Introduction

The management of both the first and second stages of labor have come under increased scrutiny due to the rapidly escalating use of cesarean delivery. The overall cesarean rate in the United States reached a record high of 32.9% in 2009 after more than a decade of continually rising rates. To put this trend into perspective, this rate represented a nearly 60% increase compared with the 20.7% rate in 1996. A workshop of the Society for Maternal-Fetal Medicine (SMFM), the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), and the American Congress of Obstetricians and Gynecologists (ACOG) was convened in 2012 to address the rising cesarean delivery rates. In brief, the workshop and the following 2014 ACOG/SMFM Obstetric Care Consensus concluded that the accepted upper limit of the second stage of labor should be increased before cesarean delivery is performed ( Table 1 ). For example, it was recommended that ≥4 hours should be allowed in the second stage of labor in nulliparous women with regional analgesia before a labor arrest disorder was diagnosed. The result is that the acceptable length of the second stage of labor now exceeds the obstetrical precepts that have been in use for more than 50 years in the United States. The NICHD workshop leaders emphasized that the new definitions of second-stage labor “…vary somewhat from published criteria and are recommended in recognition of more recent findings regarding labor progress that challenge our long-held practices….”

These very recent changes in the acceptable upper time limits for the second stage of labor set a new obstetrical care standard after >50 years of concern that long duration placed the unborn infant at risk. Have these recommendations to increase the limits of the second stage been proven to be safe? We now present our findings on the evidence used to support this new recommendation.

20th Century background on second-stage labor

The purpose in providing this background sketch of how the prevailing second stage rules up until the 2014 Obstetric Care Consensus document evolved is to provide historical context. As the reader will quickly recognize, the evidence concerning the safety of second stages >3 hours in nulliparous women with epidural and >2 hours in similar parous women is dated since most of the studies were performed when the requirements for suitable evidence were not as well developed as they are today. We present this background context not to suggest that the pre-2014 second-stage rules are necessarily correct or incorrect–but so that the reader can have a perspective on how US obstetrics got to where it is until 2014 vis-à-vis second-stage rules until 2014.

The 2-hour maximum limit for the second stage in nulliparous women was described in US obstetrics at the beginning of the 20th century when J. Whitridge Williams observed in the 1903 edition of Williams Obstetrics that longer intervals were injurious to the mother and infant. In the subsequent early years of the 20 ^th century, DeLee popularized the use of “prophylactic” forceps delivery to terminate the second stage at 2 hours. The advantages of such prophylactic forceps included protection of the maternal perineum as well as protection of the infant from a prolonged second stage. The 2-hour second-stage maximum limit appears to have become the US standard following the 1952 landmark study by Hellman and Prystowsky on the effect of the duration of the second stage of labor on infant death. In their study of >13,000 deliveries at Johns Hopkins Hospital in Baltimore, MD, Hellman and Prystowsky reported increased infant mortality after 2.5 hours in the second stage ( Figure ).

Data from Hellman and Prystowsky in 1952

Data from Hellman and Prystowsky in 1952 demonstrating increased infant mortality after 2.5 hours of second stage.

Leveno. Second-stage labor: how long is too long? Am J Obstet Gynecol 2016.

In 1977, Cohen published an investigation of the infant effects of the duration of the second stage at Beth Israel Hospital in Boston, MA. He studied 4403 term nulliparous women in whom electronic fetal heart rate monitoring had been used during labor. No significant increase was observed in stillbirth or newborn deaths with progressive lengthening of the second stage although the frequencies of newborn deaths were too small to permit meaningful statistical analysis. Cohen concluded that elective termination of the second stage of labor after a defined time period was not indicated in the absence of fetal hypoxia. Although newborn mortality was not measurably affected by second-stage labor >2 hours, infant condition at birth as measured using 1-minute and 5-minute Apgar scores <5 was significantly worse when the second stage was ≥3 hours. Epidural analgesia was used commonly in the Cohen series and it was thought to likely account for the large number of pregnancies with second-stage labors >2 hours but lasting <3 hours. Indeed, these data likely also influenced the recommendations by ACOG in 1989 to permit an additional hour for the second stage when regional analgesia was used.

In 1992, Saunders et al analyzed 25,069 births at 17 maternity hospitals in the vicinity of London, United Kingdom. A total of 2.3% of these women had second-stage labor ≥3 hours. Like Cohen, these investigators concluded that second stages up to 3 hours were safe for the infant. Also like Cohen, rates of stillbirths plus newborn deaths were too few to comment on the effects of prolongation of second-stage labor given the small number of women undelivered >3 hours.

Menticoglou et al challenged the prevailing dictums on the duration of the second stage based on their experiences in Canada. These dictums came under scrutiny at their hospitals because of the neonatal injuries associated with forceps rotations performed to shorten the second stage of labor. As a result, they allowed longer second stages in the hope that fewer operative vaginal deliveries would be necessary. In their report of >6000 nulliparous women wherein labor epidurals were used in 55%, second-stage labors exceeded the 3-hour limit in 11% of women. The length of the second stage, even in those lasting up to 6 hours, was not associated with adverse infant outcomes. These good results were attributed to careful use of electronic fetal monitoring and scalp pH measurements during labor. That said, rates of neonatal outcomes of interest were remarkably low therefore limiting measurable effect size. Nonetheless, they concluded that there was no compelling reason to intervene with a possibly difficult forceps or vacuum extraction based on prespecified permissible lengths of the second stage of labor. They offered, however, an important caveat. After 3 hours in the second stage, delivery by cesarean or other operative method increased progressively such that by 5 hours for example, the prospect for a spontaneous vaginal delivery in the subsequent hour was only 10-15%.

20th Century background on second-stage labor

The purpose in providing this background sketch of how the prevailing second stage rules up until the 2014 Obstetric Care Consensus document evolved is to provide historical context. As the reader will quickly recognize, the evidence concerning the safety of second stages >3 hours in nulliparous women with epidural and >2 hours in similar parous women is dated since most of the studies were performed when the requirements for suitable evidence were not as well developed as they are today. We present this background context not to suggest that the pre-2014 second-stage rules are necessarily correct or incorrect–but so that the reader can have a perspective on how US obstetrics got to where it is until 2014 vis-à-vis second-stage rules until 2014.

The 2-hour maximum limit for the second stage in nulliparous women was described in US obstetrics at the beginning of the 20th century when J. Whitridge Williams observed in the 1903 edition of Williams Obstetrics that longer intervals were injurious to the mother and infant. In the subsequent early years of the 20 ^th century, DeLee popularized the use of “prophylactic” forceps delivery to terminate the second stage at 2 hours. The advantages of such prophylactic forceps included protection of the maternal perineum as well as protection of the infant from a prolonged second stage. The 2-hour second-stage maximum limit appears to have become the US standard following the 1952 landmark study by Hellman and Prystowsky on the effect of the duration of the second stage of labor on infant death. In their study of >13,000 deliveries at Johns Hopkins Hospital in Baltimore, MD, Hellman and Prystowsky reported increased infant mortality after 2.5 hours in the second stage ( Figure ).

Data from Hellman and Prystowsky in 1952

Data from Hellman and Prystowsky in 1952 demonstrating increased infant mortality after 2.5 hours of second stage.

Leveno. Second-stage labor: how long is too long? Am J Obstet Gynecol 2016.

In 1977, Cohen published an investigation of the infant effects of the duration of the second stage at Beth Israel Hospital in Boston, MA. He studied 4403 term nulliparous women in whom electronic fetal heart rate monitoring had been used during labor. No significant increase was observed in stillbirth or newborn deaths with progressive lengthening of the second stage although the frequencies of newborn deaths were too small to permit meaningful statistical analysis. Cohen concluded that elective termination of the second stage of labor after a defined time period was not indicated in the absence of fetal hypoxia. Although newborn mortality was not measurably affected by second-stage labor >2 hours, infant condition at birth as measured using 1-minute and 5-minute Apgar scores <5 was significantly worse when the second stage was ≥3 hours. Epidural analgesia was used commonly in the Cohen series and it was thought to likely account for the large number of pregnancies with second-stage labors >2 hours but lasting <3 hours. Indeed, these data likely also influenced the recommendations by ACOG in 1989 to permit an additional hour for the second stage when regional analgesia was used.

In 1992, Saunders et al analyzed 25,069 births at 17 maternity hospitals in the vicinity of London, United Kingdom. A total of 2.3% of these women had second-stage labor ≥3 hours. Like Cohen, these investigators concluded that second stages up to 3 hours were safe for the infant. Also like Cohen, rates of stillbirths plus newborn deaths were too few to comment on the effects of prolongation of second-stage labor given the small number of women undelivered >3 hours.

Menticoglou et al challenged the prevailing dictums on the duration of the second stage based on their experiences in Canada. These dictums came under scrutiny at their hospitals because of the neonatal injuries associated with forceps rotations performed to shorten the second stage of labor. As a result, they allowed longer second stages in the hope that fewer operative vaginal deliveries would be necessary. In their report of >6000 nulliparous women wherein labor epidurals were used in 55%, second-stage labors exceeded the 3-hour limit in 11% of women. The length of the second stage, even in those lasting up to 6 hours, was not associated with adverse infant outcomes. These good results were attributed to careful use of electronic fetal monitoring and scalp pH measurements during labor. That said, rates of neonatal outcomes of interest were remarkably low therefore limiting measurable effect size. Nonetheless, they concluded that there was no compelling reason to intervene with a possibly difficult forceps or vacuum extraction based on prespecified permissible lengths of the second stage of labor. They offered, however, an important caveat. After 3 hours in the second stage, delivery by cesarean or other operative method increased progressively such that by 5 hours for example, the prospect for a spontaneous vaginal delivery in the subsequent hour was only 10-15%.