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Birth weight and genetics

post #1 of 26
Thread Starter 
Just curious: how much do you think genetics has to do with birth weight? A little, a lot, or not much at all?

Dh and I were both smaller babies (6 lbs 2 oz. and 6 lbs 8 oz., respectively). Does that mean we're more like to have a baby that size?

On the other hand, my mom had babies in lots of sizes: first was over 8 pounds (and breech), my next 2 sisters were 7 pounds and change each, and I was the shrimp. Am I more likely to have a bigger first baby because she did?

Or is it all about the mom's nutrition, fitness, etc. during pregnancy?

Just wondering what you all think and if you know of any evidence (anecdotal or otherwise) on this issue.
post #2 of 26
Well, I was small (5# 15oz), but also had gastroschisis.
In my mom's family, all the other babies were 8 pounds or more (my cousins, my son, my cousin's son).
Three of my cousins (two moms) were over 10.
DS was 9#5oz.
None of us had Gestational Diabetes.
Oh, my cousin and I both gained lots of weight. My aunts didn't. One of my aunts is very health conscious and exercised through all her pregnancies. I think my other aunt did too.
SO, in our family, it seems to be genetic.
post #3 of 26
In think in our family it is nutrition during pregnancy.

I was 6lbs 10oz born, DH was 7lbs. Our first daughter was 7lbs 12oz (i ate healthy) our second was 9lbs (i ate a lot of junk!).
With my SIL her first was 8lbs 14oz and she was always eating. With #2 she was only 7lbs 13oz and throu that pregnancy she tried to monoitor how much she ate.
post #4 of 26
I don't personally feel that genetics has much to do with birth weights, but thats really only because of my experience...

I was 6 lbs 11 oz at birth. I was several weeks overdue and my mom smoked during the pregnancy.

My husband was 7 lbs 14 oz and he was born by scheduled cesarean.

My children were 7 lbs 7 oz (this was a scheduled cesarean birth), 8 lbs 1 oz (spontaneous labor & birth) and 9 lbs 10 oz (another spontaneous labor & birth). I gained 36 lbs, 27 lbs and 33 lbs respectively. It was only with my last pregnancy that I really made sure to eat enough protein...until then I didnt really realize how important it was. I also exercised by walking a few miles a day with each of them.

My 9 lb 10 oz daughter is the biggest baby that my family has had.
post #5 of 26
I think it's really a combination of genetics and lifestyle (particulary nutrition). I looked after myself in almost the exact same way for both of my successful pregnancies - worked full-time to the end, exercised as much as I could, and ate very similar diets.

My son, fathered by my ex, was 7lb., 12oz. I was the same, and my ex was within a couple of ounces (I can't recall his exact weight).

My daughter, fathered by my husband, was 10lb., 2oz. My husband was 9lb., 13oz, and his brothers were all just slightly behind that - all over 9lb. So, I'm inclined to think that his genes made the difference between my two babies. The one I'm carrying right now (same father) seems to be shaping up to be a fairly large baby, as well.
post #6 of 26
I think there is the genetic factor but there are lifestyle choices as well. A pp mentioned her mom smoked during pg so if you've got something like that that depresses birthweight we can't really do a fair comparision. The women in my family have big babies. My mom's smallest was just under 9lbs and her biggest just over 10lbs. My smallest was 9lbs and my biggest was just over 10lbs. My aunts also have babies in the 9-10lbs range. None of us had GD (to the best of my knowledge). I usually gain between 35-45lbs. Nothing too huge and I try to stay somewhat active but I just have big babies. It didn't really surprise me I guess because that's just what I expected. Now my DH on the other hand was only a bit more than 8lbs at birth but he is a very big guy. I guess I've just felt it had more to do with the mom's side.
post #7 of 26
It's so hard to say . . .

Dh and I were both 8 pound babies, but both of our girls were smaller than that (7-4 and 6-13). I am a smaller framed person and it's my theory that my body knew just the right size to grow my babies. I gained a LOT with both so it's not like I wasn't getting the calories. My body just likes to grow smaller babies.
post #8 of 26
I read somewhere once that birth weight has a definate gentic link and that it was tied to the paternal side.. as in your fathers lineage.. the women in his background or something..I know my dads mom did not have a baby smaller than 9 pounds.. my kids have all been around that weight.. I was 8'9 and so was my brother.. meanwhile my moms side of the family all had 6 pound babies..
post #9 of 26
Dh was 9#12oz. I was 6#3oz. My kids have been 5#7oz, 5#4oz and 4#15 oz. So they seem to be following after me.
post #10 of 26
Hmm I've never heard to look at your dad's side. I know my paternal GM did not have big babies because her doc harrassed her so much about not gaining too much weight so I can't do a fair comparision. I had meant to say earlier that my mom and some of my aunts are quite a bit larger than I am. For a person of my size my babies really are pretty big but still I have them. My pelvis accomodates them no problem.
post #11 of 26
I guess I will chime in here as well...

I was 10lbs, my mom and her siblings were all between 10lb-12lbs at birth. And my grandmother smoked like a CHIMNEY thru all her pregnancies.

My babies were 9lb2oz and 10lb3oz. I took good care of myself w/the first, but did indulge in more crappy food and little/no excercise. With my 2nd, I gained much less weight, walked 4 miles per day, and ate wonderfully (except the icecream indulgence!). And yet my 2nd was even larger, even with less weight gain, etc.

I really think it is genetic, but I also think lifestyle factors can carry into it.
post #12 of 26
I would have to say I think it has 60% do with environmental factors like the mom's diet, weight gain, etc. and 40% genetics

I was 8 lbs 4 oz, 21.75 in long, DH was 9 lbs 8 oz. 23 in long

our son was 7 lbs 8oz and 20.5 in long

I know both my mom and my MIL ate lots of junk food and didn't exercise while prge with us whereas I ate well, mostly organic, and did exercise a few times a week.
post #13 of 26
I was 7 lbs. at birth. My mom smoked a lot and took lots of vitamin E. Besides that, I'm not sure what kind of care she got. The smallest of her kids was her 3rd - he was 6 pounds 12 ounces, the largest was 8 pounds 1 ounce.

I've had the largest baby in the family (besides GD aunt who had 10 lb. 13 ou. baby)
Darlene was 9 pounds 6 ounces at birth. I smoked off and on too during the pregnancy (Long story, DENIAL about having a baby and yes, am a non-smoker now), and I ate pretty healthy I think. Maybe a soda too many once in a while, but I say pretty healthy. I'm overweight and I lost 2 pounds I believe.

My father was 6 pounds 3 ounces, born to a non smoking or drinking mama. BUT - she was one of the smallest preemies to survive. She was only 1 pound 15 ounces when she was born in 1939 I believe. She was slower her whole life...

So I don't know. I believe it is a combination of both...
post #14 of 26
I personally don't think it is either. LOL I mean, I guess it has to be something but... DH and I were both small babies and I didn't gain ANY weight with my pg due to hyperemesis and I had an almost 10 lb baby. So, who knows!
post #15 of 26
I'd never even thought about maternal weight gain being a factor. I gained about 25 pounds with each of my first two. Of course, there was a 10 year gap between my babies, as well. Do older moms have bigger babies? No GD here, so it's not that.
post #16 of 26
I want to chime in on this thread, too.

I was 8lb,7oz and my twin brother was 8lb,4.5oz. We were born on our due date. My mom smoked throughout her pregnancy, yet we were her biggest babies (of 5 kids).

My husband weighed 7lb,8oz at birth.

Our children had the following stats:

#1: girl, 7lb,12oz, 37 weeks gestation. I had horrible eating habits, but got lots of exercise during my pregnancy. Developed pre-eclampsia, which necessitated her early birth.

#2: boy, 8lb,14oz, 36 weeks gestation. I miscarried a twin at 20 weeks, had excessive amniotic fluid, preterm labor, pre-eclampsia and a premature birth. My dates were not off (#1 and #2 are only 10.5 months apart and an amniocentesis confirmed the due date) and I did not have GD. I ate much better (more healthy) than my previous pregnancy and continued to get daily exercise.

#3: girl, 6lb,11oz, 38 weeks gestation. I ate VERY healthy but didn't get much exercise during my pregnancy.

#4/#5: boy/girl twins, 5lb,8oz & 5lb,5oz, 35 weeks gestation. I ate extremely well during this pregnancy, but got very little exercise. I developed HELLP syndrome, which necessitated their early delivery. Had they gone to term, both babies would probably have been 8+ pounds each.

#6: boy, 9lb,12oz, 39 weeks gestation. I ate the most healthy of any of my pregnancies, gained the least amount of weight and had my biggest baby. I had no complications with this pregnancy at all. I joke that finally, at age 33.5, my body had figured out how to be pregnant. :LOL

So.......I don't know what the correlation is.
post #17 of 26
at 5lb, 13oz, I was the largest girl ever born in my maternal extended family.... until DD2 came into this world at 6lb 10oz (a virtual whopper, in comparison)!
DD1 was 5lb, 6oz
my sister was 5lb, 8oz
neice was 5lb, 4oz
my mother and her two sisters were all under 6lbs, as well as my female cousins, and my cousins' girl babies.
post #18 of 26
Originally Posted by Storm Bride
I'd never even thought about maternal weight gain being a factor. I gained about 25 pounds with each of my first two. Of course, there was a 10 year gap between my babies, as well. Do older moms have bigger babies? No GD here, so it's not that.
I don't think it does have much to do with it. I mean I see movie stars and models who take the opportunity of being pg to eat and eat and eat some more and gain 60lbs+ and give birth to an average size baby. On the other hand with #1 for me in particular I was very fit and exercised regularly until I have birth, gained 35lbs and had a 9lbs baby. 35lbs is within average weight gains and yet 9lbs isn't. With my next two I gained a bit more than 40lbs and one was just over and the other just under 10lbs. 10 year gap in between #2 and #3 but #3 was slightly smaller not larger than #2. I've always read that maternal weight gain was not particularly correlated to size. I mean if a woman who was underweight only gains 6lbs during pg yes ok she's probably going to have a small baby or if a woman gains 70lbs she could still easily have an average sized baby but I think it's a limited correlation. If you're on a strict diet then yes you may starve your baby and if you pig out at a certain point that's going to your butt not your baby but otherwise within reason I don't think your weight gain is the big factor.
post #19 of 26
There is a genetic factor involved -- the pp mentioned the paternal link to birth weight. I have read the same thing. (I've also read that the length of gestation is closely linked to the father's genetic contribution.) I think what we're missing here, though, is that every baby has their own genes. They may come from parents who were big or small, but they each have their own genetic code telling them how big to be, how tall they will be later in life, etc.

Our first baby was 10lbs. My DH and I were both big babies and are tall people. I probably gained 50lbs during my pregnancy. My second baby -- same parents, same maternal weight gain, same exact gestational age -- baby weighed 8lbs 9oz. She is just a smaller person. She still is a smaller person than her older sibling -- it's just who she is.

Obviously there is an environmental link as well. Adequate protein consumption leads to bigger babies. Other factors contribute to lower birth weight.
post #20 of 26
I have read somewhere that a mother carrying a donor-egg baby still has a baby along the same size as the other women in her family, rather than the size of the babies in the donor's family. It would be interesting to see if this is reliable information or not, and would put the whole discussion in a different light.
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