Fetal growth influences lymphocyte subset counts at birth: the Generation R Study.

BACKGROUND: Preterm born and low-birth-weight infants are at risk for severe infections in infancy. It has been suggested that these infants have an immature immune system.
OBJECTIVE: To assess the associations of gestational age, birth weight and fetal growth with absolute lymphocyte subset counts at birth.
METHODS: This study was conducted in 571 infants participating in the Generation R Study, a population-based prospective cohort study from fetal life onwards. Gestational age and birth weight were obtained from midwives and hospital registries. Fetal growth was defined as increase in weight between late pregnancy and birth. Lymphocytes and T lymphocyte subset counts in cord blood were determined by 6-color flow cytometry. Multivariate linear regression models with adjustment for gender, maternal education, smoking, alcohol use, fever and mode of delivery were applied.
RESULTS: Per week increase of gestational age, T, B and NK lymphocyte counts increased with 3, 5 and 6%, respectively (p < 0.05). Helper, cytotoxic and naive T lymphocyte counts increased with 3, 4 and 5%, respectively (p < 0.05), but memory T lymphocyte counts did not. Increased birth weight and fetal growth were significantly associated with higher B lymphocyte counts, independent of gestational age, but not with the other lymphocyte subset counts.
CONCLUSIONS: Lymphocyte subset counts increase with prolonged gestation, suggesting an ongoing development of the immune system. Birth weight and fetal growth seem to influence only B lymphocyte counts.