Of women who had dystocic births, in S1 we observed that 12.3% (23) of women required emergency caesarean sections; in S2 the percentage was 12.6% (137); in S3 16.5% (116) and in S4 11.3% (17). The differences here were statistically significant (p<0.001). S1 displayed a lower percentage of transfer (29.4%), fewer cases of labor stimulated with oxytocin (31.0%) and fewer cases of induced labor (12.4%). Meanwhile, S1 displayed the highest percentages of normal births (77.5%), skin-to-skin contact between the mother and the newborn (96.3%), and early initiation of breastfeeding (88.2%).
S2 showed the highest percentage of induced labor (30.8%), serious perineal injuries including episiotomies and third- and fourth-degree perineal tears (48.9%), but this US showed the lowest percentage of postpartum hemorrhages (2.0%).
S3 displayed the greatest percentage of transfer (54.9%), of labor stimulation with oxytocin (70.4%), of the use of epidural analgesics (85.5%) and of dystocic births (37.1%).
S4 showed the lowest proportion of births with epidural analgesia (18.7%), was most likely to lack serious perineal injuries, characterized as cases where the perineum was intact or cases with second and third degree perineal tears (66.7%), and had the highest percentage of the start of labor attended by midwives (99.3%). However, this OUS also displayed the highest percentage of postpartum hemorrhages (7.3%).
We were interested in analyzing the relationship between the transfer of care between the midwife and the obstetrician and the rest of the factors that influence a birth. For the purposes of this analysis, cases of elective cesarean sections (42) were excluded. Thus, the total number of cases analyzed was 2084.
Midwives attended the start of the deliveries in 85.1% (1773/2084), and they attended during the expulsive phases of the deliveries in 59.4% (1237/2084) of cases. Meanwhile, obstetricians attended the start of the deliveries in 14.9% (311/2084) of cases, and they attended the end of deliveries in 40.6% (847/2084) of cases.
In 55.5% (1156/2084) of the deliveries, there was no TOC from the midwife to the obstetrician. In other words, in these cases midwife attended the whole labor and birth process. In terms of the distribution by US, the midwives in S1 were the least likely to transfer care (with 71.0% [132/186] attending to the labor and birth in its entirety), followed by those in S4 (69.8% [104/149]), S2 (56.0% [1076/673]) and, finally, S3 (47.1% [317/773]).
We conducted an analysis of the differences in the labor and birth processes and the associated perinatal results in each US, examining them in terms of whether or not there was a TOC during the process. For the variables analyzed, (type of start of labor, pharmacological stimulation of labor, use of epidural analgesics, type of birth and status of the perineum), statistically significant differences were found, both within each obstetric unit size and for the sample as a whole.
It is true that the midwife might not be directly responsible for the decision to induce labor, as this represents a departure from a normal birth because the onset is not spontaneous. However, this process is often determined by protocol and characterized by a shared responsibility of the midwife and the team of obstetricians .
Our analysis of the factors associated with a greater likelihood of transfer of care and the risks associated with this practice is displayed in the 2x2 tables and the odds ratio calculations (Table 2).
When there was no transfer of care, S4 recorded the highest proportion of spontaneous onset of labor [S4 93.3% (97/104), compared with S1 at 90.9% (120/132), S2 at 83.3% (502/603), and S3 at 83.0% (263/317)], and the differences found here were statistically significant (p<0.001). However, in S4 when labor is induced the likelihood of TOC is six times higher than when the onset of labor is spontaneous (OR=6.9; 95% CI: 2.5-18.6). S3 showed the highest rate of induced births attended by midwives in which no TOC occurred [17.0% (54/317), while for S2 the figure was 16.7% (101/603), for S1 it was 9.1% (12/132), and for S4 it was 6.7% (7/104)]. The differences found were statistically significant (p<0.001). S4 displayed the lowest frequency of oxytocin use in deliveries when no transfer of care occurred [13.5% (14/104)]. Meanwhile, S3 registered the highest rate of pharmacological stimulation (55.5% [176/317]). Additionally, in S4 TOC was more likely when oxytocin was used or labor was stimulated, in the latter case increasing by a factor of 29 with respect to when labor was not stimulated (OR = 29.7, 95% CI: 11.5-76.8; p <0.001).
In cases where there was no TOC, S3 registered the lowest rate of use of epidural analgesics [75.1% (238/317)], while S1 and S2 displayed the greatest tendency to administer them (78.8% ([104/132] and 78.8% [475/603], respectively). In S1, the risk of TOC was seven times higher when epidural analgesics were administered than when they were not (OR=7.0; 95% CI:1.0-30.0; p=0.003, with the rate reaching 96.3% (52/54) in these cases. The lowest prevalence of TOC associated with the use of epidural analgesics was found in S2 (OR=2.8; 95% CI: 1.9-4.1; p<0.001), where the figure was 91.3% (432/473).
In terms of the type of birth, all the spontaneous vaginal deliveries (SVD) in S4 (104/104) were attended by midwives, and therefore, there was no TOC. In contrast, none of the S4 births in which TOC occurred were SVD (0/45). Meanwhile, in S3, 35.1% (125/356) of the deliveries that featured transfers of responsibilities were SVD and attended by obstetricians. The risk of TOC associated with labor ending in dystocia was the highest in S1 (S1 OR = 11.1, 95% CI: 6.6-18.6, p <0.001; S2 OR = 4.9, 95% CI: 4.3-5.6, p <0.001; S3 OR = 3.5, 95% CI:3.0-4.1, p <0.001).
With respect to the condition of the perineum when no TOC occurred, the S4 registered the highest number of cases with intact perineum or 1st or 2nd degree perineal tears [94.2% (98/104)], compared with the figure of 72.3% (436/603) for S2. In contrast, when TOC occurred, the highest rate of intact perineum or 1st or 2nd degree perineal tears was found in S3 [44.9% (160/356)], while S4 displayed the lowest rate [4.4% (2/45)]. Meanwhile, these episiotomies or third- or fourth-degree tears were present in 95.6% (43/45) of the cases in S4 when TOC was performed. The lowest rate in this regard was found in S3 [55.1% (196/356]. Thus, when TOC occurs, the risk of episiotomy or third- or fourth-degree perineal tear (rather than an intact perineum or a first- or second-degree tear) was found in S4 to increase by a factor of 350 (OR = 351.2, 95% CI: 68.1-1810.3, p <0.001). The risk of TOC and of episiotomy or third- and fourth-degree perineal tears was the lowest in S3 (OR = 3.6, 95% CI: 2.6-4.9, p <0.001).
In addition, significant differences were found with regard to the presence of postpartum hemorrhages and early initiation of breastfeeding initiation only in the sample as a whole. This effect could be explained by the construction of a multivariate logistic regression model (Wald test) between these variables and the rest of the covariables studied, observing that the obstetric unit size, the induced onset of labor and having a episiotomy or grade III-IV injury were associated with an increasing risk of having postpartum hemorrhage. Women who had an episiotomy or a grade III-IV injury were twice as likely to have a postpartum hemorrhage compared with women who had an intact perineum or a I-II degree tear [OR=2.5; CI95%:1.4-4.4]; induction of labor is also a risk for postpartum hemorrhage [OR=1.8; CI95%:1.1-3.1]. Moreover, doing skin-to-skin was associated with an increased probability of early initiation of breastfeeding onset [OR=45.9; 95%CI: 28.89-72.77] (Table 3).