Placental ratio--its relationship with mild maternal anaemia.

To determine whether placental ratio is influenced by maternal anaemia, a retrospective observational study was performed in a regional tertiary hospital in Hong Kong. The gestational age, birthweight, placental weight, and placental ratio were studied in 152 mothers with anaemia due to thalassaemia trait, 232 mothers with anaemia due to iron deficiency, and 279 non-anaemic mothers as controls. All had singleton pregnancies. Compared to the control group, the iron deficiency group had higher placental weight (P = 0.001) and placental ratio (P < 0.001) while the thalassaemia trait group had higher placental ratio (P = 0.011) and, after including gestational age as covariate for analysis, higher placental weight (P = 0.019) as well. There was, however, no difference in the placental weight or ratio between the two anaemia groups. The placental ratio was not correlated to the haemoglobin levels at booking, third trimester, or the lowest one, in any group, but it was correlated with these three haemoglobin levels with the three groups combined. Placental ratio was also correlated to gestational age in all groups. The results confirm the observation that the placental ratio is increased in anaemic pregnancies, and indicate that anaemia, rather than underlying iron deficiency, is the cause for an increased placental ratio.