Material and Method: The present study included pregnant women between 1989 and 1990 who attended the antenatal clinics (ANC) having a gestational age less than or equal to 24 weeks. During that period, up to delivery, clinical and other potential data namely demographic and biomedical factors, maternal status, socioeconomic factors, and nutritional factors were included. The birth weight at birth less than 2,500 gm was considered LBW.

Results: Two thousand one hundred eighty four pregnant subjects who delivered live born and were still eligible, were used for analysis in the present study. The incidence of LBW was 9.2% (201/2,184). Women with body mass index (BMI) at first antenatal clinics (ANC) less than 18.5 Kg/m2 and weight gain during the second trimester less than 300 grams/week was the strongest independent risk factor for LBW (odds ratio 11.25, 95% confidence interval (CI) 5.77-21.94). The number of antenatal care less than 4, monilial vaginitis, the infestation of hookworm and strongyloides, and pregnancy-induced hypertension were independent risk factors (odds ratio 11.04, 3.14, 4.93 and 4.02 respectively).

Conclusion: The present study showed that low initial BMI, low weight gain in the second trimester, and low attendance at ANC are associated to the occurrence of LBW. The development of a scoring system for detecting high-risk of LBW in pregnant women based on a combination of antenatal factors should be pursued.

Keywords: Low birth weight, Maternal, Pregnancy, Risk factors, Thais