What: Natus Medical (NASDAQ:NTUS) is down 18% at 12:30 p.m. ET after releasing preliminary first-quarter revenue numbers that were lower than previous guidance.

So what: The medical-device company estimates it'll report first-quarter revenue of about $87.5 million "versus previous guidance of $91.5 million to $92.5 million, excluding revenue from the Venezuela Ministry of Health contract," the press release noted.

That doesn't sound like much of a miss until you notice the qualifier at the end of the quote. Management's guidance in January was for "revenue guidance of $96.5 million to $97.5 million," of which $5 million was from a contract with the Venezuela Ministry of Health contract.

So there are really two issues going on with Natus Medical. Venezuela didn't pay its $5 million bill and the company came up another $4 million short on the rest of its revenue during the quarter.

The contract with Venezuela requires a prepayment, so Natus Medical hasn't lost money on the deal. But the lack of an initial payment -- that was supposed to arrive in the fourth quarter -- injects a lot of uncertainty about whether the company can capture the $60 million in revenue that it expected to get from Venezuela this year.

President and CEO Jim Hawkins blamed the other $4 million miss on "pushouts of key orders." If those orders materialize in the second quarter and don't affect future orders, it's not really an issue. The end of the quarter is set arbitrarily after all.

Now what: At $87.5 million, revenue in the first quarter was down slightly from the $89.4 million in the year-ago quarter. If you add back some or all of that $4 million in delayed sales, revenue was flat to up slightly.

Investors will have to wait until April 20 for the full earnings release, including EPS. The previous guidance, which it seems unlikely to hit at this point, was for adjusted earnings of $0.34 to $0.35 per share, compared $0.31 per share in the year-ago quarter.

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