Correcting haemoglobin cut-offs to define anaemia in high-altitude pregnant women in Peru reduces adverse perinatal outcomes

Purpose: To determine if correction of cut-offs of haemoglobin levels to define anaemia at high altitudes affects rates of adverse perinatal outcomes. Methods: Data were obtained from 161,909 mothers and newborns whose births occurred between 1,000 and 4,500 m above sea level (masl). Anaemia was defined with or without correction of haemoglobin (Hb) for altitude as Hb <11 g/dL. Correction of haemoglobin per altitude was performed according to guidelines from the World Health Organization. Rates of stillbirths and preterm births were also calculated. Results: Stillbirth and preterm rates were significantly reduced in cases of anaemia calculated after correction of haemoglobin for altitude compared to values obtained without Hb correction. At high altitudes (3,000-4,500 masl), after Hb correction, the rate of stillbirths was reduced from 37.7 to 18.3 per 1,000 live births (p < 0.01); similarly, preterm birth rates were reduced from 13.1 to 8.76 % (p < 0.01). The odds ratios for stillbirths and for preterm births were also reduced after haemoglobin correction. Conclusion: At high altitude, correction of maternal haemoglobin should not be performed to assess the risks for preterm birth and stillbirth. In fact, using low altitude Hb cut-off is associated with predicting those at risk.