Mothers are used to waiting nine months before delivering their babies, but it seems the actual process of giving birth now takes more time than ever before.

In a study just published in the American Journal of Obstetrics and Gynecology, researchers found that for the first stage of delivery alone, labor rates have increased by almost three hours for first-time moms.

Investigators began by collecting delivery room statistics going back to the early 1960s. They then compared more than 140,000 births spanning almost five decades. Over the years, several physical differences were apparent in the women, including a higher body mass index in those delivering more recently. Those delivering after the turn of the century were also, on average, four years older. Both of these factors, noted the researchers, could contribute to longer labor.

Additionally, the investigators looked at delivery room practices and found that years ago doctors relied more on medical interventions, including the episiotomy, a surgical procedure to enlarge the vaginal opening during delivery, and the use of forceps, which were used to remove the baby from the birth canal. Both routines may well have led to quicker birthing times.

The researchers also point to the use of epidural anesthesia. This injection of painkillers helps decrease labor aches, but is also known for increasing labor times. For those moms giving birth in the past 10 years, epidural injections were used in more than half of deliveries, compared with just 4 percent of deliveries forty years ago.

Although the investigators could not point to one overriding factor, they concluded that all of the differences, when taken together, would result in longer labors. They say a re-evaluation of labor room procedures could help shorten the process and help mom and baby meet just a little more quickly.