Gestation vs. Birthweight

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Birthweight (in grams) vs. Gestation time

The CDC has better data on this, but pregnant women frequently wonder whether their late babies will be huge so I asked my survey participants for weight just for funzies. On average, babies born later are slightly bigger but not much. The difference between a baby born around 39W 0D (about 3400 g) and one born around 41 W 0D (about 3700 g) is only 300 g, or about 10.6 ounces.

There's a lot of variety too; plenty of babies born after 41 weeks weigh less than babies born around week 38 or even 37. It should be no surprise that they all just seem to grow at their own rate.

Data table

Date# BirthsAverage (g)± 3 day Average (g)Change from previous week± 3 day Average (lbs oz)
35W,0D 20 2735 2762 6 lbs, 1 oz
35W,1D 23 2652 2759 6 lbs, 1 oz
35W,2D 20 2804 2751 6 lbs, 1 oz
35W,3D 33 2831 2752 6 lbs, 1 oz
35W,4D 21 2742 2780 6 lbs, 2 oz
35W,5D 30 2721 2763 6 lbs, 1 oz
35W,6D 21 2755 2773 6 lbs, 2 oz
36W,0D 50 2859 2790 28 g (1 oz) 6 lbs, 2 oz
36W,1D 40 2612 2811 52 g (1.8 oz) 6 lbs, 3 oz
36W,2D 48 2829 2856 105 g (3.7 oz) 6 lbs, 5 oz
36W,3D 47 2907 2915 163 g (5.7 oz) 6 lbs, 7 oz
36W,4D 42 2905 2940 160 g (5.6 oz) 6 lbs, 8 oz
36W,5D 54 3013 2971 208 g (7.3 oz) 6 lbs, 9 oz
36W,6D 71 3120 3015 242 g (8.5 oz) 6 lbs, 10 oz
37W,0D 114 2982 3036 246 g (8.7 oz) 6 lbs, 11 oz
37W,1D 101 2954 3065 254 g (9 oz) 6 lbs, 12 oz
37W,2D 103 3134 3094 238 g (8.4 oz) 6 lbs, 13 oz
37W,3D 113 3081 3097 182 g (6.4 oz) 6 lbs, 13 oz
37W,4D 130 3146 3138 198 g (7 oz) 6 lbs, 15 oz
37W,5D 126 3219 3172 201 g (7.1 oz) 6 lbs, 16 oz
37W,6D 161 3121 3188 173 g (6.1 oz) 7 lbs, 0 oz
38W,0D 214 3218 3225 189 g (6.7 oz) 7 lbs, 2 oz
38W,1D 198 3222 3254 189 g (6.7 oz) 7 lbs, 3 oz
38W,2D 206 3240 3268 174 g (6.1 oz) 7 lbs, 3 oz
38W,3D 242 3335 3303 206 g (7.3 oz) 7 lbs, 5 oz
38W,4D 311 3330 3324 186 g (6.6 oz) 7 lbs, 5 oz
38W,5D 289 3314 3347 175 g (6.2 oz) 7 lbs, 6 oz
38W,6D 341 3386 3360 172 g (6.1 oz) 7 lbs, 7 oz
39W,0D 483 3352 3378 153 g (5.4 oz) 7 lbs, 7 oz
39W,1D 426 3401 3396 142 g (5 oz) 7 lbs, 8 oz
39W,2D 392 3378 3410 142 g (5 oz) 7 lbs, 8 oz
39W,3D 511 3443 3430 127 g (4.5 oz) 7 lbs, 9 oz
39W,4D 521 3450 3462 138 g (4.9 oz) 7 lbs, 10 oz
39W,5D 501 3440 3483 136 g (4.8 oz) 7 lbs, 11 oz
39W,6D 551 3517 3505 145 g (5.1 oz) 7 lbs, 12 oz
40W,0D 1015 3519 3523 145 g (5.1 oz) 7 lbs, 12 oz
40W,1D 651 3556 3540 144 g (5.1 oz) 7 lbs, 13 oz
40W,2D 589 3569 3561 151 g (5.3 oz) 7 lbs, 14 oz
40W,3D 542 3597 3576 146 g (5.1 oz) 7 lbs, 14 oz
40W,4D 528 3592 3603 141 g (5 oz) 7 lbs, 15 oz
40W,5D 550 3618 3619 136 g (4.8 oz) 7 lbs, 16 oz
40W,6D 571 3634 3638 133 g (4.7 oz) 8 lbs, 0 oz
41W,0D 612 3661 3654 131 g (4.6 oz) 8 lbs, 1 oz
41W,1D 507 3663 3670 130 g (4.6 oz) 8 lbs, 1 oz
41W,2D 401 3724 3689 128 g (4.5 oz) 8 lbs, 2 oz
41W,3D 402 3726 3703 127 g (4.5 oz) 8 lbs, 3 oz
41W,4D 299 3719 3722 119 g (4.2 oz) 8 lbs, 3 oz
41W,5D 240 3789 3742 123 g (4.3 oz) 8 lbs, 4 oz
41W,6D 201 3723 3751 113 g (4 oz) 8 lbs, 4 oz
42W,0D 190 3784 3772 118 g (4.2 oz) 8 lbs, 5 oz
42W,1D 111 3786 3792 122 g (4.3 oz) 8 lbs, 6 oz
42W,2D 67 3847 3798 109 g (3.8 oz) 8 lbs, 6 oz
42W,3D 47 4041 3833 130 g (4.6 oz) 8 lbs, 7 oz
42W,4D 19 3891 3853 131 g (4.6 oz) 8 lbs, 8 oz
42W,5D 21 3930 3894 152 g (5.4 oz) 8 lbs, 9 oz
42W,6D 12 3898 3921 170 g (6 oz) 8 lbs, 10 oz
Total responses: 14147

Due Date Survey Data

Due date statistics: A study on the length of pregnancy
Probability of delivery resulting from spontaneous labor after 35 weeks
Probability of delivery within x days of a given date
Length of pregnancy by week
Spontaneous labor and due date determination
Length of pregnancy, comparing subsequent births for individual moms
Length of pregnancy for first time vs. second & third time moms
Length of pregnancy, type of delivery
Gestation vs. Birthweight
Probablity of Induction after a given day
Average day of spontaneous labor vs. age of mother at time of birth
Are more babies born during a full moon?
What's the most common day of the week for babies to be born?
I'm still pregnant at 40W. What's it mean?
Do winter babies arrive later?
What if I know my conception date?
Are boys or girls born later?
Subsequent pregnancy date search
How do inductions bias the due date statistics?
Download the data
Birth Stories
Survey input dates

More Resources

Pregnancy Day-by-Day
Fast pregnancy calendar
Baby age calendar
EDD Icon Generator
Jo's Birth Story
Weeks vs. Months Explained
Charts generated by flot

Recent Comments

For more support, encouragement, Q&A,
you are invited to join our pregnancy forum. We are dedicated to answering complicated questions as logically as we possibly can.

learning to read

Sat Feb 2 11:42 AM by melsbells in Pregnancy & Parenting

Spacefem, thanks for the book suggestions.

Sonic, I like the way you described the sound a letter makes.

I asked a few early elementary school teachers I know this same question and wanted to share a bit of what they had to say.

They recommended starting with consonant-vowel-consonant words (CVC) with short vowel sounds, and focus on rhyming families (i.e. bat, cat, fat) and even including first consonant changes that don't make real words, like 'gat'. Then later introduce CVC with last letter changes (i.e. bad, bar, bat). They said we could try sight words at the same time and told me to do a search for the Fry sight word list.

After those CVC words aren't a problem, it was suggested to start adding an 'e' at the end of CVC words to change the vowel sound, an the meaning of the words, so introducing long vowels (i.e. cap->cape). Then after all that, we can start adding two consonants together and two vowels together. From there maybe come up with homonyms together, which can be a great way to introduce silent letters (i.e. new, knew).

How important is school?

Thu Nov 22 9:05 PM by Skeezy in Pregnancy & Parenting

I think the most important factor in any school is how much the teachers care about the students. Another important element is safety and how interactions between students can substract from learning. Many parents go to jail for quite lengthy sentences for trying to send to their kids to a safe good school.

I would say its very important, because what you learn shapes and molds yours views that make you who you are.

Unplanned, polyamorous pregnancy situation

Sun Apr 29 12:18 PM by metawidget in Pregnancy & Parenting

I'm glad you have been communicating and working things out. I wish you lots of health and love as you wrote the next chapter of this story.

I might be pregnant...

Fri Jan 5 3:16 AM by Aum in Pregnancy & Parenting

Aum, my partner and I were just discussing this. He was surprised by my taking the hard line that stopping BC or poking holes in condoms or something like that is rape, making the woman a rapist. Which should result in jail time, so she should lose custody, which should go to the father and now he has the choice of keeping the baby or putting them up for adoption.

It's unfortunate that you can't prove such a thing, but hopefully if it was actually taken seriously women would be less likely to do it because it would at least be explicitly called rape.

I understand how the justice system and the family courts would look at it. They see it as the man's sperm made it to the egg so somehow he wasn't protecting himself, he made the choice, yada yada. There's no way to prove that the woman was manipulative, withdrew BC, or "poked holes in the condom" (I think that's unheard of, but anyway).

When do you outsource parenting?

Sat Oct 14 7:47 PM by rowan in Pregnancy & Parenting

yeah I do a ton of supplemental history... :(

Sleep for babies after 6 months

Thu Jan 10 1:30 AM by Sonic# in Pregnancy & Parenting

Thank you for the stories. I try not to get caught up in comparisons, but it's so hard when someone else is like, "Oh yeah, they're sleeping through the night after six months, no problem!" and we're nudging each other when it's our turn to get up at night almost every night. Did I do something wrong? (The answer is probably no, but a lack of sleep makes it harder to get there mentally.)

I topped baby off tonight. He straight up drank 7 ounces of formula after his prunes. If he's an infiltrator, he's eating well for it. :)

How the 2nd pregnancy / labor was different from the first

Thu Sep 27 8:20 PM by antfancier in Pregnancy & Parenting

I haven’t been around for a long time, but I’m back and pregnant again. Only 6 weeks, so I can’t really comment much, but this time around it has been easier so far. Not easy, but considering I’m working and have a 2.5yr old (neither of which applied to last pregnancy), I thought I’d feel much worse. I still have ALL the symptoms and they all started at 3 weeks, just like last time (and the same as a chemical pregnancy I had too) but they don’t seem to be as constant as before. I’m really glad about that! The only thing that’s worse is back ache, ligament pain, general body aches. I assume it’s because my body is already exhausted and broken from my toddler.

posting pictures of kids and privacy

Wed Apr 25 7:29 AM by juliabonl17 in Pregnancy & Parenting

Usually, we don't share photos of our children in social media. Sometimes I can send some photos to close friends. I keep my personal life in quiet. Share with family only.

I had my 2nd baby!!!!

Wed Jan 3 8:21 PM by MFS in Pregnancy & Parenting


I am still dealing with the fact that your 11 year old is an actual 11 year old.

on being semi-pregnant

Tue Oct 3 7:18 PM by geldofc in Pregnancy & Parenting

congratulations!! i've never been pregnant but i'm jealous. i'm having baby fever lately.

kids' mail subscriptions

Wed Jan 9 6:41 PM by melsbells in Pregnancy & Parenting

We got the first box last week. Kid wanted to do the whole thing in one sitting, which was tough. He has a hard time stopping something, even when it's obvious he needs a break. He doesn't have the best conception of time yet either and kept talking about the box that would come tomorrow. So getting something once a month might help pin down the passage of time. As far as my concerns, we had a great opportunity (when he was disappointed that the Europe page didn't say anything about Finland) to talk about how a single page on a whole continent or even an individual country can't tell us what a place and culture is like. Bavaria was mentioned, so we also got to talk about how our German friend feels when people only think of Bavarian things when thinking of Germany, which she doesn't feel a connection to.

housemates + newborn = ?

Thu Aug 2 11:57 AM by melsbells in Pregnancy & Parenting

I live with my in-laws, and while there will certainly be a lot of differences from your situation, maybe there's enough similarities that my experience could be useful to you. I think the biggest thing is that everyone has their own space. Our house is sort of divided in two, so we can take the kid to our end during a tantrum. I think that distance helps, not just with in-laws not wanting to hear screaming, but as a sort of physical signal for the kid to calm down. We lived in an apartment when the kid was first born and our neighbors there probably heard more screaming/crying due to proximity.

My father-in-law spends a lot of time with the kid, mostly by choice. I sometimes wish we had more of a schedule, because at the moment, naps and bedtime are the only semi-guaranteed breaks for anyone. My spouse and father-in-law both work from home free-lance, so they don't actually have a schedule for when they need to be left alone, but at least my father-in-law has more warning with jobs scheduled out in advance.

My Ectopic Pregnancy

Tue Jan 23 8:47 PM by rowan in Pregnancy & Parenting

FYI we have a general culture in the pregnancy forum here about sharing similar stories as a way to offer support, and also about giving any medical knowledge that we've come across, since pregnancy is generally not talked about as much as it should be and you find information in random places. Since you haven't been around until now you probably didn't know that, and mels' post is well in line with forum guidelines and norms. Please don't go all mod martyr on us now that you're only just back. This is me as a friend speaking here, not with my modhat on.

I'm sorry for your loss. Ectopic pregnancies are scary, and I would like to go punch that first doctor in the face for you.

PPD is awful too. :( I hope you can get through it.

gender recognition

Thu Nov 2 1:03 PM by Nech in Pregnancy & Parenting

You can continue discussing with him the difference of a boy and a girl. Have him socialize too with the same gender. There's nothing wrong if you have go with opposite sex as long as he understands what/who he is.

So do you feel hanging out with the opposite gender at a young age can confuse a person's gender identity?

leftist parenting and gender [split from gender recognition]

Sat Sep 23 11:52 AM by Unvoiced_Apollo in Pregnancy & Parenting

gender recognition.">

If a boy who has a penis asks if he's a boy and you don't just say yes, then that's straight up lunacy.

What he decides to do with that boyhood or how he dresses is up to him. But if you're born with a penis you're a boy.

Making it airy fairy when, statistically, scientifically, less than 1% of 1% of children born have true gender dysphoria, is immoral and wrong. It's also a sign of our troubled times.

This is just my anecdotal experience but...

I have experienced bullying based on simply engaging in normal children's play with girls. Insults were attacks on both me and the girls. But I NEVER questioned my gender as a male. So if a child asks me if he's a boy and was identified biologically as one, I am going to question what influences are on the child before I answer.