For years, the received wisdom is that women should give birth earlier in their lives. There are a lot of reasons for this, many of them social, but there were medical justifications too. Children born to older women, say in their 40s, are more likely to have Down syndrome, develop Alzheimer’s, or diabetes. These arguments have convinced many people that childbirth should take place in the 20s or, at latest, the 30s in order to prevent thee natural aging of the reproductive system from interfering with a child’s health.

But according to new research, there are serious material benefits to waiting till later in life to give birth. Children born to older mothers tend to be taller, healthier, and better educated than their peers. The reason isn’t really biological though; it’s social. Every year that a woman waits to have a child is one more year that, in many countries, quality of life gets better overall. Better education, better health services, and the like mean that children born later are better off. This is the first study of it’s type, to place later childbirth within the larger social context, and not simply look at medical possibilities.

It can be hard to gauge this though. The example of a child born to a 40 year old mother in 1990 being better off than a child born to the same mother in 1970 forgets the fact that any other kid born in 1990 is better off than kids born in 1970. The choice of when to give birth is as much determined by individual factors as larger social factors. A woman might be better off, both materially and medically, in 1970 than in 1990, or the other way around. What it comes down to is an issue of planning parenthood and choosing to have children when the time is right for the mother.