A study investigated the association between use of antidepressant medication during pregnancy and the presence of a heart malformation in the offspring. Investigators enrolled two groups of women:

• 305 women who had delivered an infant with a specific heart malformation (right ventricle outflow obstruction)
• and a sample of 6030 women who delivered an infant without any birth defects.

The presence or absence of birth defects was established based on the newborn physical exam and diagnostic tests. All mothers were interviewed to determine their use of antidepressant medications during the pregnancy.

What type of study was this?