Age of first pregnancy(n = 425, obs = 639, preg = 87) | Time to next pregnancy(n = 561, obs = 1623, preg = 405) | ||||||

Variable | Exp(β) | 95% CI | P | Exp(β) | 95% CI | P | |

Age (decades)* | – | – | – | 1.00 | (0.80–1.25) | 0.992 | |

Age^{4} (decades)* | – | – | – | 0.95 | (0.93–0.96) | <0.001 | |

Hookworm | 0.34 | (0.20–0.58) | <0.001 | 0.74 | (0.60–0.91) | 0.004 | |

A. lumbricoides† | 3.06 | (1.91–4.91) | <0.001 | 1.64 | (1.16–2.33) | 0.005 | |

A. lumbricoides × age* | – | – | – | 0.68 | (0.51–0.89) | 0.006 | |

Treatment with antihelminthic | 0.43 | (0.19-0.97) | 0.042 | 0.75 | (0.58–0.97) | 0.027 | |

Education (years) | – | – | – | 0.92 | (0.86–0.99) | 0.017 | |

Speaks Spanish | – | – | – | 0.74 | (0.57–0.95) | 0.018 | |

Distance to town (10 km) | – | – | – | 0.96 | (0.91–1.00) | 0.075 | |

Season (P-spline) | – | – | <0.001 | – | – | <0.001 |

*Age is centered at 20 years. Age was continuous to the nearest tenth of a year but is shown in decades to make the parameters more easily interpretable. Because age-related changes in fecundity are nonlinear, transformations ranging from age^{2} to age^{5} were compared by AIC to select the age transformation (age^{4}) that best fit the data (fig. S3). †For the time to next pregnancy model, the roundworm parameter represents the hazard ratio at age 20.