Not really MORE but be sure to use ENOUGH. Chlorine is what your city uses to purify your drinking water. Doseages while backpacking are a few times higher, because you have less contact time, but again, please use enough chlorine treatment while pregnant.
If you contract some bacterial disease, several antibiotics can be used during pregnancy, but when there are such demands on your body, better to not get sick at all.
And if you get a parasite? That's bad. That's why pregnant women are advised to not eat sushi - the slight chance of getting a multi-cellular parasite. There are drugs to treat various parasites, but when pregnant, you're trying to nurture a particular multi-cellular "parasite" in your uterus and most (all?) anti-parasite drugs are known to cause fetal damage.
I (civil engineer) have backpacked and world-traveled during my (MD) wife's three pregnancies. She's carrying more weight, especially late in the pregnancy. He can carry a little more fuel to boil water and, when treating with chlorine, carry the treated water a little longer for her (more contact time) to be as safe as possible.