Over 40 years ago, the world's first "test tube baby" was born. Louise Joy Brown's conception via in vitro fertilization and the resulting birth ushered in a new age in modern parenthood. The idea of a baby being conceived outside of the human body was mind-blowing in 1978, but since then more than 8 million babies around the world have been born through IVF, according to International Committee Monitoring Assisted Reproductive Technologies.

IVF, originally created to fight infertility, has expanded to allow people to think beyond the traditional family and carve a new path to parenthood.

"I chose this field for the science and for the medicine and for the drama and for the excitement and for the amazing things that we can do for people," says Dr. Richard Grazi, founder of Genesis Fertility & Reproductive Medicine in Brooklyn, New York.

ABC News spent more than a year following four families on their unique IVF journeys. As different as these families are, there is one common theme: There are no guarantees on the road to parenthood.

Overcoming cancer

Aviva Love and Adam Lazaros were married in 2013 and able to naturally conceive their son Benji two years after later. When the couple was ready to try for baby No 2, they were dealt a surprising and devastating blow: Lazaros, 30, was diagnosed with testicular cancer in January 2017.

Doctors said there was a chance he may never be able to have another child.

"That was the only time I cried through the whole thing was when I got that phone call that you probably won’t have children. That was just such just a gut-wrenching blow," Lazaros told ABC News.

PHOTO: Aviva Love and Adam Lazaros of Brooklyn, New York.
ABC News
Aviva Love and Adam Lazaros of Brooklyn, New York.

That’s when the young couple turned to Grazi, who was also a friend of the family.

"Considering that Adam had to preserve his fertility by banking sperm before he went through treatment for his cancer, the most efficient way to use that sperm was in vitro fertilization and that's why we chose that route," Grazi told ABC News.

Lazaros banked his sperm before undergoing chemotherapy. Throughout treatment Lazaros kept a positive attitude, according to his wife.

"I was putting Benji to bed and I was sitting alone in the room with him; it just struck me that we were facing something where I could always be alone in the room with him," Aviva said through tears.

In August 2017, the couple received news that Lazaros was cancer-free. It marked the end of one journey and the beginning of IVF.

Love, 30, began the IVF process in 2018 under Grazi’s watchful eye. After retrieving 29 eggs the couple ended up with 20 embryos.

"Even though we have other embryos, it’s just still a lot riding on each one. You know at that point everything is out of the doctor’s hands and all squarely on my uterus," Love said as she was preparing for her first embryo transfer.

"There’s a little voice in the back of my head that’s saying, 'Of course it’s not going to work the first time,'" Lazaros said.

Less than two weeks after the transfer, Grazi called the couple in their Brooklyn apartment to tell them they were pregnant. Following the news, Love reported to Grazi’s office for her daily blood tests.

PHOTO: Dr. Richard Grazi speaks with Aviva Love before egg retrieval at Genesis Fertility & Reproductive Medicine in Brooklyn, New York.
ABC News
Dr. Richard Grazi speaks with Aviva Love before egg retrieval at Genesis Fertility & Reproductive Medicine in Brooklyn, New York.

A sonogram appointment at eight weeks revealed the fetus no longer had a heartbeat.

"I think back now to when we got the news that the implantation was successful and I wish in a way that I could erase that memory," Love said.

The couple decided to take a break to grieve their loss before beginning another round of IVF.

Aviva began her second round of IVF a few months later and is expected to give birth early this summer.

"It was a little bit different doing it a second time knowing what we know now and seeing the less happy side of IVF," Lazaros said.

Benji is excited to be a big brother, according to his parents.

Adopting an embryo

Kerri and Chris Morgan say it was love at first sight when they met for their first date on March 7, 2015. The pair had started chatting on Tinder six days prior and haven't been able to stop since that fateful swipe. On their first date, Kerri, now 35, said they talked about having kids right away.

“First trying to conceive naturally was definitely an odd feeling considering 38 years of my life, I've been trying to do the exact opposite," Chris Morgan, 38, said. "Once it wasn't happening, it was definitely stressful."

PHOTO: Kerri and Chris Morgan wait for a phone call from their fertility clinic.
ABC News
Kerri and Chris Morgan wait for a phone call from their fertility clinic.

After a number of tests, Kerri was diagnosed with low ovarian reserve and faced issues with her fallopian tubes. Six months into their marriage they began fertility treatments.

Fertility treatments can be expensive so the Morgans decided they would only try only one round of IVF. An average cycle of IVF and its associated medications can cost between $10,000 and $15,000, according to the Society for Assisted Reproductive Technology.

"We just decided to be realists and not bankrupt ourselves and put ourselves living in a box on the side of the road for the sake of having a family," Chris said.

The process, in all IVF cycles, is that the eggs are removed from a woman's ovaries during an egg retrieval and fertilized outside the body in the laboratory, where the fertilized egg cell begins to divide. The resulting embryo(s) are eventually transferred back into the uterus, and, it’s hoped, will grow uneventfully to a full-term pregnancy and live birth.

The Morgans' doctor was able to retrieve five eggs from Kerri, but the two embryos did not survive.

"It was literally like losing our children," Kerri told ABC News as her voice cracked and tears filled her eyes.

Although the grieving process was tough, the Morgans were not ready to give up on their dream of parenthood. Just as she had turned to the internet to find love, Kerri looked again to find a new path forward for her family.

When couples decide that their family is complete but still have embryos remaining in the lab, they may donate them to someone unable to conceive.

Kerri, who resides in Wappingers Falls, New York, with Chris, found Becky and Jim Sykes, a couple in West Virginia who had two male embryos left over from their own IVF process. The Sykes felt their family was complete after having two boys through IVF.

"That really spoke to me, and it just made me feel good about all the people that would be getting helped in the process of this," Chris said.

Adopting the embryos began with a profile on a website called the National Registry for Adoption, a site that connects people like the Morgans with families who have embryos left from their cycles.

There are more than 600,000 frozen embryos stored in the United States, according to the U.S. Department of Health & Human Services.