On 2017 Aug 29, David Mage commented:

In the introduction the authors write: "the peak incidence of SIDS coincides with the nadir in the physiologic anaemia of infancy (PAI)." This nadir is defined as the minimum in total (T) hemoglobin (Hb)(g/dL) vs age as the infant's fetal hemoglobin (HbF) is replaced by adult hemoglobin (HbA). This gives the relation as follows: THb = HbA + HbF, where HbF decreases with age and HbA increases with age. Differentiating the equation with respect to time t since birth we obtain the relation d(THb)/dt = d(HbA)/dt + d(HbF)/dt. That is, the nadir is the point in time when the increase in HbA plus the decrease in HbF equals 0.

However, because HbF holds oxygen more tightly than HbA does, the available oxygen (AO2) to the tissues from the blood will also have a minimum during the period between birth and the nadir in PAI. This can be seen because when the increase in HbA is equal and opposite to the decrease in HbF, d(AO2)/dt is greater than zero so the nadir in AO2 must occur earlier than the nadir in PAI.

Of course this time differential between the nadirs will be a function of gestational age and the time interval between birth and cord clamping, that relates to the placental transfusion from mother to infant that increases the infant THb.

On 2017 Aug 29, David Mage commented:

In the introduction the authors write: "the peak incidence of SIDS coincides with the nadir in the physiologic anaemia of infancy (PAI)." This nadir is defined as the minimum in total (T) hemoglobin (Hb)(g/dL) vs age as the infant's fetal hemoglobin (HbF) is replaced by adult hemoglobin (HbA). This gives the relation as follows: THb = HbA + HbF, where HbF decreases with age and HbA increases with age. Differentiating the equation with respect to time t since birth we obtain the relation d(THb)/dt = d(HbA)/dt + d(HbF)/dt. That is, the nadir is the point in time when the increase in HbA plus the decrease in HbF equals 0.

However, because HbF holds oxygen more tightly than HbA does, the available oxygen (AO2) to the tissues from the blood will also have a minimum during the period between birth and the nadir in PAI. This can be seen because when the increase in HbA is equal and opposite to the decrease in HbF, d(AO2)/dt is greater than zero so the nadir in AO2 must occur earlier than the nadir in PAI.

Of course this time differential between the nadirs will be a function of gestational age and the time interval between birth and cord clamping, that relates to the placental transfusion from mother to infant that increases the infant THb.