Low 3rd trimester haemoglobin level and the risk of post-term pregnancy

The aim of this study was to examine the association between haemoglobin (Hb) concentration during pregnancy and the risk of post-term pregnancy (PTP). Based on data from a population-based prenatal care programme in South China, a total of 102,484 women who delivered during 1995-2000 were identified. Haemoglobin concentration was determined by using standard methods. Risk of PTP was analysed according to severity of anaemia and multiple Hb categories. Multivariable logistic regression models were used to control potential confounding factors. Results showed that the overall prevalence rate of PTP in the population was 4.8% (4,947/102,484). The rate was 5.0%, 4.7% and 4.8% for women who were anaemic, while it was 4.5%, 4.4% and 4.2% for women who were non-anaemic in the 1st, 2nd and 3rd trimester, respectively. Although anaemia in either of the trimesters was not significantly associated with an increased risk of PTP, the risk was two-fold higher (odds ratio, 2.06; 95% CI, 1.18-3.59) for women whose last trimester haemoglobin concentration was lower than 80 g/l, when compared with women whose last trimester haemoglobin concentration was 140 g/l or higher. Our findings suggest that a very low 3rd trimester haemoglobin level is associated with an increased risk of PTP.