Here’s a good comeback for the next time someone again asks you that dreaded question: When are you going to have a baby? Just tell them you want your baby to be smarter. According to a new study from the London School of Economics and Political Science, waiting until you’re better established in life can boost your baby’s brain power.

Researchers studied results of cognitive tests of children born to mothers between the ages of 25 to 29 and 35 to 39. They looked at data from children born in 1958, 1970 and 2001 who took cognitive tests at ages 10 and 11. In the earlier years, kids born to young mothers posted higher scores than those born to older moms. But in 2001, the reverse was true — the children of older moms scored higher. The study results were published in the International Journal of Epidemiology.

Experts say one reason may be because in the past, moms at older ages were having their third or fourth child — not their first, as is often the case these days. It’s much easier to work on reading and language skills for one child than it is if you’re trying to raise two or three others.

Modern thirty-something moms often have the advantage of better education, solid careers and healthier lifestyles — especially, not smoking — compared with their younger counterparts. On the other hand, they can face greater health risks during pregnancy and childbirth and must conquer the challenge of having less of the energy needed to raise their children as they grow older.

So, ignore those folks who seek to remind you that the clock is ticking on becoming a parent. It may be in the best interest of your baby to wait a bit.