Obstetric outcomes in the second birth of women with a previous caesarean delivery : a retrospective cohort study from Peru

PURPOSE: To examine obstetric outcomes in the second birth of women who had undergone a previous cesarean delivery. METHODS: This was a large hospital-based retrospective cohort study. We included pregnant women who had a previous delivery (vaginal or cesarean) attending their second birth from 2001 to 2009. Main inclusion criteria were singleton pregnancies and delivery between a gestation of 24 and 41 weeks. Two cohorts were selected, being women with a previous cesarean delivery (n=7,215) and those with a vaginal one (n=23,720). Both groups were compared and logistic regression was performed to adjust for confounding variables. The obstetric outcomes included uterine rupture, placenta previa, and placental-related complications such as placental abruption, preeclampsia, and spontaneous preterm delivery. RESULTS: Women with previous cesarean delivery were more likely to have adverse outcomes such as uterine rupture (OR=12.4, 95%CI 6.8–22.3), placental abruption (OR=1.4, 95%CI 1.1–2.1), preeclampsia (OR=1.4, 95%CI 1.2–1.6), and spontaneous preterm delivery (OR=1.4, 95%CI 1.1–1.7). CONCLUSIONS: Individuals with previous cesarean section have adverse obstetric outcomes in the subsequent pregnancy, including uterine rupture, and placental-related disorders such as preeclampsia, spontaneous preterm delivery, and placental abruption.

Obstetric outcomes in the second birth of women with a previous caesarean delivery: a retrospective cohort study from Peru

Introduction
Cesarean section is by far the most common major surgical procedure in obstetrics.Currently, its rates are above the levels of reference stated by the World Health Organization (WHO), in both developed and developing countries, with a tendency to increase 1,2 .Studies based on global population in Latin America have reported a 33% rate 2 .
Delivery by cesarean section is associated with increased risk of maternal and perinatal morbidities in the current pregnancy 3 .Additionally, it has been reported an increased risk of adverse obstetric outcomes in the following pregnancy regardless of the delivery mode.These outcomes include high risk of uterine rupture, which is raising according to the number of previous cesarean section 4,5 , and of developing placental abruption 6,7 .Also, some studies have showed an enormous possibility of developing placenta previa [6][7][8] , albeit this was not confirmed by others 9 .Recently, it has been seen an association between previous cesarean section and other perinatal outcomes, such as low birth weight and small-for-gestational age infant 10,11 .
There is some evidence that previous scar in the uterus could contribute to an impaired placentation, which may be the basis of developing future placental-related complications such as placental abruption, preeclampsia, and spontaneous preterm delivery 11,12 .However, the results of studies on women with a previous cesarean and obstetric outcomes in the following pregnancy vary substantially across populations and by study design, and commonly have not accounted for important confounding factors such as maternal age, previous obstetric and medical history, parity, and prior delivery method.
We aimed at examining obstetric outcomes as uterine rupture, placental abruption, preeclampsia, and spontaneous preterm delivery in the subsequent pregnancy among women with a previous cesarean delivery compared to those with the vaginal one.

Methods
A large retrospective cohort study was conducted to examine adverse obstetric outcomes in women who delivered at a national reference centre for maternal and perinatal care (Instituto Nacional Materno-Perinatal, Lima, Peru), between January 2001 and December 2009.Demographic, obstetric, and perinatal data were collected prospectively in a standardized format, which were retrieved from an electronic database.The study protocol was approved by the local institutional review board.Inclusion criteria were: gestational age (GA) at birth between 24+0 and 41+6 weeks; birth weight of more than 500 g, and complete data on the outcome variables.Exclusion criteria included multiple pregnancies, more than one previous birth, and previous uterine surgery.The study population was divided into two groups: women with a previous cesarean delivery and those with a previous vaginal one (Figure 1).
The following obstetric outcomes were searched as potentially affected by cesarean delivery: uterine rupture (including total and partial uterine rupture according to the postoperative report); placenta previa (as per the postoperative report); placental abruption (confirmed at operation); preeclampsia; spontaneous preterm delivery (spontaneous birth before 37 weeks); low birth weight (birth weight ≤2,500 g); intrauterine death (confirmed by ultrasound); and low Apgar score at five minutes defined as score <7.Preeclampsia was defined below as systolic pressure of ≥140 mmHg or diastolic of ≥90 mmHg on at least two occasions after a gestation period of 20 weeks with proteinuria of 300 mg or more in 24 hours or at least 1+ dipstick analysis of midstream or catheter urine specimen if no 24-hour collection was available.
Maternal and obstetric characteristics included: maternal age, defined as the mother's age at time of delivery; maternal weight (in kg); previous spontaneous abortion; previous intrauterine death; and history of chronic hypertension.Normality of continuous variables was tested with the Kolmogorov-Smirnov test.Continuous variables were summarized by robust estimators (i.e.median and interquartile ranges).Comparisons between women with a previous vaginal delivery or with a cesarean section were performed by the Mann-Whitney's U test for continuous variables and χ 2 test for categorical ones.The adjusted Odds Ratios (OR) and 95% confidence intervals (CI) were calculated after multivariate logistic regression analyses adjusted for confounding factors, such as maternal age, maternal weight, previous spontaneous abortions, previous intrauterine death, preeclampsia, and chronic hypertension.All statistical analyses were carried out with STATA software (version 9.0; Stata Corporation, College Station, TX, USA).A p-value of less than 0.05 was considered significant.

Results
During the nine-year study period, 138,949 deliveries occurred in the studied hospital (Figure 1).A total of 30,935 women with a second birth filled out the inclusion criteria.Of these, 23,720 had had a previous vaginal delivery and 7,215 had had a previous delivery by cesarean section.
General and obstetrics characteristics of both groups are presented in Table 1.Median maternal age was higher in women with a previous vaginal birth (p<0.001),whereas its weight was higher in subjects with a previous cesarean section compared to those who had a previous vaginal delivery (p<0.001).People with a previous cesarean section were more likely to have had one spontaneous abortion (p=0.01).No significant differences in the number of previous intrauterine death and chronic hypertension were observed.

Discussion
The present study reported an increased risk of adverse obstetric outcomes related to placental dysfunction, such as: placental abruption, preeclampsia and spontaneous preterm delivery in the subsequent pregnancy among women with a previous cesarean section.
Not surprisingly, an association between previous cesarean section and uterine rupture was observed.We found an OR of 12.4 (95%CI 6.8-22.3),which is significant even though there is a wide confidence interval that is accordance with other previous reports [13][14][15][16][17] .To note, we included cases of partial uterine rupture (dehiscence).Although we did not report the number of patients undergoing labor, in our hospital women with a previous cesarean section gave an informed consent for the trial of labor in the index pregnancy.
The present study noticed an increased risk of placental abruption (OR=1.4) in women with a previous cesarean section, which is consistent with other analyses 18,19 .Although we did not adjust for previous history of placental abruption, our findings are similar to previous studies controlling this factor 6 .This does not show increased risk of placenta previa as reported by others 6,7,10,18,20 .Although some other studies did not find any association between previous cesarean and placenta previa 9 , there are several confounding variables that should be taken into account in prospective researches.Furthermore, our data did not allow us to classify the types of placenta previa.In contrast to Smith et al. 20 , we did not see an increased risk of intrauterine death.However, we acknowledge that our study was not powerful enough to assess this outcome.
Still, an association between previous cesarean and related-placental complications, such as preeclampsia and spontaneous preterm delivery, was also described.This is biologically plausible since the cesarean section produces a disruption of the uterine cavity and an interruption of the circulation in future areas of implantation, which could cause dysfunction in the myometrium and endometrium [11][12][13] .
A previous analysis from Daltveit et al. 11 has also reported association of previous cesarean delivery with preeclampsia even when the research was restricted to women with previous history of preeclampsia.Similarly, Kennare et al. 10 have presented a relation with preterm delivery, albeit in their study there is no information about spontaneous preterm delivery.Since spontaneous preterm delivery has been associated with placental function 21 , we wanted to go further and test the hypothesis of association with spontaneous preterm delivery.These findings warrant further researches to improve our understanding on such topic.
Although a significant difference regarding maternal age and weight was seen, the little variances seem not to be clinically relevant.The main strength of this study is that the population attending our hospital is fairly homogeneous in terms of social and economic conditions.Therefore, the analysis was restricted to women of parity 1 with a single previous cesarean or single vaginal delivery, as multiple previous cesarean or previous successful vaginal delivery are known to influence the mode of delivery planning and obstetric outcomes.However, we acknowledge that this study has a several number of limitations, including its retrospective design.We were not able to identify important confounding factors, such as the obstetric indication for the previous cesarean and the birth interval.In addition, we did not have data about the previous history of preeclampsia, induction of labor, and spontaneous preterm delivery that are important confounding factors.
Among our population, the rate of repeated cesarean was high (about 78%) which is similar to developed countries 22 .The hospital under analysis is a major referral center for maternal and perinatal care, and such number may reflect an increased proportion of women at high risk.The raised rate of cesarean sections has considerable clinical and public health importance, and any strategy for its reduction is great, including the trial of labor in women with a previous cesarean section and the recognition of short-and long-term complications.A cesarean delivery amplifies the risk of mortality and surgical complications for the mother in the next pregnancies 23 .In addition to some infrequent adverse events (i.e.placenta accreta and uterine rupture), other obstetrics outcomes such as those reported herein (i.e.placental abruption, preeclampsia and preterm delivery) might be useful in counseling and reconsidering the option of a cesarean section in a nulliparous woman.
In conclusion, a previous cesarean section increases adverse obstetric outcomes related to placental dysfunction in a subsequent pregnancy, including preeclampsia, spontaneous preterm delivery, and placental abruption.

Table 1 .
General and obstetrics characteristics of the study population

Table 2 .
Perinatal outcomes in both study groups Comparison between groups -(i): χ 2 test for all perinatal outcomes; *p<0.05.