Which of the following is NOT a component of routine blood tests during pregnancy?

Routine blood tests during pregnancy are designed to monitor the health of both the mother and the developing fetus, screening for various conditions and assessing overall well-being. The inclusion of specific tests is based on their importance in prenatal care.

Vitamin D levels, while significant for overall maternal health and fetal development, are not universally included in the standard panel of routine blood tests during pregnancy. Routine testing usually focuses on factors that can have immediate implications for maternal and fetal health, such as the Rhesus factor, which assesses the mother's blood type to prevent Rh incompatibility issues; HIV screening, which is crucial for identifying the risk of transmission to the baby; and syphilis testing, which screens for sexually transmitted infections that can cause serious complications during pregnancy.

Thus, vitamin D levels do not form part of the standard routine blood tests in pregnancy, which is why it is identified as the correct answer.