Iron deficiency affects the opioid and dopamine systems in rodent models, with a higher pain threshold. The opioid system is involved in sucrose's ability to reduce pain and distress during neonatal procedures. Thus, prenatal iron deficiency might affect response to pain and sucrose analgesia. In order to compare response to pain and sucrose during heel stick in neonates with and without iron deficiency, healthy full-term Chinese infants were randomized to receive sucrose or water by syringe beforehand, in conjunction with heel stick for metabolic screening.

Inclusion Criteria:

• Full term healthy neonates participating in the Healthy Infant Development RCT (NCT00613717) in the folic acid/early postnatal placebo group and pre- and early postnatal iron-supplemented infants.

Exclusion Criteria:

• birth weight < 2500 g gestational age ≤ 37 wk major perinatal complications major congenital anomaly multiple birth

On request after main findings are published.