A family just welcomed the first girl in the husband's lineage after a 138-year boy streak. The case shows how much we don't understand about reproduction.

• Carolyn and Andrew Clark had a daughter on March 17.
• She was the first girl born into Andrew's direct family line since the 1800s.

When Carolyn and Andrew Clark welcomed their daughter, Audrey, on March 17, they were thrilled to have a rainbow baby after a miscarriage in January 2021.

There was another reason to celebrate: Audrey is the first girl born into Andrew's direct line of descendants in more than 130 years. That means Andrew's father, grandfather, great-grandfather, and beyond had only sons. The last time the family welcomed a girl was in 1885, the family said.

Andrew first told Carolyn about the family lore when they started dating, according to "Today."

"I asked his parents to confirm that information, and they're like, 'Oh, yeah, no, we haven't had a girl in our direct line.' He's had uncles and cousins that have had girls, but in his lineage, there has not been a girl."

Carolyn was determined to break the streak.

"When we decided to start growing our family, I just was like, 'I'm going to try for it,'" she told WFAA news. "I want the girl."

After first having a little boy, Carolyn got her wish.

"It was just joy, you know, just that she was here and healthy," she said. "It made it even more special that it was a girl because it was, like, you were worth the wait and all the struggles."

An OB-GYN said the story was extraordinary

Kelli Burroughs, the department chair of obstetrics and gynecology at Memorial Hermann Sugar Land Hospital in Sugar Land, Texas, said the story was incredible.

"It just leads us to ask more questions," she said. "Like, have we really figured out gender selection?"

Science has shown that a fetus' sex is determined by the sperm. That's because eggs have an X chromosome, while sperm can have either an X or Y. When the sperm and egg join, they can make a zygote — or fertilized egg — that is either XX (a female) or XY (a male).

Despite parents' best efforts at dietary changes, timed intercourse, and other old wives' tales, there's no way to naturally control whether a fetus is male or female, Burroughs said. That's because most men have an equal number of X and Y sperm. The only option for sex selection is to do in vitro fertilization, where you can select the sex by testing the fertilized eggs and then choosing the ones with the sex you want to be transfered.

The Clarks' story shows there may be more to sperm selection than chance, Burroughs said.

"There's some medical explanation behind that," she said. "It's more than just coincidence. We thought it was black and white, but clearly something is going on with that family that goes beyond just odds."

While Burroughs has never seen a case like this, she said the sex dominance in the Clark family made her believe "there would have to be a genetic explanation." She would like to see someone study the family.

"This is, from a medical perspective, very interesting," she said.

Burroughs says finding the sex early can help with disappointment

Throughout her career, Burroughs has counseled many patients who're disappointed with the sex of their fetus. Most often, that happens when a family already has two or more of one sex and are hoping for the opposite. Sometimes, cultural norms and expectations play a role.

People who have strong feelings about the sex of their child should find out whether they're having a boy or girl as soon as they can, Burroughs said.

That gives them "time to either celebrate or to have a mind reset to be able to cope with the gender they're able to have," she said.

Studying cases like the Clarks' could ultimately help families with a sex preference, she added.

"Maybe there is something this family could contribute that could help people in the future," she said. "There is always room for us to learn, and I feel like this family opens that door."