A prenatal genetic screening test wrongly flagged a severe chromosomal condition in Amanda Webb's unborn baby. Follow-up testing showed the baby was healthy, but the result prompted doctors to investigate Webb's health at 31 weeks pregnant.

The screening suggested her baby might have trisomy 13. Follow-up testing of amniotic fluid showed the baby was healthy, according to Webb's account.

Webb was 36 and had a history of stage 1A melanoma. Doctors at UCSF told her that cancer cells in a mother's blood can sometimes contribute to false-positive results on prenatal genetic screening.

Doctors referred her to a melanoma clinic. An MRI then revealed growths on her liver, prompting further tests, including a colonoscopy, liver biopsy, CT scan and ultrasounds.

Webb said she sensed doctors were looking for something serious. The investigation eventually led to a diagnosis of stage 4 colon cancer.

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Diagnosis Comes on Husband's Birthday

Webb received the diagnosis on her husband Jon's birthday. He rushed to the hospital after the call, and the couple marked the day with cake at her bedside.

That night, they also learned they were having a boy. A nurse brought them a congratulatory card and a blue knitted hat, offering small moments of joy amid the diagnosis.

'I was just shocked,' Webb said. A high-risk obstetric nurse later held her in a hospital garden as she processed the news, according to Webb.

Webb's high-risk obstetrician later told her the pregnancy might have saved her life. Webb said the screening result led doctors to find the cancer earlier than they otherwise might have.

Webb began chemotherapy the following week. Her first three rounds were given as an inpatient so her medical team could monitor her and the pregnancy.

After her diagnosis, Webb removed pregnancy apps from her phone. She also spoke with other expectant mothers less often, saying she no longer felt able to relate to typical pregnancy concerns.

The American Cancer Society says the five-year relative survival rate for colon cancer that has spread to distant parts of the body is 13 per cent. The figure is based on earlier diagnoses, and outcomes vary by individual case.

Webb had noticed symptoms before her diagnosis but attributed them to pregnancy, running or a sensitive digestive system.

Treatment Continues After Delivery

Webb gave birth to her son, Levi, by caesarean section and resumed chemotherapy after a two-week break. Family and friends helped, including her mother, who travelled from the Midwest.

Colorectal cancer during pregnancy is rare, with a reported incidence of about 0.002 per cent of pregnancies. Reviews say diagnosis can be delayed because symptoms may resemble common pregnancy complaints.

A systematic review found that maternal prognosis depends heavily on the stage at diagnosis. It also found that reported fetal outcomes were generally favourable, although long-term data remain limited.

Common colon cancer symptoms include changes in bowel habits, blood in the stool, abdominal pain, unexplained weight loss and fatigue, according to the Mayo Clinic.

Webb, now 41, has reached five years with no evidence of disease, meaning doctors can no longer detect cancer in her body. She now watches Levi start kindergarten, a milestone she once feared missing.

To monitor for recurrence, Webb uses Signatera, a personalised blood test from Natera that analyses circulating tumour DNA. She said the test has become part of her routine cancer surveillance.

Webb hopes her story encourages people to take persistent colon cancer symptoms seriously. She has also urged people to discuss appropriate screening with their doctors.

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