Jonathan Sandhu loves cracking nerdy dad jokes. Earlier this month, his wife Mercedes Sandhu gave him four more (identical) reasons to do so.

The Texas pair celebrated the birth of identical quadruplets − Hannah, Rebecca, Lucy, and Petra − in Houston earlier this month, just in time for Mother's Day. The holiday this Sunday will look a little different for the family because they only had two children last year and now they have more than doubled that number.

"I'm excited about being able to raise these girls, and this next chapter," Mercedes said. "I know it's going to be crazy, but I'm looking forward to this."

The couple was at first shocked, and then fearful about the pregnancy, because carrying quadruplets comes with so many health risks for the mother and the babies, Mercedes said. But on May 1, Mercedes gave birth to four baby girls without any complications at Texas Children's Hospital in Houston. The quadruplets are still in the neonatal intensive care unit and are set to go home to their parents and two brothers, ages 3 and 18 months, later this summer. The quadruplets were delivered early because like in many pregnancies with more than one fetus, it's a challenging balancing act within the uterus to share nutrients from one placenta.

Identical quadruplets occur in pregnancy when one fertilized egg splits into four identical embryos, and means the siblings share the same genetic information. Fraternal twins, triplets or quadruplets occur when two or more separately fertilize eggs develop in the uterus at the same time.

How rare are identical quadruplets?

Dr. Manisha Gandhi, the maternal-fetal specialist who delivered the babies, said identical quadruplets are so rare that medical experts don't have enough available data to pinpoint just how uncommon they are.

"In science, we're so used to having the prevalence, or the rate in the population," she said. "But this is a case-by-case basis."

Some medical professionals have estimated identical quadruplets occur in one out of roughly every 11 million pregnancies, the couple said, adding that they each have no family history of twins or multiples, going back generations.

According to available historical medical records and news stories, there have been around 75 other instances of identical quadruplets conceived without assistance from reproductive technology, Jonathan said.

In February 2023, a Mississippi woman gave birth to four identical girls and one boy.

'Are you serious?'

When Mercedes saw four fetuses during her first ultrasound appointment last year, she was filled with shock and disbelief, she said.

"I'm like, 'this − this can't be right," she said. "I was crying, laughing, all at the same time."

Mercedes told her husband he could skip the appointment because she thought it would be routine. Since this pregnancy was her third, she knew Jonathan would have plenty of opportunities in the future to view sonograms.

After she called him from the exam room, he immediately left work and continued speaking to his wife on speaker phone as he drove down Houston's Interstate-45.

"Of course his first question was, 'Are you serious?'" Mercedes said. "Because we do like to joke around with each other."

Later, as word of Mercedes' pregnancy spread at Jonathan's engineering firm, many of his colleagues remained unconvinced for months that Jonathan was telling the truth − because he's known as such a prankster.

"They actually were curious if this was all building up to a big April Fool's prank," he said of his colleagues. "So they were surprised that it was actually real."

Couple was fearful of high-risk pregnancy

Mercedes' pregnancy posed health risks because all four fetuses were sharing the same placenta − an organ that forms in the uterus during pregnancy to connect a growing baby to oxygen and nutrients.

Sharing the same placenta happens in many pregnancies, but it's more risky with four babies than with three or two, Gandhi said. If one baby starts to struggle to gain nutrients properly, the way they interact with the placenta can affect the other babies' ability to gain nutrients and grow, she said.

"When you're sharing the same placenta, you're all under the same roof," Gandhi said.

The research they read was "terrifying," Jonathan said, because so much information said it was likely the mother or at least one fetus would suffer dangerous health outcomes in a pregnancy involving quadruplets.

"We were looking at like, 'Oh my gosh, are we going to lose somebody in this?,'" Jonathan said.

In the end, Mercedes delivered the four babies at 29 weeks, via a caesarian section, without any complications, she said. The journey there had its ups and down, largely because of the fear over potential health risks, she said.

"Emotionally, there were good days and bad days," Mercedes said. "I would be scared about losing one or all of them."

What was it like to be pregnant with quadruplets?

Mercedes said her third pregnancy wasn't very different from her first two, except for being much larger.

"I got bigger a lot faster," she said, explaining that she felt like she was 40 weeks pregnant at 24 weeks. She also ate a lot more, she said.

Her quadruplets certainly made their presence known, Mercedes said, explaining how her belly rumbled with the movements of four babies, often all at once.

"I did feel a lot of kicking and punching from all around my uterus," she said. "It is so funny − for the most part they were calm, but when they all started kicking − they all started kicking at the same time."

The ultimate prank

Mercedes said she definitely wanted to get pregnant a third time, and eventually wanted a total of five kids. Jonathan thought he wanted three kids max, he said, and the couple agreed this pregnancy might be Mercedes' last. Getting pregnant with surprise quadruplets means the joke will always be on Jonathan, they said.

"You got me good, Mercedes. You snuck a few more kids in there," Jonathan said.

"Just a few," Mercedes replied coyly.