"My son will be 4 weeks old on Saturday," the young woman thought glumly as she sat burning with fever and with the same dull ache in her lower belly she'd had for weeks.

She'd always been healthy and optimistic. The pregnancy had been a breeze.

Now, in a hospital hours from her newborn at home, she was feeling discouraged.

Her first pregnancy four years earlier had been complicated by prolonged labor, and she'd had a cesarean section.

With her narrow pelvis, her doctors recommended another C-section for her new son. The surgery had gone well, and she'd gone home with the healthy baby a few days later.

But within a week, everything changed. After two days of high fevers, chills, and dull pain low in her pelvis that seemed to go to her hips, she finally pulled herself from the baby and went to the emergency room.

The doctors initially didn't note anything abnormal when they did a pelvic exam.

Because she'd had the C-section, they were worried about a postsurgical infection and imaged her pelvis with a CT scan, which could show her uterus and other organs in cross section. The scan showed an enlarged uterus, but not much else.

During the time she was observed, her pain seemed to emanate more consistently from the right side of her abdomen.

In particular, dividing the belly in four quarters, her pain was most severe in the right lower quadrant of the abdomen, where the appendix is.

With no evidence of surgical infection, urinary infection, or kidney stone, the doctors worried this could be appendicitis.

The surgeon made a small incision in the right lower quadrant and found a normal- looking appendix - not the swollen and irritated one expected with appendicitis.

Looking around in that area, he noted the patient's right ovary and fallopian tube appeared to be tensely swollen. He removed those as well.

The patient recovered smoothly from the surgery, but her problems remained. She continued to have high, spiking fevers and the dull ache deep in her pelvis. She was receiving antibiotics in case she had an infection.

Two days into her hospital stay, that infection was confirmed when bacteria grew from her blood cultures. Her physicians made sure she was on the right antibiotic and repeated those blood cultures.

Though nothing more grew, the fevers did not let up. The laboratory reported no infection was found in the ovary and fallopian tube that had been removed.

After more than a week in which nothing seemed to change other than a deeper longing for home, her doctors decided to send her to another hospital for a fresh look.

The patient's husband urged her to make the trip. The baby was growing and healthy. Big sister was helping her dad and grandma. She agreed.

The obstetrical team and the infectious-diseases doctors at the second hospital looked through the thick stack of records. They called the doctors and lab technicians at the first hospital to make sure they weren't missing anything.

They agreed that if this were an infection simply due to bacteria that had grown in the blood, the fevers should have gone away by then.

Solution:

Another big question was, how did those bacteria get into the blood if there was no infection found in her belly or anywhere else they'd looked?

They reviewed the CT scan performed two weeks earlier at the other hospital.

CT scans can be done in a variety of ways. Patients are often given oral contrast, a liquid to drink before a procedure that lights up the bowels on the scan and makes it easier to contrast the inside of the intestines with what is going on in or around them.

Intravenous contrast lights up both large and small blood vessels and areas of infection. Intravenous contrast, or "IV dye," is especially useful in determining if there is any obstruction or clot in a blood vessel, such as an artery or vein. Though the ER doctor at the other hospital had wanted to give the patient contrast and had counseled her that very little would get into her breast milk, the patient refused it; she was too worried it could affect her newborn.

"That CT without contrast would miss a blood clot inside a pelvic vein, wouldn't it?" asked the intern on the infectious-diseases service.

The team explained the situation to the patient, who was more eager than anyone to get any test needed to solve her unexplained fever.

The CT scan with IV dye showed huge clots in the veins along both sides of the patient's uterus, with swelling and inflammation around the veins.

The engorged ovary the surgeon had found also made sense - it was due to a clot in the right ovarian vein. The blood clots, combined with the high fevers and bacteria from her blood, fit with a disease known as septic pelvic thrombophlebitis.

During pregnancy, the pelvic veins can become engorged with blood that can travel slowly through vessels.

At the same time, pregnant women become hypercoagulable, or more likely to form blood clots. A C-section, as with any surgery, also leads to hypercoagulability. Then, during a C-section, if bacteria get into the blood vessels, this further increases the risk of clotting. Despite all that, septic pelvic thrombophlebitis is incredibly uncommon.

Besides the antibiotics, the patient was started on a blood thinner, and her fever was gone by the next morning.

When the intern came in to see her, she had a huge smile. She was going home.

Valerianna Amorosa, an infectious-diseases doctor, practices at the Philadelphia VA Medical Center and the Hospital of the University of Pennsylvania.