Sex Transm Infect doi:10.1136/sextrans-2011-050412
  • Epidemiology
  • Original article

Pregnancy and contraceptive use among women participating in an HIV prevention trial in Tanzania

Open Access
  1. Deborah Watson-Jones1,2,4
  1. 1London School of Hygiene and Tropical Medicine, London, UK
  2. 2The African Medical and Research Foundation, Mwanza, Tanzania
  3. 3The National Institute for Medical Research, Tanzania, Mwanza, Tanzania
  4. 4Mwanza Intervention Trials Unit, National Institute for Medical Research, Tanzania, Mwanza, Tanzania
  1. Correspondence to Dr Deborah Watson-Jones, Faculty of Infectious and Tropical Diseases, Keppel St., London WC1E 7HT, UK; deborah.watson-jones{at}
  1. Contributors DW-J, RJH, DAR, CT, HW and JC conceived the study and prepared the protocol. DW-J obtained the funding and had overall responsibility for supervision and conduct of the study. MR supervised the field teams and data collection. Data analysis was done by AO and KB. AO prepared the first draft of the manuscript. All authors commented on and contributed to the final version of the manuscript.

  • Accepted 26 February 2012
  • Published Online First 21 March 2012


Objectives Information on pregnancy rates and factors associated with pregnancy and contraceptive use is important for clinical trials in women in sub-Saharan Africa where withdrawal of investigational products may be required in the event of pregnancy with a consequent effect on sample size and trial power.

Methods A prospective cohort analysis of pregnancy and contraceptive use was conducted in Tanzanian women enrolled in a randomised placebo-controlled trial of herpes simplex virus-suppressive therapy with acyclovir to measure the effect on HIV incidence in HIV-negative women and on genital and plasma HIV viral load in HIV-positive women. The cohort was followed every 3 months for 12–30 months. Women at each visit were categorised into users or non-users of contraception. Pregnancy rates and factors associated with pregnancy incidence and contraceptive use were measured.

Results Overall 254 of 1305 enrolled women became pregnant at least once during follow-up (pregnancy rate: 12.0/100 person-years). Younger age, being unmarried, higher baseline parity and changes in contraceptive method during follow-up were independently associated with pregnancy. Having paid sex and being HIV positive were associated with lower risk of pregnancy. Uptake of contraception was associated with young age, being unmarried, occupation, parity and the number and type of sexual partners.

Conclusions Data on use of contraceptive methods and risk factors for pregnancy can help to guide decisions on trial eligibility and the need for additional counselling. Mandatory reliable contraceptive use in study participants may be required to reduce pregnancy rates in studies where pregnancy is contraindicated.


  • Funding The Wellcome Trust, the United Kingdom Medical Research Council and the United Kingdom Department for International Development.

  • Competing interests None.

  • Ethics approval Ethics approval was provided by Medical Research Coordinating Committee of Tanzania and London School of Hygiene and Tropical Medicine ethics committee.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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