After months of speculation and mounting data, the Centers for Disease Control and Prevention officially confirmed Wednesday that the Zika virus does indeed cause microcephaly, a devastating birth defect in which babies are born with small, malformed heads and brains.

Researchers with the agency came to the conclusion after a review of existing data on the virus. There was no single piece of evidence that tipped the scales, the authors note. Rather, the accumulation of data from numerous sources convinced them of the link. Their analysis is published in the New England Journal of Medicine.

“This study marks a turning point in the Zika outbreak,” Tom Frieden, director of the CDC, said in a statement. “We are also launching further studies to determine whether children who have microcephaly born to mothers infected by the Zika virus is the tip of the iceberg of what we could see in damaging effects on the brain and other developmental problems.”

Zika, which is currently ripping through South and Central America and feared to be about to enter the US, generally only causes mild disease in adults. But, in pregnant women, the virus has been linked to causing not just microcephaly, but miscarriages, premature birth, vision problems in babies, and other birth defects. “We have learned that the virus is linked to a broader set of complications in pregnancy,” Anne Schuchat, CDC principal deputy director, told reporters during a White House briefing on Monday. “We continue to be learning pretty much every day,” she said, “and most of what we’re learning is not reassuring.”

A study released Monday by the journal Science found that the Zika virus preferentially kills off developing brain cells. When researchers unleashed the virus on balls of neural stem cells, which is a model for embryonic brain development, Zika destroyed them within a few days. In another experiment, the researchers grew brain organoids—another bundle of brain cells used to model brain development, this one with more structures that resemble a real brain—then infected them with Zika. The virus killed off 40 percent of the organoids’ cells.

The findings echo other study results as well as what researchers have seen in fetuses. In a study published last month, researchers reported watching the virus melt the brain of a baby in utero after the mother had been infected.

In addition to pregnancy complications, the virus is also linked to rare cases of a paralyzing autoimmune disease called Guillain-Barré syndrome. This week, researchers reported preliminary data that the virus may also cause another autoimmune disorder, called acute disseminated encephalomyelitis, which is similar to multiple sclerosis.