It's one of the biggest purchases for soon-to-be parents: a crib for baby. Beginning Tuesday, a new generation of cribs, designed to be safer, will be the only ones approved for sale — in stores, online, and even at neighborhood yard sales.

Ushering in one of the most significant changes in child safety in decades, the rule taking effect this week bans the manufacture, sale and resale of drop-side cribs. Drop-sides have a side rail that can be raised and lowered to allow parents to more easily place or lift a baby, but they have been blamed in the deaths of several dozen children.

Another significant part of the new federal standard mandates more rigorous safety tests for children's cribs before they hit the market. In the past, manufacturers were allowed to retighten screws and bolts on a crib in the middle of hardware testing meant to mimic how a child might rattle a crib — by jumping up and down or shaking a rail.

While the tests were intended to simulate a toddler in a crib, they don't mimic the reality of the parent. It's a rare parent who would know when to retighten obscure pieces of hardware on a crib during normal use by a child.

The retightening of screws and bolts during durability tests on cribs ends Tuesday, as part of the new rule approved last year by the Consumer Product Safety Commission. Stronger mattress support systems and crib slats are also a major part of the new testing.

"After 30 years of having outdated standards, CPSC delivered on its promise and created the toughest crib safety standards in the world," Commission Chairman Inez Tenenbaum told The Associated Press. "Parents can now shop for a crib with confidence."

New cribs on the market won't really look different other than the obvious absence of a movable side that drops down. Now, all four sides will be fixed and the cribs should be sturdier because of the tougher testing requirements.

Drop-side cribs have been around for decades. But they have increasingly come under scrutiny in recent years because of malfunctioning hardware, sometimes cheaper plastics, or assembly problems that can lead to the drop-side rail partially detaching. That can create a dangerous "V"-like gap with the mattress in which a baby can get caught and suffocate.

Drop-sides are blamed in the deaths of more than 30 infants and toddlers since 2000 and suspected in about a dozen other infant fatalities. Since 2007, more than 9 million drop-sides have been recalled including cribs from Evenflo and Pottery Barn Kids.

The end of drop-side cribs marks a long-awaited day for Susan Cirigliano, who lost her 6-month-old son, Bobby, when his drop-side slid off the tracks in 2004, trapping his head and neck between the mattress and the malfunctioning side rail. He suffocated.

"It's bittersweet. It is not going to change my life as far as what has already happened to us," said Cirigliano, who lives in North Bellmore on New York's Long Island. "But hopefully, it will save many more children. I am sure it will."

While drop-side cribs will no longer be made or sold, they are still being used in homes across the nation. The industry says drop-sides that haven't been recalled can be used safely as long as they are properly assembled and maintained to the manufacturer's instructions. Manufacturers do not recommend using cribs that are more than 10 years old.

Industry officials say a healthy supply of new cribs awaits shoppers.

"Our members are currently selling cribs that meet the new federal standard and parents will continue to enjoy a large selection of cribs in a range of price points," said Michael Dwyer, executive director of the Juvenile Products Manufacturers Association, a trade group that represents about 90 percent of the crib industry.

A new crib can cost from about $120 to more than $700, with about 2.4 million of them sold each year.

While manufacturers have been making cribs to the new standard for months, some retailers still have cribs in stock that will be banned on Tuesday. One estimate suggests more than 100,000 noncompliant cribs costing more than $30 million in lost sales.

The two Republican commissioners at the CPSC tried this month to secure an extension for dozens of retailers, many of them smaller ones, to allow them at least a few more months to sell their inventory.

"I would have liked to have seen a three-month grace period for retailers," Republican Commissioner Anne Northup said in an AP interview. "We should have staggered it so that if we allow manufacturers to deliver up until June 28th, we should have allowed retailers a certain amount of time for them to sell what was legal."

The three Democrats on the commission, however, blocked an extension.

The agency is allowing daycare centers, hotels and companies that rent cribs additional time to comply — until Dec. 28, 2012, before they need to purchase cribs that meet the new safety standards.

Pottery Barn Kids is recalling about 82,000 drop-side cribs because the drop-sides can detach when hardware breaks, creating a space into which a young child can become entrapped, which can lead to suffocation. A child can also fall out of the crib. Drop side incidents also occur due to incorrect assembly and with age-related wear and tear.

The Consumer Product Safety Commission announced the largest crib recall in U.S. history Monday, citing the potential dangers of cribs with dropdown sides.

The agency will recall more than 2.1 million cribs made by Stork Craft, of British Columbia, Canada, because of the risk that a child's head can get caught between the mattress and the side railing. As many as three deaths have been linked to the product. Stork Craft is one of the most widely purchased brand names in baby cribs.

This is not the first time cribs have been recalled due to such fears. Nearly 5 million cribs have been recalled over the past two years and the CPSC has considered banning dropdown sides altogether.

Included in the recall are 147,000 Stork Craft cribs produced under the Fischer-Price logo.

CPSC urges parents and caregivers to immediately stop using the recalled cribs, wait for the free repair kit, and do not attempt to fix the cribs without the kit. They should find an alternative, safe sleeping environment for their baby. Consumers should contact Stork Craft to receive a free repair kit that converts the drop-side on these cribs to a fixed side.

The cribs’ drop-side plastic hardware can break, deform, or parts can become missing.  In addition, the drop-side can be installed upside-down, which can result in broken or disengaged plastic parts.  All of these problems can cause the drop-side to detach in one or more corners. When the drop-side detaches, it creates space between the drop-side and the crib mattress. The bodies of infants and toddlers can become entrapped in the space which can lead to suffocation.  Complete detachment of drop-sides also can lead to falls from the crib.

CPSC, Health Canada, and Stork Craft are aware of 110 incidents of drop-side detachment; 67 incidents occurred in the United States and 43 in Canada.  The incidents include 15 entrapments; 12 in the U.S. and three in Canada. Four of the entrapments resulted in suffocation: a 7-month-old in Gouverneur, N.Y.; a 7-month-old in New Iberia, La.; a 6-month-old in Summersville, W.Va.; and a 9-month-old in Bronx, N.Y. 

SALT LAKE CITY (ABC 4 News) - Several crib manufacturers are calling for a ban on their own cribs. The reason? They say they're just not safe.