"Since the beginning, more girls come here than boys," she says. "I think people don't like to give boys away."
These girls are often the lucky ones.
At the entrance of the orphanage is a silver-framed crib, where parents can leave unwanted children, no questions asked. Above it, an Urdu poster reads, "Don't kill the baby, leave the baby alive in the cradle."
Edhi says she sometimes finds dead baby girls in the crib in front of the shelter. She suspects that families worry that, if they leave their daughter alive, someone will come looking for them to ask why they abandoned the child, or even ask them to take her back.
She pulls out a photo of a baby girl that had been left in the crib recently. "Look, they have burned her to death," she says. The photo shows a newborn, its umbilical cord still attached, whose tiny body is fully blackened.
But, even amid this despair, there is some hope. Edhi proudly notes that her orphanage has helped almost 20,000 boys and girls. "The children I have taken care of have become engineers, doctors, believers of Quran, good human beings," she tells me. "I have even sent girls to America," she adds with a smile.
Son preference, and its contribution to shifting the balance of the sexes, has been heavily studied in India and China. Klasen says that Pakistan has a similar problem but is often overlooked.
"If you look at the world, you see that India and Pakistan and China really stick out," he says.
But Pakistan rarely faces the same scrutiny as India or China, he notes. One reason might be that experts like Klasen haven't been able to adequately study the problem here, because Pakistan hasn't had a census since 1998, making reliable information difficult to come by.
Census data from India and China have allowed experts to closely monitor the sex ratios, watching how they change by region and over time. Pakistan's lack of solid data has left the problem there largely hidden.
"We don't have numbers for Pakistan," says Klasen. "Pakistan has been in the news for many other things and it's a very unstable country," he adds, "I don't think we will get more information soon."
In its 1998 census, Pakistan showed an overall sex ratio of 108 males to 100 females. India, in its census in 2001, had 107 males to every 100 females. In an academic article from 2003, Klasen estimated that 7.8 percent of Pakistani women and 7.9 percent of Indian women are "missing." His research, he says, suggests that Pakistan's situation has not improved since then. In a country with an estimated population of 177 million, those "missing" women and girls could number in the millions.
Researchers like Batool Zaidi, the senior program officer in Pakistan for the Population Council, an international NGO that studies reproductive health, say it won't be easy to tackle the problem without first getting hard information. "We desperately need census data to get more accurate estimates of several demographic indicators, sex ratio being one of them," she says.