But when women put off having children until their mid-30s, they have fewer children.

FORBES: Warning Bell for Developed Countries: Declining Birth Rates

Anna Cristina d'Addio, an expert on fertility policy at the OECD in Paris, thinks they will probably have fewer children in total than if they had started earlier, even though more of them now give birth in their 40s.

ECONOMIST: Most of the rich world is short of babies

The question is whether they have the same number of children as before but later, or whether they will have fewer overall.

ECONOMIST: Most of the rich world is short of babies

They are also likely to have fewer children as well as own major household durable goods.

CNN: Are one in three Africans really middle class?

But contraceptive access needs to be backed by better health infrastructure - we have abundant evidence that when parents are confident that their children will survive, they will have fewer and invest more in each of them.

CNN: Africa's birth rate: 'Why women must be free to choose'

Demographics consultant Paul Seversky, who analyzes data for districts considering reorganizing services, cited declining birth rates as people wait longer to have children and have fewer once they start.

WSJ: Declining NY enrollment blurs district lines

But they produce children who learn better, develop critical life skills, have fewer problems in childhood and adolescence, commit fewer crimes, earn more money, and just generally live happier, stabler, more productive lives.

FORBES: The Importance of Early Childhood Intervention on Student Achievement