SAN DIEGO (AP) — Genetic analysis instrument company Illumina is buying prenatal testing company Verinata Health Inc. in a deal worth up to $450 million.

Illumina Inc. said Monday that it will pay $350 million for privately-held Verinata and may pay up to an additional $100 million through 2015 if certain targets are met. The transaction will be financed mostly with available cash.

Ilumina’s shares fell $5.24, or 9.6 percent, to $49.52 in premarket trading. Its shares peaked for the past year at $57 on Dec. 20. They fell as low as $28.72 almost a year ago.

Verinata’s verifi test analyzes cell-free fetal DNA naturally found in a pregnant woman’s blood to look for missing or extra copies of chromosomes. The test can detect Down syndrome, Edwards syndrome and Patau syndrome. The test also includes the option to evaluate sex chromosome abnormalities, such as Turner syndrome, Triple X, Klinefelter syndrome and Jacobs syndrome.

Illumina, based in San Diego, expects the acquisition to reduce its 2013 adjusted earnings by about 20 cents per share and then add to its earnings starting in 2014 and beyond. Verinata is based in San Carlos, Calif.