Maternal haemoglobin levels and adverse pregnancy outcomes: individual
patient data analysis from two prospective UK pregnancy cohorts
Abstract
Objective To estimate the shape and magnitude of associations between
maternal Hb levels in the first and third trimesters of pregnancy, and
pregnancy outcomes in a high-income setting. Design Prospective cohort
studies Setting Two population based pregnancy cohorts from the UK
Population The Avon Longitudinal Study of Parents and Children(ALSPAC)
and Pregnancy Outcome Prediction Study(POPS). Methods We used
multivariable logistic regression models to examine the relationship
between Hb and pregnancy outcomes, adjusting for maternal age,
ethnicity, BMI, smoking status and parity. Main Outcome Measures Preterm
labour, low birth weight, small for gestational age(SGA),
pre-eclampsia(PET), and gestational diabetes mellitus(GDM). Results
There was no strong evidence of associations between a higher Hb (1g/dL)
in the first trimester and preterm birth (1.07: 95% CI 0.96,1.21), low
birth weight(1.09: 0.96, 1.24) and SGA (1.05; 0.96, 1.14). Higher Hb in
the third trimester was associated with preterm birth (1.43:1.28,1.61),
low birth weight(1.68: 1.48,1.90) and SGA (1.41:1.30, 1.53). Higher Hb
in the first and third trimesters were associated with PET in ALSPAC(1st
trimester- 1.38:1.07,1.76, 3rd trimester- 1.57: 1.28,1.94) but not in
POPS(1st trimester- 1.10: 0.92, 1.30, 3rd trimester- 1.10: 0.92, 1.31).
In ALSPAC(1st trimester- 1.37:0.96,1.95, 3rd trimester- 1.35:0.97,1.78)
and POPS(1st trimester- 0.94:0.77, 1.17, 3rd trimester- 0.85: 0.69,
1.01), there were no associations with GDM. Conclusion Higher maternal
Hb, in late pregnancy, may indicate a suboptimal increase in blood
volume and therefore, women at risk of adverse pregnancy outcomes.
Further research is required to investigate if this association is
causal, and to identify underlying mechanisms.