The last half century has seen a dramatic decline in the number of Catholic sisters in the US, but there are still pockets of growth, a new study reveals.

In 1966, the total number of women religious in the US stood at 181,421 but this figure has fallen substantially by 72.5 per cent to just 49,883 in 2014, according to the Center for Applied Research in the Apostolate at Georgetown University.

The study reports growth in smaller, newer institutes while the larger, more established institutes "are losing many older members who entered religious life decades ago".

"There are about as many women religious in the United States now as there were a hundred years ago," the report details.

The rate of decline was found to be roughly the same in traditionalist institutes as in less traditional institutes that do not wear the full habit.

The largest religious institute of women in the US is the Sisters of Mercy of the Americas, which in 2014 had almost 3,400 members, but this has still fallen considerably from the 13,000 it had in 1970.

The CARA researchers say a high concentration of elderly sisters characterises nearly all institutes of women religious in the US and is "perhaps the single greatest challenge to attracting new vocations".

Around a third of religious institutes in the US do not have any women in formation at present and among those that do, half have only one or two in formation.

However, an increase in vocations of women from diverse ethnic backgrounds and other countries beyond the US are helping to slow the rate of decline, with four in ten women entering in the last decade being of a non-Caucasian/Anglo race or ethnicity.

Many institutes of women religious have dealt with the steady decline in membership by reorganising their structures or merging with other communities.

And although the overall trend is decline, some institutes are experiencing growth that is more than just a temporary spike in membership.

These include institutes with established histories, like the Dominican Sisters of the Congregation of St Cecilia – known as the Nashville Dominicans.

The Religious Sisters of Mercy of Alma, in Michigan, is another example of an institute where the trajectory of growth points to further expansion in the foreseeable future. The community was established with just nine members in 1973 but is expected to be close to 100 by the end of the decade.

However, the report's authors add that the growing institutes are too few to affect the overall picture of decline.

"Whatever these institutes have done or are doing is unlikely to offset losses in the tens of thousands elsewhere. It is simply not enough," they write.

One interesting case is that of the Sisters of Charity of Seton Hill, in Greensburg, Pennsylvania. Although it is experiencing the same steady decline as other institutes, overall numbers have been buoyed by fruitful international mission in South Korea where more women have joined their fold.

Today, over half of the sisters belonging to Seton Hill are ministering in South Korea, and are a mix of US-born and native South Koreans.

"In the case of the Sisters of Charity of Seton Hill, therefore, the mission territory experienced a more robust growth in vocations than its original US foundation," the report says.

"Perhaps one day, the United States will itself become the mission territory of this religious institute with sisters coming from South Korea to minister here."