1} milk composition changes when the nursing mother get pregnant

It is said that breastmilk returns to being colostrum during
pregnancy.  I am not sure of this, but it is possible.  It does seem
that the milk supply decreases when the mother is pregnant.

2} does she has to stop, or continue nursing( why, when )

No she does not have to stop.  I am vaguely aware that WHO/UNICEF have
a statement out urging mothers to continue breastfeeding when
pregnant.  Many mothers continue nursing an older child and the new
baby.  My wife nursed 7 months while pregnant.


3} is there any deleterious effect on the fetus of a nursing mother
(growth potential differences in utero, increase risk of uterine
contractions while his brother is sucking = oxytocin release!)

There is no evidence of any problems.

4} is there any deleterious effect on the baby breast fed while the
mother has become pregnant

If the baby is still exclusively breastfeeding when the mother becomes
pregnant it is quite possible that the decreased milk supply
associated with pregnancy might cause real problems.  This is an
unusual situation, however.

Jack Newman, MD, FRCPC