GSTM1 and Stillbirth: For instance, a large Peruvian cohort study (35 000 pregnancies) reported that both low (< 9 g/dL) and high (≥ 14.5 g/dL) maternal Hb levels were associated with adverse outcomes such as stillbirth, preterm birth, and small‐for‐gestational‐age infants at both low and high altitudes [61], suggesting that elevated Hb at altitude in pregnancy is not always protective and may even be detrimental [62].