A woman's pregnancy test came back negative — but she was suffering a ruptured ectopic pregnancy

• A mom went to the hospital with bleeding at 6 weeks pregnant. It seemed she was miscarrying.
• Weeks later, she experienced a ruptured ectopic pregnancy — despite negative pregnancy tests.

A mom in her 30s suffered a ruptured ectopic pregnancy — even though a urine pregnancy test came back negative, a new case report details.

The woman, a mom of three, went to a UK hospital at about six weeks pregnant with severe bleeding.

A blood test confirmed the pregnancy, but an ultrasound didn't detect a sac. So, clinicians monitored her closely to see if she was just earlier in pregnancy than she thought — or if something else was going on, like a miscarriage or ectopic pregnancy.

Over the course of a few days, one of the latter options seemed most likely. The mom's levels of beta-human chorionic gonadotrophin (bHCG) — what pregnancy tests pick up — dropped, indicating a miscarriage. And yet, an ultrasound suggested an ectopic pregnancy.

So, doctors continued to monitor the patient every 48 hours with blood tests and ultrasounds. They didn't intervene further since her blood pressure was normal, she had no pain, and her bHCG levels were so low, Dr. Louise Dunphy, the case report's lead author, a gynecologist at Leighton Hospital in Crewe, told Insider.

By about 10 weeks pregnant, the woman developed severe pain on her right side. At this point, her urine pregnancy test was negative, but a blood test was positive. Further testing revealed a ruptured ectopic pregnancy, and "an urgent anaesthetic and gynecology review were requested," the study authors wrote.

The woman underwent surgery to remove her right fallopian tube and the pregnancy tissue. All told, she lost about 2,050 milliliters of blood and needed a transfusion, according to the study. She was discharged after three days.

Dunphy told Insider there's not enough awareness around chronic ectopic pregnancies, which describes an ectopic pregnancy with such low bHCG levels that it doesn't show up with a urine test. "This case shows the importance of requesting a blood test," she said.

Chronic ectopic pregnancies are "an enigma," the study authors say

An ectopic pregnancy is when a fertilized egg implants somewhere other than the uterus — typically, in a fallopian tube. The pregnancy is never viable, and swift treatment is critical to prevent the tube from bursting and leading to potentially life-threatening internal bleeding.

While ectopic pregnancies are usually detectable by urine pregnancy tests, in 1.6% of cases, they're only detectable via blood tests, according to the study. "It is an enigma," the study authors write, adding that only a few reports of chronic ectopic pregnancies have been published in the last decade, and many of them were discovered due to an unrelated intervention.

Chronic ectopic pregnancies — which doesn't, in fact, mean "chronic" as in enduring — are thought to occur when an ectopic pregnancy creates small, repeated ruptures that develop into a mass of blood, clots, and trophoblastic tissue, or the tissue that develops into the placenta and creates the bHCG hormone.

In these cases, it seems the trophoblastic tissue doesn't produce enough bHCG to be picked up by urine pregnancy tests, which only detect pregnancies when bHCG levels are over 25 IU/L. But anything 5 IU/L or over is a pregnancy, Dunphy said.

Chronic ectopic pregnancies can be especially difficult to diagnose, since their symptoms — like pelvic pain, irregular bleeding, or sometimes no symptoms at all — can mimic other, more common conditions that you'd expect in someone with a negative pregnancy test.

For example, a chronic ectopic could be misdiagnosed as a ruptured appendix, peptic ulcer, pelvic inflammatory disease, or urinary tract infection. But "rendering the diagnosis promptly is important," the study authors say, since like ectopic pregnancies, the chronic type can rupture the fallopian tube and become life-threatening.