Hello Dr. Ragab, here are some answers to your questions:

>>1} milk composition changes when the nursing mother get pregnant?
Yes. First, total milk supply drops, sometimes substantially. Most will
notice the change beginning around 6 weeks gestation. Around the 5th month,
the milk reverts to a more colostrum-like secretion. This is about the time
that colostrum is normally secreted during any pregnancy. The milk is still
excellent for the nursling!

>>2} does she has to stop, or continue nursing( why, when )
Usually she does NOT have to stop, although she may get very sore nipples
which are caused by the hormone changes. Some moms stop because of the
discomfort; others continue anyway. Continued breastfeeding has NOT been
shown to increase the risk of miscarriage. Many older nursing babies will
wean on their own because they don't like the taste changes in the milk as
it decreases in volume. (higher in sodium, lower in lactose)

>>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!)
No, unless her pregnancy is so risky that she has to give up all sexual
activity. Older nursing babies just don't stay at breast that long, so the
contractions are minimal. The mother should eat sufficient calories for the
pregnancy plus about 250-500 extra for lactation.

>>4} is there any deleterious effect on the baby breast fed while the
mother has become pregnant
No, not directly. Her milk supply will decrease so the child will need
another source of calories in addition to the milk which would be
age-appropriate anyway. As milk volume decreases, the protective properties
of milk are more "concentrated" so any milk the child receives is
beneficial, and of course the comfort at breast is wonderful too. Some
pregnant mothers get very annoyed at the still-nursing child, partly
because of the nipple soreness, and will press the child to wean before the
new baby is born. Whether to continue or wean is a difficult decision for
the mother - she wants to meet the needs of her nursling, yet still focus
on the unborn baby/newborn. We can be comfortable supporting either decision.

>>please reply, and what references have u got
An excellent reference is Dr. Ruth Lawrence's book "Breastfeeding, A guide
for the Medical Profession." La Leche League is another good source - their
web site is http://www.LaLecheLeague.org.
>>          dr.  amin ragab
>>            cairo , egypt

Some older nursing babies continue to breastfeed after the new baby is
born, which is referred to as "tandem nursing." This is fine for both the
older child and new baby, although some effort should be made to make sure
the new baby gets plenty of time at breast in the first few days for many
reasons.

By the way, I continued to breastfeed my first and second children into
subsequent pregnancies, and have been a breastfeeding counselor for 27 years.

Best wishes,
Linda J. Smith, BSE, FACCE, IBCLC
Lactation consultant in private practice: Bright Future Lactation Resource
Centre
Dayton, Ohio USA where it is snowing gently tonight
http://www.bflrc.com