This study makes me feel a lot better about "forgetting" to take prenatal vitamins (except for maybe once a month or so). The truth is I've just never felt good about taking them. I prefer to get my vitamins from real foods. So it's not that I didn't get plenty of folic acid in my early pregnancy. I did--peas, broccoli, greens, cereals, etc. Just not from pills.
I'd be interested to see whether folic acid from real food sources has the same negative effect on infants? I'd wager NO. Anyway... I've never been very good about taking prenatal vitamins and my kids have avoided asthma and have never had respiratory tract infections. Interesting.