Abstract
BACKGROUND:
The maternal habitus in the setting of obesity makes external monitoring of the fetal heart rate and contractions suboptimal, and internal monitors may be utilized more often in this population. Obesity is a risk factor for obstetrical infectious complications, but it is unknown whether the use of internal monitors in this population is associated with additional risks.
OBJECTIVE:
This study aimed to investigate the association between the use of an intrauterine pressure catheter and a fetal scalp electrode and maternal infectious morbidity among women with obesity.
STUDY DESIGN:
This secondary analysis of a prospective cohort study included women with singleton gestations admitted for labor at ≥37 weeks’ gestation at a tertiary care institution from 2010 to 2014. Obesity was defined as a body mass index of ≥30 kg/m2. The primary outcome was a composite maternal infectious morbidity, which included peripartum maternal fever, chorioamnionitis, and endomyometritis. Secondary outcomes were cesarean delivery and individual components of the maternal infectious composite. Multivariable logistic regression was used to compare the rates of infectious maternal morbidity, cesarean delivery, or operative vaginal delivery between patients with and without internal monitors, while adjusting for the confounders. An interaction term was included in the logistic regression models to test whether the relationship between the internal monitors and cesarean delivery or infectious morbidity was modified by the presence or absence of obesity.
RESULTS:
Of the 8482 women who met the inclusion criteria for the study, 4727 (55.7%) had obesity and 3755 (44.3%) did not have obesity. The women with obesity were more likely to have internal monitors placed during labor than those without obesity (65.4% vs 50.5%; P<.001). The use of internal monitors was associated with an increased risk for the composite maternal infectious morbidity (9.9% vs 4.1%; P<.01 and adjusted odds ratio, 2.08; 95% confidence interval, 1.70–2.55). Women with obesity had a weaker association between the use of internal monitors and maternal infectious morbidity than women without obesity (P value for interaction of .02). The incidence of cesarean delivery was also significantly higher among women who had internal monitors placed during their labor course (adjusted odds ratio, 2.84; 95% confidence interval, 2.46–3.28), and this interaction was not modified by obesity.
CONCLUSION:
Although a higher proportion of women with obesity have internal monitors placed during their labor course, they are not more susceptible to maternal infectious morbidity as a result of internal monitor use. Providers should not limit the necessary internal monitor use in women with obesity on the basis of concerns for maternal infectious morbidity.
Keywords: internal monitor, labor, maternal obesity, obstetric morbidity
Introduction
Intrapartum monitoring includes assessment of the uterine activity and fetal heart rate patterns to monitor the fetal wellbeing and to titrate oxytocin. The monitoring can be performed externally with a tocodynamometer (a strain gauge transducer) for contraction frequency and a Doppler ultrasound for fetal heart rate. Alternatively, internal monitoring can be used if external monitoring is inadequate or if detailed assessment of the contractility is needed. Intrauterine pressure catheters (IUPCs) are used for the monitoring of contractions and to provide additional information regarding the contraction duration and magnitude, as opposed to only the contraction frequency that external monitoring provides. Fetal scalp electrodes (FSEs) can also be placed for more reliable monitoring of the fetal heart rate patterns.
The use of IUPCs and FSEs has not been shown to improve labor outcomes in unselected populations of women undergoing labor induction or augmentation. Specifically, randomized trials comparing external tocodynamometry with IUPC use for contraction monitoring have not shown a difference in the cesarean delivery rates or neonatal outcomes.1–3 Because IUPCs allow for the quantification of contractile strength and calculation of Montevideo units to determine adequacy, they are still frequently used by providers in the setting of an abnormal labor course or if external monitoring is inadequate. Often the maternal habitus in the setting of obesity makes external monitoring of the fetal heart rate and contractions suboptimal, and internal monitors may be utilized more often in this population.
Although randomized controlled trials (RCTs) have not shown any adverse outcomes from using IUPCs, previous observational studies have reported increased risks of maternal fever development and postcesarean wound infection with IUPC use.4,5 Obesity is considered a proinflammatory state and is associated with higher rates of infection in the general population and in the setting of pregnancy and labor.6–10 Therefore, it is possible that women with obesity would be at a disproportionately higher risk for infectious morbidity in the setting of internal monitor use during labor, and thus, the use of internal monitoring in this population requires further attention. We hypothesized that women with obesity are more susceptible to infectious complications with internal monitor use during labor. Therefore, our objective for this study was to investigate the association between body mass index (BMI) and internal monitor use among term laboring women and to assess the risk of maternal infectious morbidity associated with internal monitoring in women with obesity.
Methods
This was a secondary analysis of a prospective cohort of women with singleton gestations admitted for spontaneous labor or induction of labor at ≥37 weeks’ gestation to the Washington University Medical Center in St. Louis, Missouri, from April 2010 to August 2014. The Washington University in St. Louis’ Human Research Protection Office approved this study. Women with multiple gestations or a fetus with anomalies were excluded. Women were also excluded from the analysis if their BMI (a primary exposure) was unknown.
Trained obstetrical research nurses abstracted detailed demographic information, the obstetrical, prenatal, and antepartum histories, labor and delivery courses, and maternal outcomes. The gestational age was based on the woman’s last menstrual period or first ultrasound.11 The BMI was calculated using the patient weight and height at the time of admission for delivery. Based on the Centers for Disease Control and Prevention’s definition, women were classified as having obesity if they had a BMI of ≥30 kg/m2, and women without obesity had a BMI of <30 kg/m2. In addition, the cohort was stratified into 5 groups by BMI (<25 kg/m2, 25–29 kg/m2, 30–34 kg/m2, 35–39 kg/m2, and ≥40 kg/m2) for some of the analyses.
The primary outcome was a composite maternal infectious morbidity. The composite maternal infectious morbidity was present if any of the following occurred: maternal fever (body temperature of ≥38.1°C), chorioamnionitis, or endomyometritis within the intrapartum or postpartum hospital course. The secondary outcomes were cesarean delivery, operative vaginal delivery, and individual components of the maternal infectious composite. Peripartum fever was defined as a body temperature of ≥38.1°C during labor or postpartum before hospital discharge. The chorioamnionitis and endomyometritis variables were assigned on the basis of a clinical diagnosis recorded in the chart during care of the patient by the primary treating obstetrical physician team. In general, our institutional protocol for a diagnosis is the presence of fever (either a persistent temperature of ≥38.1–38.9 °C or 39.0 °C on 1 occasion), exclusion of other potential sources, and presence of fundal tenderness in the case of endomyometritis or presence of additional clinical criteria as outline by the American College of Obstetricians and Gynecologists.12 These outcomes were compared between patients with and without internal monitor use, and then stratified by the presence or absence of obesity.
The baseline clinical and labor characteristics were estimated for the entire cohort and compared between the women with and without obesity using chi-square tests for the categorical variables and the student t test or Mann-Whitney U test for the continuous variables, as appropriate. Normality was tested using the Shapiro-Francia test. The rates of internal monitor use were compared using a nonparametric test for trends across the increasing BMI categories. A multivariable logistic regression was used to control for the effect of the confounders in evaluating the relationship between internal monitor use and maternal infectious morbidity, cesarean delivery, or operative vaginal delivery. The confounders included in the models were selected on the basis of the results of univariate analyses. A backward stepwise selection was then performed, keeping only the covariates that resulted in a >5% change in the adjusted odds ratio (aOR). The initial models also included maternal race, diabetes, hypertensive disorders, and group B Streptococcus (GBS) colonization status. The model fit was assessed with a Hosmer-Lemeshow goodness of fit test.13 An interaction term was included in the logistic regression models to test if the relationship between internal monitor use and cesarean delivery or infectious morbidity was modified by the presence or absence of obesity.
An a priori sample size calculation was not performed because the sample size was fixed and all the women in the cohort and who met our inclusion criteria were included in these analyses. Statistical significance was defined as a P value of <.05. Stata version 12.1 (Stata-Corp LLC, College Station, TX) was used to perform all the analyses.
Results
Of the 8482 women with available BMI data who were included in the study, 4727 (55.7%) had obesity (Figure 1). The women with obesity were older and more likely to be black and multiparous (Table 1). The women with obesity were also more likely to have maternal comorbidities (hypertensive disorders and diabetes), undergo labor induction, and have large for gestational age neonates. The women with obesity also had a longer duration from rupture of the membranes to delivery and were more likely to be positive for GBS.
FIGURE 1. Study participants and distribution of internal monitor use during labor.
BMI, body mass index; FSE, fetal scalp electrode; IUPC, intrauterine pressure catheter.
TABLE 1.
Patient demographics
| Characteristics | BMI of <30 kg/m2, n=3755 | BMI of ≥30 kg/m2, n=4727 | P value | No internal monitors, n=3494 | Any internal monitors. n=4988 | P value |
|---|---|---|---|---|---|---|
| BMI (kg/m2) | 26.3 (2.5) | 36.9 (6.5) | <.01 | 30.5 (6.1) | 33.5 (7.9) | <.01 |
| Maternal age (y) | 25.3 (6.0) | 26.1 (5.8) | <.01 | 26.0 (5.9) | 25.6 (6.0) | <.01 |
| AMA | 312 (8.3) | 445 (9.4) | .08 | 313 (9.0) | 444 (8.9) | .93 |
| Race or ethnicity | <.01 | <.01 | ||||
| Black | 2187 (58.2) | 3330 (70.5) | 2095 (60.0) | 3422 (68.6) | ||
| White | 967 (25.8) | 952 (20.1) | 867 (24.8) | 1052 (21.1) | ||
| Hispanic | 272 (7.2) | 319 (6.8) | 313 (9.0) | 278 (5.6) | ||
| Asian | 246 (6.6) | 69 (1.5) | 161 (4.6) | 154 (3.1) | ||
| Other | 83 (2.2) | 57 (1.2) | 58 (1.7) | 82 (1.6) | ||
| Nulliparous | 1763 (47.0) | 1,883 (39.8) | <.01 | 1201 (34.4) | 2445 (49.0) | <.01 |
| History of cesarean delivery | 273 (7.3) | 481 (10.2) | <.01 | 250 (7.2) | 504 (10.1) | <.01 |
| Gestational age (wk) | 39.2 (38.3–40.1) | 39.4 (38.6–40.3) | <.01 | 39.3 (38.6–40.1) | 39.4 (38.4–40.3) | .03 |
| Labor type | <.01 | <.01 | ||||
| Spontaneous | 2316 (61.7) | 2409 (51.0) | 2485 (71.1) | 2240 (44.9) | ||
| Induced | 1439 (38.3) | 2318 (49.0) | 1009 (28.9) | 2748 (55.1) | ||
| cHTN | 73 (1.9) | 328 (6.9) | <.01 | 113 (3.2) | 288 (5.8) | <.01 |
| gHTN or preeclampsia | 452 (12.0) | 1003 (21.2) | <.01 | 431 (12.3) | 1024 (20.5) | <.01 |
| Pregestational DM | 29 (0.8) | 92 (2.0) | <.01 | 36 (1.0) | 85 (1.7) | .01 |
| Gestational DM | 86 (2.3) | 174 (3.7) | <.01 | 110 (3.2) | 150 (3.0) | .71 |
| ROM duration (h) | 4.5 (2.0–8.3) | 5.5 (2.5–10.1) | <.01 | 3.0 (0.9–6.2) | 6.6 (3.6–11.0) | <.01 |
| ROM duration >12 h | 468 (12.5) | 882 (18.7) | <.01 | 280 (8.1) | 1070 (21.5) | <.01 |
| Labor duration >24 h | 246 (6.6) | 565 (12.0) | <.01 | 114 (3.3) | 697 (14.0) | <.01 |
| Birthweight (g) | 3160 (449) | 3308 (465) | <.01 | 3253 (441) | 3235 (479) | .07 |
| Macrosomia | 123 (3.3) | 341 (7.2) | <.01 | 174 (5.0) | 290 (5.9) | .10 |
| GBS | <.01 | <.01 | ||||
| Negative | 2275 (60.6) | 2714 (57.4) | 2060 (59.0) | 2931 (58.8) | ||
| Positive | 904 (24.1) | 1434 (30.3) | 897 (25.7) | 1441 (28.9) | ||
| Unknown | 574 (15.4) | 579 (12.3) | 537 (15.4) | 616 (12.4) |
Data are presented as number (percentage), mean (SD), or median (IQR).
AMA, advanced maternal age; BMI, body mass index; cHTN, chronic hypertension; DM, diabetes mellitus; GBS, group B Streptococcus; gHTN, gestational hypertension; IQR, interquartile range; ROM, rupture of membranes; SD, standard deviation.
Overall, 58.8% of the cohort had internal monitors placed during labor. Compared with women without internal monitors during labor, those with internal monitors were more likely to be nulliparous, undergo labor induction, and have a prolonged labor and rupture of membranes. Among those with internal monitors, 60% had both an IUPC and FSE placed, 32.9% only had an IUPC, and 11.1% only had an FSE. The women with obesity were more likely to have internal monitors used during labor than women without obesity (65.4% vs 50.5%; P<.001) (Figure 1). When the cohort was stratified into 5 groups by BMI, an increasing BMI was associated with a greater incidence of internal monitor use (P value for trend of <.001) (Figure 2). Among women with class III obesity (BMI of ≥40 kg/m2), 79.6% had internal monitors placed compared with only 46.4% of women with a normal BMI (BMI of <25 kg/m2). An increasing BMI was associated with increased concomitant use of an IUPC and FSE (P value for trend of <.001) (Figure 2). The use of an IUPC or FSE alone did not differ significantly between the BMI categories.
FIGURE 2. Use of internal monitors.
Use of internal monitors by BMI. The asterisk indicates P value for trend of <.001.
BMI, body mass index; FSE, fetal scalp electrode; IUPC, intrauterine pressure catheter.
The overall incidence of maternal infectious morbidity within the cohort was 7.6% (Table 2). The use of internal monitors was associated with an increased risk for the composite maternal infectious morbidity (10.0% vs 4.2%; P<.01 and aOR, 2.08; 95% confidence interval [CI], 1.70–2.55) (Table 2 and Table 3). This association was significantly modified by obesity (P value for interaction of .02). Women with obesity had a weaker association between the use of internal monitors and maternal infectious morbidity than those without obesity (aOR, 1.71; 95% CI, 1.30–2.25 for women with obesity vs aOR, 2.58; 95% CI, 1.90–3.50 for women without obesity). Because our data did not include wound complications, which would likely bias the accrual of infectious complications following a cesarean delivery, we performed a subgroup analysis among women who had vaginal deliveries. Among women who achieved a vaginal delivery, women with obesity did not have a significant risk for maternal infectious morbidity with internal monitor use (aOR, 1.23; 95% CI, 0.88–1.71), whereas women without obesity had a significantly higher rate of maternal infectious morbidity if internal monitors were used (aOR, 2.45; 95% CI, 1.73–3.47, P value for interaction of .001).
TABLE 2.
Composite maternal infectious morbidity among the entire cohort of patients with and without obesity
| Outcome | Entire cohort (N=8482) | No internal monitor (n=3494) | Any internal monitor (n=4988) | P value |
|---|---|---|---|---|
| Composite morbidity | 637 (7.5) | 142 (4.1) | 495 (9.9) | <.01 |
| Intrapartum fever | 380 (4.5) | 69 (2.0) | 311 (6.2) | <.01 |
| Postpartum fever | 314 (3.7) | 78 (2.2) | 236 (4.7) | <.01 |
| Chorioamnionitis | 380 (4.5) | 69 (2.0) | 311 (6.2) | <.01 |
| Endomyometritis | 52 (0.6) | 7 (0.2) | 45 (0.9) | <.01 |
Data are presented as number (percentage).
TABLE 3.
Primary outcome: internal monitor use and composite maternal infectious morbidity
| All deliveries (n=8482) | Vaginal deliveries (n=7072) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Total cohort | No internal monitoring | Any internal monitoring | aOR (95% CI) | P value for interaction | Total cohort | No internal monitoring | Any internal monitoring | aOR (95% CI) | P value for interaction | |
| Entire cohort | 637 (7.5) | 142 (4.1) | 495 (9.9) | 2.08 (1.70–2.55) | .02 | 365 (5.2) | 114 (3.5) | 251 (6.6) | 1.72 (1.35–2.18) | .001 |
| BMI of ≤30 kg/m2 | 385 (8.1) | 77 (4.7) | 308 (10.0) | 1.71 (1.30–2.25) | 194 (5.2) | 62 (4.2) | 132 (5.9) | 1.23 (0.88–1.71) | ||
| BMI of <30 kg/m2 | 252 (6.7) | 65 (3.5) | 187 (9.9) | 2.58 (1.90–3.50) | 171 (5.2) | 52 (3.0) | 119 (7.7) | 2.45 (1.73–3.47) | ||
Data are presented as number (percentage) unless otherwise specified. Odds ratios adjusted for the duration of rupture of membranes of >12 hours, labor duration of >24 hours, and induction.
aOR, adjusted odds ratio; BMI, body mass index; CI, confidence interval.
Women who needed an IUPC or FSE were also more likely to require a cesarean delivery (aOR, 2.84; 95% CI, 2.46–3.28) (Table 4) or an operative vaginal delivery (aOR, 2.74; 95% CI, 2.16–3.49) (Table 4) than those who did not have internal monitors placed during labor. When the cohort was stratified by the type of internal monitors used (IUPC and FSE, IUPC alone, or FSE alone), the association with higher cesarean rates remained significant for all types and combinations of internal monitors. Although women with obesity had higher rates of cesarean and operative vaginal deliveries, the relationship between internal monitor use and the delivery mode was not modified by obesity (P values for interaction of .97 and .25, respectively) (Table 4).
TABLE 4.
Secondary outcome: internal monitor use and cesarean or operative vaginal delivery rates by obesity
| Cesarean delivery | ||||
|---|---|---|---|---|
| No internal monitor | Any internal monitor | aOR (95% CI) | P value for interaction | |
| Entire cohort | 277 (7.9) | 1.178 (23.6) | 2.84 (2.46–3.28) | |
| BMI of ≥30 kg/m2 | 157 (9.6) | 836 (27.0) | 2.68 (2.22–3.24) | .97 |
| BMI of <30 kg/m2 | 120 (6.5) | 342 (18.0) | 2.77 (2.21–3.48) | |
| Operative vaginal deliverya | ||||
| No internal monitor | Any internal monitor | aOR (95% CI) | P value for interaction | |
| Entire cohort | 99 (3.1) | 310 (8.1) | 2.74 (2.16–3.49) | |
| BMI of ≥30 kg/m2 | 34 (2.3) | 170 (7.54) | 3.36 (2.29–4.94) | .25 |
| BMI of <30 kg/m2 | 65 (3.7) | 140 (9.0) | 2.51 (1.83–3.44) | |
Odds ratios adjusted for the duration of rupture of membranes of >12 hours and induction.
aOR, adjusted odds ratio; BMI, body mass index; CI, confidence interval.
Analysis includes only vaginal deliveries.
Discussion
Principal findings
In this large modern cohort of women laboring at term, we found that an increased BMI is associated with a higher incidence of concomitant IUPC and FSE use. The majority (65%) of women with obesity ultimately have internal monitors placed during labor. All patients with internal monitors have an increased risk for maternal infectious morbidity, however, this risk is to be higher in women without obesity than in those with obesity. Finally, women who needed internal monitoring during labor were also more likely to require a cesarean or operative vaginal delivery. This effect does not seem to be modified by obesity.
Results
The concomitant use of FSE and IUPC drove the association between an increased BMI and a higher prevalence of internal monitor use. This can be attributed to factors such as higher rates of abnormal labor progress among women with obesity or an inability to reliably monitor contractions and fetal heart rate with external monitors in this population. Because rates of isolated IUPC or FSE use did not differ between the BMI groups, we suspect that the increase in concomitant use of internal monitoring reflects a difficulty with reliable external monitoring among women with obesity. Previous studies have shown that maternal obesity is associated with being unmonitored for longer time periods using external electronic fetal monitoring.14 We predict that when the maternal body habitus limits external monitoring, both the tocodynamometer and Doppler ultrasound readouts are affected. Therefore, the increase in concomitant IUPC and FSE use among women with obesity may be a reflection of internal monitor use because of suboptimal signals from external monitors, rather than labor dystocia. If an IUPC is being placed to calculate Montevideo units and quantitate contraction adequacy in the setting of an abnormal labor progress, an FSE is often not necessary and the providers may forgo its placement. Similarly, an FSE being placed because of a nonreassuring fetal status and frequent maternal repositioning, does not necessitate concomitant IUPC placement. Alternatively, because previous studies have shown that obesity is associated with a prolonged first stage of labor, it is also possible that the increase in IUPC and FSE use among women with obesity is because of the higher rates of labor dystocia in this population.15 Upon placement of an IUPC, the providers may have a lower threshold for simultaneous FSE placement with the knowledge that there is also the potential for inadequate monitoring with the external Doppler ultrasound owing to the maternal habitus.
Among women who achieved a vaginal delivery, we found that internal monitor use was associated with an increased risk for maternal infectious morbidity only in women without obesity. This was in contrast to our hypothesis in which we expected obesity to be a risk factor for infectious morbidity. This result likely represents the differential selection bias between the 2 populations or a difference in provider management. It is possible that women without obesity had internal monitors placed primarily as a response to abnormal labor progression, whereas women with obesity were more likely to have internal monitors placed to increase the reliability of monitoring. Alternatively, the increased morbidity of an emergent cesarean delivery in women with obesity may cause providers to have a lower tolerance for abnormal labor in these women and proceed with a cesarean delivery earlier in the labor course. Therefore, the risks of prolonged labor may be decreased among women with obesity at the expense of increased cesarean rates. Irrespective of the reasons, our finding that the use of internal monitors is not associated with a higher risk of infectious maternal morbidity among women with obesity is important considering that a greater proportion of these women require their use.
The increased rate of infectious maternal morbidity among women with internal monitor use during labor, particularly in those with a BMI of <30, may raise concern. We hypothesize that this is likely a result of selection bias because IUPCs are typically placed when an abnormal labor is diagnosed and are thus associated with prolonged labor and the rupture of membranes. A previous RCT did not find an association between IUPC use and intrapartum or postpartum maternal intrauterine infection,1,16 suggesting that IUPC use in an unselected population does not portend an increased risk of infection. It is perhaps the indication for IUPC placement, such as prolonged labor, that is a confounder and the true risk factor for infection. However, this hypothesis does not have adequate supporting data to conclude that internal monitor use is not associated with increased infectious morbidity in selected populations. It is possible, for example, that IUPC placement in women with a prolonged rupture of membranes is an independent risk factor for intrauterine infection. In addition, the previously mentioned RCT was performed in 2004 to 2007 in the Netherlands. The demographics of this populations are likely quite different from those of our cohort and women in the United States in general, and the results may not be generalizable.
The higher rate of cesarean delivery among women with internal monitor placement has been shown previously4 and is likely a reflection of the selected population because internal monitors are typically used in the setting of labor dystocia to allow for further oxytocin titration. Although the use of internal monitors is associated with increased rates of cesarean delivery, retrospective data cannot determine if their placement decreases the baseline risk for a cesarean delivery. A previous RCT showed that there was no difference in the rates of cesarean or operative deliveries with internal tocodynamometry use.1 However, the average BMI in this study was 25 kg/m2, and thus, we cannot extrapolate these findings to a population with obesity where external monitoring is often inadequate. In addition, because there is evidence for altered oxytocin requirements in women with obesity,17,18 this may be a population that differentially benefits from more accurate monitoring of contraction force.
Strengths and limitations
The large sample size is a strength of this study because it allowed us to determine the risk of rare outcomes like infectious morbidity and allowed for detailed subgroup analyses within the cohort. The detailed patient clinical characteristics, labor course, and maternal outcomes were additional strengths, allowing us to study the interactions and control for potential confounders. However, our findings should be considered in the context of the following limitations. Our database did not contain information regarding the indication for internal monitor placement, which prevented us from differentiating between the true associations and the baseline differences in the provider behavior. We also do not have data regarding the duration of internal monitor use. Because internal monitors, particularly IUPCs, have the potential for introducing bacteria into the amniotic cavity, it is reasonable to hypothesize that earlier internal monitor placement and a longer duration of use would increase the risk of maternal infection.19 We did adjust for a prolonged rupture of membrane duration as a surrogate for this lack of information. We also do not know if some internal monitors were placed after the development of maternal fever, in which case they could not be the source. We anticipate that this is a small subset of patients. Finally, we were unable to analyze the neonatal infectious morbidity within this cohort. However, previous data did not show a significant association between internal monitor use and neonatal morbidity.4
The use of a composite outcome may be viewed as a weakness, but it was necessary to detect the differences in rare outcomes and interactions. Chorioamnionitis and endomyometritis are objective signs of maternal infection and are associated with adverse obstetrical and neonatal outcomes. Although isolated peripartum fever is not always caused by maternal infection, it has been shown to be associated with serious maternal and neonatal complications, including increased risks of operative delivery, low Apgar scores, postpartum hemorrhage, and perinatal mortality.20,21 In addition, an isolated maternal fever can lead to a sepsis workup and prophylaxis in the neonate.22 We included this outcomes because it is both clinically relevant and captures a subset of patients at a high risk for morbidity.
Finally, we were only able to evaluate the short-term maternal outcomes, specifically the outcomes available before hospital discharge. Therefore, we were unable to evaluate the risks of postcesarean wound infections or delayed endomyometritis. A recent secondary analysis reported an increased risk of postcesarean wound infections associated with IUPC use during labor,5 however, this was for an older cohort between 1999 to 2003 and before the institution of prophylactic antibiotic administration before incision at the time of a cesarean delivery and before addition of azithromycin as an adjunct to standard prophylaxis in the setting of nonelective cesarean deliveries.23–25 Therefore, the possible association between IUPC use and postcesarean wound infections should be studied in the context of a more modern obstetrical practice.
Clinical implications
Our data demonstrate that although women with obesity are more likely to have internal monitors placed during labor, they are not at an increased risk for infectious morbidity. Often the maternal body habitus in the setting of obesity precludes adequate external fetal heart rate and contraction monitoring. Evidence reporting that internal monitoring does not increase the maternal infectious morbidity should allow providers more liberal use of internal monitors in this population of laboring women when indicated for.
Research implications
This study analyzed the association between maternal obesity, internal monitor use, and maternal infectious morbidity during labor. Further research is needed to determine whether indications for internal monitor placement modify the maternal risk. In addition, the association between internal monitors and neonatal morbidity in and delayed maternal infection should be assessed among women with obesity. Finally, although prior RCTs did not show a difference in the cesarean delivery rates or operative deliveries with internal tocodynamometry use,1 women with obesity may differentially benefit from more accurate monitoring of the contraction force during labor. Our data showing that maternal obesity does not lead to an increased risk of infectious morbidity with internal monitor use allow for further research to determine whether IUPC use among women with obesity may decrease cesarean delivery rates.
Conclusions
We found that although a higher proportion of women with obesity have internal monitors placed during their labor course, they are not more susceptible to maternal infectious morbidity. Providers should continue judicial use of internal monitors, given that there is limited data on the outcomes in select populations. However, our data suggest that there is no need for additional hesitation regarding an indicated use of internal monitors for women with obesity based on maternal infectious morbidity.
AJOG MFM at a Glance.
Why was this study conducted?
This study was conducted to determine whether women with obesity are at a higher risk for infectious morbidity than women without obesity when internal monitors are used during labor.
Key findings
A higher proportion of women with obesity have internal monitors placed during the course of their labor. However, women with obesity are not more susceptible to maternal infectious morbidity associated with internal monitor use during labor compared with women without obesity.
What does this add to what is known?
Our findings show that in the setting of internal monitor use, obesity is not a risk factor for maternal fever, chorioamnionitis, or endomyometritis. This is important because women with obesity are more likely to have internal monitors placed during labor.
Acknowledgments
N.R. is supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development of the National Institutes of Health under award number K23HD098315, the Foundation for Society of Maternal-Fetal Medicine, the American Association of Obstetricians and Gynecologists Foundation, and the Doris Duke Charitable Foundation.
Footnotes
The authors report no conflict of interest.
Presented at the 40th annual pregnancy meeting of the Society for Maternal-Fetal Medicine, Grapevine, TX, February 3e8, 2020.
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