Participants with anaemia (Hb < 10.5 g/dL) at < 18 weeks’ gestation tended to have 2.74 times higher odds for prehypertension than women without anaemia (OR: 2.74, 95% CI: 0.97, 7.80, p = 0.058). The gene discussed is GSTM1; the disease is anemia (phenotype).