We can’t change genes but we can have some impact on their expression (epigenetics). All your efforts to reduce allergic potential may not pan out but there are known factors that reduce a child’s risk of developing allergies. Healthy flora helps to prevent the development of allergies. The earlier formula supplements are given, the more likely a child will develop allergies at some point. Formula, iron supplements, or any solid foods or juices quickly disrupt the healthy flora that only exclusive breastmilk can provide. Even one bottle of formula in the first week or so is shown to prevent the gut flora from ever quite developing the highly protective gut milieu generally provided by exclusive breastmilk – allergy protective as well as immune protective.
Twins are a special challenge when it comes to exclusive breastfeeding. You might want to look into EatsOnFeets or HumanMilk4HumanBabies before the birth so you can have your finger on some donor milk options should the need arise (but I think you can do it all yourself !) Try to keep your newborns on exclusive breastmilk for at least the first several weeks; hopefully longer.
Of course, that’s just one link to allergy development. Studies are a little mixed on whether a mother can reduce the chances of her child developing allergies by avoiding foods during her pregnancy, though results slant a little toward it being worth the effort if there are significant concerns. Even though cow’s milk proteins are not one of your daughter’s allergies, they are the number one allergen and different children develop different allergies. I personally would try to avoid dairy, eggs, peanuts, and nuts after the 6 month point when it’s thought the fetus has enough immune system developed to possibly create some antibodies. The big time for your good 100% avoidance of these foods will be once your children are born.
Since twins are often born early and spend some time in the NICU, make sure you are in there with your first drops of colostrum to line their intestines as soon as possible after birth and keep it going. This will help to establish healthy flora before unwanted hospital flora begin to homestead. Colostrum also helps to speed the maturity of the newborn guts, reducing the chances of potential allergens leaking through their intestinal walls. Do not allow the hospital to supplement with formulas or “human milk fortifiers,” which come from cow’s milk, unless there are simply no other options for nourishment. (I have 3 pages of info on feeding preemies on my website – see links at top of this page to the other two: http://thebabybond.com/Premature_Infant_Feeding_Options.html) There are fortifiers made from solely human sources and these do not have drawbacks, but I don’t believe they’re very easy to acquire. (?) Most NICUs should have access to donor milk. If formula is required, amino-acid formulas are the least allergenic and highly hydrolyzed milk formulas are the next choice.
You can begin taking probiotics around 6 months’ gestation (as we assume the babies could come early) and continuing through a few of months after birth in order to increase the amount of flora you pass in your milk. Taking fish oil (DHA and EPA) to increase the omega-3 fatty acids in your milk can help reduce allergic potential as well. These measures can also help to heal your own flora, if needed, as your babies’ floras will depend greatly upon your own.