Objective
Cesarean delivery rates are on the rise in many countries, including the United States. There is mounting evidence that cesarean delivery is associated with adverse reproductive outcomes in subsequent pregnancies. The purpose of this article is to review those outcomes in a well-defined cohort of pregnant women.
Study Design
In a cohort of primigravid women from the Danish National Birth Cohort with known baseline exposure characteristics, we stratified women by method of first delivery, vaginal or cesarean, and evaluated for appearance of adverse reproductive events in subsequent pregnancies.
Results
After adjusting for age, body mass index, alcohol, smoking, and socioeconomic status, women who underwent cesarean delivery at first birth were at increased risk in their subsequent pregnancy for anemia (odds ratio [OR], 2.8; 95% confidence interval [CI], 2.3–3.4), placental abruption (OR, 2.3; 95% CI, 1.5–3.6), uterine rupture (OR, 268; 95% CI, 65.6–999), and hysterectomy (OR, 28.8; 95% CI, 3.1–263.8).
Conclusion
Women who deliver their first baby with a cesarean are at increased risk of adverse reproductive outcomes in subsequent pregnancies and should be counseled accordingly.
Cesarean delivery rates in developed countries are on the rise, with a mean of 21% and ranging from 6.2% to 36% of births. In 2007, cesarean births represented 31.8% of all births in the United States—an all-time high. In contrast, only 19.1% of births were delivered by cesarean in Denmark in 2005. Currently, there is no consensus regarding what the “ideal” cesarean rate should be; however, many researchers, clinicians, and women purport that when cesarean rates rise too high, “the risks to reproductive health may outweigh the benefits.” There is mounting evidence that cesarean delivery is associated with not only short-term health consequences such as bleeding, infection, impaired breast-feeding, and infant bonding, but perhaps more important, adverse reproductive outcomes in subsequent pregnancies such as ectopic pregnancy, abnormal placentation, and hysterectomy. The rising trend in cesarean delivery rates across the world suggests that women and their health care providers are unaware of these risks or perhaps consider these risks to be negligible.
To evaluate the role of cesarean on subsequent reproductive outcomes, our study examined the long-term reproductive outcomes in women who had an initial vaginal delivery compared to those with an initial cesarean delivery using the Danish National Birth Cohort (DNBC). Based on previous studies, we hypothesize that even after control of baseline confounders, women who have a cesarean delivery in their first pregnancy are at increased risk for adverse short- and long-term reproductive events than women who have a vaginal delivery in the first pregnancy.
Materials and Methods
The DNBC has been described extensively. The main features of the registry are repeated here for convenience. Women are recruited at their first health care visit during early pregnancy. Approximately 30% of Danish women participate in the DNBC, representing 60% of those invited. This cohort has been validated to produce similar associations with those who do not participate in the cohort.
After approval from the Danish Data Protection Agency, we identified a cohort of 26,059 primigravid women who participated in the DNBC during their first pregnancy and had at least 1 subsequent pregnancy with documented outcomes during the study period, October 1994 through August 2010. We excluded 1220 women (1061 women who had codes for vaginal delivery and cesarean at the same time, 94 women who had an abortion as the first outcome, 30 women who were gravida 2 at initiation of cohort, 4 women who had codes for delivery and abortion at the same time, and 31 women who were missing key background variables). The remaining 24,839 women comprised the study population for this analysis.
Baseline exposure characteristics were collected via interview and included data on lifestyle factors, health problems, and social conditions. Our primary outcomes were chosen based on literature review and analysis of risk and were stratified across the reproductive continuum and included the following: pregnancy loss (spontaneous abortion [SAB], ectopic pregnancy, intrauterine fetal demise [IUFD]) and antepartum or labor complications (preterm birth, anemia, postpartum hemorrhage, placenta previa, placenta accreta, abruption, uterine rupture, and hysterectomy).
International Statistical Classification of Diseases, 10th Revision coding as well as Danish procedure codes were used to identify delivery type and primary outcomes. The codes are listed in the Appendix . Categorical and continuous testing was performed with χ 2 and Student t test, respectively, with a significance level of P < .05 for all outcomes after the first delivery. Multiple logistic regression models were fitted to estimate the adjusted odds ratio of the first delivery by cesarean on each outcome. The presence of each outcome was then examined using the second delivery only as around 70% of women in this cohort delivered only 1 or 2 infants and to avoid oversampling the more fecund. Poisson regression models were used to estimate the adjusted effect of first delivery by cesarean on the number of SAB and ectopic pregnancies after the initial delivery and before the second delivery. Baseline adjustment for possible confounders included age, body mass index (BMI), alcohol use, tobacco use, and a marker for socioeconomic status based on income and occupation of both partners and grouped into 3 levels. Statistical analysis was performed with software (SAS, version 9.2; SAS Institute Inc, Cary, NC.
Results
Table 1 lists the background characteristics of the cohort identified at the initial interview by first delivery route. Women who experienced a cesarean delivery at the time of their first pregnancy were older, heavier, more likely to have undergone treatment for infertility, and less likely to have been on oral contraceptives prior to pregnancy. They were more likely to have asthma, hypertension during pregnancy, and urinary tract disease. With regard to social behaviors, women undergoing cesarean were more likely to be employed and were less likely to exercise or be in school or vocational training.
| Category at interview | Vaginal, n = 21,499 | Cesarean, n = 3340 | P value |
|---|---|---|---|
| Physical | |||
| Mean age, y | 27.4 | 28.2 | < .0001 |
| Mean weight, kg | 66.55 | 68.34 | < .0001 |
| Mean height, cm | 169.2 | 167.5 | < .0001 |
| Mean BMI | 23.23 | 24.35 | < .0001 |
| Pregnancy status | |||
| Oral contraceptive pills in 4 mo prior | 35% | 31% | < .0001 |
| Infertility treatment prior to pregnancy | 22% | 25% | .0063 |
| Pregnancy planning | |||
| Planned | 77% | 78% | |
| Partly | 13% | 13% | |
| No | 10% | 9% | |
| Medical conditions | |||
| Vaginal bleeding in pregnancy | 19% | 18% | .5639 |
| Vaginal infection in pregnancy | 10% | 10% | .3670 |
| Metabolic disorder | 1.4% | 1.4% | .2331 |
| Asthma | 9.4% | 10.4% | .0147 |
| Mental disorder, neurosis | 6.5% | 6.2% | .8238 |
| Anemia | 9.5% | 9.7% | .4025 |
| Urinary tract disease | 39% | 42% | .0061 |
| Urinary tract disease in pregnancy | 37% | 40% | .0136 |
| Hypertension | |||
| Yes | 4% | 5% | |
| Only in pregnancy | 0.4% | 0.6% | |
| No | 96% | 94% | |
| Social behaviors | |||
| Tobacco in pregnancy | 24% | 25% | .2392 |
| Exercise | 47% | 44% | .0010 |
| In school/training | 19% | 16% | < .0001 |
| Have spouse/partner | 98% | 98% | .8942 |
| Mean tobacco/d (cigarettes) | 7.6 | 8.1 | .0126 |
| Alcohol (any) | 21% | 20% | .4789 |
| Median beer/wk | 0 | 0 | .8579 |
| Median wine/wk | 0 | 0 | .9710 |
| Median spirits/wk | 0 | 0 | .1337 |
| Mean fish in meal/wk | 2.1 | 2.1 | .9029 |
| Median fish in meal/wk | 2.9 | 2.9 | .5198 |
| Of those smoking currently | |||
| Yes, daily | 47% | 44% | |
| Yes, <daily | 7% | 6% | |
| No | 47% | 50% | |
| Employed | |||
| Yes, 1 job | 79% | 82% | |
| Yes, 2 jobs | 0.2% | 0.3% | |
| Yes, >2 jobs | 0.02% | 0 | |
| No | 21% | 18% | |
| Partner supported | |||
| Unemployed | 18% | 18% | |
| Rehabilitation | 4% | 3% | |
| Social benefit | 5% | 4% | |
| Pension | 1% | 2% | |
| Wife | 4% | 4% | |
| Grant/education/training | 61% | 61% | |
| Leave | 2% | 1% | |
| Sick | 2% | 3% | |
| Socioeconomic status | |||
| High | 56.52% | 54.94% | |
| Mid | 36.34% | 37.35% | |
| Low | 7.14% | 7.72% |
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