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 16 2649 2750 6 lbs, 1 oz
35W,1D 21 2629 2743 6 lbs, 1 oz
35W,2D 16 2780 2733 6 lbs, 0 oz
35W,3D 29 2875 2736 6 lbs, 1 oz
35W,4D 19 2716 2783 6 lbs, 2 oz
35W,5D 27 2696 2770 6 lbs, 2 oz
35W,6D 21 2755 2785 6 lbs, 2 oz
36W,0D 42 2898 2795 45 g (1.6 oz) 6 lbs, 3 oz
36W,1D 37 2631 2822 79 g (2.8 oz) 6 lbs, 4 oz
36W,2D 42 2850 2863 130 g (4.6 oz) 6 lbs, 5 oz
36W,3D 44 2897 2918 182 g (6.4 oz) 6 lbs, 7 oz
36W,4D 36 2941 2935 152 g (5.4 oz) 6 lbs, 8 oz
36W,5D 43 2995 2968 198 g (7 oz) 6 lbs, 9 oz
36W,6D 56 3115 3014 229 g (8.1 oz) 6 lbs, 10 oz
37W,0D 103 2970 3035 240 g (8.5 oz) 6 lbs, 11 oz
37W,1D 88 2961 3066 244 g (8.6 oz) 6 lbs, 12 oz
37W,2D 89 3151 3092 229 g (8.1 oz) 6 lbs, 13 oz
37W,3D 103 3068 3098 180 g (6.3 oz) 6 lbs, 13 oz
37W,4D 121 3161 3146 211 g (7.4 oz) 6 lbs, 15 oz
37W,5D 102 3208 3177 209 g (7.4 oz) 7 lbs, 0 oz
37W,6D 144 3134 3189 175 g (6.2 oz) 7 lbs, 0 oz
38W,0D 190 3237 3229 194 g (6.8 oz) 7 lbs, 2 oz
38W,1D 171 3220 3257 191 g (6.7 oz) 7 lbs, 3 oz
38W,2D 185 3232 3272 180 g (6.3 oz) 7 lbs, 3 oz
38W,3D 213 3339 3308 210 g (7.4 oz) 7 lbs, 5 oz
38W,4D 268 3334 3325 179 g (6.3 oz) 7 lbs, 5 oz
38W,5D 243 3323 3347 170 g (6 oz) 7 lbs, 6 oz
38W,6D 300 3394 3361 172 g (6.1 oz) 7 lbs, 7 oz
39W,0D 415 3348 3376 147 g (5.2 oz) 7 lbs, 7 oz
39W,1D 374 3396 3396 139 g (4.9 oz) 7 lbs, 8 oz
39W,2D 342 3371 3410 138 g (4.9 oz) 7 lbs, 8 oz
39W,3D 449 3432 3429 121 g (4.3 oz) 7 lbs, 9 oz
39W,4D 460 3462 3462 137 g (4.8 oz) 7 lbs, 10 oz
39W,5D 432 3442 3483 136 g (4.8 oz) 7 lbs, 11 oz
39W,6D 487 3517 3505 144 g (5.1 oz) 7 lbs, 12 oz
40W,0D 893 3520 3525 149 g (5.3 oz) 7 lbs, 12 oz
40W,1D 571 3548 3541 145 g (5.1 oz) 7 lbs, 13 oz
40W,2D 506 3577 3561 151 g (5.3 oz) 7 lbs, 14 oz
40W,3D 485 3590 3576 147 g (5.2 oz) 7 lbs, 14 oz
40W,4D 465 3595 3602 140 g (4.9 oz) 7 lbs, 15 oz
40W,5D 462 3621 3620 137 g (4.8 oz) 7 lbs, 16 oz
40W,6D 497 3631 3638 133 g (4.7 oz) 8 lbs, 0 oz
41W,0D 529 3658 3657 132 g (4.7 oz) 8 lbs, 1 oz
41W,1D 425 3671 3673 132 g (4.7 oz) 8 lbs, 2 oz
41W,2D 342 3729 3692 131 g (4.6 oz) 8 lbs, 2 oz
41W,3D 343 3737 3707 131 g (4.6 oz) 8 lbs, 3 oz
41W,4D 256 3725 3727 125 g (4.4 oz) 8 lbs, 3 oz
41W,5D 206 3790 3745 125 g (4.4 oz) 8 lbs, 4 oz
41W,6D 175 3721 3753 115 g (4.1 oz) 8 lbs, 4 oz
42W,0D 162 3774 3771 114 g (4 oz) 8 lbs, 5 oz
42W,1D 96 3782 3789 116 g (4.1 oz) 8 lbs, 6 oz
42W,2D 58 3833 3792 100 g (3.5 oz) 8 lbs, 6 oz
42W,3D 41 4056 3825 118 g (4.2 oz) 8 lbs, 7 oz
42W,4D 17 3879 3845 118 g (4.2 oz) 8 lbs, 8 oz
42W,5D 17 3876 3883 138 g (4.9 oz) 8 lbs, 9 oz
42W,6D 12 3898 3911 158 g (5.6 oz) 8 lbs, 10 oz
Total responses: 12302

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?
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.


Sun Aug 13 5:21 PM by Taurwen in Pregnancy & Parenting

If I remember correctly, all that stuff about fertility dropping dramatically at 35 is based on old and flawed data, so don't let the idea of TTC being so much harder let you scare you too much (obviously fertility drops, but it's not that bad). There are other considerations as you get older (at 29 I need more sleep than I did at 25) but nothing that really prevents you.

Timing will never be perfect, but it can be optimal.

bad reasons for having a baby

Tue Aug 1 1:47 AM by rowan in Pregnancy & Parenting

but I take them to restaurants so I know they end up hating 90% of the things they ask for.

- kid would like a sibling

- maybe people are right about end of life stuff

That's about it. I hated being pregnant, the last time I was pregnant the hormones were... really awful. Plus kid is now pretty big so another one would be weird and we gave away all our stuff. ;)

how do you travel?

Mon Jun 19 11:00 AM by DarkOne in Pregnancy & Parenting

We're traveling with a 2 yo and a 4yo this week. A 2 hr flight connecting to a 4 hr flight. I broke down and got tablets and headphones, now I just need to load them with movies/games. I'm packing treats and stickers and crayons and notepads. I'm almost positive I'll be carrying on a (very compactable) pillow, 'cause they don't give those out anymore on board. I'm banning toys that can roll several aisles fwd or back when inevitably dropped (besides the crayons). I was planning on gum for ascent/descent, but I think the suckers for the 2yo will be better. I'm so not looking forward to these flights. Maybe the kids will surprise me and be awesome. I'm not worried about the 4yo. But the 2yo...

Bilingual Toddler

Wed May 3 10:19 PM by Nachos in Pregnancy & Parenting

Bilingualism! This is something I know a lot about! My last job was to speak English to my class in a partial immersion school and the kids picked up English so fast but spoke back to me in German. We worked on saying different words in German and in English and it meaning the same thing and I read English books to them. They differentiated pretty well but most of them came from a mono-lingual family background.

I can still highly recommend this book: ( for bilingual children. Some very good advice in there.

Also, keep speaking English! Toddlers forget fast when a language is no longer present.

Yay bilingualism!

New parent help/suggestions

Sat Jan 14 10:07 PM by antfancier in Pregnancy & Parenting

I agree with everything lyra211 said and will add a few more.

Things you don't need:

Anything soft, fluffy or furry. My baby couldn't care less about minky blankets and soft toys. Plus they seem more gross to clean when they get covered in bodily fluids.

Clothes that look like adult clothes. It's so difficult to squeeze baby thighs into miniature corduroys or denim jeans which have no give to the fabric.

Baby washcloths. Babies make a disproportionate amount of mess so you need adult size washcloths to clean them up.

Things that were super useful:

A folding changing mat. I have a SkipHop one which has enough storage for wipes and diapers, which was all I needed to carry with me when I had a newborn. Now that he's bigger, I appreciate the larger size of the mat because the one that came with my diaper bag is way too small.

Balls. They were the first thing he played with and still his favourite toys. At the beginning he liked one made by Oball which was easy to pick up, and a soft fabric one which made a crinkly noise. Now he loves throwing a soft rubber ball and watching it bounce.

Postpartum issues: things that can go wrong after

Wed Aug 9 5:24 PM by rowan in Pregnancy & Parenting

ugh that totes doesn't just happen during c-section. I had a friend who found out when she was having (other) surgery years later and they stitched her up since "they were in there anyway". Honestly I think I also have it but it doesn't cause problems *most* of the time (sometimes stabby pain but no one takes it seriously so idk).

Just Can't Let It Go

Wed Jul 26 1:18 AM by Taurwen in Pregnancy & Parenting

We didn't find out specifically because we didn't want a lot of pink stuff if it was a girl.

Somehow MIL has still given us a ton of pink clothing that she'll change him into everytime she comes over.

I hate pink.

Another baby stars

Thu Jun 15 6:54 AM by StarsInUrEye in Pregnancy & Parenting

Thanks for the congratulations and encouragement.

I had an appointment with the obgyn today. He seems to think I'm even farther along than he originally thought. I didn't have an ultrasound. He just went by the size of my uterus. It's well over my belly button now. He's sending me to a high risk Dr. Asap and then I'm suppost to see him again on the 29th. By then he said they will have a better idea as to how far along I actually am. So far the pregnancy is going well. I did have complications with my first one and went to a specialist but this time I'm being referred to one because I'm old lol. They automatically send women when they are 35 and older.

What did I just say?

Wed Mar 15 12:25 PM by mariareese in Pregnancy & Parenting

Looking to know about the system and biology :D hehe ..

Activities for 1-3 yo's

Sat Jan 14 7:07 PM by antfancier in Pregnancy & Parenting

I find has lots of inspiring ideas. Some look like they take quite a bit of prep, but if you're doing it for a whole class then it might be worth it. You can sort activities by age as well so it's easier to search.

How to deal with opinionated toddlers (or babies or kids)

Tue Aug 1 1:57 AM by rowan in Pregnancy & Parenting

Ooof. My kid is very social, needs to be around someone all the time. It's ... challenging, as you've found. It does get better as they gain their own interests. But it took a long time to get past clingy.

Not having read your post, but just the heading, my response was "wine." But after reading your post, I thought "wine."

Yes. After bedtime.

Also, honestly the only way we made it through was we would take turns being the center of focus. We still do this, divide and conquer (and she's only one kid, hell). Also, I know people are like really limit screen time BUT if you really need to get something done one episode of e.g. Daniel Tiger or Paw Patrol or whatever isn't gonna be too bad. I think DarkOne has some good ideas too.

Good luck.

Happiest Baby on the Block

Wed Jul 12 4:52 PM by antfancier in Pregnancy & Parenting

My mum gave me 'Your Baby and Child' by Penelope Leach, which is what she used when she had me. It covers from birth to five years. I read the first section about newborns in preparation. After having the baby, I realised I have zero time or brain power to do anything so I never got around to the rest of it. In general, I liked the book though. It's a simple overview and has nice color photos.

To all Moms: Where do you go for financial concerns?

Tue May 9 4:18 PM by rowan in Pregnancy & Parenting

My father in law does financial advising so we kind of have an in-house advisor? But seriously someone with expertise is great. There are various "how to do finances" through our local community ed, which I'd probably consider if I didn't already have someone to ask. Maybe something like that near you? Libraries also sometimes have programs.

Also I know you can do wills and stuff on your own but honestly I found it super useful to talk through it with a lawyer who does that. She thought of things we never would have. (hm really should revisit now that kid is older) It was a one time fee and not that bad.

We do most of our banking through a credit union. Have been happy with them. We refinanced our mortgage through them when we did that. I remember the big credit union bust ages ago, but there are lots more protections in place now and big banks can be pretty awful.

stuffed animals

Thu Feb 23 1:20 AM by antfancier in Pregnancy & Parenting

My brother's favorite stuffed animal was a thing we called 'gerbil'. I actually don't know what it was because we found it in the street (not sure what my mum was thinking in allowing him to pick it up, let alone keep it) and it had already lost an eye and was unidentifiable, but he became really attached to it. We almost missed a flight once because he dropped it in the airport and we had to go back to look for it.

Today for the first time my 11month old showed interest in a stuffed animal. Just before Christmas we received a box from Amazon with a giant bear inside. No gift wrap, no note. Just a bear the size of my child. It's been sat in his room and ignored completely, despite him exploring literally everything else that is in there. Then, out of the blue, he made a beeline for it and tried to pull its eyes out.

tactile stuff

Wed Jan 4 6:14 AM by Neko in Pregnancy & Parenting

All the pliable/crafty stuff I can think of has been mentioned. ETA: I lied. Bread dough!

But if generally tactile surfaces also apply, mermaid sequin pillows are comforting. It was one of my impulse buys at a department store about a month ago. I couldn't stop petting the display. The sequined side seemed like it wouldn't be comfortable to rest on but it hasn't been an issue. My stepdad really likes them so I got him one for giftmas and he said it helps distract him when chronic pain keeps him awake at night.

I haven't field tested them on my nieces and nephews yet. That could be fun.