Labor dystocia and its association with interpregnancy interval

Inconsistent definitions of prolonged labor in international literature: a scoping review

Objective

Prolonged labor is the commonest indication for intrapartum cesarean section, but definitions are inconsistent and some common definitions were recently found to overestimate the speed of physiological labor. The objective of this review is to establish an overview of synonyms and definitions used in the literature for prolonged labor, separated into first and second stages, and establish types of definitions used.

Data sources

A systematic search was conducted in PubMed, Embase, Web of Science, Cochrane Library, Emcare, and Academic Search Premier.

Study eligibility criteria

All articles in English that (1) attempted to define prolonged labor, (2) included a definition of prolonged labor, or (3) included any synonym for prolonged labor, were included.

Methods

Data on study design, year of publication, country or region of origin, synonyms used, definition of prolonged first and/or second stage, and origin of provided definition (if not primarily established by the study) were collected into a database.

Results

In total, 3402 abstracts and 536 full-text papers were screened, and 232 papers were included. Our search established 53 synonyms for prolonged labor. Forty-three studies defined prolonged labor and 189 studies adopted a definition of prolonged labor. Definitions for prolonged first stage of labor were categorized into: time-based (n=14), progress-based (n=12), clinician-based (n=5), or outcome-based (n=4). For the 33 studies defining prolonged second stage, the majority of definitions (n=25) were time-based, either based on total duration or duration of no descent of the presenting part.

Conclusions

Despite efforts to arrive at uniform labor curves, there is still little uniformity in definitions of prolonged labor. Consensus on which definition to use is called for, in order to safely and respectfully allow physiological labor progress, ensure timely management, and assess and compare incidence of prolonged labor between settings.

Interpregnancy interval after vacuum delivery and subsequent perinatal outcomes

OBJECTIVE

To evaluate whether a short interpregnancy interval (IPI) after vacuum extraction (VE), poses similar perinatal risks in a subsequent pregnancy.

METHODS

This was a retrospective, single-center cohort study between 2011 and 2021. Nulliparous women with term, singleton VE deliveries and with known pregnancy outcomes in their subsequent pregnancy were eligible for inclusion in the study. Each woman was allocated into one of two groups based on the IPI, <18 months and between 18 and 60 months. The primary outcome was the risk of spontaneous preterm birth (PTB) <37 weeks in the consecutive birth.

RESULTS

We included 1094 pregnancies: 212 (19.4%) with IPI <18 months and 882 (80.6%) with IPI between 18 and 60 months following the previous VE delivery. The VE characteristics were comparable between the groups. Young maternal age was a risk factor for a short IPI (28.0 ± 4.8 vs 30.3 ± 4 years, P < 0.01). Spontaneous PTB <37 weeks was significantly higher in the IPI <18 months group with 18-60 months (7.1% vs 2.6%, P = 0.002). Polynomial regression analysis also confirmed a significantly increased risk of preterm birth <37 weeks (P < 0.01). Short IPI <18 months was also associated with an increase in the risk of low birthweight <2500 g (6.1% vs 2.8%, P = 0.02) and admission to the neonatal intensive care unit (6.1% vs 2.6%, P = 0.013). The incidence of recurrent VE, albeit significant (2.3% vs 4.9%, P = 0.049), was low in both groups. No differences were noted in any of the other secondary outcomes.

CONCLUSION

Short IPI (<18 months) following term VE delivery is associated with higher neonatal risks, particularly PTB, in the subsequent pregnancy. These findings are particularly important when counseling women planning an optimal IPI.

Birth Spacing and Parents' Physical and Mental Health: An Analysis Using Individual and Sibling Fixed Effects

An extensive literature has examined the relationship between birth spacing and subsequent health outcomes for parents, particularly for mothers. However, this research has drawn almost exclusively on observational research designs, and almost all studies have been limited to adjusting for observable factors that could confound the relationship between birth spacing and health outcomes. In this study, we use Norwegian register data to examine the relationship between birth spacing and the number of general practitioner consultations for mothers' and fathers' physical and mental health concerns immediately after childbirth (1-5 and 6-11 months after childbirth), in the medium term (5-6 years after childbearing), and in the long term (10-11 years after childbearing). To examine short-term health outcomes, we estimate individual fixed-effects models: we hold constant factors that could influence parents' birth spacing behavior and their health, comparing health outcomes after different births to the same parent. We apply sibling fixed effects in our analysis of medium- and long-term outcomes, holding constant mothers' and fathers' family backgrounds. The results from our analyses that do not apply individual or sibling fixed effects are consistent with much of the previous literature: shorter and longer birth intervals are associated with worse health outcomes than birth intervals of approximately 2-3 years. Estimates from individual fixed-effects models suggest that particularly short intervals have a modest negative effect on maternal mental health in the short term, with more ambiguous evidence that particularly short or long intervals might modestly influence short-, medium-, and long-term physical health outcomes. Overall, these results are consistent with small to negligible effects of birth spacing behavior on (non-pregnancy-related) parental health outcomes.

Birth spacing and risk of adverse pregnancy and birth outcomes: A systematic review and dose-response meta-analysis

INTRODUCTION

The association between extreme birth spacing and adverse outcomes is controversial, and available evidence is fragmented into different classifications of birth spacing.

MATERIAL AND METHODS

We conducted a systematic review of observational studies to evaluate the association between birth spacing (i.e., interpregnancy interval and interoutcome interval) and adverse outcomes (i.e., pregnancy complications, adverse birth outcomes). Pooled odds ratios (ORs) with 95% confidence intervals (CI) were calculated using a random-effects model, and the dose-response relationships were evaluated using generalized least squares trend estimation.

RESULTS

A total of 129 studies involving 46 874 843 pregnancies were included. In the general population, compared with an interpregnancy interval of 18-23 months, extreme intervals (<6 months and ≥ 60 months) were associated with an increased risk of adverse outcomes, including preterm birth, small for gestational age, low birthweight, fetal death, birth defects, early neonatal death, and premature rupture of fetal membranes (pooled OR range: 1.08-1.56; p < 0.05). The dose-response analyses further confirmed these J-shaped relationships (pnon-linear  < 0.001-0.009). Long interpregnancy interval was only associated with an increased risk of preeclampsia and gestational diabetes (pnon-linear  < 0.005 and pnon-linear  < 0.001, respectively). Similar associations were observed between interoutcome interval and risk of low birthweight and preterm birth (pnon-linear  < 0.001). Moreover, interoutcome interval of ≥60 months was associated with an increased risk of cesarean delivery (pooled OR 1.72, 95% CI 1.04-2.83). For pregnancies following preterm births, an interpregnancy interval of 9 months was not associated with an increased risk of preterm birth, according to dose-response analyses (pnon-linear  = 0.008). Based on limited evidence, we did not observe significant associations between interpregnancy interval or interoutcome interval after pregnancy losses and risk of small for gestational age, fetal death, miscarriage, or preeclampsia (pooled OR range: 0.76-1.21; p > 0.05).

CONCLUSIONS

Extreme birth spacing has extensive adverse effects on maternal and infant health. In the general population, interpregnancy interval of 18-23 months may be associated with potential benefits for both mothers and infants. For women with previous preterm birth, the optimal birth spacing may be 9 months.

Impact of the interpregnancy interval after cesarean delivery on subsequent perinatal risks: a retrospective study

PURPOSE

To assess the impact of the interpregnancy interval (IPI) after cesarean delivery on the risks of adverse perinatal events during subsequent pregnancies.

METHODS

We retrospectively examined perinatal outcomes of subsequent pregnancies of women whose most recent birth experience involved cesarean delivery at our hospital between January 2014 and December 2019. IPI was defined as the time between live birth and subsequent conception. Three IPI groups: < 18 months, 18-60 months, and > 60 months, were assessed. The risks of preterm birth, preeclampsia, placenta previa, placental abruption, fetal growth restriction, and successful vaginal birth were compared among the three IPI groups using uni- and multivariate analyses.

RESULTS

We registered 592 births after cesarean delivery: 178, 288, and 126 in the IPI < 18 months, 18-60 months, and > 60 months groups, respectively. The groups did not differ significantly regarding perinatal outcomes. The multivariate analysis revealed no significant differences in the risks of adverse perinatal outcomes among all groups. The odds ratios (ORs) for preterm birth at < 37 weeks of gestation were 1.24 and 1.64 for those in the < 18 months and > 60 months groups, respectively (P = 0.362 and P = 0.055, respectively). The groups did not differ significantly regarding vaginal birth success rate (ORs 1.72 for the < 18 months group, 0.49 for the > 60 months group; P = 0.486 and P = 0.446, respectively).

CONCLUSION

After cesarean delivery, IPIs shorter than 18 months and longer than 60 months do not significantly impact the risks of adverse perinatal outcomes or successful vaginal birth compared with IPIs of 18-60 months.

Golgi Reassembly Stacking Protein 2 Modulates Myometrial Contractility during Labor by Affecting ATP Production

The mechanism of maintaining myometrial contractions during labor remains unclear. Autophagy has been reported to be activated in laboring myometrium, along with the high expression of Golgi reassembly stacking protein 2 (GORASP2), a protein capable of regulating autophagy activation. This study aimed to investigate the role and mechanism of GORASP2 in uterine contractions during labor. Western blot confirmed the increased expression of GORASP2 in laboring myometrium. Furthermore, the knockdown of GORASP2 in primary human myometrial smooth muscle cells (hMSMCs) using siRNA resulted in reduced cell contractility. This phenomenon was independent of the contraction-associated protein and autophagy. Differential mRNAs were analyzed using RNA sequencing. Subsequently, KEGG pathway analysis identified that GORASP2 knockdown suppressed several energy metabolism pathways. Furthermore, reduced ATP levels and aerobic respiration impairment were observed in measuring the oxygen consumption rate (OCR). These findings suggest that GORASP2 is up-regulated in the myometrium during labor and modulates myometrial contractility mainly by maintaining ATP production.

New insights on labor progression: a systematic review

The past 20 years witnessed an invigoration of research on labor progression and a change of thinking regarding normal labor. New evidence is emerging, and more advanced statistical methods are applied to labor progression analyses. Given the wide variations in the onset of active labor and the pattern of labor progression, there is an emerging consensus that the definition of abnormal labor may not be related to an idealized or average labor curve. Alternative approaches to guide labor management have been proposed; for example, using an upper limit of a distribution of labor duration to define abnormally slow labor. Nonetheless, the methods of labor assessment are still primitive and subject to error; more objective measures and more advanced instruments are needed to identify the onset of active labor, monitor labor progression, and define when labor duration is associated with maternal/child risk. Cervical dilation alone may be insufficient to define active labor, and incorporating more physical and biochemical measures may improve accuracy of diagnosing active labor onset and progression. Because the association between duration of labor and perinatal outcomes is rather complex and influenced by various underlying and iatrogenic conditions, future research must carefully explore how to integrate statistical cut-points with clinical outcomes to reach a practical definition of labor abnormalities. Finally, research regarding the complex labor process may benefit from new approaches, such as machine learning technologies and artificial intelligence to improve the predictability of successful vaginal delivery with normal perinatal outcomes.

The effect of ultrasonographically measured fetal adipose tissue components on labor

AIM

To investigate whether increased fetal adiposity diagnosed ultrasonographical is associated with labor dystocia, and increased risk of operative delivery.

METHOD

This was a prospective study and included 400 pregnant women between 37 and 41 weeks of gestation. In addition to standard ultrasonographic measurements, we evaluated fetal soft tissue thickness before delivery. We also recorded data on delivery method, shoulder dystocia, fetal birthweight and labor duration. We considered the period between 6 and 10 cm cervical opening as the active phase, and the period from full dilation to birth as the second stage.

RESULTS

While the vaginal delivery rate was 77.3%, a cesarean was performed in 22.7% of pregnant women. We found a positive correlation between fetal adipose tissue components and durations of the active phase and second-stage labor and the baby's birthweight. Also, we examined and determined that cesarean section and labor dystocia increased as the fetus adipose tissue thickness increased. We investigated the effect of parameters on the study results with logistic regression analysis and possible threshold values with receiver operating characteristics analysis.

CONCLUSION

Our study evaluated the fetal adipose tissue complex during delivery was significant in terms of labor dystocia and operative delivery. We think it may be a guide for future studies in the literature.

Assessing feasibility and maternal acceptability of a biomechanically-optimized supine birth position: A pilot study

BACKGROUND

In order to manage a protracted second stage of labor, "eminence-based" birth positions have been suggested by some healthcare professionals. Recent biomechanical studies have promoted the use of an optimized supine birthing position in this setting. However, uncertainty exists regarding the feasibility of this posture, and its acceptability by women. This pilot study primarily aimed to assess these characteristics.

OBJECTIVE AND METHODS

In this monocentric prospective study, 20 women with a protracted second stage of labor were asked to maintain a biomechanically-optimized position for at least 20 minutes at full dilatation. This posture is similar to the McRoberts' maneuver. Maintaining the position for 20 minutes or more was considered clinically relevant and indicative of feasibility and acceptability. Satisfaction with the position was assessed using a Visual Analogue Scale (VAS). A sub-group analysis was performed to assess eventual differences between more and less satisfied patients, according to the median of patients' satisfaction scores.

RESULTS

Seventeen patients (85%) maintained the optimized position for at least 20 minutes. The median satisfaction score of these participants was 8 (interquartile range: 1) out of 10. No significant differences were found between the two sub-groups (satisfaction score <8 vs satisfaction score ≥8) regarding general and obstetric characteristics, as well as obstetrical and fetal outcomes.

CONCLUSION

The optimized position is acceptable and feasible for women experiencing a protracted second stage of labor. Further clinical studies are needed to assess the efficiency of such positions when women undergo an obstructed labor.

Recurrent short interpregnancy interval: Maternal and neonatal outcomes

OBJECTIVE

To evaluate maternal and neonatal outcomes associated with recurrent short interpregnancy interval (IPI) in women in their third delivery.

METHODS

A retrospective computerized database study of all women who delivered their first three consecutive deliveries in a single tertiary medical center over 20 years (1999-2019). Maternal and neonatal outcomes of women with recurrent short IPI (<6 months between the 1st and 2nd pregnancy and the 2nd and 3rd pregnancy) were compared to women with recurrent optimal IPI (18-48 months), and to women with a single short IPI (<6 months between the 1st and 2nd pregnancy followed by an optimal IPI of 18-48 months between the 2nd and 3rd pregnancy). Additionally, in the recurrent short IPI groups, outcomes of the 2nd and 3rd pregnancies were compared in order to achieve an ideal adjustment to background characteristics. Univariate analysis was followed by multiple logistic regression models; adjusted odds ratios (aORs) and 95% confidence intervals (CIs) were calculated.

RESULTS

During the study period 10,569 women had three consecutive deliveries at our medical center, of those 338 (3.2%) women had recurrent short IPIs, and 1,021 (9.7%) had recurrent optimal IPIs. Recurrent short IPI was associated with a significantly higher risk of maternal anemia (Hb < 10gr%) on admission to labor (aOR 3.4 [95% CI 1.09-10.65], p = 0.04) and higher risk of small for gestational age neonates (aOR 10.4 [95% CI 2.32-46.93], p < 0.01), as compared with women with recurrent optimal IPI and significantly higher rates of low neonatal birth weights (2500 gr) and anemia (Hb < 10gr%) alongside lower rates of operative vaginal deliveries as compared with women with single short IPI followed by an optimal IPI. In the recurrent short IPI groups, the 3rd deliveries had significantly higher rates of in-labor cesarean and anemia (Hb < 10gr%) on admission as compared to their 2nd deliveries.

CONCLUSION

Recurrent short IPI is associated with maternal anemia and small for gestational age neonates. Guiding patients towards prolongation of the IPI should include explanatory comments on these outcomes.

Defining arrest in the first and second stages of labor

Normal labor is identified as regular uterine contractions in addition to dilation and effacement of the cervix. It is necessary to define normal labor in order to delineate when a woman's labor pattern diverges from that observed in most women. Labor irregularities are subdivided into protraction disorders and arrest disorders. Identifying abnormal labor patterns and initiating appropriate interventions is essential because prolonged labor is associated with an increase in perinatal morbidity. The aim of this review was to delineate both normal labor progress and also discuss the current evidence-based diagnosis and treatment of protraction and arrest disorders. Many subtleties go into defining the boundaries of the first and second stages of labor. Historically, the Friedman curve established normal limits; but currently Zhang has advanced these definitions by accounting for current demographical characteristics and practice environments. The most significant variables for defining normal progress of labor are parity and regional anesthesia status. The most common causes of labor abnormalities are uterine inactivity, obesity, cephalopelvic disproportion and fetal malposition. Risks of extending the first and/or second stage of labor include postpartum hemorrhage, intraamniotic infection and potentially an increase in neonatal adverse outcomes. The management of labor disorders consists of oxytocin administration, amniotomy, intrauterine pressure catheter use and shared decision-making regarding proceeding with expectant management, operative vaginal delivery or cesarean delivery after weighing the risks and benefits of each option. The decision to extend the duration of labor is personalized for each mother-baby dyad and should be agreed upon depending on individual maternal and fetal circumstances.

Prolonged interpregnancy interval: how does it impact the length of second stage of labor?

Objectives Short interpregnancy intervals (IPI) have been linked to multiple adverse maternal and neonatal outcomes, but less is known about prolonged IPI, including its relationship with labor progression. The objective of the study was to investigate whether prolonged IPIs are associated with longer second stages of labor. Methods A perinatal database from Kaiser Permanente Hawaii was used to identify 442 women with a prolonged IPI ≥60 months. Four hundred forty two nulliparous and 442 multiparous women with an IPI 18-59 months were selected as comparison groups. The primary outcome was second stage of labor duration. Perinatal outcomes were compared between these groups. Results The median (IQR) second stage of labor duration was 76 (38-141) min in nulliparous women, 15 (9-28) min in multiparous women, and 18 (10-38) min in women with a prolonged IPI (p<0.0001). Pairwise comparisons revealed significantly different second stage duration in the nulliparous group compared to both the multiparous and prolonged IPI groups, but no difference between the multiparous and prolonged IPI groups. There was a significant association with the length of the IPI; median duration 30 (12-61) min for IPI ≥120 months vs. 15 (9-27) min for IPI 18-59 months and 16 (9-31) min for IPI 60-119 months (p=0.0014). Conclusions The second stage of labor did not differ in women with a prolonged IPI compared to normal multiparous women. Women with an IPI ≥120 months had a significantly longer second stage vs. those with a shorter IPI. These findings provide a better understanding of labor progression in pregnancies with a prolonged IPI.

Uterus Modeling from Cell to Organ Level: towards Better Understanding of Physiological Basis of Uterine Activity

The relatively limited understanding of the physiology of uterine activation prevents us from achieving optimal clinical outcomes for managing serious pregnancy disorders such as preterm birth or uterine dystocia. There is increasing awareness that multi-scale computational modeling of the uterus is a promising approach for providing a qualitative and quantitative description of uterine physiology. The overarching objective of such approach is to coalesce previously fragmentary information into a predictive and testable model of uterine activity that, in turn, informs the development of new diagnostic and therapeutic approaches to these pressing clinical problems. This article assesses current progress towards this goal. We summarize the electrophysiological basis of uterine activation as presently understood and review recent research approaches to uterine modeling at different scales from single cell to tissue, whole organ and organism with particular focus on transformative data in the last decade. We describe the positives and limitations of these approaches, thereby identifying key gaps in our knowledge on which to focus, in parallel, future computational and biological research efforts.

Evaluation of the labour process with serial transperineal ultrasonography and prediction of the type of birth

OBJECTIVES

The purpose of this study is to follow the birth process with transperineal ultrasonography (TPU) and predict the delivery method using angle of progression (AOP).

METHODS

The study included 134 patients. The AOP was examined with TPU in the lithotomy position applied at 4-h intervals, not at a time of straining or contractions. The relationship was examined between AOP and those who continued with vaginal delivery, and those who underwent caesarean section delivery.

RESULTS

A total of 122 (91%) patients had vaginal delivery and 12 (9%) patients had cesarean delivery. In patients giving vaginal delivery, progress in AOP was observed in every 4-h measurement, but not in patients with cesarean section. In the ROC analysis, if 70% sensitivity and 75% specificity with AOP degree >132.5°, the patient was expected to have vaginal delivery with a probability of 77.5% (95% CI 0.62-0.93; p=0.002).

CONCLUSIONS

Rather than repeating digital examinations, the labour process can be monitored with serial TPU and the type of delivery can be predicted. There is a need for further studies for the measurement of AOP with TPU to become a part of clinical practice in the monitoring of the whole labour process.

The association between interpregnancy interval and severe maternal morbidities using revised national birth certificate data: A probabilistic bias analysis

BACKGROUND

Severe maternal morbidity continues to be on the rise in the US. Short birth spacing is a modifiable risk factor associated with maternal morbidity, yet few studies have examined this association, possibly due to few available data sources to examine these rare events.

OBJECTIVE

To examine the association between interpregnancy interval (IPI) and severe maternal morbidity using near-national birth certificate data and account for known under-reporting using probabilistic bias analysis.

METHODS

We used revised 2014-2017 birth certificate data, restricting to resident women with a non-first-born singleton birth. We examined the following: (a) maternal blood transfusion, (b) admission to intensive care unit (ICU), (c) uterine rupture (among women with a prior caesarean delivery) and (d) third- or fourth-degree perineal laceration (among vaginal deliveries) by IPI categories (<6, 6-11, 12-17, 18-23, 24-59 and 60+ months). Risk ratios and 95% confidence intervals were estimated using log-binomial regression, adjusting for select maternal characteristics. Probabilistic bias analyses were performed.

RESULTS

Compared with IPI 18 to 23 months, adjusted models revealed that the risk of maternal transfusion followed a U-shaped curve with IPI, while risk of ICU admission and perineal laceration increased with longer IPI. Risk of uterine rupture was highest among IPI <6 months. With the exception of maternal transfusion, these findings persisted regardless of the extent or type of misclassification examined in bias analyses.

CONCLUSIONS

Associations between IPI and maternal morbidity varied by outcome, even after adjusting for misclassification of SMM. Differences across maternal health outcomes should be considered when counselling and making recommendations regarding optimal birth spacing.

First assessed cervical dilatation: is it associated with oxytocin augmentation during labour? A retrospective cohort study in a university hospital in Switzerland

OBJECTIVES

The primary objective of this study was to examine the association between the first assessed cervical dilatation in a labourward and the use of oxytocin augmentation during labour. Further analysis was performed by examining the actual stage of labour at the point oxytocin was first administered to those women.

DESIGN

Retrospective cohort study with the data collected from the medical records of the hospital.

SETTING

University Hospital Bern, Switzerland PARTICIPANTS: 1933 term nulliparous and multiparous women with a singleton pregnancy giving birth during the period June 2013 and May 2017, representing Robson groups 1 and 3.

MEASUREMENTS AND FINDINGS

Descriptive statistics and multivariable logistic regression models were performed. It was found that for the entire process of labour, nulliparous and multiparous women (n = 1933) with a first cervical dilatation of 5 or more cm were less likely to be augmented with oxytocin (OR 0.64, 95% CI 0.46; 0.88 and OR 0.56, 95% CI 0.38; 0.82, respectively) compared to women with a first cervical dilatation of less than 5 cm. Out of these augmented women (n = 746) having a first cervical dilatation of 5 or more cm, they had a lower likelihood of being augmented during the first stage of labour compared to women with a first cervical dilatation of less than 5 cm (OR 0.45, 95% CI 0.29; 0.7 for nulliparae and OR 0.32, 95% CI 0.16; 0.6 for multiparae). Additionally, it was observed that other factors contributed to the application of oxytocin. One such example was that epidural analgesia was associated with a high risk of oxytocin augmentation in nulliparae (OR 13.88, 95% CI 9.29; 20.74) and multiparae (OR 15.52, 95% CI 9.94; 24.22). The application of oxytocin was also found to affect the caesarean section rate in nulliparous and multiparous women as it was 20% and 13% respectively for those with oxytocin versus 13% and 4% respectively for those without oxytocin.

KEY CONCLUSIONS

Early admission to the labourward is associated with an increased use of oxytocin to augment labour, particularly, during the first stage of labour. Epidural analgesia is a main predictor for oxytocin augmentation in nulliparous and multiparous women.

IMPLICATIONS FOR PRACTICE

Pregnant women warrant more appropriate support during early labour, avoiding early maternal exhaustion and excessive obstetrical interventions.

Association between long interpregnancy intervals and cesarean delivery due to arrest disorders

BACKGROUND

It is hypothesized that pregnancy causes time-limited physiologic adaptations of the reproductive system, such as increased blood flow to the uterus. With long interpregnancy intervals, those adaptations may regress, and maternal physiologic characteristics may revert to those of primigravid women. Therefore, it is plausible that long interpregnancy interval is associated with cesarean delivery, especially due to arrest disorders (failed induction of labor, arrest of dilation, or arrest of descent).

OBJECTIVE

To examine the association between interpregnancy interval and cesarean delivery due to arrest disorders in multiparous women without a history of cesarean delivery.

MATERIALS AND METHODS

This was a retrospective cohort study of all women who had more than 1 singleton pregnancy at 23 weeks' gestation or greater at MedStar Washington Hospital Center from January 2009 to June 2018. We defined the interpregnancy interval as the duration from the birth of the preceding offspring to the date of conception of the index offspring. We a priori decided to categorize women based on the interpregnancy interval (less than 18 months, 18-59 months, and 60 months or greater). Our primary outcome was cesarean delivery due to arrest disorders. We also examined overall cesarean delivery and cesarean delivery due to nonreassuring fetal heart tracing. Multivariable logistic regression was performed to calculate adjusted odds ratios and 95% confidence intervals, controlling for predefined covariates.

RESULTS

Of 2741 women, 1143 (41.7%), 1369 (49.9%), and 229 (8.4%) had an interpregnancy interval of less than 18 months, 18-59 months, and 60 months or more, respectively. After adjusting for confounders, an interpregnancy interval of 60 months or more compared to an interpregnancy interval of 18-59 months was associated with increased odds of cesarean delivery due to arrest disorders (4.8% vs 1.3%; adjusted odds ratio, 3.06; 95% confidence interval, 1.34-6.97) and cesarean delivery due to arrest of dilation (3.1% vs 0.7%; adjusted odds ratio, 3.24; 95% confidence interval, 1.10-9.59). An interpregnancy interval of less than 18 months compared to an interpregnancy interval of 18-59 months was associated with decreased odds of cesarean delivery due to nonreassuring fetal heart tracing (2.4% vs 4.1%; adjusted odds ratio, 0.55; 95% confidence interval, 0.32-0.92).

CONCLUSION

An interpregnancy interval of 60 months or greater compared to an interpregnancy interval of 18-59 months was associated with increased odds of cesarean delivery due to arrest disorders. Beneficial effects on postpartum adaptations in the reproductive system may regress as interpregnancy interval increases.

Long interpregnancy interval and mode of delivery

PURPOSE

WHO sets 24 months as the ideal minimum interpregnancy interval (IPI) to minimize maternal and perinatal adverse outcomes. Some studies suggest that an interval longer than 59 months may affect these outcomes, but little is known about its influence on labor. The primary objective of this study was to compare the cesarean delivery rate between primiparous women with a long IPI and, on the one hand, primiparous women with an ideal minimum IPI of 18-24 months and, on the other hand, with nulliparous women.

METHODS

This retrospective cohort study of 17 years included nulliparas and primiparas who gave birth to live singleton fetuses in cephalic presentation after 22 weeks of gestation. Women with an IPI < 18 months or from 24 to 59 months were excluded, as were women with planned cesarean. We analyzed three groups: primiparous women with a long IPI defined as > 59 months, primiparous women with an ideal minimum IPI (18-24 months), and nulliparous women.

RESULTS

The study included 18,503 women: 1342 women in the "long IPI" group, 1388 in the "ideal minimum IPI" group, and 15,773 in the nulliparous women group. The cesarean delivery rate was significantly higher in the long compared to the ideal minimum IPI group [12.2% vs. 6.3%, respectively; aOR = 2.2 (95% CI 1.6-3.1)], but both groups had similar durations of labor, regardless of mode of delivery. Women in the long IPI group had significantly lower cesarean rates than nulliparous women [12.2% and 14.3%, respectively; aOR = 0.5 (95% CI 0.4-0.7)], and the nulliparous women had a significantly longer mean duration of labor.

CONCLUSIONS

Primiparas with a long IPI, compared with ideal minimal IPI have a higher risk of cesarean delivery during labor. Compared with nulliparous women, primiparous women with a long IPI had a lower cesarean rate.

Risk for Cesarean section in women of advanced maternal age under the changed reproductive policy in China: A cohort study in a tertiary hospital in southwestern China

AIM

To describe changed epidemiological features of advanced maternal age (AMA) and to examine the effect of AMA on the risk for Cesarean section (CS) in a Chinese pregnant population.

METHODS

This retrospective single-center cohort study investigated the changes of epidemiological features of AMA parturients with respect to the revised reproductive policy in China in 43 702 singleton deliveries with live birth at ≥28 weeks managed from January 2005 to December 2016. We also evaluated the pregnancy outcomes in different age groups and risk factors of CS with multivariate analysis.

RESULTS

In this 12-year study period, the average maternal age increased from 28.5 to 30.2 years, and the proportion of AMA raised from 6.5% to 17.2%. AMA was significantly associated with increased risk of adverse pregnancy outcomes, and after adjustment for confounding factors, AMA remained a significant independent risk factor for CS. Furthermore, the effect of AMA in nulliparous women on the risk of CS was more significant than in multiparous women, while the history of previous CS (adjusted odds ratio 39.85) and interdelivery interval ≥10 years (adjusted odds ratio 1.52) also increased the risk of CS in multiparous women.

CONCLUSION

AMA increased the risk of a number of adverse pregnancy outcomes, and was independently associated with increased risk for CS. The increasing number of AMA parturients with risk factors is likely to increase CS rate in China in the near future, thus it is imperative to reduce the rate of primary CS as a matter of policy.

Interpregnancy interval and risk of stillbirth: a population-based case control study

PURPOSE

We examined the association between interpregnancy intervals (IPIs) and stillbirth (defined as fetal death ≥20 weeks), as both short and long IPIs have been associated with adverse perinatal outcomes. Prior pregnancy loss is also a known risk factor for stillbirth, and women who suffer a prior loss often have shorter IPIs. For these reasons, we also sought to quantify the proportion of the association between prior pregnancy loss and subsequent stillbirth risk that may be attributed to a short IPI.

METHODS

We used data from the Stillbirth Collaborative Research Network, a multisite case-control study conducted in 2006-2008, restricted to singleton pregnancies among multiparous or multigravid women (985 controls and 291 cases). We accounted for complex sample design and nonparticipation with weighted multivariable logistic regression.

RESULTS

In the adjusted models, IPIs <6 months, as compared with a reference of 18-23 months, were associated with increased odds of stillbirth (aOR 1.6, 95% CI: 0.8, 3.4). Long IPIs (60-100 months) were also associated with an increased odds of stillbirth (aOR 2.4, 95% CI: 1.2, 4.5). After control for covariates, about one-fifth (21.2%) of the association of prior pregnancy loss (stillbirth, ectopic pregnancy, molar pregnancy, or spontaneous abortion) and stillbirth may be attributable to a short IPI.

CONCLUSIONS

Our results suggest that women who experience a prior pregnancy loss may benefit from additional counseling on adequate birth spacing to reduce subsequent stillbirth risk.

Report of the Office of Population Affairs' expert work group meeting on short birth spacing and adverse pregnancy outcomes: Methodological quality of existing studies and future directions for research

BACKGROUND

The World Health Organization (WHO) recommends that women wait at least 24 months after a livebirth before attempting a subsequent pregnancy to reduce the risk of adverse maternal, perinatal, and infant health outcomes. However, the applicability of the WHO recommendations for women in the United States is unclear, as breast feeding, nutrition, maternal age at first birth, and total fertility rate differs substantially between the United States and the low- and middle-resource countries upon which most of the evidence is based.

METHODS

To inform guideline development for birth spacing specific to women in the United States, the Office of Population Affairs (OPA) convened an expert work group meeting in Washington, DC, on 14-15 September 2017 among reproductive, perinatal, paediatric, social, and public health epidemiologists; obstetrician-gynaecologists; biostatisticians; and experts in evidence synthesis related to women's health.

RESULTS

Presentations and discussion topics included the methodological quality of existing studies, evaluation of the evidence for causal effects of short interpregnancy intervals on adverse perinatal and maternal health outcomes, good practices for future research, and identification of research gaps and priorities for future work.

CONCLUSIONS

This report provides an overview of the presentations, discussions, and conclusions from the expert work group meeting.

Short interpregnancy intervals and adverse maternal outcomes in high-resource settings: An updated systematic review

BACKGROUND

Currently, no federal guidelines provide recommendations on healthy birth spacing for women in the United States. This systematic review summarises associations between short interpregnancy intervals and adverse maternal outcomes to inform the development of birth spacing recommendations for the United States.

METHODS

PubMed/Medline, POPLINE, EMBASE, CINAHL, the Cochrane Database of Systematic Reviews, and a previous systematic review were searched to identify relevant articles published from 1 January 2006 and 1 May 2017. Included studies reported maternal health outcomes following a short versus longer interpregnancy interval, were conducted in high-resource settings, and adjusted estimates for at least maternal age. Two investigators independently assessed study quality and applicability using established methods.

RESULTS

Seven cohort studies met inclusion criteria. There was limited but consistent evidence that short interpregnancy interval is associated with increased risk of precipitous labour and decreased risks of labour dystocia. There was some evidence that short interpregnancy interval is associated with increased risks of subsequent pre-pregnancy obesity and gestational diabetes, and decreased risk of preeclampsia. Among women with a previous caesarean delivery, short interpregnancy interval was associated with increased risk of uterine rupture in one study. No studies reported outcomes related to maternal depression, interpregnancy weight gain, maternal anaemia, or maternal mortality.

CONCLUSIONS

In studies from high-resource settings, short interpregnancy intervals are associated with both increased and decreased risks of adverse maternal outcomes. However, most outcomes were evaluated in single studies, and the strength of evidence supporting associations is low.

Adolescent Contraception Use after Pregnancy, an Opportunity for Improvement

STUDY OBJECTIVE

To describe contraceptive method use by adolescent women in the 6 months after any pregnancy.

DESIGN

We conducted a secondary analysis of the 2011-2013 and 2013-2015 cycles of the National Survey of Family Growth.

SETTING

This survey is a nationally-representative population-based survey of reproductive aged women in the United States.

PARTICIPANTS

The sample included respondents who had at least 1 pregnancy that ended within the contraceptive calendar period as well as before the month of the respondent's 20th birthday. Women were included even if they did not have a full 6 months' worth of data.

INTERVENTIONS AND MAIN OUTCOME MEASURES

We examined contraception method use at 1, 2, 4, and 6 months post pregnancy regardless of pregnancy outcome (live birth, induced abortion, or miscarriage).

RESULTS

Our sample consisted of 337 women with a mean age of 18.5 years. Almost half (N = 158, weighted percentage = 43.5%) of adolescents were using no method of contraception at 1 month post pregnancy. By 6 months post pregnancy, only 143 of 287 women with data through 6 months (weighted percentage = 49.7%) were using more effective methods of contraception (long-acting reversible contraception or hormonal methods), and 83 of these 287 were using no method (weighted percentage = 29.2%), including 61 of 261 women who reported that their last pregnancy was unwanted. Women from racial and ethnic minorities were less likely to use the most effective contraceptive methods. Rapid repeat pregnancy occurred among 44 of 209 women in the subsample with 18 months' follow-up data (weighted percentage = 16.9%). Only 56 of 337 adolescents (weighted percentage = 19.0%) used long-acting reversible contraceptive methods at any time post pregnancy regardless of pregnancy outcome.

CONCLUSION

Contraceptive use, especially of the most effective methods, remains low for adolescent women by 6 months post pregnancy.

Effect of interpregnancy interval on adverse pregnancy outcomes in northern Tanzania: a registry-based retrospective cohort study

Background

Both short and long interpregnancy intervals have been associated with an increased risk of adverse pregnancy outcomes. There is limited information about the impact of interpregnancy interval on pregnancy (IPI) outcomes in Tanzania. The objective of this study was to assess the effect of IPI on adverse pregnancy outcomes.

Methods

We performed a retrospective cohort study using maternally-linked data from Kilimanjaro Christian Medical Centre (KCMC) birth registry. A total of 17,030 singlet births from women who delivered singleton infant at KCMC from 2000 to 2010 were studied. Women with multi-fetal gestations and those who were referred from rural areas for various medical reasons were excluded. Outcome variables were preterm birth, low birth weight infants and perinatal death. A multiple logistic regression was used to assess the association between IPI and pregnancy outcomes.

Results

The median IPI was 36 months. Compared with IPIs of 24–36 months (referent group), short interpregnancy intervals (<24 months) was associated with preterm delivery (OR 1 · 52; 95 % CI 1.31–1.74); low birth weight (OR 1 · 61; 95 % CI 1 · 34–1.72) and perinatal death, (OR 1 · 63; 95 % CI 1.22–1.91). The IPI of 37–59 months or longer were also associated with higher risks of preterm birth and low birth weight, but not with perinatal death.

Conclusions

Our study confirmed that both short and long IPI are independent risk factors for adverse pregnancy outcomes. These finding emphasize the importance of providing support for family planning programs which will support optimal IPI and improve pregnancy outcomes.

Impact of interpregnancy interval on the subsequent risk of adverse perinatal outcomes

AIM

The aim of this study was to investigate the impact of interpregnancy interval as a risk factor on multiple adverse perinatal outcomes.

MATERIAL AND METHODS

Interpregnancy intervals and confounding factors were determined for healthy pregnancies (controls [n = 357]) and for pregnancies complicated by adverse perinatal outcomes. Interpregnancy interval was categorized as <6, 6-11, 12-17, 18-23, 24-35 and ≥36 months. Adverse outcomes included spontaneous labor leading to preterm birth (n = 265), preterm premature rupture of membranes (n = 245), pre-eclampsia (n = 286), gestational diabetes (n = 302), abnormal placentation (n = 154), anemia (n = 314), congenital anomalies (n = 459), post-partum hemorrhage (n = 326) and small for gestational age (n = 168). Multivariate logistic regression analysis was performed to assess the association of each outcome with the interpregnancy interval categories.

RESULTS

Spontaneous labor leading to preterm birth (odds ratio [OR], 1.86; 95% confidence interval [CI], 1.13-1.97), preterm premature rupture of membranes (OR, 1.69; 95%CI, 1.28-2.39), congenital anomalies (OR, 1.38; 95%CI, 1.09-1.76) and small for gestational age (OR, 1.68; 95%CI, 1.14-2.34) were significantly associated with intervals of <6 months. Among congenital anomalies, short interpregnancy interval represents an increased risk for cardiac defects (OR, 1.55; 95%CI, 1.09-5.46), neural tube defects (OR, 2.06; 95%CI, 1.32-7.64) and central nervous system anomalies (OR, 1.45; 95%CI, 1.12-3.65).

CONCLUSION

Short interpregnancy interval is an independent risk factor for adverse perinatal outcomes.

THE EFFECT OF PREGNANCY SPACING ON FETAL SURVIVAL AND NEONATAL MORTALITY IN RWANDA: A HECKMAN SELECTION ANALYSIS

Most studies on birth intervals and infant mortality ignore pregnancies that do not result in live births. Yet, fetal deaths are important in infant mortality analyses for three reasons: ignoring fetal deaths between two live births lengthens the measured interval between births, implying that short intervals are underestimated; the recommended inter-pregnancy interval (IPI) after a fetal loss is shorter (6 months) than after a live birth (24 months), as the effect of IPI on outcomes might differ according to the previous type of pregnancy outcome; fetal death will selectively reduce the population at risk of neonatal mortality, leading to biased results. This study uses the Heckman selection model to simultaneously estimate the combined effect of IPI duration and the type of pregnancy outcome at the start of the interval on pregnancy survival and neonatal mortality. The analysis is based on retrospective data from the Rwanda Demographic Health Surveys of 2000, 2005 and 2010. The results show a significant selection effect. After controlling for the selection bias, short (60 months) intervals after a fetal death reduce the chances of pregnancy survival, but no longer have an effect on neonatal mortality. For intervals starting with a live birth, the reverse is true. Short intervals (<24 months) do not affect pregnancy survival but increase the odds of neonatal mortality. If the previous child died in infancy, the highest odds are found for neonatal death regardless of the IPI duration.

Simulating uterine contraction by using an electro-chemo-mechanical model

Contractions of uterine smooth muscle cells consist of a chain of physiological processes. These contractions provide the required force to expel the fetus from the uterus. The inclusion of these physiological processes is, therefore, imperative when studying uterine contractions. In this study, an electro-chemo-mechanical model to replicate the excitation, activation, and contraction of uterine smooth muscle cells is developed. The presented modeling strategy enables efficient integration of knowledge about physiological processes at the cellular level to the organ level. The model is implemented in a three-dimensional finite element setting to simulate uterus contraction during labor in response to electrical discharges generated by pacemaker cells and propagated within the myometrium via gap junctions. Important clinical factors, such as uterine electrical activity and intrauterine pressure, are predicted using this simulation. The predictions are in agreement with clinically measured data reported in the literature. A parameter study is also carried out to investigate the impact of physiologically related parameters on the uterine contractility.

Does the interval since vaginal delivery influence the chance of vaginal birth after cesarean?

OBJECTIVE

To examine the association between interval since vaginal delivery and vaginal birth after cesarean (VBAC).

METHODS

Women with one prior low transverse cesarean and a prior vaginal delivery undergoing a trial of labor after cesarean at term were included in this cohort study. Multivariable analyses were performed to determine whether length of time since prior vaginal delivery was independently associated with VBAC and, if so, whether its inclusion enhanced the predictive capacity of previously published models.

RESULTS

Of the 5628 women included, 4901 (87%) achieved a VBAC. Each additional year since vaginal delivery decreased the odds of VBAC by 11% (95% CI: 10-13%). When added to an existing predictive model that included only factors available at early prenatal care, interval since vaginal delivery marginally improved the model's predictive ability (area under the curve [AUC] 0.73 versus 0.71, p < 0.01). When added to a model that included factors available proximate to the time of delivery, the addition of interval since vaginal delivery did not change the AUC (0.76 versus 0.75, p = 0.08).

CONCLUSIONS

A longer interval since vaginal delivery is associated with a decreased odd of VBAC. However, the addition of this interval to VBAC prediction models does not substantively improve their predictive ability.

Interpregnancy interval and obstetrical complications

Obstetricians are often presented with questions regarding the optimal interpregnancy interval (IPI). Short IPI has been associated with adverse perinatal and maternal outcomes, ranging from preterm birth and low birth weight to neonatal and maternal morbidity and mortality. Long IPI has in turn been associated with increased risk for preeclampsia and labor dystocia. In this review, we discuss the data regarding these associations along with recent studies revealing associations of short IPI with birth defects, schizophrenia, and autism. The optimal IPI may vary for different subgroups. We discuss the consequences of short IPI in women with a prior cesarean section, in particular the increased risk for uterine rupture and the considerations regarding a trial of labor in this subgroup. We review studies examining the interaction between short IPI and advanced maternal age and discuss the risk-benefit assessment for these women. Finally, we turn our attention to women after a stillbirth or an abortion, who often desire to conceive again with minimal delay. We discuss studies speaking in favor of a shorter IPI in this group. The accumulated data allow for the reevaluation of current IPI recommendations and management guidelines for women in general and among subpopulations with special circumstances. In particular, we suggest lowering the current minimal IPI recommendation to only 18 months (vs 24 months according to the latest World Health Organization recommendations), with even shorter recommended minimal IPI for women of advanced age and those who conceive after a spontaneous or induced abortion.

Effects of birth spacing on maternal, perinatal, infant, and child health: a systematic review of causal mechanisms

This systematic review of 58 observational studies identified hypothetical causal mechanisms explaining the effects of short and long intervals between pregnancies on maternal, perinatal, infant, and child health, and critically examined the scientific evidence for each causal mechanism hypothesized. The following hypothetical causal mechanisms for explaining the association between short intervals and adverse outcomes were identified: maternal nutritional depletion, folate depletion, cervical insufficiency, vertical transmission of infections, suboptimal lactation related to breastfeeding-pregnancy overlap, sibling competition, transmission of infectious diseases among siblings, incomplete healing of uterine scar from previous cesarean delivery, and abnormal remodeling of endometrial blood vessels. Women's physiological regression is the only hypothetical causal mechanism that has been proposed to explain the association between long intervals and adverse outcomes. We found growing evidence supporting most of these hypotheses.

Meperidine for uterine dystocia and its effect on duration of labor and neonatal acid-base status: a randomized clinical trial

AIM

The aim of this study was to evaluate the effectiveness of meperidine, administered during the first stage of labor in patients with uterine dystocia, on the duration of labor and neonatal acid-base status at birth.

MATERIAL AND METHODS

We randomly assigned 240 nulliparous women with a singleton pregnancy at term who were diagnosed with uterine dystocia in labor at 4-6-cm cervical dilatation to receive either a single dose of 50 mg meperidine in 10 mL of saline (slow intravenous injection over 2 min) or 10 mL of isotonic saline (control group). The primary outcome measures were duration of labor (from the time of beginning of the intervention to the time of the expulsion of the fetal head) and umbilical cord arterial acid-base status.

RESULTS

The evidence revealed no statistically significant difference between the two groups in length of labor (188.2 ± 92.3 min in the meperidine group compared to 205.4 ± 96.1 min in the placebo group, P = 0.159). The pH of the umbilical cord arterial samples was lower in the meperidine group than in the control group, although the difference was not statistically significant (P = 0.089).

CONCLUSION

Because of the absence of any beneficial effect of meperidine on uterine dystocia, its use in labor should be limited to pain relief in the absence of epidural analgesia.

Effect of interpregnancy interval on adverse perinatal outcomes--a national study

BACKGROUND

The interpregnancy interval (IPI) has been reported to influence the outcome of pregnancy and birth. We performed a national study in Israel to determine the impact of IPI on multiple adverse perinatal outcomes.

STUDY DESIGN

This longitudinal cohort study used birth certificates of siblings born to the same biological mother, with at least one previous birth and a subsequent singleton pregnancy. Adverse pregnancy outcomes included preterm delivery, very preterm birth, small for gestational age (SGA), very SGA (VSGA), early neonatal death and major congenital malformations. Multivariate logistic regression was performed for each outcome.

RESULTS

The study included 440,838 of a total of 846,845 reported live births in Israel over 5 years; excluded were primiparas (32%), multifetal births (4.9%) and those with incomplete data (10.9%). For IPIs shorter than 6 months, there were significantly increased risks for preterm birth (OR=1.23), SGA (OR=1.14), VSGA (OR=1.15), early neonatal death (OR=1.62) and congenital malformations (OR=1.14). Intervals of 60 months or longer had higher risks for preterm birth (OR=1.39) and VSGA (OR=1.16).

CONCLUSION

Optimal IPI recommendation of >11 months is an accessible and low-cost means to improve multiple adverse perinatal outcomes.

Obstetric risk indicators for labour dystocia in nulliparous women: a multi-centre cohort study

BACKGROUND

In nulliparous women dystocia is the most common obstetric problem and its etiology is largely unknown. The frequency of augmentation and cesarean delivery related to dystocia is high although it is not clear if a slow progress justifies the interventions. Studies of risk factors for dystocia often do not provide diagnostic criteria for the diagnosis. The aim of the present study was to identify obstetric and clinical risk indicators of dystocia defined by strict and explicit criteria.

METHODS

A multi-centre population based cohort study with prospectively collected data from 2810 nulliparous women in term spontaneous labour with a singleton infant in cephalic presentation. Data were collected by self-administered questionnaires and clinical data-records. Logistic regression analyses were used to estimate adjusted Odds Ratios (OR) and 95% confidence intervals (CI) are given.

RESULTS

The following characteristics, present at admission to hospital, were associated with dystocia during labour (OR, 95% CI): dilatation of cervix < 4 cm (1.63, 1.38-1.92), tense cervix (1.31, 1.04-1.65), thick lower segment (1.32, 1.09-1.61), fetal head above the inter-spinal diameter (2.29, 1.80-2.92) and poor fetal head-to-cervix contact (1.83, 1.31-2.56). The use of epidural analgesia (5.65, 4.33-7.38) was also associated with dystocia.

CONCLUSION

Vaginal examinations at admission provide useful information on risk indicators for dystocia. The strongest risk indicator was use of epidural analgesia and if part of that is causal, it is of concern.

Cesarean delivery for abnormal labor

Cesarean delivery is indicated at any stage in the labor process in the presence of nonreassuring fetal status or when conservative measures fail in the setting of abnormal labor. In the absence of maternal or fetal indications for expedited delivery, cesarean delivery is not indicated for latent phase disorders. When to intervene for protracted labor is arguable, but slow rates of labor progress are consistent with safe vaginal delivery. Cesarean delivery in the second stage should be avoided for at least 4 hours if there is progressive fetal descent.

Effects of birth spacing on maternal health: a systematic review

The objective of the study was to explore the association between birth spacing and risk of adverse maternal outcomes. The study was a systematic review of observational studies that examined the relationship between interpregnancy or birth intervals and adverse maternal outcomes. Twenty-two studies met the inclusion criteria. Overall, long interpregnancy intervals, possibly longer than 5 years, are independently associated with an increased risk of preeclampsia. There is emerging evidence that women with long interpregnancy intervals are at increased risk for labor dystocia and that short intervals are associated with increased risks of uterine rupture in women attempting a vaginal birth after previous cesarean delivery and uteroplacental bleeding disorders (placental abruption and placenta previa). Less clear is the association between short intervals and other adverse outcomes such as maternal death and anemia. Long interpregnancy intervals are independently associated with an increased risk of preeclampsia. Both short and long interpregnancy intervals seem to be related to other adverse maternal outcomes, but more research is needed.