Conceived and designed the experiments: GG JK GC. Performed the experiments: GG LGB MN KM TN SR BM MM NN. Analyzed the data: KF. Wrote the paper: MHL. Reviewed manuscript drafts and provided scientific input: GG GdB KF GC.
The authors have declared that no competing interests exist.
HIV prevention trials are increasingly being conducted in sub-Saharan Africa. Women at risk for HIV are also at risk of pregnancy. To maximize safety, women agree to avoid pregnancy during trials, yet pregnancies occur. Using data from the HVTN 503/“Phambili” vaccine trial, we report pregnancy incidence during and after the vaccination period and identify factors, measured at screening, associated with incident pregnancy.
To enrol in the trial, women agreed and were supported to avoid pregnancy until 1 month after their third and final vaccination (“vaccination period”), corresponding to the first 7 months of follow-up. Unsterilized women, pooled across study arms, were analyzed. Poisson regression compared pregnancy rates during and after the vaccination period. Cox proportional hazards regression identified associations with first pregnancy.
Among 352 women (median age 23 yrs; median follow-up 1.5 yrs), pregnancy incidence was 9.6/100 women-years overall and 6.8/100 w-yrs and 11.3/100 w-yrs during and after the vaccination period, respectively [Rate Ratio = 0.60 (0.32–1.14), p = 0.10]. In multivariable analysis, pregnancy was reduced among women who: enrolled at sites providing contraception on-site [HR = 0.43, 95% CI (0.22–0.86)]; entered the trial as injectable contraceptive users [HR = 0.37 (0.21–0.67)] or as consistent condom users (trend) [HR = 0.54 (0.28–1.04)]. Compared with women with a single partner of HIV-unknown status, pregnancy rates were increased among women with: a single partner whose status was HIV-negative [HR = 2.34(1.16–4.73)] and; 2 partners both of HIV-unknown status [HR = 4.42(1.59–12.29)]. Women with 2 more of these risk factors: marijuana use, heavy drinking, or use of either during sex, had increased pregnancy incidence [HR = 2.66 (1.24–5.72)].
It is possible to screen South African women for pregnancy risk at trial entry. Providing injectable contraception for free on-site and supporting consistent condom use may reduce incident pregnancy. Screening should determine the substance use, partnering, and HIV status of both members of the couple for both pregnancy and HIV prevention.
SA National Health Research Database DOH-27-0207-1539;
Clinical trials to test effectiveness of HIV preventive methods are increasingly being conducted in Sub-Saharan Africa where HIV incidence is high. Women at risk for HIV recruited for these trials are also often at high risk of pregnancy, yet are asked to avoid pregnancy whilst on investigational products regardless of the trial phase, as safety to the unborn child is usually unknown. In microbicide trials, women are tested for pregnancy frequently and are taken off study product if they become pregnant. In vaccine trials, women commit to avoiding pregnancy during the vaccination period, and the vaccination schedule is halted if a woman becomes pregnant. Being able to identify women at higher risk for pregnancy at screening may enhance participant safety and minimizes time off study product, which increases trial efficiency
While pregnancy incidence rates were as high as 64/100 woman-years (/100 w-yrs) in early microbicide trials
Factors associated with pregnancy in HIV prevention trials conducted in sub-Saharan Africa are only now being reported. In an analysis of multiple trials, use of injectable hormonal contraception was associated with reduced pregnancy incidence
Using data from women who participated in the HVTN 503 “Phambili” trial testing an HIV vaccine, we report pregnancy rates and outcomes during and after the vaccination period, and identify factors reported at screening that were associated with incident pregnancy during this trial. We also evaluated associations of contraception and condom use during the trial with pregnancy incidence as such use may be modified by trial staff through counselling and enhanced access. Findings from this analysis may improve screening and support of women in minimizing pregnancy during future HIV prevention trials in sub-Saharan Africa.
This analysis was approved by the ethics boards governing all 5 trial sites, including the University of KwaZulu Natal (2 sites), The University of Cape Town, The University of the Witwatersrand, and the Medical University of South Africa, as well as the London School of Hygiene and Tropical Medicine (statistician, author KF), the Medicines Control Council of South Africa and the Genetically Modified Organism Review Committee of the South African Department of Agriculture.
While these data derive from a randomized trial
Women enrolled in HVTN 503 “Phambili”, an HIV vaccine trial, comprised the source population for this analysis
Detailed exclusion criteria are available elsewhere
Of the 801 persons enrolled, 360 were women, and 352 were at risk for pregnancy at enrolment and included in this analysis (n = 7 women were surgically sterilized before screening; n = 1 was later determined to be pregnant at enrolment).
Data on demographics, contraceptive and condom use, sexual behaviour, sexual partners (numbers, HIV status and risk profile), substance use, and history of sexually transmitted infection (STI) were collected via structured, face-to-face interviews by nurses during the screening period (referred to as screening or baseline variables). Screening could take place up to 56 days prior to enrolment, and women had their screening interviews a median of 15 days prior to enrolment. At screening all variables were asked in reference to the six months prior, except contraception and condoms which referred to current use. Use of condoms was asked in two ways: whether currently being used via a single question, and through a series of questions about condom use in the 6 months prior, by partner type and whether condom use with that partner type was consistent or not. Both condom use variables were examined given mixed evidence on the role of condom use in pregnancy prevention; each variable was considered separately in modelling to avoid collinearity.
One site-level variable was considered. Three of the research sites supplied free hormonal contraception (injectables or the pill), throughout the trial. At the remaining sites women were referred to free public sector clinics for injectables or oral contractive pills. Sites were categorized by whether hormonal contraception was available on or off site.
Contraceptive, condom use, and partner data were also collected at 3, 7, 12 and 18 months of follow up, and data from the latter 3 visits were analysed as they provided non-overlapping information (questions referred to “last 6 months”). We analysed current condom use (yes/no), consistent condom use, and hormonal contraception use during the trial. Data on other forms of protection were too infrequent for analysis. Contraceptive use during the trial (time-varying variables) was not independent of use at screening, and therefore the former were not included in multivariable modelling.
The main outcome variable was first pregnancy during follow up, whether within or outside the vaccination period. Pregnancies were measured in 1 of 2 ways: either via a ß-HCG urine pregnancy test, or by dating the pregnancy from last menstrual period if a woman reported being, or was clinically noted as, pregnant. Of the 48 pregnancies observed, 30 (62%) were confirmed with a urine pregnancy test; 85% (11/13) and 54% (19/35) of pregnancies were confirmed with a urine test during the vaccination period, and post-vaccination period, respectively. Date of incident pregnancy was defined either as 14 days after the last menstrual period (LMP), or if LMP was unknown, then as the estimated date of delivery date minus 266 days.
Vaccinations were scheduled to occur at enrolment and months 1 and 6. All women were counselled and supported to avoid pregnancy during the vaccination period, defined as the period from enrolment (first vaccine) until 1 month after last vaccination – or the first 7 months of follow up for each woman. The protocol specified pregnancy testing before each vaccination was administered, and thus pregnancy testing was routinely done during the vaccination period. After the vaccination period, pregnancy testing was done if indicated or requested by the participant. The differential in pregnancy testing during and after the vaccination period was to avoid administration of the experimental vaccine to a pregnant woman.
Enrolment for this trial started 24 January 2007. Enrolment and all vaccinations were unexpectedly halted on 19 September 2007 when it became known, through another trial testing the same product, that the vaccine product under testing was not effective in preventing HIV or reducing early post-infection viral load. The Phambili trial was testing the same product as the Step trial (HVTN 502)
Given the varied pregnancy prevention messages after vaccinations were stopped, we considered several ways of defining the vaccination period. Upon further examination of the frequency of pregnancy testing, and despite variations in pregnancy counselling, pregnancy testing remained largely in line with the protocol: 87% of women were tested for pregnancy at the end of their initially-scheduled vaccination period, and pregnancy testing became less frequent thereafter. Therefore we defined the vaccination period as the first 7 months of follow up. We calculated pregnancy rates stratified by the vaccination period (during versus after), with the expectation that observed pregnancy rates may have been under-estimated in the post-vaccination period. We show pregnancy outcomes overall and stratified by vaccination period; data were too spare for further statistical analysis.
The follow-up period for this analysis spans from 24 January 2007, the first date a vaccination occurred, through 5 May 2009 when data were pulled for this analysis. The enrolment period spanned from 24 January through 18 September 2007. Women contributed person years from first vaccination to first pregnancy defined as the last menstrual period plus 14 days, or the date of her last visit within the follow-up timeframe noted above. For women with multiple pregnancies (3 women had 2 pregnancies) only the first pregnancy was counted.
To describe the enrolled sample, we calculated the frequency of women’s demographic, contraceptive use, sexual behaviour and risk profiles as measured at screening. Overall pregnancy incidence is expressed per 100 women-years with an associated 95% confidence interval. Pregnancy incidence was stratified by socio-demographics, behaviours, partner profile, and vaccination period. Poisson regression was used to compare pregnancy rates during and after the vaccination period. Cox proportional hazards regression was used to assess predictors measured at screening with time to first pregnancy, and to assess the role of contraceptive use during the trial by allowing contraceptive use to be time varying. Given the modest sample size and the need for parsimony during model building, only contraceptive use was considered for the time-varying analysis, and interaction terms to test for joint effects were not evaluated To show joint effects of the identified behavioural risk factors, pregnancy rates stratified by number of risk behaviours (none or one versus two or more) were shown.
Women (n = 352) were predominantly young (median 23 years, inter-quartile range (IQR) 20–27) and Black African 98.9% (
Column % (n) | Rate per 100 woman yrs (No. pregnancies/woman yrs) | Unadjusted Rate Ratio (95% CI) | P-value | |
|
(352) | 9.6 (48/501) | – | – |
|
0.24 | |||
18–20 | 28.7 (101) | 11.3 (16/142) | 1 | |
21–25 | 38.9 (137) | 9.9 (19/192) | 0.89 (0.46–1.72) | |
26–30 | 20.2 (71) | 10.7 (11/103) | 0.94 (0.44–2.03) | |
31–35 | 12.2 (43) | 3.1 (2/64) | 0.28 (0.06–1.23) | |
|
0.53 | |||
Black | 98.9 (348) | 9.5 (47/496) | 1 | |
Mixed | 1.1 (4) | 19.4 (1/5) | 2.05 (0.28–14.8) | |
|
||||
Yes | 68.8 (242) | 8.3 (29/348) | 0.68 (0.38–1.21) | |
No | 31.3 (110) | 12.4 (19/153) | 1 | 0.20 |
|
||||
|
||||
Yes | 57.1 (201) | 8.6 (25/290) | 0.78 (0.44–1.38) | |
No | 42.9 (151) | 10.9 (23/211) | 1 | 0.39 |
|
||||
Yes | 79.6 (280) | 10.4 (42/403) | 1.72 (0.73–4.05) | |
No | 20.5 (72) | 6.1 (6/98) | 1 | 0.19 |
|
||||
Yes | 13.4 (47) | 15.4 (10/65) | 1.80 (0.90–3.62) | |
No | 86.6 (305) | 8.7 (38/436) | 1 | 0.12 |
|
||||
Yes | 58.5 (206) | 6.4 (19/296) | 0.46 (0.26–0.81) | |
No | 41.5 (146) | 14.2 (29/205) | 1 | 0.007 |
|
||||
|
||||
Yes | – |
8.5 (26/328) | 0.60 (0.34–1.07) | 0.09 |
No | 12.0 (22/173) | 1 | ||
|
||||
Yes | – |
8.8 (33/375) | 0.76 (0.41–1.41) | 0.40 |
No | 11.9 (15/126) | 1 | ||
|
||||
Yes | – |
16.7 (13/78) | 2.02 (1.07–3.83) | 0.04 |
No | 8.3 (35/423) | 1 | ||
|
||||
Yes | – |
6.6 (22/330) | 0.41 (0.23–0.71) | 0.002 |
No | 15.5 (26/168) | 1 |
Data from multiple time points contribute to this statistic, number for each time point not shown.
At screening, most women (58.5%) self-reported use of injectable contraception while 13.4% reported oral contraceptive pill use (
Column % (n) | Rate per 100 woman yrs (No. pregnancies/woman yrs) | Unadjusted Rate Ratio (95% CI) | P-value | |
|
(352) | 9.6 (48/501) | – | – |
≥ 2 such activities | 9.9 (35) | 18.3 (9/49) | 2.02 (0.96–4.23) | 0.15 |
1 such activity | 18.2 (64) |
7.1 (7/99) | 0.80 (0.35–1.81) | |
None | 71.9 (253) | 9.1 (32/253) | 1 | |
|
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Yes | 5.1 (18) | 20.8 (5/24) | 2.38 (0.94–6.01) | 0.10 |
No | 95.9 (334) | 9.0 (43/477) | 1 | |
|
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No partner | 14.2 (50) | 10.5 (7/67) | 1.13 (0.50–2.56) | 0.99 |
Causal only | 2.3 (8) | 10.3 (1/10 | 1.12 (0.15–8.19) | |
Main partner only | 74.4 (262) | 9.3 (35/375) | 1 | |
Main & casual partners | 9.1 (32) | 10.0 (5/50) | 1.07 (0.42–2.74) | |
|
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Yes | 8.8 (26) | 7.8 (3/38) | 0.79 (0.24–2.57) | 0.68 |
No | 91.2 (268) | 9.6 (37/386) | 1 | |
|
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Lives with main partner | 45.5 (160) | 9.0 (21/233) | 1 | 0.92 |
Does not live with main partner | 38.1 (134) | 9.9 (19/192) | 1.09 (0.59–2.03) | |
No main partner | 16.5 (58) | 10.5 (8/76) | 1.17 (0.52–2.64) | |
|
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≥2 partners | 15.6 (55) | 11.5 (9/78) | 1.25 (0.60–2.58) | 0.56 |
1 partner | 84.4 (297) | 9.2 (39/423) | 1 | |
|
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≥1 partner(s) |
48.9 (172) | 8.4 (20/239) | 0.78 (0.44–1.38) | 0.39 |
No such partners (knows status) | 51.1 (180) | 10.7 (28/262) | 1 | |
|
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>2 partners varied knowledge | 9.5 (33) | 6.2 (3/48) | 1.04 (0.29–3.72) | 0.05 |
2 partners both unknown status | 6.3 (22) | 20.0 (6/30) | 3.42 (1.26–9.25) | |
1 partner known negative | 46.4 (162) | 12.0 (28/234) | 2.03 (1.01–4.07) | |
1 partner unknown status | 37.8 (132) | 6.0 (11/184) | 1 |
Refers to six months prior to screening interview.
Heavy drinking defined as 5 or more alcoholic drinks in one day; 81% (52/64) of these women were heavy drinkers.
Includes women with partners where HIV status was either all unknown, or status known for 1 of multiple partners.
Excludes 3 women with known HIV-positive partners as data too scant for a separate stratum. No pregnancies occurred among these women.
Of 51 total pregnancies, 48 first pregnancies occurred, or 13.6% (48/352) of women became pregnant. Overall pregnancy incidence was 9.6/100 w-yrs [48/501.1 w-yrs, 95% confidence interval (CI) 7.22 –12.71]. Pregnancy incidence during and after the vaccination period was 6.8 and 11.3/100 w-yrs, respectively; RR 0.60 (95%CI: 0.32–1.14; p = 0.10) (
Pregnancy rates | Outcome of pregnancy |
Row % (n) | ||||
Full-termlife birth | Prematurelife birth | Fetal death/still birth | Spontaneousabortion | Ectopic pregnancy | Electiveabortion | |
|
||||||
9.6 (48/501) |
47 (20) | 16 (7) | 2 (1) | 7 (3) | 2 (1) | 26 (11) |
|
||||||
6.8 (13/191) |
23 (3) | 23 (3) | 0 | 8 (1) | 0 | 46 (6) |
|
||||||
11.3 (35/310) |
57 (17) | 13 (4) | 3 (1) | 7 (2) | 3 (1) | 17 (5) |
Outcome of pregnancy not known for 5 women.
Number of pregnancies/woman years.
Defined as the period between a woman’s first scheduled vaccination through 1 month after the third, and final scheduled vaccination for that woman.
Pregnancy rates were lower among women using injectable contraception at screening (hazard ratio [HR] 0.46, 95% CI 0.26 –0.81) (
Pregnancy rates were reduced among women who reported using injectable contraception during the trial [HR = 0.41 (0.23–0.71)] (
Pregnancy rates were reduced among women enrolled at a trial site that provided hormonal contraception, who entered the study as consistent condom users or as users of injectable contraceptives (
Unadjusted Rate Ratio | Adjusted |
p-value | |
|
|||
Yes | 0.68 | 0.43 (0.22–0.86) | 0.02 |
No | 1 | 1 | |
Yes | 0.78 | 0.54 (0.28–1.04) | 0.07 |
No | 1 | 1 | |
|
|||
Yes | 0.46 | 0.37 (0.21–0.67) | 0.0009 |
No | 1 | 1 | |
≥ 2 such activities | 2.02 | 2.66 (1.24–5.72) | 0.05 |
1 such activity | 0.80 | 0.85 (0.36–2.02) | |
None | 1 | 1 | |
>2 partners mixed knowledge of status | 1.04 | 1.01 (0.27–3.74) | 0.01 |
2 partners both unknown status | 3.42 | 4.42 (1.59–12.29) | |
1 partner known negative | 2.03 | 2.34 (1.16–4.73) | |
1 partner unknown status | 1 | 1 |
Final model does not include 3 women with known HIV-positive partners as this stratum was too thin for modeling.
Adjusted for all other variables in the model; for variables with >2 levels the overall p value shown.
Heavy drinking defined as 5 or more alcoholic drinks in one day.
Overall the pregnancy rate was at the low end of the range observed in other HIV prevention trials, on par with the one other vaccine trial reporting on pregnancy incidence in sub-Saharan Africa
The proportion of elective abortions appeared to be elevated for pregnancies conceived during the vaccination period, compared with those conceived later, although we cannot conclude this with certainty because the study was not powered to evaluate this finding. We do not have information on women’s motivations, but a range of explanations for these elective terminations are possible. These may include: more immediate access to the health care system during trial participation; that women perceived it was unsafe to conceive a pregnancy during the vaccination period as they were advised to be on contraception during this time; or may simply reflect that pregnancies in the post-vaccination period were more often intended given women’s agreement to avoid them during the vaccination period. We lack detail on the circumstances of the elective abortions, but this procedure is legal in South Africa. Regarding pregnancy outcomes, those observed here were on par with another trial
Encouraging was that predictive factors were identified, over-and-above the requirement that women use at least two forms of contraception as was required in this trial. All of the additional factors can be readily measured during screening for a large clinical trial, some are modifiable at trial entry, and preventive measures were associated with at least a halving in pregnancy risk. It is likely that the convenience, immediacy, certainty, and quality-of-care associated with on-site injectable contraceptive access is critical to its preventive role, as this finding is buttressed by another trial showing that women obtaining contraception off-site were at increased pregnancy risk
We also found that women who entered the trial using, and who continued to use, injectable contraceptives, but not oral contraceptive pills, were less likely to get pregnant. Despite being counter-intuitive, this finding has also been observed elsewhere: in a South African microbicide trial, pregnancy rates were 11.5/100 w-yrs among oral contraceptive users and <2.0/100 w-yrs among women on injectables
Regarding condoms, how use is measured is important for distinguishing between casual and consistent users, as we found that only the latter group was at lowered pregnancy risk. Condom use measured via a single, “yes/no” question about “current” use, was not predictive, while consistent condom use, derived from a series of questions enquiring about condom use by each partner type during a specified timeframe, showed a trend toward halving pregnancy risk in the adjusted analysis. Careful measurements of condom use to determine consistent use has also been shown as protective by Reid et al., and use at last sex before study entry (but as not as one’s main method) by Halpern et al. in trial settings. Together these findings suggest that condoms may be a viable method for pregnancy prevention, so long as they are used consistently or recently. In contrast, if only a single, non-specific condom use measure is employed and women say “yes” to current condom use without further corroboration, (either in response to additional questioning or by failing to demonstrate familiarity with condoms when using a model) these women should be flagged as those in need of more intensive pregnancy counselling and support.
Pregnancy was also a function of HIV status, and number, of partners. Using women with a single partner of unknown HIV status as a reference, we were able to examine the unique impact of HIV status alone (by comparing pregnancy rates of women with only one partner with unknown status vs. negative HIV status) and of multiple partners (by comparing the impact of 1 versus 2 partners among women who didn’t know their partners’ HIV status). Regarding the former, knowing a sex partner’s HIV status may be emerging as a partnership factor of interest. Not knowing a partner’s HIV status may be a marker of a newer relationship where HIV status has not yet been discussed and so women were taking greater precautions against becoming pregnant. Alternatively, it may reflect a relationship where HIV status cannot be discussed, and thus women were hesitant to cement the relationship further with a pregnancy. We were unable to test these hypotheses as we lacked data on relationship duration and disclosure. This finding deserves further research. Regarding multiple partners, this may be a marker for women with more risky behaviour in general, as multiple partnering is also a risk factor for HIV. It is unclear whether the multiple partnering seen here is due to commercial transactions, as almost no women reported engaging in commercial sex when specifically asked (data not shown as it was extremely uncommon).
While almost twenty percent of the sample reported heavy drinking, it was heavy drinking along with either marijuana use, or concurrent drinking and sex that were associated with a two fold risk of pregnancy. Heavy drinking and recreational drug use are well-established risk factor for HIV in South Africa
Strengths of this analysis are that it is the first report from a vaccine trial on risk factors for pregnancy and the longitudinal design with high retention enhanced ability to make causal inferences. Factors examined were all collected within the context of a typical clinical trial, and didn’t require specialized interviewing techniques, yet were highly predictive of pregnancy risk. This bodes well for future trials as women can be readily screened for pregnancy using a few questions. Limitations of this analysis were the variable pregnancy prevention messages and pregnancy outcome ascertainment once the trial was interrupted. Nonetheless, we were still able to make valid comparisons within the dataset as the direction of the bias was known, but given the lack of systematic pregnancy testing in the post-vaccination period, overall pregnancy rates may be underestimated.
It is possible to efficiently screen women for pregnancy risk, and concrete steps such as providing injectable hormonal contraception for free on-site, and supporting consistent condom users, can reduce pregnancy risk among South African women in HIV trials. Additionally, among women with a single partner, differential knowledge of male partners’ HIV status impacts pregnancy rates and is a new finding that deserves further research to illuminate the underlying reason for its association with pregnancy. Given long-standing calls to better integrate family planning and HIV/STI risk reduction counselling, clinical trialists and health counsellors should make it a point to enquire about the number of, and male partner’s HIV status as a potential modifier of pregnancy and HIV risk. Together, these few simple steps may help to maximize the safety of the mother and children conceived during HIV prevention trials.
The opinions expressed in this article are those of the authors and do not represent the official views of the National Institute of Allergy and Infectious Disease.