Among adolescent women in the United States, 70% report sexual activity by age 191 and each year, 8–10% become pregnant.2,3 Of those adolescents who give birth, 17–35% will become pregnant again within a year of delivery.4,5 Oral contraceptives (OCs) are the favored prescription contraceptive method among adolescent women, but continuation rates are poor, with as many as 43% discontinuing use within 6 months of commencement.6 Experience with subdermal progesterone implants in adolescents have shown method continuation rates that vary from 71%7 to 93% at 12 months.6 The introduction of depot medroxyprogesterone acetate into the United States in 1992 produced an opportunity to improve contraceptive compliance among teenagers because the method is convenient (requiring injection only once every 3 months), effective, and coitus independent. Initial studies have reported continuation rates at 6 months of 66%8 and 78%.9 The aim of this prospective study was to examine contraceptive continuation and the incidence of repeat pregnancy at 12 months among postpartum adolescent women under the age of 18 years. Specifically, those choosing depot medroxyprogesterone acetate were compared with those choosing OCs; the reasons for discontinuation of contraceptive method, menstrual cycle control, and condom usage are reported.
Materials and Methods
The study protocol was approved by the University of Louisville Human Studies Committee. The study population consisted of 206 women under 18 years who delivered at our institution between January 8, 1997 and December 31, 1997. Patient accrual in the study was for 12 months and all patients were followed-up for a minimum of 12 months. Patients who fulfilled the entry criteria were identified through the labor and delivery database and all patients were enrolled before hospital discharge by one investigator (JP) using a standard questionnaire. The enrollment questionnaire inquired about type and length of contraceptive use before the index pregnancy, contraceptive failure, whether the index pregnancy had been planned, intention to breast-feed, and intended postpartum contraceptive method. Patients electing to commence OCs were given two packets of pills containing 30–35 μg ethinyl estradiol (EZ) along with a prescription for a 3-month supply at hospital discharge. They were instructed to commence the pills exactly 2 weeks from the date of delivery. Patients receiving depot medroxyprogesterone acetate were given a 150-mg intramuscular injection before hospital discharge. Contraceptive commencement was defined as the date of initial injection for depot medroxyprogesterone acetate users and the date of package issue for OC users. Discontinuation of contraception was recorded as 12 weeks after the last injection for depot medroxyprogesterone acetate users and the cessation date of pill intake for OC users. The medical records of all patients who ceased contraception were reviewed. Patients deemed lost to follow-up were considered to have continued contraception up to their last recorded clinic visit.
All patients were scheduled for a routine 6-week postpartum visit at one of six clinics that service the area. Enrolled patients were contacted by phone at 3, 6, 9, and 12 months following the index delivery and asked identical questions each time from a standard follow-up questionnaire. Each adolescent was asked about continued use of birth control and whether this had changed from the method chosen immediately postpartum. Questions regarding reasons for discontinuation, subsequent pregnancy, menstrual cycle control, and condom usage were also asked. If the patient answered yes to the question of subsequent pregnancy, the medical records were reviewed to confirm this. Pregnancy was defined as a positive urine or serum test for hCG. All pregnancies were dated according to last menstrual period (LMP) and verified by delivery date, gestation, and if this was not available, by the earliest recorded ultrasound. Menstrual control on chosen contraceptive method was assessed by asking patients to characterize their period as normal, irregular, infrequent, too frequent, or no period at all. Condom usage postpartum was recorded as yes or no and if the response was yes, then the patient was asked to quantify this use as regular or irregular.
If the patient could not be reached by phone, the questionnaire was mailed to the home address given at the time of delivery. If this was unsuccessful, review of the medical records at follow-up clinic was undertaken and the questionnaire was completed by one of the authors. If details of follow-up could not be obtained after this process, the patient was deemed lost to follow-up.
Statistical analysis was performed using SPSS version 8.0 (SPSS Inc., Chicago, IL). Categoric data were analyzed using χ2 and Fisher exact test. Mann-Whitney U test was performed for nonparametric data. Standard deviation (SD) was reported for mean and median values. Median method continuation and mean time to repeat pregnancy for both depot medroxyprogesterone acetate and OCs were estimated using Kaplan-Meier survival analysis where standard error (SE) and 95% confidence intervals (CI) were reported. The mean time to repeat pregnancy was reported instead of the median time whenever the pregnancy rate had not reached 50% at the end of the follow-up period. Log rank analysis was performed to determine any statistically significant difference between the groups. Statistical significance for all characteristics was set at P < .05. All reported P values are two sided.
There were 206 adolescents who fulfilled entry criteria for the study during the designated time period. Of these, 20 patients delivered and were discharged from hospital at a time when an investigator was unavailable to obtain informed consent, seven patients refused to take part in the study because they were not planning to use contraception, and two patients were medically unwell postpartum. The sample population consisted of 177 adolescents who chose depot medroxyprogesterone acetate (n = 99), OCs (n = 73), condoms (n = 3), and subdermal progesterone implants (n = 2). Adolescents choosing condoms and subdermal progesterone implants were excluded from final analysis as were 50 patients who enrolled but could not be contacted for follow-up. The final analysis included 122 patients (depot medroxyprogesterone acetate [n = 76] and OCs [n = 46]) with available follow-up data that were obtained by mail (46%), chart review (35%), and telephone (19%).
There was no significant difference in mean age (P = .47), gravidity (P = .78), or parity (P = .84) between those adolescents who chose to use OCs postpartum compared with depot medroxyprogesterone acetate (Table 1). Patients who did not attend follow-up visits (n = 50) were of similar age (mean 16.19 years), race (46% black, 52% white), gravidity (median 1, range 1–4), and parity (median 0, range 0–2) to those who did attend follow-up appointments (n = 122).
The majority of adolescents (n = 111, 91%) stated that the index pregnancy was unplanned. At the time of conception, 105 (86%) were not using any contraception. Of the 17 (14%) adolescents who were using contraception, eight used OCs, eight used condoms, and one used depot medroxyprogesterone acetate. Seven of these patients stopped using contraception before conception and ten described contraceptive failures: seven broken condoms and three who missed pills. Length of contraceptive use before the recent pregnancy did not differ between those who chose depot medroxyprogesterone acetate or OCs postpartum (median 12 months, range 4–60 months, and median 12 months, range 3–12 months, respectively, P = .89). All patients were asked a retrospective, yes-no question about whether they had difficulty obtaining contraception; 119 (98.3%) replied no. In addition, all women were asked whether they intended to breast-feed, 22 (18%) replied yes.
Postpartum contraceptive continuation curves for OCs and depot medroxyprogesterone acetate are presented in Figure 1, where continuation percent represents the percentage of patients still using the method at any given time during the follow-up period. The P value, calculated using log rank analysis, denotes a statistically significant difference in contraceptive continuation between the two curves. Median contraceptive continuation was 8.7 months (SE 1.5 months, 95% CI 5.6, 11.8 months). For those patients using OCs, the median continuation was 7.4 months (SE 1.5 months, 95% CI 4.55, 10.3 months) with 55.6% (SE 7%) and 27.4% (SE 7%) continuing at 6 and 12 months, respectively. Among depot medroxyprogesterone acetate users, the median continuation time was estimated to be greater than 17.8 months (the continuation rate had not decreased to 50% at study conclusion). However, continuation rates among depot medroxyprogesterone acetate users at 6 and 12 months were 71.4% (SE 5%) and 55.3% (SE 7%), respectively. Patients who used depot medroxyprogesterone acetate were significantly more likely to continue this method of contraception at 12 months than those choosing OCs (P = .002) (Figure 1). To assess the effect of censoring, the time to continuation analysis was also calculated with uncensored data, therefore assuming that all uncontactable patients had discontinued contraception as of their last recorded visit. In this worst-case-scenario analysis, there was no statistically significant difference between OC and depot medroxyprogesterone acetate continuation (P = .61). Of the 33 patients who discontinued OCs, ten changed to depot medroxyprogesterone acetate, seven to condoms, and 16 were not using any contraception. Among the 28 patients who ceased depot medroxyprogesterone acetate, 13 changed to OCs, nine used condoms, and six were not using any contraception. All patients who discontinued the contraception they had commenced immediately postpartum were asked to provide their reasons. Of 61 patients who discontinued, 49 (80%) gave a reason (Table 2). The experience of at least one side effect was cited as the reason for discontinuation in 11 of 24 (46%) OC users and 23 of 25 (92%) depot medroxyprogesterone acetate users (P = .004). The most common side effects among OC users were nausea and an inability to remember to take the pill; among depot medroxyprogesterone acetate users it was disrupted menstrual cycles and perceived weight gain. Among contraceptive discontinuers in either group, the experience of more than one side effect was common.
Eleven adolescents who chose OCs (11 of 46, 24%) and two (2 of 76, 3%) who selected depot medroxyprogesterone acetate became pregnant during the 12-month follow-up period and all pregnancies occurred after the 3-month postpartum visit. The overall incidence of repeat pregnancy at 12 months postpartum was 10.6%. The relative risk (RR) for repeat pregnancy in adolescents using OCs compared with depot medroxyprogesterone acetate was 9.09 (95% CI 2.1, 39.2). Among adolescents who selected OCs, the mean time to repeat pregnancy was 13.2 months (SE 1.18 months, 95% CI 10.9, 15.6 months) and for those who chose depot medroxyprogesterone acetate it was estimated to be 17.1 months (SE 0.4 months, 95% CI 16.1, 18 months). The mean time to repeat pregnancy was significantly longer for those adolescents who chose depot medroxyprogesterone acetate compared with those who chose OCs (P < .001). This is demonstrated in Figure 2 where percent not pregnant refers to the number of patients using either contraceptive method who were not pregnant during the follow-up period. The P value was derived using log rank analysis and designates a statistically significant difference in time to pregnancy between the curves. Of the 13 adolescents who became pregnant, ten had term deliveries and data on three patients were incomplete: one transferred out of the area at 30 weeks' gestation and two had first-trimester bleeding, presented to the emergency room for ultrasound, and did not attend for follow-up. All patients had discontinued contraception (stopped taking OCs or were late for their depot medroxyprogesterone acetate injection) before becoming pregnant.
Menstrual cycle patterns for 112 (91.8%) patients using postpartum contraception are presented in Table 3. The menstrual cycle was most commonly described as normal among OC users and irregular among depot medroxyprogesterone acetate users. The RR of an abnormal menstrual cycle for patients using depot medroxyprogesterone acetate compared with OCs was 1.59 (95% CI 1.15, 2.19). The number of patients in each subcategory was felt to be too small to produce meaningful further analysis.
Condom usage, in addition to postpartum OCs or depot medroxyprogesterone acetate use, was assessed. Responses were gathered from all patients by questionnaire or medical record review. Fifty-three (43.4%) patients reported using condoms (20 OCs and 33 depot medroxyprogesterone acetate users, respectively) and 49 (97%) reported regular use. There was no significant difference in condom usage between depot medroxyprogesterone acetate and OCs users (P = 1.0).
This prospective cohort study demonstrates that when compared with adolescent mothers using OCs, those using depot medroxyprogesterone acetate have a higher method continuation and a lower incidence of repeat pregnancy at 12 months postpartum. However, overall method continuation rates in this population remain disappointingly low with only 27% and 55% of OC and depot medroxyprogesterone acetate users, respectively, continuing at 12 months postpartum. Our results for OC continuation are similar to those of O'Dell et al,10 who in a retrospective study of postpartum adolescents, showed a 12-month continuation rate of 32%. Therefore, OC continuity among adolescent mothers may be lower than in adolescents in general where 12-month continuation rates of 40–50% have been reported.11–13 Therefore, it is possible that low OC continuation rates among adolescent mothers may be an indication of particular problems such as low motivation along with lack of support or time, making OCs a less attractive option for women in this population. These issues could be addressed in future research on the subject. In contrast, depot medroxyprogesterone acetate continuation among adolescent mothers appears similar to nulliparous adolescents with reported continuation rates of 40–42% at 12 months.14,15 A reassuring practice among the adolescents we studied was the use of an alternative form of contraception if the method initially chosen postpartum was discontinued. Among those who ceased contraception, 61% commenced another method, most commonly depot medroxyprogesterone acetate for those initially using OCs and OCs for those initially using depot medroxyprogesterone acetate. Therefore, although method continuation rates were low at 12 months, the majority of adolescent mothers we saw were using some form of contraception in the year following delivery. This is in contrast to their prepregnancy behavior where 86% were not using contraception at the time of conception. Poor prepregnancy contraceptive utilization was not the result of poor access to service, as 98% of our teens reported that they knew how to obtain contraception.
Side effects are an important reason for inconsistent use of contraception among adolescents. In our study, although contraceptive discontinuation was lower among depot medroxyprogesterone acetate than OC users, side effects were more likely to be the reason for discontinuation in those patients using depot medroxyprogesterone acetate. This is consistent with the findings of O'Dell et al10 who found that among adolescent mothers commencing birth control within 6 weeks of delivery, 58% of OC users and 93% of depot medroxyprogesterone acetate users cited side effects as the reason for contraceptive discontinuation. The most common adverse effects encountered were irregular menstrual cycles and perceived weight gain (though this was not formally quantified in our study) among depot medroxyprogesterone acetate users, and nausea and an inability to remember to take the pill in those using OCs. This suggests that the reasons for contraceptive discontinuation in adolescent mothers are very similar to those described by nulliparous adolescents using depot medroxyprogesterone acetate and OCs.8,12,14 When adolescents are given a list of possible side effects and asked to indicate those they have experienced, fatigue9 and depression8 have been reported with both depot medroxyprogesterone acetate and OCs. These factors are cited less often (and by none of our patients) when adolescents are asked to provide their own reasons for discontinuation. In addition, these complaints are common among adolescents not using contraception,9,15 so their prevalence as side effects is difficult to quantify. Other reported reasons for inconsistent use of birth control among adolescents include lack of a steady committed sexual relationship or infrequent sex,16,17 dissatisfaction with the medical visit or method dispensed,18,19 poor self esteem, or educational aspirations.16,20 These issues were not addressed in our study.
Recent studies comparing postpartum depot medroxyprogesterone acetate or subdermal progesterone implant use with OC use report overall repeat pregnancy rates of 16%10 and 20%21 at 15-month follow-up. This is comparable to our study where 10.6% of the cohort experienced repeat pregnancy within 12 months. The factor that consistently predicts repeat pregnancy among postpartum adolescents is selection of OCs over depot medroxyprogesterone acetate or subdermal progesterone implants as the primary method of birth control.10,21 This is demonstrated by 12-month postpartum repeat pregnancy rates ranging from 25–38%10,12,21 for OC users compared with 11% for those choosing depot medroxyprogesterone acetate.10 Among our patients, the mean time to repeat pregnancy was significantly shorter for OC users when compared with those using depot medroxyprogesterone acetate; this is reflected in pregnancy rates at 12 months of 24% among postpartum adolescents using OCs compared with 2.6% in those choosing depot medroxyprogesterone acetate. The lower pregnancy rates with depot medroxyprogesterone acetate may be the result of a higher continuation rate and less opportunity for noncompliance among users along with its prolonged duration of action, due to slow release from the injection site or fatty tissue accumulation.22 In addition, the inhibitory effect of long-acting progesterone on the hypothalamic pituitary axis may persist for some time after discontinuation, resulting in a delayed return of fertility.23
We assessed condom usage among adolescents using postpartum hormonal contraception. Overall use was poor, with only 43% of patients using condoms. However, 97% of those using condoms claimed to use them regularly. It has been suggested that adolescent users of implantable contraceptives are less likely to use condoms because they perceive that implants are extremely effective at preventing pregnancy.6 However, among our patients there was no significant difference in condom usage between OCs and depot medroxyprogesterone acetate users.
There are some limitations in our study. Although postpartum contraceptive method was not randomized, we were specifically interested in choice of contraception by adolescent mothers and randomization would not have allowed this assessment. The fact that subsequent visits were not conducted at a single site may have jeopardized our ability to adequately follow-up on our patients, as 28% of our initial enrollment did not keep scheduled return clinic visits. We believe that although every effort to contact the women in our study was made, it is possible that those patients who were lost to follow-up were obtaining contraception outside the designated clinics. However, repeat attendance appears to be a consistent problem in many studies dealing with adolescent contraception.9,12,19 Additional analysis of the discontinuation data was performed in the absence of censoring, therefore assuming that all those patients who were lost to follow-up had discontinued contraception at the time of the last available clinic visit. This analysis failed to reveal a significant difference between the OC and depot medroxyprogesterone acetate users in terms contraceptive continuation. Comparison of our data, both censored and uncensored, with the literature is difficult because the majority of studies investigating teenage contraception do not report both analyses. A very similar, retrospective study to ours10 demonstrated almost identical enrollment (161 patients) and lost to follow-up data (48 patients). The authors concluded that there was no difference in contraceptive continuation at 12 months; however, there was no separate analysis or comment about censoring to enable adequate comparison to our study. Therefore, the issue of censoring is an important consideration for further studies in this area.
Our study demonstrates that among adolescent mothers younger than 18 years of age, followed for 12 months postpartum, injections of depot medroxyprogesterone acetate every 3 months resulted in a higher contraceptive method continuation and a lower incidence of repeat pregnancy than OCs. Further prospective studies are required to see if these results are consistent in the long term and translate into lower teenage pregnancy rates. Since cycle disruption among depot medroxyprogesterone acetate users and missed pills among OC users were the most common reasons for contraceptive discontinuation, we recommend that patients be thoroughly counseled regarding these problems at contraceptive prescription.
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© 2000 The American College of Obstetricians and Gynecologists
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