Only because you asked :
Your babies kidneys can have significantly less renal tubules than those of a nonsmoker's baby. Permanently, for life they can have poor renal function.
The SIDS stats are terrifying, and implicate smoking in many, many cases. Your risk of SIDS decreases amazingly if you don't smoke. The stats are broken down into whether or not you smoked in pg or the baby is just exposed post birth, and again, it does mske a difference if you stop now.
The placnta of a smoker is grey/black, gritty and degrading at birth, compared to the red, fleshy healthy ones
Think also of your dc1 & 2 - you increase their risk of respiratory illness, ear infections & hearing problems.
Think also of you, smoking related illnesses are awful. Smoking resets your brain so that when ypu become unwell medics cannot necessarily give you the oxygen ypu will badly want.
Think of your wallet, fags are so expensive. You could have that money towards a longer mat lwave, nice mat clothes, a nice baby bag etc.
It is so hard to give up because it is an addiction. Seek help & support. Good luck.