Adverse Pregnancy Outcomes and Sexual Violence Among Female Sex Workers Who Inject Drugs on the United States–Mexico Border

Abstract

This study examines the prevalence of miscarriage/stillbirth among female sex workers who inject drugs (FSW-IDUs) and measures its associations with physical and sexual violence. Baseline data from 582 FSW-IDUs enrolled in an HIV intervention study in Tijuana and Ciudad Juárez, Mexico were used for current analyses. 30% of participants had experienced at least one miscarriage/stillbirth, 51% had experienced sexual violence, and 49% had experienced physical violence. History of miscarriage/stillbirth was associated with sexual violence (adjusted odds ratio [aOR] = 1.7, p = .02) but not physical violence. Additional reproductive risks associated with miscarriage/stillbirth included high numbers of male clients in the previous month (aOR = 1.1 per 30 clients, p = 0.04), history of abortion (aOR = 3.7, p < .001), and higher number of pregnancies (aOR = 1.4 per additional pregnancy, p < .001). Programs and research with this population should integrate reproductive health and consider gender-based violence.

Gender-based violence is a violation of human rights with a substantial global burden (15%–70% prevalence of intimate partner violence worldwide) and serious public health implications (Garcia-Moreno, Jansen, Ellsberg, Heise, & Watts, 2006). Women who experience violence during pregnancy have increased risks of adverse health outcomes, including miscarriage (Alio, Nana, & Salihu, 2009; Johri et al., 2011; Silverman, Gupta, Decker, Kapur, & Raj, 2007; Stockl, Filippi, Watts, & Mbwambo, 2012; Taft, Watson, & Lee, 2004), induced abortion (Stockl et al., 2012), preterm birth (Sanchez et al., 2012), postpartum hemorrhage, fetal death, and low birth weight infants (Meuleners, Lee, Janssen, & Fraser, 2011; N. N. Sarkar, 2008). Victims of this abuse are also more vulnerable to unintended pregnancies (Pallitto & O’Campo, 2004; N. N. Sarkar, 2008). Despite this evidence in the general population, determination of the associations between physical and sexual violence and adverse pregnancy outcomes for female sex workers (FSWs) remains limited.

FSWs face heavy exposure to violence, with physical and sexual violence prevalence estimates exceeding 40% in several countries, including Canada, Thailand, and India (Decker, McCauley, Phuengsamran, Janyam, & Silverman, 2011; K. Sarkar et al., 2008; Shannon et al., 2009; Swain, Saggurti, Battala, Verma, & Jain, 2011; Ulibarri et al., 2010). These levels are due in part to the double burden of violence faced by FSWs, for whom both intimate partners and clients are potential perpetrators (Decker et al., 2010; Panchanadeswaran et al., 2008; Shannon et al., 2009; Ulibarri et al., 2011). Understanding the relationship between this violence and maternal health is critical because the pervasive levels of violence among FSWs further compromise the reproductive health of a population with generally limited access to health services (Harcourt et al., 2010; Kayembe et al., 2008).

FSWs have increased risks for adverse pregnancy outcomes beyond violence. They are at higher risk of unprotected sex with multiple partners, elevating their vulnerability to several reproductive health concerns including unwanted pregnancy, pregnancy loss, and sexually transmitted infections (STIs; Patterson et al., 2009; Swain et al., 2011; Wee, Barrett, Lian, Jayabaskar, & Chan, 2004). Examination of these concerns among FSWs who inject drugs (FSW-IDUs) is particularly needed because substance use is associated with increased risk for violence from clients and intimate partners (Panchanadeswaran et al., 2008; Ulibarri et al., 2011) and with reproductive health concerns (Keegan, Parva, Finnegan, Gerson, & Belden, 2010; Pinkham & Malinowska-Sempruch, 2008). Finally, migration, which is prevalent along the United States–Mexico border region where this study population lives, has been linked with both HIV/STIs and violence (K. Sarkar et al., 2008; Strathdee et al., 2008).

Despite their multiple sources of risk for adverse pregnancy outcomes, few studies have examined the reproductive health status of FSW-IDUs on the United States–Mexico border or elsewhere, and involuntary termination of pregnancy in this population has received no attention in the research literature. The increased interest in the health of FSWs in recent years has largely been focused on HIV (Couture et al., 2011; Scorgie et al., 2011; Yi et al., 2010) but has neglected consideration of reproductive health risks in this population.

Addressing this gap in the field, this study had two specific aims: First, we aimed to assess the prevalence of miscarriage/stillbirth among FSW-IDUs in two Mexican–United States border cities known for high rates of violence, Tijuana and Cuidad Juárez; Second, we aimed to examine associations between a history of physical and sexual violence and miscarriage/stillbirth beyond that which would be expected from known risk factors such as higher fertility (Bulletti, Flamigni, & Giacomucci, 1996), STIs (Denney & Culhane, 2009; Genc & Ledger, 2000; Mårdh, 2002; McGregor et al., 1995; Watson-Jones et al., 2002), and recent substance abuse (Keegan et al., 2010; Ness et al., 1999)— characteristics common to this population and known otherwise to heighten risk for these reproductive health outcomes. Answering these questions will expand the evidence base for services to prevent and mitigate sequelae—including miscarriage and stillbirth—of the high levels of violence experienced by FSW-IDUs.

METHODOLOGY

Study Population and Procedures

From October 2008 to July 2010, FSW-IDUs in Tijuana, Baja California and Ciudad Juárez, Chihuahua were enrolled in a behavioral intervention study designed to reduce risky behaviors associated with both sexual and injection drug use activities. The recruitment process and eligibility criteria have been described in detail elsewhere (Strathdee et al., 2011). In brief, outreach workers approached and screened women who were potentially FSWs working at bars, street corners, and motels. Eligibility criteria included being at least 18 years old, having unprotected vaginal or anal sex with a male client in the past month, having injected drugs and shared injection equipment within the past month, agreeing to accept free STI treatment (if needed), and being able to provide written, informed consent. Participants agreed to participate in interviewer-administered surveys and biological testing for STIs every 4 months during the study period. Data were collected by interviewer-administered survey as well as biological testing for HIV and other STIs. The study protocol was approved by institutional review boards at the University of California, San Diego, Tijuana General Hospital, the Universidad Autonoma de Ciudad Juárez and CENSIDA (Centro National para la Preventión y el Control del VIH y el SIDA) and written consent was given by all subjects. The total sample was 622 FSW-IDUs. For the purposes of this study, we used baseline data from the subsample of participants who reported ever being pregnant (N = 582).

Study Instrument and Measures

The study instrument has been described in detail previously, and included items assessing sociodemographics, migration history, violence history, sex work history, substance abuse history, reproductive health history, and health care use (Strathdee et al., 2011). Questionnaire domains were informed by the Risk Environment Framework, a multifaceted framework of social and structural risks, as originally proposed by Rhodes (2002, 2009). Rhodes (2002, 2009) posits that the “risk environment” maintains risky behaviors in vulnerable populations such as FSW-IDUs, such that the context and history of violence, for example, inhibits health protective behaviors and compromises health, although lack of protective behaviors may in turn also affect risk for violence. This framework has been used to understand violence as a risk factor for HIV/STI in this and similar populations (Goldenberg et al., 2011; Strathdee et al., 2011; Urada, Morisky, Hernandez, & Strathdee, 2012) and is being expanded in this study to understand reproductive health.

Independent Variables

The primary independent variables, physical and sexual violence, were assessed via a series of items created for use in this survey. Questions on the history of violence included lifetime experience of sexual violence (“Have you ever been forced or coerced to have nonconsensual sex against your will?”), age at first sexual violence, and median number of times experienced sexual violence. Physical violence was assessed by lifetime experience (“Have you ever been physically abused [i.e., hit or assaulted]?”), as well as age at first physical violence and median number of times experienced physical violence.

Other independent variables were viewed as covariates and organized into six domains: sociodemographics, migration, sex work, substance abuse, reproductive health, and health care use. Sociodemographic questions assessed participants’ age, language abilities, marital status, education level, and income. Migration questions included whether or not participants were born in the city of interview, whether they had ever travelled to the United States, whether they had moved to the city of interview because of deportation from the United States, and how long they had lived in the city of interview. Questions on the history of sex work included age of entry into sex work, how many years participants had been engaged in sex work, and the number of male clients in the previous month. Reproductive health history questions included age at first pregnancy, number of pregnancies, lifetime experience of induced abortion, male condom use in the past month (with clients or intimate partners), and non-condom contraceptive use in the past 6 months.

Substance abuse questions included average number of injections per day in the previous month; lifetime use of cocaine, heroin, and methamphetamine; alcohol consumption patterns; and history of drug treatment. A composite cocaine use variable was created from cocaine use, crack use, cocaine/heroin combination use, and cocaine/methamphetamine combination use. A composite heroin use variable was created from heroin use alone and heroin use in combination with other drugs (i.e., methamphetamine and cocaine). A composite methamphetamine use variable was created from methamphetamine use, cocaine/methamphetamine use, and heroin/methamphetamine use. Heavy alcohol use was measured by self-report (frequency of five or more alcoholic drinks at once in the past month).

Finally, health care use questions included whether participants had ever had a gynecological visit, the number of gynecological visits per year, whether participants had ever treated STIs with home remedies, whether they had ever received treatment for a drug-related problem including methadone maintenance, and the number of times treated for a drug-related problem.

Dependent Variable

The dependent variable was constructed from a question asking participants “How many miscarriages/stillbirths have you had?” Continuous responses were dichotomized into “ever” and “never.”

Laboratory Testing

Blood and urine samples were obtained for HIV and STI testing. HIV was assessed via rapid test (Determine, Abbott Pharmaceuticals, Boston, MA) and confirmatory testing on all positive rapid tests, using HIV-1 enzyme immunoassay and immunofluorescence assay. Syphilis was initially screened by rapid test (Determine Syphilis TP; Abbott Pharmaceuticals, Boston, MA), and reactive samples received confirmatory testing with the Treponema pallidum particle agglutination assay (TPPA; Fujirebio, Wilmington, DE, USA). Both active syphilis (syphilis titer ≥ 1:8) and lifetime syphilis infection were confirmed. Chlamydia and gonorrhea were initially diagnosed by rapid test (BioStar OIA GC and CHLAMYDIA), and samples that screened positive then received confirmatory testing using transcription-mediated assay (TMA; Genprobe, San Diego, CA). This rapid testing was discontinued in March 2009 following CDC recommendations, after which all Chlamydia and gonorrhea diagnosis was done by urine testing using TMA (Genprobe, San Diego, CA). Trichomoniasis and bacterial vaginosis were diagnosed by rapid testing (respectively OSOM Trichomonas Rapid Test and OSOM BVBlue Test, Genzyme diagnostics, San Diego, CA). All confirmatory testing was conducted by the San Diego County Health Department. Women testing positive for these STIs received free counseling and treatment, and were also referred to the local municipal health department for follow-up. HIV cases received posttest counseling and were referred to the Municipal HIV/STI Specialty Clinic in Tijuana.

Statistical Analysis

Miscarriage/stillbirth ratio was calculated as the number of miscarriages/stillbirths reported divided by the total number of pregnancies reported. To assess group differences between women who experienced miscarriage/stillbirth versus those who had not, continuous variables were analyzed using Wilcoxon’s rank sum tests (all continuous variables were non-normally distributed). Categorical variables were analyzed using Pearson’s chi-square tests and Fisher’s exact test (for expected frequencies <5). All variables were examined for collinearity and outliers. Interview location was excluded from analyses because of its high correlation with methamphetamine use (Pearson’s correlation coefficient = 0.7).

Bivariate and multivariate logistic regression was used to assess the association between sexual violence, physical violence (independent variables), and lifetime experience of miscarriage/stillbirth (dependent variable), after controlling for relevant covariates. All regression models were adjusted for overdispersion. Covariates that had <0.10 significance levels in bivariate analyses were considered for inclusion in multivariate models, as well as age, a known risk factor for miscarriage/stillbirth (Lawn et al., 2009; Nybo Andersen, Wohlfahrt, Christens, Olsen, & Melbye, 2000). Multivariate logistic regression was conducted using the likelihood ratio test to compare nested models. Variables that achieved p values of ≤.05 were retained, and models were assessed for goodness of fit. The potential interaction between physical violence and sexual violence on the odds of miscarriage/stillbirth was also assessed.

RESULTS

Sample Characteristics

Of the 582 FSW-IDUs surveyed in Tijuana (n = 285) and Ciudad Juárez (n = 297) who reported ever having been pregnant, women were an average of 34 years old (range: 18–60 years), had given birth to an average of 3.1 children, and had a mean of 3.6 pregnancies. Nearly one-third of respondents (30%) had experienced at least one miscarriage/stillbirth, with a reported miscarriage/stillbirth ratio of 12.4 per 100 pregnancies. Half had experienced sexual violence (51%) or physical violence (49%), and 35% had experienced both. On average, women were younger when they first experienced sexual violence compared to physical violence (16.8 years vs. 20.1 years, respectively). Sexual violence was less frequent than physical violence, with an average of 11 events of sexual violence (standard deviation [SD] = 21.8) per participant, compared to more than 28 average events of physical violence (SD = 54.5).

Bivariate Associations

Participants with a history of miscarriage or stillbirth did not differ significantly from those who had not experienced a miscarriage or stillbirth with respect to sociodemographic characteristics such as English language skills, marital status, education, age, or income (Table 1). The two groups also had similar migration histories with the exception of city of origin—women who had experienced a miscarriage/stillbirth were significantly more likely to have been born outside the city where they were working compared to those who had never experienced a miscarriage/stillbirth (81% vs. 69%, p < .01).

TABLE 1.

Characteristics of FSW-IDUs in Tijuana and Ciudad Juárez and Bivariate Associations With Lifetime Experience of Miscarriage or Stillbirth

Characteristics	All Subjects (N = 582)		Ever Had Miscarriage/Stillbirth (N = 174)		Never Had Miscarriage/Stillbirth (N = 408)		χ2/Z-test statistica	Odds Ratio
	n	%	n	%	n	%		OR	95% CI
Sociodemographics
Speaks English							0.05
Yes	147	25.3	45	25.9	102	25.0		1.05	(0.69, 1.57)
No	435	74.7	129	74.1	306	75.0		REF
Marital status							4.32
Never married	282	48.5	85	48.9	197	48.3		REF
Currently married	220	37.8	58	33.3	162	39.7		0.83	(0.56, 1.23)
Previously married	80	13.7	31	17.8	49	12.0		1.47	(0.88, 2.46)
Education							0.13
Lower than secondary	429	73.7	130	74.7	299	73.3		REF
Secondary or higher	153	26.3	44	25.3	109	26.7		0.93	(0.62, 1.39)
Ageb	33.0	12.0	34.0	11.0	33.0	12.0	1.58	1.02	(0.99, 1.04)
Average monthly income ≥3,500 pesos							2.22
Yes	275	47.6	91	52.3	184	45.5		1.31	(0.92, 1.87)
No	303	52.4	83	47.7	220	54.5		REF
Migration History
Years lived in city of interviewb	12.1	13.9	12.3	14.3	12.1	13.4	−0.23	1.00	(0.98, 1.02)
Born outside of city of interview							8.18***
Yes	421	72.3	140	80.5	281	68.9		1.86***	(1.21, 2.86)
No	161	27.7	34	19.5	127	31.1		REF
Moved to city of interview because of deportation from United States							0.56
Yes	49	8.4	14	13.0	35	16.1		0.77	(0.40, 1.51)
No	276	84.9	94	87.0	182	83.9		REF
Travelled to United States (ever)							2.96*
Yes	296	50.9	98	56.3	198	48.5		1.37*	(0.96, 1.95)
No	286	49.1	76	43.7	210	51.5		REF
Sex Work History
Age of entry into sex workb	19.0	8.5	19.5	8.0	18.0	8.0	2.59***	1.04**	(1.01, 1.07)
Years of sex workb	12.0	11.0	11.0	11.0	12.0	12.0	−1.15	0.99	(0.97, 1.01)
Number of male clients (per 30 clients)b,c	30.0	70.0	48.0	70.0	24.0	62.0	4.04****	1.17***	(1.05, 1.30)
Substance Abuse History
Number of drug injections/dayb,c	4.0	2.0	3.0	2.0	4.0	2.0	−0.81	0.88**	(0.78, 1.00)
Greater than 5 alcoholic drinks at a timec							0.14
Yes	267	45.9	88	79.3	179	81.0		0.90	(0.51, 1.59)
No	65	19.6	23	20.7	42	19.0		REF
Cocaine/crack use (ever)							7.68***
Yes	430	73.9	142	81.6	288	70.6		1.85***	(1.19, 2.87)
No	152	26.1	32	18.4	120	29.4		REF
Heroin use (ever)							0.36e
Yes	570	97.9	169	97.1	401	98.3		0.59	(0.19, 1.89)
No	12	2.1	5	2.9	7	1.7		REF
Methamphetamine use (ever)							8.15***
Yes	303	52.2	75	43.1	228	56.0		0.60***	(0.42, 0.85)
No	278	47.9	99	56.9	179	44.0		REF
Reproductive Health History
Age at first pregnancyb	16.0	3.0	16.0	4.0	16.0	4.0	−2.91***	0.92**	(0.85, 0.99)
Number of pregnanciesb	3.0	3.0	4.0	3.0	3.0	2.0	7.58****	1.44****	(1.21, 1.72)
Induced abortion (ever)							36.10****
Yes	51	8.8	34	19.5	17	4.2		5.59****	(3.03, 10.32)
No	531	91.2	140	80.5	391	95.8		REF
Male condom usec,d							3.87**
Yes	219	37.6	76	43.7	143	35.1		REF
No	363	62.4	98	56.3	265	65.0		0.70**	(0.48, 1.00)
Non-condom contraceptive usee							0.20
Yes	219	37.7	68	39.1	151	37.1		REF
No	362	62.3	106	60.9	256	62.9		0.92	(0.64, 1.32)
HIV							3.50*
Positive	33	5.7	5	2.9	28	6.9		0.41*	(0.15, 1.07)
Negative	547	94.3	167	97.1	380	93.1		REF
Chlamydia							0.10
Positive	76	13.1	24	13.8	52	12.8		1.09	(0.65, 1.83)
Negative	504	86.9	150	86.2	354	87.2		REF
Gonorrhea							0.18f
Positive	10	1.9	5	3.2	5	1.4		2.36	(0.67, 8.26)
Negative	507	98.1	151	96.8	356	98.6		REF
Bacterial vaginosis							0.03
Positive	231	39.7	70	40.2	161	39.5		1.03	(0.72, 1.48)
Negative	351	60.3	104	59.8	247	60.5		REF
Trichomoniasis							0.48
Positive	213	36.6	60	34.5	153	37.5		0.88	(0.61, 1.27)
Negative	369	63.4	114	65.5	255	62.5		REF
Syphilis (lifetime)							0.01
Positive	160	28.1	47	27.8	113	28.2		0.98	(0.66, 1.47)
Negative	410	71.9	122	72.2	288	71.8		REF
Health Care Use
Gynecological visit (ever)							2.00
Yes	113	19.4	40	23.1	73	18.0		1.37	(0.89, 2.11)
No	465	80.5	133	76.9	332	82.0		REF
Treated STIs with home remedies (ever)							0.54
Yes	146	25.1	47	27.2	99	24.3		1.16	(0.78, 1.74)
No	435	74.9	126	72.8	309	75.7		REF
Enrolled in methadone program (ever)							0.05
Yes	56	18.5	18	17.8	38	18.9		0.93	(0.50, 1.73)
No	246	81.5	83	82.2	163	81.1		REF
Received treatment for drug-related problem (ever)							4.06**
Yes	304	52.2	102	58.6	202	49.5		1.45**	(1.01, 2.07)
No	278	47.8	72	41.4	206	50.5		REF
Sexual and Physical Violence History
Sexual violence/rape (ever)							12.06****
Yes	296	50.9	108	62.4	188	46.7		1.90****	(1.32, 2.74)
No	280	48.6	65	37.6	215	53.4		REF
Age at first sexual violence/rapeb	15.0	11.0	15.0	11.0	16.0	10.0	−1.36	0.98	(0.96, 1.01)
Physical violence (ever)							6.16**
Yes	287	49.3	100	57.8	187	46.5		1.58**	(1.10, 2.26)
No	288	50.1	73	42.2	215	53.5		REF
Age at first physical violenceb	19.0	9.0	19.0	10.5	18.0	8.0	0.69	1.01	(0.98, 1.04)

Note. Because of missing values, certain percentages may have denominators smaller than those indicated in the column headings. FSW-IDs = female sex workers who inject drugs. REF = Reference group.

^aChi-square test statistic for categorical variables, Wilcoxon’s rank sum test z statistic for continuous variables.

^bContinuous variable; median and interquartile range presented in place of sample size and percent.

^cIn previous month.

^dDuring vaginal, anal or oral sex with male clients, or during vaginal/anal sex with spouse/steady partner.

^eIn previous 6 months.

^fExpected counts are less than 5; displaying P value for Fisher’s exact test.

^*p < .10.

^**p < .05.

^***p < .01.

^****p < .001.

FSW-IDUs who had experienced miscarriage/stillbirth reported servicing twice as many clients in the past month as those who had not had miscarriage/stillbirth (median 48 vs. 24, p < .01). However, the former group entered sex work at an older age than their counterparts who had not experienced miscarriage/stillbirth (median age 19.5 vs. 18.0, p < .01). There was no significant difference between groups with respect to the duration of time they had been engaged in sex work.

Overall, our sample of FSW-IDUs reported heavy drug use, with a median of four injections per day in the past month. Those who had a history of miscarriage/stillbirth were more likely to have ever used cocaine (82% vs. 71%, p < .01) than their counterparts but were less likely to have used methamphetamine (43% vs. 56%, p < .01). There was no difference between the two groups regarding heroin use (98% of respondents reported having ever used heroin) or alcohol use (46% of respondents reported consuming more than 5 drinks at a time in the past 30 days).

In terms of reproductive health history, FSW-IDUs who had experienced miscarriage/stillbirth were, on average, slightly younger when they first became pregnant (16.3 years compared to 17.1 years, p < .01), and had had more pregnancies (4.6 vs. 3.1 per woman, p < .01). Women who reported having had induced abortions were much more likely to also report a previous miscarriage/stillbirth (20% vs. 4%, p < .01, p < .0001). Contraceptive use was low, with only 38% of FSW-IDUs reporting condom use in the past month and 38% reporting non-condom contraceptive use in the past 6 months. Contraceptive use associations were variable, with more women who had had miscarriages/stillbirths reporting condom use in the past month compared to their counterparts (44% vs. 35%, p = .05). There was no significant difference between groups in terms of non-condom contraceptive use.

Overall, 74% of FSW-IDUs had at least one laboratory-diagnosed STI, but HIV was the only STI that was marginally different between the two groups. Fewer FSW-IDUs with a history of miscarriage/stillbirth were HIV-infected compared with those with no history of miscarriage/stillbirth (3% vs. 7%, p = .06).

In terms of health care use, only 19% of respondents indicated that they had ever had a gynecological visit, and 25% indicated that they had treated STIs with home remedies. Neither gynecological visits nor home remedy treatment of STIs varied significantly between groups. FSW-IDUs with a history of miscarriage/stillbirth were more likely to have ever received treatment for a drug-related problem (59% vs. 50%, p = .04), and reported receiving drug treatment an average of 3.3 times. Of the 10% of FSW-IDUs who had ever enrolled in a methadone treatment program, there was no significant difference between groups.

FSW-IDUs with a history of miscarriage/stillbirth were more likely to have experienced sexual violence (62% vs. 47%, p < .01), physical violence (58% vs. 47%, p = .01), and both sexual and physical violence (43% vs. 31%, p < .01) than their counterparts, although neither the age at first sexual and first physical violence nor the number of events differed significantly between the two groups.

Multivariate Associations

In the final multivariate regression model, sexual violence was significantly associated with a lifetime experience of miscarriage/stillbirth (aOR = 1.68; Table 2). Additional significant covariates in the model included number of male clients in the previous month (aOR = 1.13 for every 30 clients), lifetime experience of induced abortion (aOR = 3.70), and number of pregnancies (aOR = 1.43). Although physical violence was significantly associated with miscarriage/stillbirth in bivariate analysis, neither physical violence nor the physical/sexual violence interaction was significantly associated with miscarriage/stillbirth in the final model.

TABLE 2.

Multivariate Factors Associated With Lifetime Experience of Miscarriage or Stillbirth Among Female Sex Workers Who Inject Drugs in Tijuana and Ciudad Juárez

	Adjusted Odds Ratio
	aOR	95% CI
Sexual violence/rape (ever)	1.68**	1.07, 2.62
Number of male clients in previous month (per 30 clients)	1.13**	1.01, 1.27
Induced abortion (ever)	3.70****	1.74, 7.86
Number of pregnancies	1.43****	1.26, 1.61

Note. CI = confidence interval.

^**p < .05.

^****p < .001.

DISCUSSION

Although rates of miscarriage/stillbirth among FSW-IDUs in Tijuana and Ciudad Juárez are in line with global averages, the lifetime burden of miscarriage/stillbirth is substantial because of the high number of pregnancies among this relatively young population of women. In addition, women in this study reported very high levels of both sexual and physical violence. Approximately half of the sample experienced sexual or physical violence at some point in their lives, and more than one-third of women experienced both sexual and physical violence. These levels of sexual abuse in particular are strikingly higher than rates of violence seen in general populations of women (World Health Organization, 2005) but is similar to those seen among other samples of FSWs (Decker et al., 2011; Panchanadeswaran et al., 2008; Shannon et al., 2009; Swain et al., 2011; Ulibarri et al., 2010). Our findings suggest that sexual violence is an important factor in explaining the lifetime burden of miscarriage/stillbirth among FSW-IDUs, even after controlling for other known risk factors such as recent substance use.

Although physical violence has been associated with miscarriage/stillbirth in other populations (Alio et al., 2009; Silverman et al., 2007; Taft et al., 2004), this was not the case for FSW-IDUs in Tijuana and Ciudad Juárez. We hypothesized that the association between physical violence and miscarriage/stillbirth was being masked by sexual violence. This masking could be a consequence of sexual violence having greater capacity to result in sexual trauma and thus miscarriage/stillbirth, relative to physical trauma. However, exploratory modeling indicated no significant masking. Alternatively, because sexual violence was experienced at a younger age on average than physical violence, it may have potentiated its influence on the reproductive health of this population. The average age at first pregnancy for FSW-IDUs was 16.8 years, the same age as the first event of sexual violence. Because women in this age range are more likely to experience pregnancy loss than women in their 20s (Nybo Andersen et al., 2000), we also hypothesized that the combination of early pregnancy and early sexual violence could be masking the effects of the physical violence which generally started at an older age. Exploratory modeling again did not show significant masking. It is also possible that our measure of physical abuse may have been inadequate to detect the association between physical abuse and miscarriage in this population, particularly given how pervasive physical abuse was. Data from this population on the level of severity of physical abuse may provide more insight on this issue than was possible in this study.

Factors related to high levels of unprotected sexual activity appear to be important components of the reproductive health profile of this highly vulnerable and marginalized population. FSW-IDUs who had had a miscarriage/stillbirth had more male clients in the past month. They also had significantly more transactions with nonregular clients compared to other women. This difference in clientele may contribute to other factors associated with miscarriage/stillbirth. Only 40% of FSW-IDUs reported using condoms in the previous month, a low uptake that may have a partially financial explanation—respondents indicated that they made on average 27%–39% more for sexual intercourse without a condom than they would have using a condom. High levels of unprotected sex are more likely to result in unwanted pregnancies and subsequent induced abortions, as well as placing women at risk of acquiring STIs that may contribute to miscarriage/stillbirth, including syphilis, Chlamydia, and bacterial vaginosis (Denney & Culhane, 2009; Genc & Ledger, 2000; Mårdh, 2002; McGregor et al., 1995; Watson-Jones et al., 2002). Although these STIs did not show strong associations with miscarriage/stillbirth in our cross-sectional analysis, their cumulative effects over several years of sex work may have contributed to negative reproductive health outcomes. These negative outcomes may also be related to damage from unsafe induced abortion techniques (56% of the induced abortions reported in this population were unsafe; unpublished data), a consequence of the lack of safe abortion services available to these women. These multiple sources of risk and their association with adverse pregnancy outcomes underline the use of using a social and structural framework such as the Risk Environment (Rhodes, 2002, 2009) to examine reproductive health status among FSW-IDU, building on previous research documenting the value of this framework in explaining HIV and drug risks in this population (e.g., Goldenberg et al., 2011; Strathdee et al., 2011).

LIMITATIONS

Although these findings provide important insight into reproductive health concerns for FSW-IDUs, they should be considered in light of some important study limitations. The survey instrument aggregated miscarriage and stillbirth into one question. These are distinct events, and although many risk factors do overlap, they do have unique attributes from a biological and behavioral perspective. Future research would be stronger if these outcomes were separated so that individual determinants could be examined in greater detail. In addition, several known risk factors such as tobacco usage (Einarson & Riordarí, 2009; Keegan et al., 2010; Ness et al., 1999), nutritional status (Kramer & Kakuma, 2003; Yakoob et al., 2009), antenatal care (Barros et al., 2010; Bhutta, Darmstadt, Haws, Yakoob, & Lawn, 2009), and other types of abuse (e.g., emotional abuse; Alio, et al., 2009) were not included in data collection. Because of the design of the study instrument, this analysis was also unable to assess and control for wanted versus unwanted pregnancy. Finally, because these data were obtained from a cross-sectional survey in which many measures—including the primary independent and dependent variables—used an “ever” time frame, it is not possible to draw causal inferences about predictors of miscarriage and stillbirth. It is also not possible to identify the chronological relationship between experiences of violence, adverse pregnancy outcomes, active sex work, or injection drug use. Furthermore, prospective study of sex worker populations is necessary to better understand their experiences with sexual violence and its ramifications. Despite these limitations, this study represents an important step in understanding the burden of violence, and the reproductive health status and needs of a highly marginalized and vulnerable population.

CONCLUSIONS

This study documents a notable miscarriage/stillbirth prevalence among FSW-IDUs in the United States–Mexico border region and reveals that sexual violence is significantly associated with such pregnancy loss. These findings add to the growing body of literature documenting substantial burdens of violence among FSWs, and the effects this violence may have on the reproductive health of this vulnerable group. The results are particularly important in the context of the high levels of injection drug use on the United States–Mexico border and the relationship of that drug use to sexual abuse (Ulibarri et al., 2011). Programs targeted at reducing sexual violence against FSWs would play an important role in reducing the substantial burden of adverse pregnancy outcomes in this population of women who face violence from partners and clients, as well as risks associated with their active substance abuse. Additional research on this neglected agenda along with targeted programmatic intervention will help to support these populations and leverage the limited resources available to offer the maximum support toward improving the reproductive health and reproductive health rights of these marginalized women.