In wealthy countries, some very premature babies are saved in intensive care units. In poor countries, they often die or develop blindness, retardation, lung problems or cerebral palsy.

Now a new study has found that in women at high risk of premature birth, a pessary — a small silicon collar placed around the neck of the cervix (as seen on ultrasound, above) — may delay birth until a newborn has a greater chance of survival.

It also appears affordable, at least in middle-income countries, since pessaries cost less than $50 each and could be made cheaply if demand was greater. Placing one normally requires an ultrasound scan, but ultrasound machines are fairly common in hospitals and clinics in all but the poorest countries.

The study, published in The Lancet last month, was the first randomized trial of pessaries for this purpose.

Various pessary designs have been around for centuries, usually to prevent the uterus from prolapsing into the vagina or causing stress incontinence.

For this trial, doctors at five Spanish hospitals divided in half a group of 385 women, all of whom had cervixes less than an inch long, which put them at high risk for early labor. Only 6 percent of the women who got pessaries give birth prematurely, compared with 27 percent of those who did not get them.

Exactly why pessaries delay labor is unclear. In an editorial, The Lancet said the study raises the “novel and exciting possibility” that the load-bearing capacities of pelvic organs are important in pregnancy and starting labor.