Lexington, as the couple plan to name him, lost his two older sisters, Violet, 5, and Iris, 4, in an apparent gas explosion last July 24 that destroyed a Hopkinton apartment building and shattered the Carey family.

``I'm very excited we're having another child, but I feel bad and I feel guilty,'' Heath said from the porch of the couple's Onset trailer, bordered by a garden of iris and a violet-adorned bird bath.

``When he grows up he's going to see the pictures and ask about them and we're going to have to tell him,'' Heath said, his head bowed.

Lexington almost never was. Heath, 27, had a vasectomy after the birth of the couple's second daughter, Iris. It was reversed in October, but the odds were against the couple, married five years.

Tara, 28, got pregnant three months later.

``His sperm cells were so low after the operation the doctors can't believe she's pregnant,'' said Cindy Germain, Tara's mother.

Lexington is due mid-October.

Ultrasound photos of Lexington are tacked to the refrigerator next to a flier announcing what would have been Iris' fifth birthday and an invitation to a candlelight vigil Thursday, the one-year anniversary of the deadly blast - the cause of which remains a mystery.

Butterflies will be released at the sisters' joint Milford grave Thursday morning after a private ceremony. A vigil is planned for 7 p.m. where the building once stood at 65 Main St.

``We physically didn't die, but our life ended that day. We're never going to be the same,'' said Tara.

A joint probe by the state fire marshal and Department of Telecommunications and Energy has yet to determine the cause of the explosion - originally blamed on a gas leak.

``We live every day looking for answers,'' Germain said, her voice wavering. ``I just want to know why my granddaughters died.''

The Careys and their attorney blame the tragedy on a faulty pipe fitting that corroded and cracked, releasing gas into the building.

The milestones that never will be bother Tara and Heath the most.

``Violet was complaining just weeks before (the blast) of her teeth just starting to hurt. We know they would have lost teeth by now,'' Tara said, rubbing her forearm where an ID bracelet tattoo reads, ``Violet. Love. Iris.''

Heath has the same mark, a replica of the jewelry their daughters were wearing when buried together in one casket. The couple also share matching tattoos of blue hearts between their thumb and pointer finger on their right hands and an eternity symbol in the same place on their left hands.