I don't know about heart defects but the hospital gave it to me at 21wks and 26wks for severe nausea and vomiting. It gave me terrible constipation but baby's heart is fine according to last scan at almost 32wks.
I took it very early on in my pregnancy. I'm 25 weeks now and baby girl is just fine.
Yeah I'm taking it for that to. When I took it it gave me a headache and I had the chills but I feel completely better now.
I took it my entire first pregnancy my son is now a healthy 3 1/2 year old.