One-week-old baby’s rotundity can be initially determined by observing the knee intervals of the baby in the supine position, after which a visit to the hospital can be made for further determination. First of all, parents can let the one-week-old baby in the supine position, and then together the baby’s bilateral ankles. When the baby’s ankles are together, the bilateral knee joint interval is large, such as reached about ten centimeters, then suspect that the baby may have O-shaped legs. For this condition, parents can take their babies to the hospital for X-ray of the lower limbs to have their babies’ conditions professionally evaluated. O-shaped legs can be caused by a variety of causes, such as rickets or low muscle strength of the lower limbs. O-legs caused by rickets can be treated with calcium or vitamin D supplements. For O-legs caused by low muscle strength, it may be necessary to wear orthopedic braces or other methods of lower limb muscle strength exercise. If you suspect that your baby has O-shaped legs, you need to consult a specialist as soon as possible to make a clear diagnosis and then carry out targeted treatment.