Codeine

[Ele34]

How many Weeks before birth do you stop taking codeine phosphate so it doesn't affect baby at birth

From bumps:

Breathing problems at birth
Codeine affects breathing in some people. It is possible that codeine taken by a mother near delivery may be still in a baby’s bloodstream at birth and could cause the baby to have temporary breathing problems. Only one small study has investigated this. Although this study did not show that babies exposed to codeine during pregnancy are at increased risk of having breathing problems around the time of birth, information on more pregnant women is needed to be sure.

If you have taken codeine around the time of delivery your doctor may advise that your baby’s breathing is monitored after birth. If you are likely to be taking codeine towards the end of pregnancy it is advisable to plan, with your health care provider, where you are going to have your baby so that, if necessary, arrangements for your baby to be monitored are already in place.

Withdrawal symptoms at birth (‘neonatal withdrawal’)
Codeine is altered in the body to morphine. Studies have shown that some babies who have been exposed to morphine in the womb experience withdrawal symptoms after birth (as a result of no longer getting morphine through the placenta). Taking codeine near to the end of pregnancy may also cause neonatal withdrawal. If you have taken codeine around the time of delivery your baby may be monitored for a few days after birth.

It doesn't say in weeks. Just around the time of labour.

Withdrawal from morphine is usually around a week.