Figure 5.

Unadjusted smoothed rates and fitted adjusted relative rates of PE for boy births (a,b) and girl births (c,d) in Norway. The smoothed curve in (a), and (c) is based on a moving average of outcomes that uses a window encompassing $\pm 30\text{d}$ from each day of the year, thus estimating the fraction with PE among pregnancies conceived at each day of the year. The fitted relative rates shown in (b), and (d) are based on the first harmonic (sine and cosine) fit separately to each of the fetal sex categories, with models that are adjusted for the covariates maternal age, maternal age squared, education, primiparity, smoking (in three categories), marital status, region (in three categories), and interaction between primiparity and region. The curve shown is based on entering the fetal-sex–specific mean for all covariates, centering the estimated log hazard ratio and then exponentiating it.