But while medical testing requirements are comparatively strong, other US regulations are much looser than in some other nations — a fact that has been a boon to the US industry, but has also led to controversy. Though donor insemination has been legally recognized in the US since the 1970s, it’s still sometimes referred to as a legal Wild West in need of more policing.

Unlike many countries, the US allows men to donate anonymously and to be paid for doing so, leading to a comparatively larger donor pool; sperm donations in other countries plummeted following laws prohibiting anonymous donation or payment. After Britain ended anonymity for sperm donors in 2005, the wait for sperm could take years — in part because fewer men agreed to share their sperm with multiple women or with women they didn’t know personally. In Canada, concerns about the commercialization of human reproduction led to a ban on paying donors in 2005; by 2011 a single sperm bank with 35 active donors made up the entire national supply, according to the Toronto magazine The Grid. (In contrast, SSB alone has more than 140 active donors). Today, more than 90 percent of donor sperm used in Canada is imported from the US.

But loose regulations can also lead to complications. Something else the U.S. doesn’t regulate is family size — how many children can be born to a single donor. While there are nonbinding guidelines (the American Society of Reproductive Medicine suggests no more than 25 offspring per population of 800,000) and many US sperm banks operate under their own limits, there is no law limiting how often, or at how many sperm banks, a man can donate.

Other countries have much stricter rules. Some restrict the total number of children, while others place their limits on numbers of “families” — how many different mothers are involved. The UK prohibits more than 10 families for a single donor, while France caps at six, China at five, and New Zealand only allows four.

Since banks that hope to sell internationally have to abide by the limits of whatever countries import their sperm, those laws can sometimes serve as a check on the wilder U.S. market. SSB’s default is a global maximum of 25 families, but selling in some areas requires further restrictions. “There are certain areas of Australia where, once I send a donor there, that’s the only place they can go,” says Allard.

But not all sperm banks are as careful. Over the past several years, a number of stories of men with dozens of donor children have appeared in the media. One man is known to have sired over 150 children via two separate sperm banks, though that fact only emerged once mothers and children used his donor number (every donor has a unique one) to track each other down via the Internet. Some are simply interested in connecting with other families with whom they share an important bond, but others are motivated by worries about consanguinity — what happens if unwitting half-siblings end up falling for each other down the road? Advice columnist Emily Yoffe received a question from a man who claimed to have discovered that he and his wife, the happily married parents of three children, share the same donor father. (Yoffe advised him to tell his wife, then try to make peace with the information).

Some groups are pushing for an end to anonymous donation, but any U.S. sperm banks, conscious of the donor drop-off in other countries, are resistant to the idea. Instead, some of the largest are reportedly attempting to create a national, centralized registry of sperm and egg donors, which would allow donors to remain anonymous but also make them easier to track.

Other scandals have recently brought attention to more of the potential downsides of gaps in regulation. The U.S. requires screening for infectious diseases like HIV and Hepatitis, but not for genetic diseases — and sperm donors are known to have inadvertently passed such diseases onto children. Many sperm banks do screen for diseases such as cystic fibrosis, but there’s no federal requirement for them to do so.

Wendy Kramer, a mother who conceived her son with donated sperm and later founded the Donor Sibling Registry, a site that helps donor-conceived children find their siblings, is an outspoken advocate for more regulation, including required genetic testing, an end to donor anonymity, limits on the number of children per donor, and a mandatory, centralized system for tracking recipients, donors and successful births. She says her goal is to make the industry more responsive to the needs of those conceived via donation. “Again and again,” she says, “we have heard on the site from donor-conceived adults who have a strong desire to understand this invisible side of themselves.”