Obesity and Contraception: Emerging Issues

Amitasrigowri S. Murthy, M.D., M.P.H., F.A.W.G.

Disclosures

Semin Reprod Med. 2010;28(2):156-163. 

In This Article

Contraceptive Methods

Combined Hormonal Methods

Oral Contraceptives Obesity may impact the efficacy of combined hormonal contraception (CHC), particularly the oral contraceptive (OC). One possible mechanism of this effect is dilution; steroids may have decreased availability due to increased circulating blood volume or fat sequestration. Obese women may also have different metabolism of steroids than normal weight women.[17] Although premarketing studies generally exclude women >130% of ideal body weight, recent studies have examined the efficacy of CHC in women who are overweight or obese. Holt et al published two studies, the first a retrospective analysis of data on 755 randomly selected women.[18] All women were on the OC pill, with doses of ethinyl estradiol from 20 mcg to 50 mcg. Contraceptive efficacy was measured as number of pregnancies over woman-years of use. Subjects who were in the heaviest quartile (>70 kg) had the highest number of pregnancies. Those on pills containing ≤35 micrograms of estrogen were also noted to have the highest number of pregnancies and correspondingly increased risk of contraceptive failure (relative risk, 4.5; 95% CI, 1.4 to 14.4). Limitations of this study include self-report of both weight and contraceptive failure with no confirmation of pregnancy and self-report of type of OCP used. A major limitation is that the highest weight quartile was similar to that of the overall population and not to that of an obese population.

Holt then examined a prospective cohort of a similar group of women using similar pills (n = 1000).[19] Weight was studied as BMI measurements, not quartiles; weight was self-reported. The association of heavier weight with higher pregnancy failure rates continued. Subjects with a BMI between 27.4 and 32.2 kg/m2 had increased odds of failure with confirmation of pregnancy (OR, 1.58; 95% CI, 1.11 to 2.24).

In the 2002 NSFG, obese women were 30% more likely to experience a failure while using OC. Hispanic or black women were more likely to be overweight or obese as compared with white women, and they had higher rates of contraceptive failure.[20] These findings were not significant, however, and could be due to biases in self-reporting.

Most other data have not found an increased risk of pill failure in obese women.[21–25] Trussell et al reviewed studies examining contraceptive efficacy in obese women and with the exception of the studies just mentioned, obesity conferred no increased risk of failure.[26] Two of the eight studies were prospective clinical trials, and the others were analyses of existing databases. The two clinical trials had measured body weights and were able to confirm that there was no increased risk of failure with OC use in women either overweight or obese.[21,22]

A recent study looking at the impact of obesity on the pharmacokinetics of OCs suggests that the ability to reach steady state of hormone levels is decreased in obese women. It may take 3 to 5 days longer for hormone levels in obese women to achieve the steady state levels necessary to allow for hypothalamic pituitary ovarian inhibition.[27] If this finding is replicated, it may have significance for initiation of combined hormonal contraception and the need for a backup method for a longer period in obese women.

Transdermal Patch

There is minimal data about the effects of weight on the efficacy of the contraceptive patch (Ortho Evra/Evra, Ortho-McNeil, Raritan, NJ). In the analysis of pooled data from the contraceptive patch approval studies (n = 3319), there were 15 pregnancies; 5 pregnancies were noted to be in women weighing >90 kg.[28] The product labeling recommends cautious use of the patch in women >90 kg due to possible decreased efficacy. Pharmacokinetic studies of the patch reveal that all four recommended site applications of the patch are efficacious, with similar levels of hormones on blood assays. The only difference in levels was seen when the patch was placed on the abdomen; lower levels of hormones were seen with abdominal placement, although these levels were still within the reference ranges of efficacy.[29]

Vaginal Ring

Efficacy of the vaginal ring (NuvaRing, Schering-Plough, Kenilworth, NJ) is very high; in a study evaluating >23,000 cycles of ring use, only 21 pregnancies occurred.[30] No prospective studies have examined ring use in those who are either overweight or obese; none of the preapproval studies included women weighing >80 kg. Efficacy is thought to be similar in obese as in normal weight women due to local absorption of medication through the vaginal mucosa.[31] A reanalysis of phase III data for the ring was performed, and no pregnancies were noted in heavier women (N = 6047; weight range, 88 to 272 pounds).[32] Given that the vaginal delivery of hormones in the ring bypasses first-pass metabolism by the liver, hormone levels may be higher in obese women, allowing for improved hypothalamic pituitary ovarian inhibition and perhaps improved efficacy.

Cycle Control

Obese women often have irregular ovulation, due to high levels of insulin and testosterone.[33] An epidemiological study looking at characteristics of menstrual cycles in women noted that women who were heavier tended to have longer and irregular menstrual cycles.[34] The odds of having a long cycle increased in a stepwise manner for women with a BMI >23. The prevalence of breakthrough bleeding or spotting in obese women using combined hormonal methods is unknown. A retrospective analysis of data from a study evaluating 2893 women (613 were overweight or obese) using two different formulations of a low-dose OC found that rates of breakthrough bleeding or spotting were not different across weight categories.[35] Although good cycle control with the ring has been shown in trials,[30,32] there is no data about cycle control and ring use by overweight or obese women.

Progestin-only Methods

Progestin-only Pills

Very little data support the decreased efficacy of progestin-only pills in obese women. A small British study of progestin-only pill users in 1974 demonstrated no increase in failure rates in obese women; the study's findings are limited by a single weight measurement and no mention of the number of obese women.[36] A more recent European study on OC surveillance monitored >50,000 OC users and found no association between obesity and users of progestin-only pills.[37] The number of obese women in the study, however, was not mentioned.

Contraceptive Injection

There are no data to support decreased efficacy with use of depot medroxyprogesterone acetate (DMPA) in obese women. A direct comparison between intramuscular (IM) DMPA and subcutaneous (SC) DMPA evaluated efficacy after 2 years of use (N = 534; 25% in each arm of the study had a BMI >30).[38] Although results were not reported by weight group, there were a significant number of obese women enrolled, and efficacy was high in both groups, with no pregnancies in the SC group and one pregnancy in the IM group.

DMPA use is associated with weight gain, particularly in those who are already obese.[39] In a clinical trial in which subjects used OCs, DMPA, or no birth control, obese women on DMPA (n = 15) gained >20 pounds (9 kg); normal weight women on DMPA (n = 100) gained between 8 and 10 pounds (4 kg). Weight gain was even more pronounced in obese adolescents and tended to occur more in the first year of use. When compared with nonobese DMPA users or to combined OC users, obese DMPA users were significantly more likely to gain weight. In 2008, the WHO expert working group classified DMPA use in obese adolescents as category 2; all other progestin-only methods were category 1. All methods of progestin-only contraception are classified as category 1 in obese women.

Contraceptive Implant

Preclinical trials of Implanon (Schering-Plough, Kenilworth, NJ) did not include women >130% above ideal body weight. The trials included 134 women who weighed >70 kg, and no pregnancies were seen in this group.[40] Data from preclinical trials followed a subset of women to assess ovulation during Implanon use over 3 years (N = 40); three women had ovulatory cycles near the end of year 3 but did not become pregnant (company training slides). Product labeling encourages clinical judgment regarding the 3-year limit in obese women; given the paucity of data, no definitive statement can be made regarding the efficacy of Implanon in obese women.

Side effects of Implanon include irregular bleeding. Patterns of irregular bleeding do not seem to be affected by weight, although very little data exist to confirm this.[38]

Intrauterine Devices

The copper intrauterine device (IUD) ParaGard (Teva Pharmaceuticals; Tikva, Israel) has spermicidal—and therefore local—effects on the uterine environment. Although there are no studies of the ParaGard in obese women, there should be no decreased efficacy. The Mirena intrauterine system (Bayer HealthCare Pharmaceuticals, Inc., Wayne, NJ) increases cervical mucus viscosity, impeding sperm entry into the uterine cavity, and changes in tubal fluid, which impair sperm migration. Because the Mirena also works by local effect, its efficacy also should not be affected by obesity. Placement of IUDs into the uterus may be more difficult in obese women. Longer instruments or an examination table with a higher weight capacity may be required.

Noncontraceptive Benefits Both the copper IUD and the Mirena intrauterine system offer protection from endometrial cancer; although no pattern of duration of IUD use conveying protection could be discerned.[41] Use of Mirena protects the endometrium from unopposed estrogen during anovulatory cycles and can reduce blood loss in women with menorrhagia.[41,42]

Sterilization

In the United States, interval sterilization is usually performed via laparoscopic tubal ligation. Obesity carries additional risks from general anesthesia and the increased risk of failure of entry into the peritoneal cavity, trauma to bowel, and vascular injury.[14,43] Anesthetic complications can arise from poor visualization of bony landmarks, need for longer needles, and the risk of difficult intubation. In addition, extra weight on the thorax and pressure from the abdomen can make ventilation during laparoscopy difficult. A steep Trendelenburg position may not be feasible due to the difficulty ventilating the patient as a result of the increased weight on the thorax. Because surgery is often more difficult in the obese, surgical time is increased thereby extending the time spent under anesthesia.

In a subset analysis of data from the U.S. Collaborative Review of Sterilization study, complications from interval laparoscopy were evaluated. Obese women had a 70% increased risk of complication (OR, 1.7; 95% CI, 1.2 to 2.6), although obesity was not as significant a risk factor as diabetes or use of general anesthesia.[44] It is unclear if the increased risk in obese women is due to the coexistence of comorbid conditions. Hysteroscopic sterilization such as the Essure Permanent Birth Control System (Conceptus, Inc., Mountain View, CA) or the Adiana Permanent Contraception System (Hologic, Inc., Bedford, MA) may be a better option of permanent contraception for obese women. Hysteroscopic entry could provide better visualization and decreased anesthesia risks because these procedures can be performed in the office under local anesthesia.

Barrier Methods

Barrier methods of contraception are user initiated and coital dependent, and they include male and female condoms, cervical caps, diaphragms, and spermicides. There has been renewed interest in and increased use of barrier methods due to increased education and awareness of prevention of sexually transmitted diseases including HIV. The most commonly used methods include male and female condoms, cervical caps, diaphragms, and spermicides. Barrier methods have some advantages when compared with longer acting or hormonal methods; they do not cause systemic side effects and do not alter bleeding patterns. A woman who needs contraception only intermittently may prefer them, and they are immediately effective. When used correctly, barrier methods—particularly the diaphragm and cervical cap—decrease the incidence of cervical cancer by half. Barrier methods alone, however, are not nearly as effective as hormonal or intrauterine contraception at preventing pregnancy. These methods can be a good option for obese patients because they are not weight dependent. Diaphragms would require assessment of fit if a woman undergoes significant weight change; the efficacy of cervical caps is affected more by parity than weight. There are no known effects of obesity on efficacy of other commonly used barriers such as condoms or spermicides.

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