Commercial surrogacy is estimated to be worth more than $1bn a year in India. While pregnant, some surrogate mothers live in dormitories - which critics call baby factories. They give childless couples the family they have longed for, but what is it like for the women who carry someone else's child for money?
"In India families are close. You are ready to do anything for your children," says 28-year-old Vasanti.
"To see my children get everything I ever dreamt of, that's why I have become a surrogate."
Vasanti is pregnant, but not with her own child - she is carrying a Japanese couple's baby. For this she will be paid $8,000 (£4,967), enough to build a new house and send her own two children, aged five and seven, to an English-speaking school - something she never thought was possible.
"I'm happy from the bottom of my heart," says Vasanti.
She was implanted with their embryo in the small city of Anand in Gujarat and will spend the next nine months living in a nearby dormitory with about 100 other surrogate mothers, all patients of Dr Nayna Patel.
There are up to 10 surrogate mothers in each room. The women have their meals and vitamins delivered to them and are encouraged to rest. Vasanti, however, cannot help feeling restless.
"At night I wander around because I can't sleep. As my tummy is getting bigger and the baby is growing I am getting really bored," says Vasanti.
"Now I want to go home really soon to be with my children and my husband."
The rules of the house forbid the women from having sex during the pregnancy, and emphasise that neither the doctor nor the hospital, nor the couple whose baby it is, are responsible for any complications.
If the mother is bearing twins she receives a higher fee - $10,000. If she miscarries within three months, she receives $600. The couples are charged around $28,000 for a pregnancy that leads to a successful birth.
Dr Patel, who runs the IVF clinic and the dormitory and delivers the babies, acknowledges that many people find her work offensive.
"I have faced criticism. I am facing it and I will be facing it, because this, according to many, is a controversial subject," she says.
"There are a lot of allegations that this is just a business, this is just baby-selling, a baby-making factory, and all these phrases used to hurt."
Some say that the surrogates are being exploited, but Patel argues that the worlds of big business, glamour and politics are harsher.
"I feel that each and every person in this society is using one or the other person," Patel says.
In her opinion, the mothers are getting a fair deal.
"These surrogates are doing the physical work, agreed, and they are being compensated for that. They know that there is no gain without pain," she says.
While they stay in the surrogate house, Patel says the women are taught new skills such as embroidery so that they can earn a living after they leave.
And the money they earn is huge by local standards. Vasanti's payment, which she receives in instalments, dwarfs her husband Ashok's monthly income of about $40 a month.
Some mothers come back again after giving birth once. Three times is the maximum Patel allows.
There are a number of reasons why India is "the surrogacy hub of the world", she says. Good medical technology is available and the cost is comparatively low. But the legal situation is also favourable, Patel argues.
"The surrogate has no right over the baby or no duties towards the baby, so that makes it easier. Whereas in the Western world... the birth mother is considered as the mother and the birth certificate will have her name."
Not having the surrogate's name on the birth certificate can make it harder for the children to find out about the surrogate mother who gave birth to them if one day they want to gain an understanding of their past.
India has one third of the world's poorest people and critics argue that poverty is a major factor in the women's decision to become a surrogate.
"There are… many needy females in India," says Patel. "The food, shelter, clothing and medicine, healthcare is not free for all in India. People have to fend for themselves."
Patel says she encourages the women to use their earnings wisely. Vasanti and her husband are building a new home.
"The house I live in at the moment is a rented house, this one will be much better," says Ashok.
"My parents will be pleased that their son and his wife have managed to build a house. Our status in society will go up, which will be a good thing."
But the new house comes at a price. It will not be built in the same area as their old one, because of hostility from neighbours.
"If you are at home then everyone knows that we are doing surrogacy, that this is a test tube baby, and they use bad language. So then we can't stay there safely," says Vasanti.
As she nears her due date, Vasanti becomes more anxious about the birth.
"I don't know anything about whether my couple will come and take my baby straight away, or if it will stay with me for 10, 15 days, 20 days. I might not even get to see it," she says.
Vasanti is moved to hospital and after a protracted labour, Patel decides to give her a caesarean section.
It's a boy - usually a cause for celebration in India, but Vasanti is concerned that the Japanese couple had originally wanted a girl.
The baby is taken directly to a neonatal hospital where his parents will be able to collect him and take him to Japan.
Vasanti is tearful as she remembers the moment she caught a glimpse of him.
"I saw him when I had my caesarean. I saw my son, but then they took him straight away. I must have seen him for five seconds, so I saw that he was living.
"The couple wanted a girl and it's a boy. It's good whether it's a boy or a girl. She's got a child at least."
As the tiny baby boy she has carried for the past nine months starts his new life, Vasanti is beginning hers. She lives in her new house with her family and her children attend an English-speaking school.
"My children are growing day by day and we want a good future," says Vasanti.
"That's why we [did] this, and not in my entire life do I want my daughter to be a surrogate mother."
House of Surrogates will be broadcast on Tuesday 1 October at 21:00 BST on BBC Four. Or catch up later on BBC iPlayer