Weight gain in pregnancy is related to all except:
Average maternal weight gain during pregnancy is 11-12 kg
Factors which affect maternal weight gain during pregnancy are:

Pre pregnancy weight: If the pre pregnancy weight is more than normal (obese), there is a tendency to gain excessive weight during pregnancy.
Race and ethnicity: American women tend to put on more weight during pregnancy as compared to Asians and Africans.
Socio economic status: Women from higher socio economic group have more weight gain as compared to women from lower socio economic group. This is because malnutrition prevents optimum weight gain.
Associated conditions like women with gestational/over diabetes mellitus, twins and polyhydramnios have higher weight gain during pregnancy
Parity: Multigravida females tend to gain less weigh than primigravida

Smoking does not affect maternal weight gain during pregnancy, Smoking affects fetal weight gain and is one of the causes of IUGR.
“Studies have, indicated a lack of relationship between smoking and maternal weight gain while demonstrating a direct relationship between smoking and fetal grown rate.” 
Remember:
Rapid weight gain, i.e. more than 0.5 kg a week or 2 kg per month is an early manifestation of preeclampsia.

Stationary or falling weight suggests IUGR or IUD.
In pregnancy – the amount of water retained is 6.5 L at term
Ethnicity
Smoking
Socio economic status
Pre conceptional weight