Gestation vs. Birthweight

[ Survey Results Intro | All Charts | Take the survey ]

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 2758 6 lbs, 1 oz
35W,1D 23 2652 2755 6 lbs, 1 oz
35W,2D 21 2780 2746 6 lbs, 1 oz
35W,3D 33 2831 2748 6 lbs, 1 oz
35W,4D 21 2742 2777 6 lbs, 2 oz
35W,5D 31 2714 2760 6 lbs, 1 oz
35W,6D 22 2757 2770 6 lbs, 2 oz
36W,0D 50 2859 2787 29 g (1 oz) 6 lbs, 2 oz
36W,1D 40 2612 2808 53 g (1.9 oz) 6 lbs, 3 oz
36W,2D 49 2821 2854 108 g (3.8 oz) 6 lbs, 5 oz
36W,3D 47 2907 2914 166 g (5.9 oz) 6 lbs, 7 oz
36W,4D 42 2905 2940 163 g (5.7 oz) 6 lbs, 8 oz
36W,5D 54 3013 2971 211 g (7.4 oz) 6 lbs, 9 oz
36W,6D 71 3120 3014 244 g (8.6 oz) 6 lbs, 10 oz
37W,0D 115 2986 3035 248 g (8.7 oz) 6 lbs, 11 oz
37W,1D 102 2956 3065 257 g (9.1 oz) 6 lbs, 12 oz
37W,2D 106 3118 3094 240 g (8.5 oz) 6 lbs, 13 oz
37W,3D 113 3081 3097 183 g (6.5 oz) 6 lbs, 13 oz
37W,4D 134 3149 3138 198 g (7 oz) 6 lbs, 15 oz
37W,5D 128 3218 3170 199 g (7 oz) 6 lbs, 16 oz
37W,6D 168 3124 3187 173 g (6.1 oz) 7 lbs, 0 oz
38W,0D 221 3220 3223 188 g (6.6 oz) 7 lbs, 2 oz
38W,1D 202 3213 3251 186 g (6.6 oz) 7 lbs, 3 oz
38W,2D 209 3242 3265 171 g (6 oz) 7 lbs, 3 oz
38W,3D 245 3328 3300 203 g (7.2 oz) 7 lbs, 4 oz
38W,4D 315 3326 3321 183 g (6.5 oz) 7 lbs, 5 oz
38W,5D 294 3312 3344 174 g (6.1 oz) 7 lbs, 6 oz
38W,6D 345 3382 3358 171 g (6 oz) 7 lbs, 6 oz
39W,0D 491 3354 3377 154 g (5.4 oz) 7 lbs, 7 oz
39W,1D 432 3397 3395 144 g (5.1 oz) 7 lbs, 8 oz
39W,2D 397 3377 3410 145 g (5.1 oz) 7 lbs, 8 oz
39W,3D 520 3444 3430 130 g (4.6 oz) 7 lbs, 9 oz
39W,4D 526 3450 3462 141 g (5 oz) 7 lbs, 10 oz
39W,5D 514 3442 3483 139 g (4.9 oz) 7 lbs, 11 oz
39W,6D 558 3514 3504 146 g (5.1 oz) 7 lbs, 12 oz
40W,0D 1030 3518 3523 146 g (5.1 oz) 7 lbs, 12 oz
40W,1D 661 3554 3540 145 g (5.1 oz) 7 lbs, 13 oz
40W,2D 603 3568 3561 151 g (5.3 oz) 7 lbs, 14 oz
40W,3D 548 3600 3576 146 g (5.1 oz) 7 lbs, 14 oz
40W,4D 536 3596 3604 142 g (5 oz) 7 lbs, 15 oz
40W,5D 559 3619 3620 137 g (4.8 oz) 7 lbs, 16 oz
40W,6D 580 3633 3639 135 g (4.8 oz) 8 lbs, 0 oz
41W,0D 619 3661 3654 131 g (4.6 oz) 8 lbs, 1 oz
41W,1D 513 3660 3669 129 g (4.6 oz) 8 lbs, 1 oz
41W,2D 405 3721 3688 127 g (4.5 oz) 8 lbs, 2 oz
41W,3D 410 3724 3703 127 g (4.5 oz) 8 lbs, 3 oz
41W,4D 309 3718 3721 117 g (4.1 oz) 8 lbs, 3 oz
41W,5D 243 3796 3742 122 g (4.3 oz) 8 lbs, 4 oz
41W,6D 208 3722 3752 113 g (4 oz) 8 lbs, 4 oz
42W,0D 195 3789 3773 119 g (4.2 oz) 8 lbs, 5 oz
42W,1D 111 3786 3795 126 g (4.4 oz) 8 lbs, 6 oz
42W,2D 67 3847 3798 110 g (3.9 oz) 8 lbs, 6 oz
42W,3D 47 4041 3834 131 g (4.6 oz) 8 lbs, 7 oz
42W,4D 19 3891 3852 131 g (4.6 oz) 8 lbs, 8 oz
42W,5D 23 3909 3892 150 g (5.3 oz) 8 lbs, 9 oz
42W,6D 12 3898 3917 165 g (5.8 oz) 8 lbs, 10 oz
Total responses: 14375

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

Wed May 22 8:34 PM by Nachos in Pregnancy & Parenting

Late to the party, sorry.

When I worked in a biligual Kita, the kids picked up loads from simply being read to and pointing out the different things. Sometimes a question came up ("that is a pferd", "it's called horse in English", "ok horse") and it's good to know both languages to understand what the kid is saying, but reading is a good together activity :)

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.