Expert says, the birth rates in the United State (US) have dropped to their lowest rate in 30 years, marking a cultural shift as women delay motherhood.

Some 3.85 million babies were born in the US in 2017, the fewest since 1987, as births among women in their teens and 20s decreased.

Both the number of births per thousand - and fertility - a lifetime average forecast - fell.

Declining birth rates are common as countries become more developed.

The US fertility rate is lower than the UK's but the US still has a higher fertility rate than many other countries.

While births decreased among younger women in the US last year, it rose in women aged between 40 and 44.