Objective
We sought to evaluate the association between the rate of repeat adolescent births and mode of delivery.
Study Design
This was a retrospective cohort study of 899 adolescents delivering in Rhode Island. Repeat birth rates were calculated and compared between adolescents delivering their first baby via cesarean vs vaginally. Fisher’s exact test, Wilcoxon rank sum test, and survival analysis methods were utilized.
Results
Total repeat birth rate within 2 years was 15.9% with 17.4% for the cesarean cohort and 15.6% for the vaginal birth cohort (relative risk, 1.12; 95% confidence interval, 0.77–1.62). Median duration to repeat birth in the cesarean cohort was 20 months; for the vaginal birth cohort it was 17.6 months.
Conclusion
Repeat birth within 2 years of index birth for teen mothers whose first birth was a cesarean vs vaginal delivery was not statistically different; the trend in time to next delivery may give us information about when to direct interventions to prevent second pregnancies.
Adolescent pregnancy continues to be a significant public health issue in the United States. An estimated 10% of US adolescents become pregnant annually, and approximately 400,000 teens give birth. Further, among teens who have a first baby, approximately 50% of teen mothers become pregnant again within 2 years of having their first baby with approximately half of these pregnancies resulting in live births. The risk of poor outcomes associated with teen childbearing with respect to both mothers and their children is compounded by having a second child. For example, adolescents having a second child are less likely to return to school or become economically self-sufficient. They are also more likely to initiate prenatal care late in their pregnancy, placing them at higher risk for adverse obstetric outcomes. Finally, additional births to adolescents appear to have a significant negative impact on behavioral outcomes and the health status of their children.
Several studies have attempted to evaluate factors that may predict risk for repeat births in adolescent mothers, for example, education level, race, social support, and birth control methods. Other studies examining interventions with first-time adolescent mothers to prevent repeat birth have had mixed results. The idea that repeat childbearing in adolescents is entirely “accidental” has not been supported clinically or in the literature; in reality, a significant proportion of repeat adolescent pregnancies are intended. Similar to older adults, teens report a desire to closely space their children for reasons related to ease of child rearing and establishing a family.
An increasing proportion of births in the US occur by cesarean delivery, with approximately 30% of live births in 2006 being delivered by cesarean. Notably, a woman’s experience with prior birth has been shown to play a role in her decision to have a future pregnancy. For example, studies in adult women have shown that initial delivery by cesarean section is associated with a longer time to next conception when compared with women who delivered vaginally. A recent study examining whether a longer length of time to a next pregnancy was voluntary or involuntary demonstrated that women who had an elective cesarean were more likely to voluntarily delay or avoid another pregnancy. The reasons most frequently cited in the cesarean delivery group were issues related to postoperative recovery.
Given that approximate 25% of adolescent mothers will experience a repeat birth within 2 years, and the implications of having a second closely spaced birth, it is important to explore additional factors that may aid in identifying adolescents at high risk for repeat pregnancy. Based on information about the link between mode of delivery and birth spacing, it is plausible that mode of delivery with the first birth may be a factor influencing the likelihood that an adolescent will experience a closely spaced subsequent birth.
The objective of this study was to evaluate the relationship between mode of delivery in adolescent mothers and second birth within 2 years of a first birth. Based on prior research investigating mode of delivery and future childbearing, as well as clinical experience, we hypothesized that adolescent mothers who had cesarean deliveries would have a lower rate of repeat births within 2 years after a first birth compared with adolescents who had a vaginal delivery.
Materials and Methods
To determine the rate of repeat teen birth within 2 years of the index birth, we conducted a retrospective cohort study of teen mothers in Rhode Island who gave birth in 2004 and linked their records to subsequent births within 2 years. Rhode Island birth records for the year 2004 were searched to identify mothers aged ≤19 years having their first singleton live birth. Because of the relatively low number of twin births to this age group, teens whose first live birth resulted in twins were excluded. Institutional and Rhode Island Department of Health Institutional Review Board approval were obtained (Women and Infants Hospital 08-0065 and Health-Rhode Island Institutional Review Board no. 2008-06; approval letters available upon request).
Our exposure variable was mode of delivery (vaginal and cesarean). The primary outcome measure was repeat birth within 2 years. To determine an appropriate time frame for our cohort that would give us an appropriate sample size for our hypothesis, we made several a priori assumptions about the rates of delivery and repeat births based on clinical impressions and the literature. We assumed an overall 70% vaginal delivery rate and 30% cesarean delivery rate based on our institution practices. We estimated the total repeat teen birth rate at 2 years to be 17%, with a 10% repeat birth rate in the group with a history of primary cesarean delivery and a 20% repeat birth rate in the group with a history of a spontaneous vaginal delivery. The alpha was set at 0.05 and beta was set at 0.2. We determined that the total number of patients needed to detect the 10% difference in repeat births between the groups was 507. Since there are >1200 births to teens each year in Rhode Island with approximately 80% of them being first births, we determined that 1 year’s worth of data would be enough for the study sample. We chose 2004 to give us the most recent data with enough lag time for follow-up.
To identify those teens who had their first birth in 2004 and had a second birth within 2 years, birth records for the years 2004 through 2006 were searched and those teens who had records matching them to a second live birth within 24 months were identified. Once a match was made, the information was confirmed with additional identifiers. For example, if a match was made based on medical record number, the match was confirmed with name and date of birth to ensure the accuracy of the match. The records were then linked. All patient-identifying information was destroyed after all matches and linkages were confirmed and data collection was completed.
Vital records provided the following baseline characteristic data: race, ethnicity, education level, marital status, number of prenatal visits, number of prior pregnancies not resulting in live birth, and substance abuse. Obstetric outcome information included gestational age at delivery, birthweight, and pregnancy complications. Pregnancy complications included a wide range of prenatal and obstetric issues. The most common diagnoses recorded were fever, meconium, dysfunctional labor, cephalopelvic disproportion, and fetal distress. For the second pregnancy, in addition to the same pregnancy-related information collected for the first birth, we recorded time to second delivery as interdelivery interval.
For the data analysis, categorical variables were compared with Fisher’s exact test; continuous variables were summarized by medians and ranges; and groups were compared using the Wilcoxon rank sum test. If a particular data point was missing, it was not included in the analysis for that parameter. A time-to-event analysis was conducted to explore possible trends regarding interdelivery interval based on mode of delivery.
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