(Reuters) – many things are faster now that 50 years ago, but the arrival in the world of a baby in a natural way seems to not be one of them, according to a study of the U.S. Government.

Compared to the 1960s, American women have taken in the last two years or three hours longer in giving birth, according to the researchers of the National Institute of American health care, which they said the finding suggests that doctors may need to rethink the definition of what is a “normal” birth.

According to data published in the American Journal of Obstetrics & Gynecology, additional time is derived from the first stage of labor – the longest part of the process, before the stage of “push”.

Mothers are also different. On average, they are older and weigh more, and their newborn infants are also larger.

“But even when we take into account these demographic changes, childbirth is even longer,” said principal researcher Katherine Laughon, of the National Institute of child health and human development.

Although Laughon said that the study could not fully identify possible reasons for the difference, one partial explanation could be the relief of pain of the anesthesia epidural, which is much more common today than 50 years ago. It is known that the epidural may slow delivery between 40 and 90 minutes.

Data are based on two Government studies in different decades.

One, between 1959 and 1966, included some 39,500 women who gave birth at that time, while the other tracked more than 98,000 women who had a baby between 2002 and 2008. All women had a natural, not induced childbirth.

When arrives the time of delivery, first-time mothers in recent years take 2.6 hours longer in the first stage, compared with their counterparts in the 1960s. The difference was reduced to two hours in women who had already been mothers previously.

Current women are much more likely to use anesthesia epidural – 55 per cent, compared with 4 percent of the of 50 years ago. Twelve percent had a delivery by caesarean section compared with three per cent in the 1960s, while 31 percent them was oxytocin, which stimulates contractions, compared to 12 per cent of 50 years ago.

Laughon pointed out that many more women have now caused births or caesarean section planned compared with a few decades ago, so the number of women who currently have a natural childbirth may differ in some way of its counterparts of 50 years ago.

But whatever the underlying reasons, doctors may need to redefine the idea of a “normal” birth, a concept which is based on the form of giving birth of women half a century ago.

For example, doctors have thought that a birth is abnormal if there is no change in the neck of the uterus after two hours in the part “active” of the first stage of labor. At that time, you can intervene either giving oxytocin or doing a c-section.

Laughon stated that the conclusion is that there would be a new concept of “normal”, adding: “I think that we need to revise the definition of”abnormal”delivery, and the time in which it can intervene”.

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