Contrary to popular belief, you are NOT risking miscarriage while nursing your toddler. As long as you are not at risk for miscarriage or premature labor, nursing while pregnant is perfectly safe! A friend of mine was still nursing her toddler and switched ob's 3 times before she found one that supported her nursing while pregnant. Unfortunately even practitioners are misinformed about breastfeeding!
From Dr. Sears website: "This was a topic of debate many years ago. It used to be felt that breastfeeding while pregnant can steal important nutrients from the fetus and can increase the risk of miscarriage. Now we know that this is not true. Many research studies have demonstrated no nutritional risk to the fetus, and no increased risk of miscarriage. I encourage pregnant moms to continue to breastfeed as long as they want to.
There is, however, one situation where breastfeeding during pregnancy is NOT considered safe. For moms who have a history of miscarriages or preterm labor (labor beginning before 37 weeks gestation) with previous pregnancies, breastfeeding may increase the risk of these events occurring again. Why? Because breastfeeding releases a hormone into mom's bloodstream that can cause the uterus to contract. If a mom's uterus is especially sensitive to this hormone (i.e., if a mom has had preterm labor or miscarriages before) then breastfeeding MAY trigger the uterus to contract.
However, most women's uteruses are NOT sensitive to this breastfeeding hormone. It is therefore safe to breastfeed during pregnancy.
You should discuss this issue with your own midwife or obstetrician.
And this is from La Leche League:
Good luck Momma!