Decreased thymus size in full-term newborn infants of smoking mothers

Prenatal exposure to tobacco can have significant effects on infants. The objective was to investigate whether maternal smoking affects the size of the thymus.

A group of 50 pregnant women who smoked throughout pregnancy and a control group of 92 non-smoking pregnant women were studied. The full-term newborn babies' length, weight, and head circumference were measured. The size of the thymus was assessed by sonography during the first six hours of life in both the study group and the control group newborns.

The results of the anthropometric measurements in respect of length (50.36+/-2.27, 50.15+/-1.40 cm, p=0.51), weight (3.43+/-5.13, 3.57+/-4.38 kg, p=0.07), head circumference (34.47+/-1.22, 34.57+/-0.93 cm, p=0.62), and head circumference/weight ratio ((9.94+/-1.40, 9.79+/-1.16 cm/kg, p=0.50) were not significantly different between the patient and control groups, respectively. The thymic index (Ti) and thymic index/weight ratio (Ti/w) of the newborns of the smoking group were lower than in the controls (8.70+/-5.80 vs. 13.26+/-5.46, p<0.001 and 2.47+/-1.55 vs. 3.69+/-1.43, p<0.001, respectively). Moreover, the birth weight, head circumference/weight ratio, Ti, and Ti/w of the newborns of those smoking more than 10 cigarettes per day were significantly lower than those smoking less than 10 (3.08+/-0.55 vs. 3.58+/-0.45, p<0.001; 10.65+/-1.84 vs. 9.67+/-1.11, p=0.03; 5.95+/-4 vs. 10.25+/-6.12, p=0.01; and 1.82+/-1.08 vs. 2.84+/-1.66, p=0.02, respectively).

These results show that smoking while pregnant has a significant effect on the general involution of the newborn and size of the thymus, which plays an important role in the immune system.