What factors afffects baby's birth weight?

OK, so I am trying for a VBA2C and ONE of the reasons that they think I had trouble with my last labour (aside from the fact that baby was posterior and I was tied down to the bed for my entire hospital part of my labour) was because she was 4.1kg when she was born. Which to me doesn't seem that big, yes it's not small, but she was no giant either. And they seem to think that I am small??? Before I was preg I was 55kg and 167cm tall (so I don't think that small??)

So, the Brisbane Mater is willing to let me give VBA2C a go, but they want to see me again at 34 weeks to do a scan and see what the size of the baby is then (which I have also heard is no guarantee), and then discuss if they are still happy for me to try a VBA2C ... which I know they can't say no to anyway.

So, my question is ... is there anything in particular that will affect the size of this baby? I put on quite a bit of weight with my last baby. I started at 58kg and put on 17.7kg. If I watch my weight this time (and no I'm not going to be crazy, but just watch the junk food etc) is that going to make a difference to the size of my baby?

Also does exercise affect the size of the baby? Someone said that because I exercise a lot, the baby got extra oxygen and therefore grew better???

Also, I didn't go into labour until 41 weeks. They won't induce me this time (thank goodness) and are happy to let me go over, but that also increases the size of baby ... the longer he/she is in there the more he/she grows.

So what can I do to help not having a big baby? Anything??

I don't think so - as far as I know, baby takes what it wants from you, but I dont' think it matters if you are putting in extra calories in, it will take what it needs to grow.

I know smaller women than you that have had huge babies (bigger than 4kg) so I don't think its necessarily a size thing, although my OB was concerned I had GD because DD1 was 3.9kg. I don't - I just breed good sized bubbas!

A lot is just down to genetics.
GD can affect birthweight but not all mums of big babies had GD ( mine were both over 4.5kilos)
Your baby will take what they need from you. You could always see a dietician if you want to.

Oh and just coming back in to mention that DD2 was lighter than DD1 - so it doesn't mean that the next one will weigh the same :D

I'm about the same size as you - apparently 'normal' pelvis - and had a 4.29kg baby at 42 weeks gestation. Due to fetal distress, the OB pulled him out with forceps. I figure if I'm flat on my back with legs in stirrups (ie, pelvis at smallest) and I can still fit forceps and a baby then I can birth a much bigger one in a better position.
I think the main determinant of a baby's size at birth is the functioning of your placenta. There's not much you can do about it unless you want to take up smoking...? That restricts blood flow to the placenta and can reduce baby's birth weight.

I weighed 97kg when I fell pregnant with DS. I was 108kg when he was born and he weighed 10lb 13oz or 4.9kg. Doctors say that its because of my weight. But I think it is due to how much nutrients etc the baby gets from you while you are pregnant, and genetics would also play a part. But who really knows. I am a firm believer that you grow a baby to size that your body can handle and birth. Obviously there are exceptions to the rule.

I really don't think anything affects it other that bub. Also the scans are totally not accurate. My first was 4kgs and she was 11 days late, they told me all along she would be a 'good' size 9whatever that means) and with DS I was attempting a VBAC and was having scans every 2 days from 6 days overdue up until 14 days over and they never once said anything about his size. I remember asking if he was big at the last scan at 12 days over and the answer was no he was average. He was 10lbs - 4.5kgs so really I would just trust that your body and baby know what they are doing and yes bub might be bigger and also might be smaller but either way you can do it! I am 5ft1 (156cms) too so not exactly tall for such big bubs and my gf who is about 5ft6 had a 10 lb14 bub naturally and then a 9lber and then her 3rd was 7 lb!!!

ETA: I put on 15kgs and 20kgs in my pregnancies respectively and was a starting weight of 65kg which is on the bigger side for my height but nothing major.

Well, I don't think there's anything you can do TBH.
Our babies were,

DD1 - 3.320kg (7lb5oz) 8 days post dates
DD2 - 3.885kg (8lb9oz) 7 days post dates
DS - 3.840kg (8lb7.5oz) 2 days early
DD3 - 3.450kg (7lb9oz) 5 days post dates

So no matter when bubs is born, they will just weigh what they weigh. I am not a big person. I do not believe for a second that your weight or gain have anything to do with it. I put on minimal amount of weight (5 - 6 kgs) in each pregnancy, but had good sized babies. They all have the same father & didn't get bigger the more I had as people expect.

Smoking 'may' make a difference, but I highly doubt you'd want to go there, & a friend of mine's DS was 10lb 10oz at 16 days post dates, even though she smoked through her pregnancy. Another friends bub was only 6lb9oz, less than her first, at 7 days post dates & I believe the smoking may have had an affect there.

Its all about the baby itself & chance. All I can say is do what you can do to have a healthy baby. Your body will take care of the rest.
I really don't think bub's size was the issue. The position of bub was more likely the problem.

What ever happens, good luck with your birth :)

I lost somewhere between 7 and 10 kilos last pregnancy and in the 3rd tri only put on 5 kilo of baby weigh...and P was a normal 8 pound 3 ounces...so I don't think exercise or HEALTHY weight loss/gain has any effect on the bub. That's not including dangerous eating habits, obsessive exercise or gestational diabetes of course.

My SIL was a VERY heavy smoker during pregnancy and she only had a 6 pounder, but not sure if the smoking had anything to do with that directly...although I have read that it makes babies smaller.

i have never smoked and i am regular ish height 165, had 2 babies on their edd's, 5lb 13- 2.65 and 6lb 2 oz- and there was nothing known to cause their weights. ate well and exercised, put on 20kg eeeeekkkkk! but they are both fine and healthy now.
I agree that you just have what you have, unless there are gd or complications i guess.
one thing i might add- i hate people saying " oh you had it easy" coz they were small. I hate that!

hope you have a fabulous vba2c x