Given below are two statements. One is labeled as Assertion (A) and the other is labeled as Reason (R). 
Assertion (A) : During pregnancy, the level of thyroxine is increased in the maternal blood.
Reason (R) : Pregnancy is characterised by metabolic changes in the mother.
In the light of the above statements, choose the most appropriate answer from the options given below.

Both (A) and (R) are correct, and (R) is the correct explanation of (A).

A is correct. Normal thyroxine levels are 4.5 to 11.2 mcg/dL (micrograms per deciliter). During pregnancy, the level of thyroxine (T4) increases in the maternal blood. 

R is correct. During pregnancy, the maternal body undergoes various hormonal and metabolic changes to support the growth and development of the fetus. The metabolic changes that occur in the mother’s body are necessary to meet the increased demands of the growing fetus. These changes ensure that sufficient nutrients and energy are available to support the development of the baby and maintain the overall well-being of the mother during pregnancy.

R is the correct explanation of A. Thyroxine plays a crucial role in regulating the body’s metabolism, and its elevated levels during pregnancy help in providing adequate energy and nutrients for both the mother
and the developing baby.