Abstract
Objectives
The aim of this study is to calculate the trends in the use of labor analgesia in vaginal twin pregnancies at or after 37+0 weeks of gestation and evaluate the use of different labor analgesia in vaginal twin deliveries when compared to vaginal singleton pregnancies.
Study design
Data from the National Medical Birth Register during the years 2004–2018 was used to evaluate the usage of labor analgesia in vaginal twin deliveries at or after 37+0 weeks of gestation when compared to a comparison group consisting of singleton deliveries at or after 37+0 weeks of gestation. These results are presented as adjusted risk ratios (aORs) with 95% confidence intervals (Cis). The model was adjusted by maternal age and gestational diabetes, year of the pregnancy, and labor induction.
Results
A total of 3060 twin deliveries and 669 718 singleton deliveries (comparison group) were included in our study. The use of spinal analgesia in vaginal twin deliveries has shown a steadily growing trend increasing from 7.8% (95% Ci 4.8, 12.0) in 2004–24.8% (95% Ci 16.0, 33.0) in 2018. When compared to singleton deliveries, there was increased use of epidural analgesia (57.3% vs 46.1%, aOR 1.41; 95% Ci 1.31, 1.51), but lower use of spinal analgesia (12.3% vs 16.7%, aOR 0.66; 95% Ci 0.59, 0.73), another medical (7.9% vs 12.5%, aOR 0.55; 95% Ci 0.48, 0.63), and nonmedical analgesia (21.8% vs 30.2%, aOR 0.69, 95% Ci 0.63, 0.76) observed among women with twin pregnancies.
Conclusions
The main finding of this study was that women with twin pregnancies had a higher rate of epidural analgesia than women with singleton pregnancies. The results of this study should be acknowledged by midwives, obstetricians, and anesthesiologists to provide optimal pain relief for mothers with twin pregnancies and encourage researchers to further research on this topic.
Keywords: Twin pregnancy, Epidural, Epidemiology
Introduction
Twin deliveries constitute 2–3% of all deliveries [1]. In Finland, perinatal mortality and early neonatal mortality in twins have continuously decreased during the years 1987–2014, decreasing from 45 per 1000 neonates for the first twin and 54 per 1000 neonates for the second twin in 1987–6.5 per 1000 neonates for the first twin and 11.9 per 1000 neonates for second twin in 2014 [2]. However, especially the delivery of second twin is still facing more complications, and research on minimizing these challenges is warranted [2]. However, the information on the use of labor analgesia in twin pregnancies is currently lacking.
Previous literature has only focused on the effects of epidural analgesia on maternal and fetal outcomes in twin pregnancies. In these studies, epidural analgesia was found to be the optimal option in terms of delivery mode and health of the twins, as it shortened the mean time of labor and made possible the performance of all necessary instrumental and obstetrical maneuvers, without additional anesthesia or adverse effects on the second twin [3], [4], [5]. However, a study published in 2019 found that epidural analgesia in twin pregnancies prolongs the second stage of labor in both twins [6]. In 2021, a study assessed the effects of epidural analgesia on the mode of delivery for the second twin and found that the risk for CS was reduced [7]. However, despite these findings, there are currently no reports on the use of different labor analgesia in twin pregnancies.
Based on our hypothesis, the need for pain relief might be increased due to more challenging labor. Women with twin pregnancies may have an increased need for labor analgesia due to a higher incidence of uterine hyperstimulation, increased pressure on the uterus and birth canal, increased risk of complications, and higher likelihood of medical interventions, resulting in more challenging and possibly more painful labor [8], [9]. Thus, the aim of this study is to calculate the trends in the use of labor analgesia in vaginal twin pregnancies at or after 37+0 weeks of gestation and evaluate the use for different labor analgesia in these vaginal twin deliveries, when compared to vaginal singleton pregnancies.
Materials and methods
In this nationwide retrospective register-based cohort study, data from the National Medical Birth Register (MBR) was used to evaluate the usage of labor analgesia in twin pregnancies when compared to singleton deliveries. The MBR is maintained by the Finnish Institute for Health and Welfare. The study encompassed the timeframe from January 1st, 2004 to December 31st, 2018.
The MBR encompasses data regarding pregnancies, delivery metrics, and perinatal results for all births with a birthweight of ≥ 500 g or a gestational age of ≥ 22+0 weeks. The MBR boasts extensive coverage and exceptional data quality, with a nearly 100% current coverage rate [10]. We included all spontaneous and assisted (vaginal breech, forceps, or vacuum delivery) vaginal deliveries occurring after 37+0 weeks of gestation in our study. Elective or urgent CS as a mode of delivery (n = 129 353), deliveries occurring before 37+0 weeks of gestation (n = 40,015), triplets or more (n = 144), and out-of-hospital deliveries (n = 2301) were excluded from the labor analgesia analysis. Twin pregnancies with CS as a mode of delivery for both twins were excluded, but pregnancies with vaginal delivery for the first twin and CS for the second twin were included. Only vaginal deliveries at or after 37+0 weeks of gestation were included, as the rate of preterm deliveries and cesarean section (CS) is higher among twin pregnancies, and these have markable effects on the use of pain reliefs. A total of 672 778 pregnancies were included in this study. Forming of the study groups is shown as a flowchart in Fig. 1.
Fig. 1.
Flowchart of the study groups. Full-term twin pregnancies, with at least the first neonate born vaginally at or after 37+0 weeks of gestation, were compared to the comparison group consisting of singleton vaginal deliveries at or after 37+0 weeks of gestation.
Statistics
The primary focus of our study was the utilization of labor analgesia. We categorized the analgesia methods into various groups, including neuraxial analgesia (epidural, spinal, and combined), pudendal, paracervical, nitrous oxide, other medical options (including opiates), other non-medical alternatives (such as bath, aqua bubbles, and TENS), and the absence of analgesia. These categories were analyzed as dichotomous variables (yes or no), as the register lacks more detailed information, such as specific dosage used. The register only gathers information on intrapartum analgesia used during vaginal delivery, thus, the medical analgesia used during CS is not included. One patient may have had none or many of these analgesias during the labor. In addition, the annual trends in the use of labor analgesia in twin pregnancies were analyzed for the most common pain reliefs (epidural, spinal, paracervical, pudendal, and nitrous oxide). These results are presented as annual proportions of all vaginal twin deliveries. Continuous variables were reported as mean with standard deviation. Categorized variables were presented as absolute numbers and percentages with 95% confidence intervals (Cis). The Cis for proportions were calculated using Poisson regression. To analyze the odds for different labor analgesia, when confounding factors were considered, adjusted odds ratios (aORs) with 95% Cis were calculated. The model was adjusted by maternal age, maternal gestational diabetes, year of the pregnancy, and labor induction. We performed adjustments by selecting variables for a multivariable model based on directed acyclic graphs (DAGs) constructed using the online software DAGitty (dagitty.net), which is freely available [11]. The utilization of the DAG approach aids in the selection of covariates to be incorporated into conventional statistical methods, thereby minimizing the potential bias in the resulting estimate [12]. The variables incorporated into the DAGs were selected by considering established risk factors and hypothesized causal pathways [13], [14], [15], [16], [17]. DAGitty automatically provides suggested sets of adjustment variables that may impact the primary outcome. (Supplementary Table 1). The findings of this study are presented in accordance with the STROBE guidelines [18]. The statistical analysis was conducted utilizing R version 4.0.3.w.
Ethics
The ethical review process for retrospective studies utilizing routinely collected healthcare data was waived by the Ethical Committee of Tampere University Hospital, based on the regulations outlined in the law of medical research 488/1999 and the law of patient rights 785/1992. Each patient in the MBR is assigned a pseudonymized identification number, which was generated by the Finnish data authority Findata. The authors of the study did not have access to the pseudonymization key. In adherence to Finnish regulations (The law of secondary use of routinely collected healthcare data 552/2019), obtaining informed written consent was not required as the study design was retrospective and did not involve direct patient contact. The study protocol underwent evaluation by Findata, and permission for data access was granted accordingly.
Results
A total of 3060 twin deliveries at or after 37+0 weeks of gestation with at least the first neonate born vaginally were included in this study. The comparison group consisted of a total of 669 718 singleton vaginal deliveries at or after 37+0 weeks of gestation. Women with twin pregnancies were older than those in the comparison group (mean 30.8 years vs 29.6 years). A higher proportion of women with twin pregnancies had been diagnosed with gestational diabetes, than those who were in the comparison group (13.5%; 95% Ci 12.2, 14.8 vs 11.9%; 95% Ci 11.8, 12.0). A notably higher proportion of twin pregnancies had labor induction (66.2%; 95% Ci 63.3, 69.1 vs 20.5%, 95% Ci 20.4, 20.7). Background information on the study groups is shown in Table 1.
Table 1.
Background information on study cohorts. Twin pregnancies, with at least the first neonate born vaginally at or after 37+0 weeks of gestation, were compared to the comparison group consisting of singleton pregnancies at or after 37+0 weeks of gestation. The proportions are presented with 95% confidence intervals (Cis).
| Twin pregnancy |
Comparison group |
|||
|---|---|---|---|---|
| Total number of patients |
3060 |
669 718 |
||
| n | % (95% Ci) | n | % (95% Ci) | |
| Age (mean; sd) | 30.8 (4.9) | 29.6 (5.3) | ||
| Nulliparous | 969 | 31.7 (29.7, 33.7) | 263,018 | 39.3 (39.1, 39.4) |
| Maternal smoking status | ||||
| smoker | 402 | 13.1 (11.9, 14.5) | 96,446 | 14.4 (14.3, 14.5) |
| Unknown | 60 | 2.0 (1.5, 2.5) | 17,601 | 2.6 (2.6, 2.7) |
| Maternal BMI* (mean; sd) | 24.4 (4.7) | 24.2 (4.7) | ||
| BMI missing | 146 | 4.8 (4.0, 5.6) | 28,130 | 4.2 (4.2, 4.3) |
| Diagnosed gestational diabetes | 412 | 13.5 (12.2, 14.8) | 79,674 | 11.9 (11.8, 12.0) |
| Labor induction | 2025 | 66.2 (63.3, 69.1) | 137,553 | 20.5 (20.4, 20.7) |
| Obstetric complications | ||||
| tear of perineum | 19 | 0.6 (0.4, 1.0) | 6981 | 10.4 (10.2, 10.7) |
| episiotomy | 894 | 29.2 (27.3, 31.2) | 164,972 | 24.6 (24.5, 24.8) |
** Mode of delivery for the first newborn in twin pregnancies
BMI = Pre-pregnancy body mass index (kg/m2)
The higher proportion for vaginal breech deliveries (3.7%, 95% Ci 3.0, 4.4 vs 0.6%, 95% Ci), and vacuum or forceps deliveries (19.2%, 95% Ci 17.7, 20.8 vs 10.3%, 95% Ci 10.3, 10.4) was observed among twin pregnancies when compared to comparison group consisting of singleton pregnancies. Only 2.5% (95% Ci 2.0, 3.2) of vaginal twin deliveries for the first twin ended up as a CS for the second twin. (Table 2).
Table 2.
Mode of delivery for both twins in the twin group, and mode of delivery in the comparison group. The proportions are presented with 95% confidence intervals (Cis). CS = Cesarean section.
| Twin pregnancy |
Comparison group |
|||
|---|---|---|---|---|
| Total number of patients |
3060 |
669 718 |
||
| n | % (95% Ci) | n | % (95% Ci) | |
| Mode of delivery for the first twin | ||||
| spontaneous vaginal | 2360 | 77.1 (74.0, 80.3) | 596,055 | 89.0 (88.8, 89.2) |
| vaginal breech delivery | 113 | 3.7 (3.0, 4.4) | 4289 | 0.6 (0.6, 0.7) |
| vacuum or forceps | 587 | 19.2 (17.7, 20.8) | 69,374 | 10.3 (10.3,10.4) |
| Mode of delivery for the second twin | ||||
| spontaneous vaginal | 1831 | 59.8 (57.1, 62.6) | - | |
| vaginal breech delivery | 585 | 19.1 (17.6, 20.7) | - | |
| vacuum or forceps | 566 | 18.5 (17.0, 20.1) | - | |
| urgent or emergency CS | 78 | 2.5 (2.0, 3.2) | - |
There was increased use of epidural analgesia (57.3% vs 46.1%, aOR 1.41; 95% Ci 1.31, 1.51) observed among women with twin pregnancies at or after 37+0 weeks of gestation when compared to the comparison group consisting of singleton pregnancies at or after 37+0 weeks of gestation. However, the use of spinal (12.3% vs 16.7%, aOR 0.66; 95% Ci 0.59, 0.73), another medical (7.9% vs 12.5%, aOR 0.55; 95% Ci 0.48, 0.63), and nonmedical analgesia (21.8% vs 30.2%, aOR 0.69, 95% Ci 0.63, 0.76) was lower among women with twin pregnancies, when compared to the comparison group. Both groups had low proportions of women who delivered completely without analgesia (0.0% and 0.2%). (Table 3).
Table 3.
Use of labor analgesia among both study cohorts. Twin pregnancies, with at least the first neonate born vaginally at or after 37+0 weeks of gestation, were compared to the comparison group consisting of singleton vaginal pregnancies at or after 37+0 weeks of gestation. Values are numbers (proportion). The results are presented as adjusted odds ratios (aOR) with 95% confidence intervals (Cis).
| Twin pregnancy |
Comparison group |
||||
|---|---|---|---|---|---|
| Total number of patients |
3060 |
669 718 |
|||
| n | % (95% Ci) | n | % (95% Ci) | aOR* (95% Ci) | |
| Labor analgesia | |||||
| epidural | 1753 | 57.3 (54.6, 60.0) | 308,845 | 46.1 (46.0, 46.3) | 1.41 (1.31, 1.51) |
| spinal | 376 | 12.3 (11.1, 13.6) | 111,791 | 16.7 (16.6, 16.8) | 0.66 (0.59, 0.73) |
| combined spinal-epidural | 56 | 1.8 (1.4, 2.4) | 12,116 | 1.8 (1.8, 1.8) | 0.90 (0.68, 1.16) |
| paracervical block | 494 | 16.1 (14.8, 17.6) | 117,199 | 17.5 (17.4, 17.6) | 0.90 (0.81, 0.99) |
| pudendal block | 276 | 9.0 (8.0, 10.1) | 57,154 | 8.5 (8.5, 8.6) | 1.09 (0.96, 1.24) |
| nitrous oxide | 1647 | 53.8 (51.3, 56.5) | 377,046 | 56.3 (56.1, 56.5) | 0.87 (0.81, 0.94) |
| other medical analgesia | 243 | 7.9 (7.0, 9.0) | 83,872 | 12.5 (12.4, 12.6) | 0.55 (0.48, 0.63) |
| non-medical analgesia | 668 | 21.8 (20.2, 23.6) | 201,934 | 30.2 (30.0, 30.3) | 0.69 (0.63, 0.76) |
| no analgesia | 0 | - | 1688 | 0.2 (0.2, 0.3) | - |
Adjusted by maternal age, maternal gestational diabetes, year of the pregnancy, and labor induction.
During the years 2004–2018, the use of epidural, nitrous oxide, and paracervical in vaginal twin pregnancies has remained stable in Finland, except for the year 2006, when the use of nitrous oxide (33%) and epidural analgesia (36%) decreased markedly. However, the proportion of spinal analgesia has shown a steadily growing trend during the years 2004–2018, increasing from 7.8% (95% Ci 4.8, 12.0) in 2004–24.8% (95% Ci 16.0, 33.0) in 2018. (Fig. 2 and supplementary Table 1).
Fig. 2.
Annual trends (proportion) in the use of labor analgesia for the most common types of pain reliefs (epidural, nitrous oxide, paracervical, spinal, pudendal) in twin pregnancies with at least first neonate born vaginally during the years 2004–2018 in Finland.
Discussion
The main finding of this study was that women with twin pregnancies had higher use of epidural analgesia than women with singleton pregnancies. However, the use of other analgesia, especially spinal, other medical, and nonmedical analgesia was lower. In addition, the use of spinal analgesia showed an evenly increasing trend in vaginal twin pregnancies during our study period.
The use for epidural analgesia was notably higher among twin pregnancies, where at least the first neonate was born vaginally when compared to singleton pregnancies. This is also supported by the findings in previous literature [3], [4], [5]. These studies concluded that epidural analgesia was the best choice for the mode of delivery and the health of twins, as it reduced the average duration of labor and allowed for all required instrumental and obstetric procedures to be performed, without the need for supplementary anesthesia or any negative effects on the second twin [3], [4], [5]. However, compared to our study, the study sample was relatively small, and these studies were published in 1977, meaning that the use of labor analgesia may have undergone additional changes and advancements since then, including the development of new techniques and drugs, increased focus on personalized pain management, and improved safety measures [3], [4], [5]. There are also few recently published studies on this topic. In 2019, a study revealed that the use of epidural analgesia during twin pregnancies can extend the second stage of labor for both twins, while in 2021, another study examined the impact of epidural analgesia on the delivery mode for the second twin and demonstrated a lower risk of cesarean section [6], [7] However, in our study the exact reason for the increased proportion of epidural analgesia in twin pregnancies remains unknown due to the register-based study design. Confounding factors, such as higher maternal age and body mass index, gestational diabetes, and a higher proportion of instrumental vaginal deliveries (possibly requiring more pain relief in advance) among women with twin pregnancies might partly explain the higher proportion [13], but the aORs still showed markedly increased odds for epidural analgesia among women with twin pregnancies. However, according to a recent study in Finland, women with gestational diabetes, to which women with twins are at higher risk [14], had no higher proportion for labor analgesia [15].
There is no literature on the rate or effects of other medical analgesia, such as spinal, pudendal, paracervical, or nitrous oxide. Interestingly, the use of spinal, other medical, and nonmedical analgesia was lower among women with twin pregnancies. The exact reason for this remains unknown but may be due to the higher use of epidural analgesia used among twin deliveries. In addition, the proportion of the use of spinal analgesia showed an evenly increasing trend during the years 2004–2018 in Finland. However, this is most likely explained by the fact that the use of spinal analgesia has also had an increasing trend in singleton deliveries in Finland [13]. Interestingly, the use of epidural analgesia and nitrous oxide temporarily decreased strongly in 2006, but the reason for this remains unknown. This could possibly be due to changes in patient preferences, incorrect registration, or changes in clinical guidelines, but the exact reason for this is unknown. The results of this study can be useful for healthcare providers when counseling women with twin pregnancies on their pain management options during labor. Women who are aware of the higher rates of epidural analgesia use in twin pregnancies may feel more confident and reassured that effective pain relief will be available to them during labor. This, in turn, may lead to higher levels of satisfaction with their overall childbirth experience.
The primary advantage of this study lies in its comprehensive nationwide register coverage, which encompasses nearly all deliveries in Finland [10]. Furthermore, the register demonstrates high levels of validity and precision, adding to the strength of the study [10]. The primary constraint of this study is the absence of data regarding attempted analgesia methods, as the register only captures successful instances of analgesia. Another limitation stems from the lack of information on analgesic doses, leaving potential distinctions between the two groups unexplored. Additionally, the register solely collects data on intrapartum analgesia, and thus, postpartum analgesia was not analyzed. Furthermore, since the data originates from a nationwide register, regional variations within Finland are not accounted for.
Conclusion
Women with twin pregnancies had a higher use of epidural analgesia, than women with singleton pregnancies. However, the use of other analgesia, especially spinal, other medical, and nonmedical analgesia was lower. During our study period, the proportions for spinal analgesia had an evenly increasing trend in twin pregnancies with at least the first neonate born vaginally. The results of this study should be acknowledged by midwives, obstetricians, and anesthesiologists to provide optimal pain relief for mothers with twin pregnancies and encourage researchers to further research on this topic.
Declaration of Competing Interest
The authors declare no conflict of interest.
Footnotes
Supplementary data associated with this article can be found in the online version at doi:10.1016/j.eurox.2023.100232.
Appendix A. Supplementary material
Supplementary material
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Supplementary material
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