“I haven’t had a case in my entire career that has impacted my life as much as this case has,” said Parnham. “It’s something about the kids.”

During Yates’ 2002 trial, which drew international attention, many couldn’t fathom how a 36-year-old mother could drown her own children in a bathtub. The definitions of postpartum depression and psychosis were not yet commonly known. In order to defend Yates, Parnham had to educate the public about mental illness.

“When a person is suffering from mental illness and is in a psychotic state, they make decisions based on their own reality,” he said. “They don’t have a decision-making process based on rational thinking.”

The case brought mental health awareness, and postpartum mental illness in particular, into public awareness. Since it happened, more therapists, psychiatrists and medical professionals have dedicated their careers to helping women struggling after giving birth. More resources and interventions have also become available.

“Over the years, we’ve seen more and more women speak up and ask for help,” said Dr. Sherry Duson, a licensed therapist and counselor who founded the Center for Postpartum Family Health in Houston . “And there’s a greater understanding among OB-GYN pediatricians that perinatal mental illness is common and treatable and needs to be addressed.”

Yates believed killing the children was the only way to save them from herself and eternal damnation, she told police when she reported the June 20, 2001 deaths.

Yates pleaded not guilty by reason of insanity, but she was initially convicted of capital murder and sentenced to life in prison. The conviction was reversed in 2005 due to false testimony given by a California psychiatrist.

Jurors believed Yates when she was retried in 2006. They found her not guilty and she was sent to a mental hospital in Kerrville, where she’s stayed since 2007. Each year Yates is offered a hearing to determine if it’s safe to release her. And each year she forgoes the hearing, said Parnham.

The children’s father, Rusty Yates, was accused of ignoring red flags that his wife needed help, including one doctor who testified he warned the father not to leave Andrea alone with the kids. Yates said during the trials that he was never told that his wife was psychotic and wouldn’t have left the children alone with her if he’d known. Attempts to reach him for comment were not successful.

Yates divorced Andrea in 2004. The former NASA engineer said he forgave his ex-wife in an Investigation Discovery documentary released last year. He also said he regularly visits her at the mental hospital. Rusty Yates remarried in 2006 and had another child. He has since divorced his second wife.

Why postpartum psychosis occurs

It’s important to distinguish the difference between postpartum depression and anxiety and psychosis, said Dr. Karen Horst, medical director for the Women’s Place at Texas Children’s Hospital’s Pavillion for Women.

“It’s so common for moms I’m treating to be worried that they will do something horrific because of how they’re feeling,” said Horst.

While postpartum depression is the No. 1 complication of pregnancy, postpartum psychosis is extremely rare, said Duson, affecting about .1 percentof new mothers.

Psychosis is a break from reality that usually involves hallucinations, hearing voices and delusions.

“The person is no longer dealing with the here and now,” said Duson.

Yates believed cartoons were sending her messages and that she was possessed by Satan, the woman’s psychiatrist testified.

“She was not in her right mind and was not capable of rational thought,” said Duson. “She should have never been left alone with the children.”

Psychosis after childbirth can be caused by several factors.

“One of the most common understandings is related to a bipolar disorder,” Duson said. “The mother might have the brain chemistry disorder and not know. Under stress, it can be triggered in a big way.”

History of trauma, especially childhood sexual abuse, can be a contributing factor, said Horst, as can a lack of support. Having many children in a short period of time coupled with ongoing postpartum depression with psychotic features left untreated can be another cause.

Those underlying factors combined with the usual stressors of having a baby, such as sleep deprivation and hormonal changes, can trigger psychosis.

In Yates’ case, she told police she hadn’t eaten, slept or bathed in days. Before her children were killed, Yates was prescribed antipsychotic medications by multiple doctors but stopped taking them, according to court testimony. A doctor testified she had diagnosed Yates with psychotic depression and advised her to not have any more children.

Yates’ case demonstrates that no one is immune from the effects of untreated mental illness, said Duson.

Before she drowned her children, Yates had a life that many would admire. She was captain of her swim team at Milby High School in Houston’s east end and was valedictorian when she graduated in 1982. She was a registered nurse at MD Anderson Cancer Center until 1994.

“Those who knew her said she really cared about being a good mom,” said Duson. “For her to get that ill without people realizing it is just a horrible tragedy.”

All postpartum mental illness, including psychosis, is treatable, said Horst.

Advances since the Yates case

In the years since the Yates case, awareness of mental health and illness has increased exponentially.

Parnham and his wife, Mary, created the Yates Children Memorial Fund to raise awareness about postpartum depression and psychosis. Since 2002, the effort has trained thousands of medical and healthcare professionals to know the signs of the illness and learn how to treat it.

Yates is happy the foundation is making a positive impact for other mothers and their children, the Parnhams said.

The Yates case in part drove Duson to open her group private practice in 2014, which now has six therapists who provide services on a sliding scale.

As a struggling new mother herself in 2001, Duson said she couldn’t find any experts on the subject. So she began doing the research herself. When the Yates case happened, she started getting calls from journalists asking her to explain postpartum mental illnesses.

“I realized that there was no one focusing on this in terms of an expert specialty,” she said. “I was determined to become the resource for new moms that Andrea and others didn’t have.”

In the last five years, Parnham said he’s noticed a shift resulting in more public awareness.

“I applaud that,” he said. “The public knows now that mental illness is a real illness.”

That’s in part due to a concerted effort among mental health professionals to decrease stigma and normalize therapy in recent years, said Duson.

“Many doctors regularly screen women for depression after childbirth now,” she said. “They’ve become aware that there are huge needs in perinatal mental health and that tragedies don’t need to happen.”