Association between pregnancy and socio-demographic and behavioural factors
| Number pregnancies/person-years | Pregnancy rate/100 person-years | Unadjusted rate ratio (95% CI) | Adjusted rate ratio (95% CI)* | |
| Socio-demographic and behavioural factors at baseline | ||||
| Age (years) | p<0.001 | p<0.001 | ||
| 16–19 | 30/79 | 38.06 | 5.55 (3.57 to 8.62) | 19.98 (11.47 to 34.82) |
| 20–24 | 80/404 | 19.83 | 2.89 (2.06 to 4.05) | 6.13 (4.12 to 9.13) |
| 25–29 | 86/700 | 12.28 | 1.79 (1.28 to 2.50) | 3.14 (2.18 to 4.52) |
| 30–35 | 58/845 | 6.86 | 1 | 1 |
| Educational level | p=0.005 | p=0.11 | ||
| None | 25/239 | 10.47 | 1 | 1 |
| Incomplete primary | 61/328 | 18.60 | 1.78 (1.12 to 2.83) | 1.64 (1.01 to 2.65) |
| Completed primary/higher | 168/1461 | 11.50 | 1.10 (0.72 to 1.67) | 1.32 (0.85 to 2.03) |
| Marital status | p=0.01 | p=0.02 | ||
| Married/living as married | 60/532 | 11.29 | 1 | 1 |
| Divorced/separated/widowed | 127/1115 | 11.39 | 1.01 (0.74 to 1.37) | 1.24 (0.91 to 1.69) |
| Single | 67/381 | 17.58 | 1.56 (1.10 to 2.21) | 1.76 (1.18 to 2.64) |
| Occupational group at screening | p=0.05 | p=0.22 | ||
| Local food handler | 139/1026 | 13.55 | 1 | 1 |
| Guesthouse | 19/185 | 10.24 | 0.76 (0.47 to 1.22) | 1.19 (0.73 to 1.94) |
| Bar worker | 41/317 | 12.91 | 0.95 (0.67 to 1.35) | 1.23 (0.85 to 1.79) |
| Local brew seller | 11/182 | 6.06 | 0.45 (0.24 to 0.83) | 0.62 (0.33 to 1.15) |
| Restaurant/cafe/grocery | 44/318 | 13.84 | 1.02 (0.73 to 1.43) | 1.22 (0.86 to 1.72) |
| Number of children ever had | p=0.28 | p<0.001 | ||
| None | 31/299 | 10.37 | 1 | 1 |
| 1 | 78/523 | 14.91 | 1.44 (0.95 to 2.18) | 2.77 (1.77 to 4.34) |
| 2–4 | 128/1053 | 12.16 | 1.17 (0.79 to 1.74) | 5.11 (3.14 to 8.31) |
| ≥5 | 17/153 | 11.09 | 1.07 (0.59 to 1.93) | 8.30 (4.09 to 16.86) |
| Wish to have children in future | p=0.43 | p=0.38 | ||
| No | 102/875 | 11.65 | 1 | 1 |
| Yes | 147/1123 | 13.09 | 1.12 (0.87 to 1.45) | 0.84 (0.63 to 1.12) |
| Don't know | 5/25 | 19.66 | 1.69 (0.69 to 4.14) | 1.31 (0.52 to 3.26) |
| Any regular partner | p=0.88 | p=0.26 | ||
| Yes | 212/1685 | 12.58 | 1 | 1 |
| No | 42/343 | 12.26 | 0.97 (0.70 to 1.36) | 0.82 (0.57 to 1.16) |
| Living with partner | p=0.54 | p=0.64 | ||
| In the same house | 60/541 | 11.10 | 1 | 1 |
| Apart, meet weekly | 104/818 | 12.72 | 1.15 (0.83 to 1.57) | 0.93 (0.49 to 1.73) |
| Apart, meet 3 monthly or less | 46/311 | 14.78 | 1.33 (0.91 to 1.96) | 1.05 (0.56 to 1.99) |
| No regular partner | 42/343 | 12.26 | 1.10 (0.74 to 1.64) | 0.79 (0.40 to 1.56) |
| Time varying behavioural factors during follow-up | ||||
| Current contraceptive method | p<0.001 | p<0.001 | ||
| Combined oral contraceptive | 83/771 | 10.77 | 1 | 1 |
| Injection | 19/516 | 3.68 | 0.34 (0.21 to 0.56) | 0.29 (0.18 to 0.48) |
| Condom | 49/480 | 10.21 | 0.95 (0.67 to 1.35) | 1.26 (0.88 to 1.81) |
| Nothing | 100/248 | 40.26 | 3.74 (2.79 to 5.00) | 5.84 (4.31 to 7.91) |
| Intrauterine contraceptive device | 0/10 | – | ||
| Sexual partners in the last 3 months | p=0.03 | p=0.96 | ||
| 0–1 | 193/1407 | 13.72 | 1 | 1 |
| 2 | 41/427 | 9.59 | 0.70 (0.50 to 0.98) | 0.94 (0.52 to 1.70) |
| ≥3 | 17/193 | 8.79 | 0.64 (0.39 to 1.05) | 1.00 (0.46 to 2.17) |
| Paid sex in the past 3 months | p=0.002 | p<0.001 | ||
| No | 198/1423 | 13.92 | 1 | 1 |
| Yes | 53/605 | 8.77 | 0.63 (0.47 to 0.85) | 0.59 (0.43 to 0.81) |
| Current HIV status | p<0.001 | p<0.001 | ||
| Negative | 180/1197 | 15.04 | 1 | 1 |
| Positive | 74/831 | 8.90 | 0.59 (0.45 to 0.78) | 0.55 (0.42 to 0.73) |
| HIV positive and aware | p=0.73 | p=0.59† | ||
| No | 27/319 | 8.45 | 1 | 1 |
| Yes | 47/512 | 9.18 | 1.09 (0.68 to 1.74) | 0.87 (0.54 to 1.42) |
| HIV negative and aware | p=0.11 | p=0.40† | ||
| No | 44/356 | 12.34 | 1 | 1 |
| Yes | 136/840 | 16.19 | 1.31 (0.93 to 1.84) | 1.16 (0.82 to 1.63) |
| Change in contraceptive method‡ | p<0.001 | p<0.001§ | ||
| No change in method (using modern contraception) | 136/1417 | 9.60 | 1 | 1 |
| Start modern contraception | 10/198 | 5.04 | 0.53 (0.28 to 1.00) | 0.56 (0.29 to 1.07) |
| Stop modern contraception | 60/60 | 100.5 | 10.47 (7.72 to 14.18) | 11.16 (8.18 to 15.23) |
| No change in method (not using modern contraception) | 40/188 | 21.23 | 2.21 (1.55 to 3.15) | 3.67 (2.54 to 5.29) |
| Using modern contraception, change method | 5/162 | 3.08 | 0.32 (0.13 to 0.78) | 0.32 (0.13 to 0.77) |
↵* Adjusted for independent predictors of pregnancy: age group, marital status, number of children, current contraceptive method, paid sex in the past 3 months and HIV status.
↵† Both variables relating to HIV status and knowledge of HIV status included in model at the same time, adjusted for independent predictors of pregnancy listed in first footnote. Shows association between pregnancy rate and knowledge of HIV status separately among HIV-positive and HIV-negative women.
↵‡ Contraceptive method reported at current visit compared with that reported at previous visit. Modern contraception defined as combined oral contraceptive (COC), injection, condom or IUCD. Analysed as a time-updated variable, so distinguishes between periods when women report no change in a particular method (eg, report using COC at current and previous visit), start/stop using a modern method or change between two modern methods (eg, using COC at current and condom at previous visit).
↵§ Adjusted for all independent predictors of pregnancy listed in first footnote, except for current contraceptive method.