The goals of our research were to describe the frequency and outcomes of prolonged second stage of labor in freestanding birth centers, under current practice conditions. We found that 2.3% of healthy nulliparous women giving birth in freestanding birth centers, and 6.6% of parous women, had prolonged second stages of labor. Even in this low-risk group of women, as the length of the second stage of labor increased, transfers for complications were significantly more frequent for all newborns, and maternal postpartum transfers for complications were significantly more frequent for multiparous women. For multiparous women, hemorrhage, retained placenta, maternal fever, and severe perineal lacerations were more common with longer second stages of labor; for their newborns, use of positive pressure ventilation and sepsis were more common. Hemorrhage and retained placenta were more common for multiparous women despite more frequent use of active third stage management for women with prolonged second stage of labor, suggesting use of active third stage management was suboptimal in this sample. Indications for transfers also differed with longer second stages for multiparous women; higher proportions of maternal postpartum transfers were for repair of severe laceration and higher proportions of newborn transfers were for respiratory problems.
Incidence of some of the outcomes in the study differ from generally quoted incidence of these complications, likely reflecting distinctive aspects of the population. Reported postpartum hemorrhages in our dataset, between 9.7% and 16.1% depending on group, are higher than nationally reported incidence of 1 to 5% [23]. In this dataset, postpartum hemorrhage was defined as estimated blood loss of greater than 500 cc, as opposed to the new, more stringent definition of blood loss greater than 1000 cc. Additionally, birth centers primarily reported estimated blood losses, which are less accurate than quantitative blood losses [24]. As average blood loss from vaginal birth is approximately 500 cc, these percentages of women exceeding 500 cc seem realistic [25]. Fewer than 10% of women reported with blood losses greater than 500 cc required transfer to the hospital for care, supporting that the majority of cases of hemorrhage had estimated blood loss slightly greater than 500cc and did not result in substantial morbidity. Studies of home birth have found similar incidence of blood loss greater than 500 cc [26]. The incidence of maternal postpartum fever of 0.0 to 0.5% is lower than the generally quoted 1-4% incidence of chorioamnionitis, but reflects that birth center midwives will transfer women to the hospital who exhibit fever during labor [27]. Few newborns required positive pressure ventilation, but we were unable to determine frequency of positive pressure ventilation in a similar low risk group.
This is the first study demonstrating that for births in a community setting, postpartum and neonatal complications requiring transfer to the hospital are more common as the length of the second stage of labor increases. Consistent with data from hospital studies, even in this low risk, low-intervention population, maternal [1, 8, 28,29,30,31] and newborn [1, 8, 28, 29] complications were higher with longer second stages. Apparent lower rates of transfer among primiparous women with second stages longer than 4 hours are likely due to small numbers of women in this group. There were significantly more perinatal deaths (intrapartum and neonatal) for multiparous women with second stage labors longer than 2 hours, but given small numbers, (3 deaths each for second stages shorter and longer than 2 hours), this should be interpreted cautiously. These outcomes occurred despite the fact that midwives transferred women to the hospital during labor if they developed risk factors that made the midwives think that the hospital was the more appropriate birth site.
Our finding that indications for transfer change for multiparous women and their newborns after longer second stage labor is novel, but consistent with research performed in hospital settings. A higher proportion of women transferred for repair of severe perineal lacerations after a long second stage; this is consistent with hospital studies finding that these lacerations are more common with prolonged second stage [1, 8, 29]. Similarly, more newborn transfers were for respiratory issues after prolonged second stage. This is consistent with hospital studies finding that newborns born after prolonged second stage have higher incidence of low Apgar scores, umbilical artery pH less than 7, need for resuscitation, and intensive care unit admission [1, 29].
This study should not be interpreted as making general statements about complications of prolonged second stage, which have been well-established. The sample we analyzed was highly censored. Women who began labor in the birth center transferred to the hospital during both the first and second stages for various indications, including prolonged second stage of labor itself. Thus, we cannot make general statements about outcomes of prolonged second stage. Rather, results should be interpreted in light of the aims of the study, to describe outcomes of prolonged second stage as it currently occurs in freestanding birth centers. When interpreted in this light, its value is highlighting that even when midwives follow clinical practice guidelines and use their best clinical judgment to transfer women at high risk, complications are still more frequent in women with prolonged second stages.
This study represents the first time birth center providers have data from their practice setting to use for development of clinical practice guidelines. We found that most birth centers have practice guidelines for management of the second stage of labor that include transfer to the hospital setting after a certain length of time without progress. Given the findings that even with continually progressive second stages resulting in spontaneous vaginal births, medical indications for postpartum and newborn transfer to a hospital increase with longer second stage of labor, birth center providers and their consulting physicians should consider guidelines that include transferring women to hospital after a fixed number of hours of pushing. Consistent with research on prolonged second stage in hospitals, there does not appear to be an inflection point where outcomes worsen dramatically, but rather a steady increase in complications [3]. Precise guidelines for transfer timing would depend on distance from the hospital and a birth center’s individual circumstances, but midwives should be concerned about long second stages and a time frame between 2 and 3 hours for transfer might balance likelihood of safe vaginal birth with maternal and newborn risks.
In future analyses using this dataset we will explore further questions. The first is whether outcomes would be better if women were transferred to the hospital sooner during prolonged second stage of labor. For newborns, the most common indication for transfer was respiratory issues. These could potentially be mitigated by operative birth to end the second stage of labor and so might support earlier transfer. The most common indication for postpartum transfer for multiparous women was for repair of severe perineal lacerations. It is possible that perineal outcome for a spontaneous vaginal birth would be similar regardless of birth site, but exploration of this complication could provide information to guide clinical decision-making. A second area of research is whether we can identify characteristics that are associated with better or worse outcomes after prolonged second stage of labor. Perhaps better risk stratification could guide decision-making about transfers.
This study benefits from the use of a large, validated, national dataset that allows us to explore relatively rare outcomes. It has the limitations of any observational study based on a clinical dataset. While transfers, the primary outcomes, are required fields in the PDR and are consistently documented and have been validated [20], there is a substantial amount of missing data for the exposure (length of second stage) and some secondary outcomes, and these findings should be interpreted cautiously. Length of second stage was collected as a categorical variable, and the ranges go up to 1.5 hours. Thus, we do not know, for instance, how risk changed between 2 and 3.5 hours of second stage of labor. The highest category is for greater than 5 hours, not allowing us to explore outcomes of very long second stages of labor separately. Additionally, length of second stage may not have been collected consistently across all birth centers, as not all midwives perform vaginal exams to confirm full dilatation. It is unlikely, however, that any research protocol could precisely capture the moment of full dilatation to document onset of second stage labor. We believe that the possibility that there is some under-reporting of the length of second stage does not diminish the main results of this research. Since only approximately one third of birth centers contribute data to the PDR, birth centers that contribute data may differ in a systematic way from birth centers that do not contribute data. They may have more staff, which could facilitate data collection, or may be more connected to AABC, which could result in more use of AABC’s professional development resources to maintain current, high quality care. This potential for differences between birth centers that collect data and those that do not limits the generalizability of the study results.