When Jenica Andersen felt the tug for a second child at age 37, the single mom weighed her options: wait until she meets Mr. Right or choose a sperm donor and go it alone.

The first option didn’t look promising. The idea of a sperm donor wasn’t appealing, either, because she wanted her child to have an active father, just like her 4-year-old son has. After doing some research, Ms. Andersen discovered another option: subscription-based websites such as PollenTree.com and Modamily that match would-be parents who want to share custody of a child without any romantic expectations. It’s a lot like a divorce, without the wedding or the arguments.

Given the prominence in today’s society of both single parenthood and online dating, this digital approach could be seen as a natural progression. It could also be considered shocking or even, as some have called it, an affront to marriage.

“It’s a controversial approach to creating a family and there are people who balk at it, but the idealized version of a man and woman falling in love is shortsighted,” said Ms. Andersen, now 38—and pregnant.

Using technology to find a platonic parenting partner comes at a time when it seems harder than ever to meet anyone the old-fashioned way. As people spend more time building their careers, it can be difficult to forge relationships outside the office, where romance has become verboten. And as the cost of living has increased, it has become harder for many people to consider marriage or children until later in life—all factors that have resulted in a declining fertility rate in the U.S.