A mom tells of having baby during brutal 3-month migrant journey: Reporter's notebook

The freight train looks like any other until it gets closer -- that's when the silhouettes dotting the tops of the train cars come into view.

Hundreds of migrants are on board, some waving and smiling at us as they pass by, other miserable and downtrodden, trying their best to hide from the merciless midday sun.

We're about 20 miles south of the U.S.-Mexico border along train tracks that bring cargo from farther south in the Mexican state of Chihuahua.

The train is not designed to carry people, but carry people it does. Migrants hitch a ride for what will be, for most, the last leg of a journey months in the making.

When the train creaks to a stop, the migrants climb down. The young men leap off, a competition of sorts to see who can jump down the quickest. For the elderly, it's a ginger descent down iron-rung ladders fixed to the train car sides.

And for those with children, it's a human chain of sorts. Moms hang children over the sides and lower them down into the waiting arms of other migrants below.

That's where we met Mildret Paz and her family, from Venezuela: her husband, their 5-year old daughter, their 1-year old son and, in her arms, a 1-month-old baby named Melany. They left three months ago for their journey north.

It took us a second to do the math -- a 1-month-old, a three-month journey.

Melany was born along the brutal migration route north.

"I had the baby in the Darién," Paz told us. "It was so hard because after I had her, you had to keep walking. So painful."

The Darién she refers to is the infamous Darién Gap, a harsh strip of jungle that straddles the Colombia-Panama border. For the vast majority of migrants heading north to the United States, there is no other option but to pass through.

It is muddy, steep and replete with criminal groups preying on migrants.

"We didn't have any money for tests or ultrasounds," Paz said. "I didn't think I was so far along or that I would have her in the jungle."

She went into labor while walking and had to immediately stop.

Soon by her side were members of one of the indigenous groups that live on the Panamanian side of the border, though she doesn't know which one.

"They helped me. After I had [Melany], they helped her and they carried her," Paz said, doing so until they made it out of the jungle.

They gave the baby what clothes they could, using the onesies meant for her 1-year-old brother. They were way too big, but she was warm and she was alive, and that's all that mattered.

From there, the family continued northward, through Panama, then Costa Rica, Honduras, Guatemala and into Mexico.

Several more weeks of walking led them to the train that led them to us.

"The trip has been so difficult, with no money, no nothing. We've been hungry, cold, everything, but thanks to God we are here," Paz said.

They had about a four-hour walk to the border before they planned to turn themselves into Border Patrol.

Whether they're admitted into the United States or returned to Venezuela remains an open question.

"We came to work," Paz said. "We want to give our children better lives. I can't give that to them in Venezuela."