From NHS website:
When you smoke, you breathe in over 4,000 chemicals from the cigarette. The smoke goes from your lungs, into your bloodstream and that blood flows to your placenta and umbilical cord, right into your babys body. This causes your baby to struggle for oxygen and their tiny heart to beat even faster. The chemicals from the cigarette smoke also stop essential nutrients from reaching your baby. This affects:
your babys heart, making it work harder
your babys growth rate
the development of your babys brain
Effects on your babys health
If you smoke during pregnancy, your baby:
is at increased risk of stillbirth
is more likely to be born early (prematurely; before week 37 of the pregnancy), which can cause feeding, breathing and health problems
wont cope as well with any birth complications
is more likely to be born underweight. On average, babies of smokers are 200g (8oz) lighter than other babies. A low birth weight adds to the risks of stillbirth, and makes your baby weaker and at greater risk of disease with a higher risk of hearing loss, learning difficulties and sight problems as well as cerebral palsy
is more likely to have a problem keeping warm
is at increased risk of cot death
is more likely to get infections as a child, such as inflammation of the middle ear, and have health conditions that require hospital treatment, such as asthma
is more likely to smoke when theyre older
Low birth weight in babies is also linked to problems that develop as an adult, such as:
coronary heart disease: when your hearts blood supply is blocked
type 2 diabetes: a condition caused by too much glucose in the blood
Effects on your health
If you smoke during pregnancy:
youre more likely to have morning sickness
youre more likely to have complications during the pregnancy for example, an ectopic pregnancy (when a fertilised egg implants itself outside the womb)
your risk of miscarriage and having a stillbirth is increased
your risk of a premature birth is increased
youre at increased risk of placental abruption (when the placenta detaches from your womb before your baby is born), which is dangerous for both you and your baby
Smoking also increases your risk of:
cancer: nine out of ten cases of lung cancer are caused by smoking
heart disease: smokers are twice as likely to have a heart attack than people who have never smoked