pounds lol... I'm thinking this baby is going to be more like 8 pounds. My only thought was that they tell you to go off of 26 weeks because maybe from that point on is usually when babies start to really put the fat on, hence why not gaining as much in that time would result in a skewed output?

I assume that's the reason.

charityann02 · December 2015

I got 7lbs. 8oz. Which is funny because that is the average weight between my husband and I when we were born!!!

robinj716 · April 2016

For those who did this, how accurate was it?! It estimated my baby's weight at 6 pounds 6 ounces and he was born 6.8! Pretty darn close! Interesting to see!

willkc · April 2016

My estimated weight was 6 lbs 13 oz and he was 8 lbs 9 oz.

egraves4 · April 2016

I never was able to get mine to work, it kept telling me she was going to be like 6 pounds and we ended up being 8 lbs. 12 oz... but I think mine was human error.

meg+on+the+DL · April 2016

Mine said 6lb 14oz. She was 7lb 2oz. So it was pretty dang close.

Kimbarbour08 · May 2016

So I had gotten 6.96 lbs and he wound up being 7.5, not super far off!

DrillSergeantCat · May 2016

It said Harrison would weigh 8.5 pounds. He was 8lbs 15oz. Closer to what the ultrasound showed. Oh...and he was a week early.

SarahChristine12 · May 2016

Mine said 8lbs 3oz. Caleb was 8lbs 13oz at birth and he was almost 2 weeks early.

knottie80e71cfff37ffdaa · January 2019

Yeah I dunno about this. It says mines going to be 6.64 lbs but at 28 weeks my baby was already weighing in at 3.8 lbs so I'm thinking it'll be a little bigger than 6.64 lbs haha

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