BACKGROUNDFor decades, birth weight doubling time (BWDT) has been used as an indicator for the assessment of physical growth of infants. However, the relevant data in the literature were obtained mainly from western subjects and no similar studies have been carried out for South EastAsian or otherAsian countries.

OBJECTIVETo determine BWDT and related variables forThai infants.

METHODSA study was conducted from January to August 1999 at the well baby clinic of Bamrasnaradura Hospital. Apparently normal infants (335) with birth weight between 2,500 and 4,000 grams were recruited and followed up until they had doubled their birth weights. Data on infant birth weight, sex, mother education, occupation, income and feeding practices were collected.

RESULTSThe mean BWDT was 114 days which was slightly less than that given in previous reports. Male infants doubled their birth weights in less time (104 days) than females (123 days) and the difference was statistically significant (p < 0.001). Infants with lower birth weights doubled their birth weights earlier than those with higher birth weights (p < 0.001). Infants who were not given complementary food had shorter BWDT than those who were (p < 0.001), but we could not demonstrate any significant association between BWDT and type of food, mother's education or family income (p > 0.05). Factors that did affect BWDT were birth weight, sex, daily weight gain and use of complementary food. However, by multivariate analysis only birth weight and daily weight gain showed significant association with BWDT (p < 0.001).

CONCLUSIONBoth prenatal and postnatal factors may affect BWDT significantly.