Sitting on her porch, 26-year-old Brandy Hummel gently rubbed her rounded belly to soothe the babies inside. But the growing twins kicking within are not hers.
They were implanted in her uterus as fertilized embryos about six months ago, after she agreed to be the surrogate mother, or gestational carrier, for a couple who lives about 400 kilometers (250 miles) away in New York City.
The contract, as well as an intensive screening process, was negotiated by lawyer Melissa Brisman, based in New Jersey.
Paying a woman to effectively "rent" her reproductive organs is prohibited in several US states, including New York. But laws in other places such as Pennsylvania, where first-time carrier Hummel lives, are more surrogate-friendly.
Brisman's office facilitates more than 150 such births each year, and she estimates that there could be as many as 6000 in the US annually.
Official numbers give significantly lower estimates, perhaps because many surrogate births go unreported. But in Brisman's nearly 13 years of drawing up such arrangements, she has seen a dramatic rise in demand.
Much of the increase has been among same-sex couples, as well as people from countries where surrogacy is illegal.
The practice has also gained interest thanks to celebrities like "Sex and the City" star Sarah Jessica Parker, who recently had twin girls with her husband Matthew Broderick through a surrogate.
For many women, surrogacy is the only path towards having children when they cannot get pregnant on their own.
After beating cancer, Dina Feivelson, the biological mother of the twins, was ready with her husband Neil to start a family.
But doctors told her it would be too dangerous for her to get pregnant, so she decided to hire someone else to help achieve their dream.
"We did have these 24 frozen embryos," she explained, sitting on a couch surrounded by the many sonogram photos that Hummel sends her every couple of weeks. "We needed to find a way to make them from embryos into babies."
In addition to covering Hummel's medical bills and other expenses, the Feivelsons pay her about 2,100 dollars a month during the process, which includes in vitro fertilization procedures.
But the Hummels insist it's not all about the money, which they have put away in the bank.
They live comfortably in a newly-built home and both work full time, making more than enough money to pay their bills.
Many people involved in surrogacy arrangements insist that altruism is an essential ingredient.
"I would hope that someone would do this for me if I couldn't have had my own son," Hummel said.
And she added: "I just love being pregnant. I actually feel my healthiest when I am pregnant." Currently battling the "terrible twos" with their own son, though, the Hummels don't plan to raise any more children.
Hummel first heard of surrogacy at the daycare center where she sends her son. The woman who runs the center also carried another couple's child.
But controversy has arisen in several cases where the surrogate mother refused to give up the babies once she had delivered.
So agencies like Brisman's require surrogates to go through intensive psychological exams in addition to physical health evaluations.
Her office receives between 50 to 100 applications from potential surrogates per week, interviews 10 to 20, and ultimately accepts about five or six.
Brisman is confident that the screening process for carriers, especially the psychological evaluations, ensures the handover of the baby will go smoothly.
"I haven't had any compensated carriers not wanting to give it up," she said.
In most cases, the carrying mother's rights are terminated while she is still pregnant, so that even if the intended parents couldn't take the baby, it would be put in the custody of a guardian appointed by the intended parents.
Each contract is custom tailored to the parties involved and the state where the surrogate lives, and delineates what would happen in the case of a miscarriage or other complications which may affect the babies or require extra medical attention for the carrier.
In their contract, the Feivelsons and the Hummels have agreed to remain in contact after the birth of the twins, so that Brandy and her husband Mark can see the children grow up through photos and post cards.
"We really have a nice working relationship," said Dina Feivelson. "I really respect that it's her body and she's putting a lot of herself in it. And in turn she recognizes that they're our babies."