Final answer:
The most accurate method to measure a 20-month-old child's length is by using a recumbent measuring board, as it ensures the child is accurately measured from head to heel in a fixed position.
Step-by-step explanation:
The most accurate method to obtain the length measurement of a 20-month-old child is b. laying on a recumbent measuring board. This method ensures that the child is in a fixed position and the length can be accurately measured from the top of the head to the heel.
During routine health evaluations, ensuring accurate measurements of a child's growth is essential. It helps in assessing their developmental progress in relation to normative growth charts. As babies often grow rapidly in the first year of life, significant deviations from growth patterns could indicate undernourishment or potential health issues. Conversely, a faster-than-normal increase in weight may be a warning sign for future obesity concerns.
Typically, children at 20 months may not always stand steadily or cooperate when measured against a tape measure. Therefore, the use of a recumbent measuring board is the preferred approach when precision is required. While the child lies down, it's easier to align the head and feet properly for a precise measurement that caregivers and healthcare professionals can use for accurate health assessments.