Breastfeeding while pregnant

I have heard and am still hearing different schools of thoughts on this : Is it ok for pregnant woman to breastfeed her child when she's pregnant?

Two friends (one who is about to give birth to the second child and the other who has just gave birth to her third child) told me recently that their doctors had advised them to stop breastfeeding their 1+ old toddlers when they are pregnant.And just today,one of my sisters-in-law advised me to do the same.They believe that it may be harmful to the unborn child or that the child may not be getting enough nutrients.

I checked on a baby website that I've religiously read since I was pregnant with my first.This is the excerpt :

Is it still possible to breastfeed my son while pregnant with my next baby?

Yes. Your body will carry on producing milk throughout your pregnancy. It's even possible to continue feeding your son after your new baby is born - this is called tandem feeding.

Breastfeeding during pregnancy is fine for most women, although it's important to eat well. Hormonal changes in the early days may give you sensitive nipples making breastfeeding difficult. Nipple stimulation through breastfeeding or making love will cause mild uterine contractions, but, for most women, these are not strong enough to create a problem. However, if you have a history of premature delivery or miscarriage,or if you are bleeding, then you might need to think about weaning your older child.

During the fourth or fifth months of your pregnancy, your milk reverts to colostrum (the nourishing pre-milk produced by your breasts in the first few days after birth), so the taste changes and volume decreases. Some children decide to wean themselves at this point, although others persevere. If your son wants to continue, don't worry about using your colostrum up; your body will continue to produce this special milk until your new baby needs it. If your son is under a year old, and therefore nutritionally dependent on your milk, you might need to keep track of his weight gain at this point.

It is also worth thinking about whether you want to continue feeding your son once your new baby arrives. If tandem feeding is not for you, it will probably be less traumatic to wean him while you are pregnant rather then waiting until the new baby arrives and he is in danger of feeling usurped anyway. If you are not yet pregnant, but trying, bear in mind that it can be harder to conceive while still breastfeeding, as some women find they don't ovulate until they wean.

I have yet to hear what my doctor has to say on this.I am,of course,still breastfeeding my son,but on lesser occasions even before I conceived my second.I only breastfeed him once before his nap,and two or three times during nightfeeds.

I would love to hear comments from mothers out there who are or had been in this situation.