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 13 2750 2770 6 lbs, 2 oz
35W,1D 20 2620 2757 6 lbs, 1 oz
35W,2D 15 2784 2744 6 lbs, 1 oz
35W,3D 28 2878 2738 6 lbs, 1 oz
35W,4D 18 2703 2778 6 lbs, 2 oz
35W,5D 26 2698 2770 6 lbs, 2 oz
35W,6D 19 2700 2786 6 lbs, 2 oz
36W,0D 41 2904 2799 29 g (1 oz) 6 lbs, 3 oz
36W,1D 34 2643 2828 71 g (2.5 oz) 6 lbs, 4 oz
36W,2D 41 2857 2869 125 g (4.4 oz) 6 lbs, 5 oz
36W,3D 40 2919 2929 191 g (6.7 oz) 6 lbs, 7 oz
36W,4D 36 2941 2946 168 g (5.9 oz) 6 lbs, 8 oz
36W,5D 43 2995 2974 204 g (7.2 oz) 6 lbs, 9 oz
36W,6D 54 3132 3020 234 g (8.3 oz) 6 lbs, 11 oz
37W,0D 100 2975 3039 240 g (8.5 oz) 6 lbs, 11 oz
37W,1D 84 2956 3070 242 g (8.5 oz) 6 lbs, 12 oz
37W,2D 84 3161 3097 228 g (8 oz) 6 lbs, 13 oz
37W,3D 96 3077 3103 174 g (6.1 oz) 6 lbs, 13 oz
37W,4D 114 3163 3153 207 g (7.3 oz) 6 lbs, 15 oz
37W,5D 99 3209 3184 210 g (7.4 oz) 7 lbs, 0 oz
37W,6D 140 3143 3195 175 g (6.2 oz) 7 lbs, 1 oz
38W,0D 179 3254 3233 194 g (6.8 oz) 7 lbs, 2 oz
38W,1D 165 3218 3263 193 g (6.8 oz) 7 lbs, 3 oz
38W,2D 172 3235 3279 182 g (6.4 oz) 7 lbs, 4 oz
38W,3D 204 3336 3312 209 g (7.4 oz) 7 lbs, 5 oz
38W,4D 250 3349 3328 175 g (6.2 oz) 7 lbs, 5 oz
38W,5D 232 3330 3350 166 g (5.9 oz) 7 lbs, 6 oz
38W,6D 285 3387 3365 170 g (6 oz) 7 lbs, 7 oz
39W,0D 394 3352 3380 147 g (5.2 oz) 7 lbs, 7 oz
39W,1D 350 3397 3398 135 g (4.8 oz) 7 lbs, 8 oz
39W,2D 330 3381 3411 132 g (4.7 oz) 7 lbs, 8 oz
39W,3D 428 3429 3431 119 g (4.2 oz) 7 lbs, 9 oz
39W,4D 436 3463 3464 136 g (4.8 oz) 7 lbs, 10 oz
39W,5D 413 3443 3485 135 g (4.8 oz) 7 lbs, 11 oz
39W,6D 464 3521 3507 142 g (5 oz) 7 lbs, 12 oz
40W,0D 850 3523 3526 146 g (5.1 oz) 7 lbs, 12 oz
40W,1D 542 3551 3542 144 g (5.1 oz) 7 lbs, 13 oz
40W,2D 474 3579 3563 152 g (5.4 oz) 7 lbs, 14 oz
40W,3D 460 3591 3578 147 g (5.2 oz) 7 lbs, 14 oz
40W,4D 439 3590 3604 140 g (4.9 oz) 7 lbs, 15 oz
40W,5D 439 3626 3621 136 g (4.8 oz) 7 lbs, 16 oz
40W,6D 475 3637 3640 133 g (4.7 oz) 8 lbs, 0 oz
41W,0D 502 3659 3659 133 g (4.7 oz) 8 lbs, 1 oz
41W,1D 404 3669 3676 134 g (4.7 oz) 8 lbs, 2 oz
41W,2D 322 3735 3693 130 g (4.6 oz) 8 lbs, 2 oz
41W,3D 328 3737 3707 129 g (4.6 oz) 8 lbs, 3 oz
41W,4D 242 3723 3725 121 g (4.3 oz) 8 lbs, 3 oz
41W,5D 198 3787 3743 122 g (4.3 oz) 8 lbs, 4 oz
41W,6D 167 3714 3749 109 g (3.8 oz) 8 lbs, 4 oz
42W,0D 154 3757 3766 107 g (3.8 oz) 8 lbs, 5 oz
42W,1D 88 3779 3784 108 g (3.8 oz) 8 lbs, 5 oz
42W,2D 57 3838 3784 91 g (3.2 oz) 8 lbs, 5 oz
42W,3D 40 4049 3815 108 g (3.8 oz) 8 lbs, 7 oz
42W,4D 17 3879 3838 113 g (4 oz) 8 lbs, 7 oz
42W,5D 16 3849 3872 129 g (4.6 oz) 8 lbs, 9 oz
42W,6D 11 3794 3892 143 g (5 oz) 8 lbs, 9 oz
Total responses: 11687

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

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you are invited to join our pregnancy forum. We are dedicated to answering complicated questions as logically as we possibly can.

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.

Academic redshirting

Wed Dec 7 8:22 PM by Nachos in Pregnancy & Parenting

I'm on the fence about this. I was always the youngest in my class because I was born 2 days before the cut off. I started school JUST after my 5th birthday (Go England.... not...) and this made a huge gap between me and the oldest kids in the class who were almost a whole year older. However, even though I might have struggled more then I'm ok now, you know? It might have even been helpful for me, pushing myself to learn more and try and be smarter. My sister was held back for a year in preschool in Germany because she didn't speak German well enough for the first grade and so she has always been the oldest in class and she's not really as academic as me. This is all anecdata of course, but interesting to ponder over.

kids' obsessions

Sat Oct 15 8:08 PM by melsbells in Pregnancy & Parenting

I could see saunas becoming an obsession for a number of very social reasons as well, depending on your family's sauna practices. I honestly can't think of any common themes or rituals shared by all branches of my U.S. family, other than like eating together, but that seems too banal(/essential for survival) to really become an obsession. My Finnish family, on the other hand, all sauna as a social ritual. Whether or not you allow your kid in saunas yet, if there's a lot of exposure to the ritual, they could probably pick up on the social importance. It might make sense that kids are probably wired to pick up on things that the adults in their life think are important (**not a child psychologist**).
<...> I know I was super into the instant evaporation of water and associated *hissssss* the first time I was in a sauna at like age seven.
This is an excellent point. And although I know they exist, I haven't encountered any Finns who don't like sauna. There are a lot of steps to it. The kid gets to help their grandfather build the fire when we're together, knows that wood burning saunas are better than electric saunas, and absolutely loves the sound of the water hitting the hot stones. I can't imitate the sound as well as the kid does.

Don't give your kids antidepressants.

Thu Sep 15 9:13 PM by Nachos in Pregnancy & Parenting

Mental health issues will never start to hurt, therefore no preemptive treatment is needed.

Mental health issues hurt, take it from me. There are many psychosomatic disorders out there which affect your body even though the real problem is in your mind. But to get better, you HAVE to treat both. Pre-emptive treatment also can stop some disorders from becoming too bad. And yes, sometimes drugs can be very very helpful.

I don't think you know what you're talking about and all this "I know because of divine intuition" bullshit is starting to piss me off. if you ask others for sources, be kind enough to provide some yourself.

If this thread continues to be shit-slinging, I will lock it.

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. ... _active_40

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

protective restrictions for children

Tue Dec 6 10:08 PM by melsbells in Pregnancy & Parenting

The Wolfpack, a documentary about six bright teenage brothers have spent their entire lives locked away from society in a manhattan housing project. all they know of the outside is gleaned from the movies they watch obsessively (and recreate meticulously). yet as adolescence looms, they dream of escape, ever more urgently, into the beckoning world. The film is coming from the bias that the parents have wronged their children. We're told that in the past they have left the apartment, only as a group, and up to eight times a year. One year they didn't get out at all. It's unclear what the objective of these outings were. The film leaves a lot unanswered. We know they are homeschooled by their mother, who's a certified teacher, but what the homeschooling looked like is never examined. I can't help but think that these kids all around really healthy, charming, affectionate, considerate, welcoming, really only positive adjectives come to mind.

Sleep Training for Parents and Infants

Sat Oct 1 9:34 PM by antfancier in Pregnancy & Parenting

Thank you! I'm currently stuck under 20lbs of sleeping baby because all day time naps have to be in my arms or they don't happen.

learning to use a toilet

Sun Sep 11 2:33 PM by Angelica in Pregnancy & Parenting

My statement was meant to indicate that I'm not finished with my thoughts on this topic, rather than to create drama.

I believe parents in this world universally make a big mistake when it comes time to start thinking about their children using the toilet. Kids feel forced to do it, and this breeds resentment and damages their self-esteem. Having the father (the mother is needed in the battle against the patriarchy) stay home with the children and homeschool them while they haven't yet decided to train themselves is the way to avoid humiliation by their more-repressed peers.

I would also like to point out that limiting elimination to the toilet at any age creates situations where the person's health is compromised due to the lack of availability of a bathroom. In these situations, I strongly advise parents to let their children wear diapers no matter their age. Retention can lead to kidney stones, intestinal damage, urinary tract infections and harmful bacteria and toxins in the bloodstream.

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.

development balalnce

Fri Dec 16 5:02 PM by rinn in Pregnancy & Parenting

I was proficient in fine/gross motor skills and cognitive development for my age, but I was further behind in speech/language development and social/emotional development. I caught up in them perhaps by ages 5-7, with vestiges of social issues lasting longer (like my temper). There was nothing inherently bad about being a bit off in timing, though in my case my imbalance was severe enough that I did need professional help from a speech pathologist.

....New social situations make me feel somewhat awkward, but I've also learned that many other people feel the same way about novel contexts, so I think I'm with the curve there.

geez, are you my twin, sonic? XD

I grew up with definite lag in speech/language development. I had a speech pathologist in elementary school work on my -L-'s, -r-'s and -th-'s; and when I essentially "graduated" from it I was taken out of the IEP program. my mom and I now see that being a mistake. middle school went decently, but I struggled in language arts; and by the time I went into high school I was struggling in my history/English humanities course and Algebra. I struggled in English classes because of my inability to express myself through language clearly, and I struggled in algebra because I couldn't follow a thing my teacher was saying (we had someone tutor me who literally asked why she was tutoring me because I grasped the concepts five minutes after her explaining it).

Parents Warned they Could Lose Custody of Fourteen-Year-Old Over This

Mon Nov 7 3:33 AM by garbage videos in Pregnancy & Parenting

It is wrong to lock horses in cages and breed them as if they are slaves.
I sincerely hope that you aren't condoning slavery with that implication that it isn't wrong to keep humans in cages and force them to "breed". It's probably just an unfortunate word choice.
I said it is wrong to put horses in cages and breed them as slaves. So I don't know how you read things. Frankly you are irritating me because I shouldn't have to explain how I said 2+2=4 when you are accusing me of saying 2+2=5. In this age people should have mastered how to read clearly and I shouldn't have to micromanage my text and clear what I have already layed out clearly for you.

To be fair, if the girl is a Female to Male transsexual, her hormones are not so important, at an old age Male hormones will mutate her body and have the same effect. But with boy's its more tragic and serious. Boys who want to be girls, must stop their toxic T at an early age, or else their face will be permanently ugly and bony

bringing children up naturist

Sat Sep 24 1:18 AM by filmmakingally in Pregnancy & Parenting

It's about teaching children to make love so that they do it themselves. Love has no age or genetic requirement. It's healthy for young siblings to make love, and it's unhealthy if they don't. Sexual repression of children fucks them up as adults. Because the parents are secretive about it, children get the idea that it's bad, which starts the process of sexual repression.

Gross. Yuck. Eww. I've run out of ways to express how disgusted I am with what you've said here. Ewwwwwww!!!!!!!

No, siblings should not make love. It is in our genetic interest that we don't do this. Ever. This is a cultural universal.

Middle grade / Beginning Chapter Books

Fri Sep 9 8:01 PM by melsbells in Pregnancy & Parenting

I think a big driver in getting them to read is to find stories that they like.
Definitely this. I once tutored a kid who had been held back twice in elementary school and was still a couple grade levels behind on reading skills. He was given a book from the Captain Underpants series because it was supposed to be at his reading level but he thought it was utterly stupid. I don't think we ever found books that both matched his reading level and maturity level, but once we started reading books better suited to his interests, it didn't matter that they were more difficult.

One of my cousins kids read the Warriors series and was really into it. She was bulllied in school, but I don't think it was instigated by her reading choices.

I don't know any recent books for this age group but I've heard great things about the Adventure Time comics.