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Summary Table

Feature	Detail
Risk Factors	Cesarean delivery (single strongest risk factor), prolonged rupture of membranes (>18 hours), prolonged labor, multiple vaginal examinations, internal fetal monitoring, manual placental removal, low socioeconomic status, bacterial vaginosis, group B Streptococcus colonization, chorioamnionitis during labor
Etiology	Polymicrobial ascending infection of the uterine decidua and myometrium; mix of aerobic organisms (group A and B Streptococcus, Enterococcus, E. coli, Klebsiella) and anaerobes (Bacteroides, Peptostreptococcus, Clostridium). Ureaplasma urealyticum and Mycoplasma hominis are also implicated in late-onset cases
Patient Presentation	Fever (typically >38.0 C / 100.4 F) developing within the first 5 days postpartum, with uterine tenderness, malaise, and sometimes foul-smelling lochia
Classic Physical Exam	Uterine fundal tenderness on palpation, purulent or malodorous lochia, tachycardia proportional to fever. The uterus may feel boggy or subinvoluted
Key Diagnostic Results	Clinical diagnosis based on postpartum fever plus uterine tenderness. Leukocytosis with left shift supports but does not confirm (WBC is physiologically elevated postpartum). Blood cultures obtained before antibiotics but do not delay treatment. Endometrial cultures are not routinely performed
Management	IV clindamycin plus gentamicin is first-line. Add ampicillin if no improvement in 48 hours (to cover Enterococcus). Continue IV antibiotics until the patient is afebrile and clinically improved for 24 to 48 hours, then discontinue without oral antibiotics
Keywords	"Postpartum fever," "uterine tenderness," "foul-smelling lochia," "after cesarean delivery," "polymicrobial infection"

1. Pathophysiology

Postpartum endometritis results from ascending bacterial contamination of the uterine cavity during labor and delivery. The endometrium (decidua) and, in more severe cases, the myometrium become infected by organisms that colonize the lower genital tract. During labor, the cervix dilates and the protective mucus barrier is disrupted, allowing vaginal flora to migrate upward. Any intervention that introduces foreign material into the uterine cavity or prolongs the exposure window amplifies this risk.

The infection is almost always polymicrobial, involving a synergistic mix of aerobic gram-positive cocci, aerobic gram-negative rods, and anaerobes. This is a key concept: no single organism dominates, which is why broad-spectrum combination therapy is required rather than a narrow-spectrum agent. The anaerobic component is particularly important because the postpartum uterus, with its devitalized tissue, blood clots, and areas of placental separation, creates a relatively hypoxic environment that favors anaerobic proliferation.

Cesarean delivery dramatically increases the risk (5 to 20 times higher than vaginal delivery) because the surgical incision creates a direct wound in the myometrium, introduces a larger bacterial inoculum into the uterine cavity, and leaves behind suture material that serves as a nidus for infection. The devitalized tissue along the hysterotomy incision line is especially vulnerable. This is why prophylactic antibiotics before cesarean section (typically a single dose of cefazolin given within 60 minutes before skin incision) have become standard practice and have significantly reduced endometritis rates.

The inflammatory cascade follows a predictable pattern: bacterial invasion triggers a neutrophilic response in the decidua, causing uterine wall edema, tenderness, and impaired contractility. The impaired contractility explains why the uterus may feel boggy and why lochia drainage can become stagnant and malodorous. Systemic signs (fever, tachycardia, leukocytosis) reflect cytokine-mediated inflammation once the infection is established.

Late-onset endometritis (occurring after hospital discharge, typically 1 to 6 weeks postpartum) is more commonly associated with Chlamydia trachomatis or genital mycoplasmas (Ureaplasma, Mycoplasma hominis) and tends to present with a more indolent course compared to the acute early-onset form.

2. Classification and Clinical Manifestation

Classification	Timing	Typical Organisms	Clinical Features
Early-onset	Within 48 to 72 hours postpartum	Polymicrobial: group A/B Streptococcus, E. coli, Bacteroides, Peptostreptococcus, Enterococcus	High fever (>38.5 C), prominent uterine tenderness, purulent/foul lochia, tachycardia, malaise. More common after cesarean delivery
Late-onset	3 days to 6 weeks postpartum	Chlamydia trachomatis, Ureaplasma urealyticum, Mycoplasma hominis	Low-grade fever, milder uterine tenderness, vaginal bleeding or discharge. More common after vaginal delivery. May present after hospital discharge

Clinical presentation by system:

System	Findings
Constitutional	Fever (>38.0 C on any two of the first 10 postpartum days, excluding the first 24 hours), chills, malaise, anorexia
Uterine	Fundal tenderness (hallmark finding), boggy or subinvoluted uterus, purulent or foul-smelling lochia
Cardiovascular	Tachycardia proportional to fever
Gastrointestinal	Lower abdominal pain, sometimes ileus in severe cases
Severe / Complicated	Parametrial extension (broad ligament phlegmon or abscess), septic pelvic thrombophlebitis, peritonitis, sepsis, wound infection at the hysterotomy or episiotomy site

A critical exam point: the first 24 hours postpartum are excluded from the classic definition of puerperal fever, because low-grade temperature elevations in this window are common due to dehydration, atelectasis, and the physiologic stress of delivery. A fever that develops after the first 24 hours and is accompanied by uterine tenderness should be treated as endometritis until proven otherwise.

3. Diagnostic Workup

Test	Role	Key Findings
Clinical assessment	Best initial and primary diagnostic method	Fever + uterine tenderness in a postpartum patient. This is sufficient to initiate treatment
Complete blood count	Supportive	Leukocytosis with left shift. However, WBC is physiologically elevated postpartum (up to 25,000 to 30,000/microL), so this is not reliable in isolation
Blood cultures	Obtained before starting antibiotics	Positive in approximately 10 to 20% of cases. Does not delay treatment. Useful if the patient fails to respond to empiric therapy
Endometrial cultures	Not routinely recommended	Contamination by cervicovaginal flora makes interpretation unreliable. Reserved for refractory cases
Pelvic ultrasound	When complication is suspected	Evaluates for retained products of conception, pelvic abscess, or wound hematoma/seroma at the hysterotomy site
CT abdomen/pelvis with contrast	Suspected abscess or septic pelvic thrombophlebitis	Identifies parametrial abscess, broad ligament phlegmon, or thrombosis of the ovarian veins
CT venography or MRI	Gold standard for septic pelvic thrombophlebitis	Demonstrates thrombus in ovarian or pelvic veins when persistent fever despite appropriate antibiotics raises clinical suspicion

Postpartum endometritis is fundamentally a clinical diagnosis. The combination of postpartum fever and uterine tenderness in the appropriate time frame is both the best initial test and the working diagnostic standard. There is no single confirmatory laboratory test that clinches the diagnosis, and this is a frequently tested concept: students often look for a definitive lab marker and waste time, when in reality the correct next step is to start empiric IV antibiotics immediately after obtaining blood cultures.

The CBC is ordered as part of the standard workup, but interpreting the WBC count requires caution. Postpartum leukocytosis is physiologic (particularly after cesarean delivery and in patients who received corticosteroids for fetal lung maturity), so a WBC of 18,000 to 20,000/microL alone does not confirm infection. A rising trend or bandemia (left shift) is more meaningful than the absolute number.

Blood cultures are drawn before antibiotics are given, following standard principles of infection management. However, they are positive in only a minority of cases. Their primary utility is in guiding therapy if the patient does not respond to first-line treatment.

Endometrial cultures are a classic distractor. Test-writers may offer this as an answer choice, but transcervical cultures are contaminated by vaginal flora and therefore unreliable. They are not part of the standard workup.

Imaging is not part of the initial diagnostic approach. Pelvic ultrasound becomes relevant when you suspect a complication such as retained products, abscess, or wound breakdown. CT imaging enters the picture when the patient remains febrile despite 48 to 72 hours of appropriate antibiotics, raising concern for septic pelvic thrombophlebitis or pelvic abscess.

4. Management and Treatment

Setting	Regimen	Details
First-line (standard)	Clindamycin + Gentamicin	Clindamycin 900 mg IV every 8 hours + Gentamicin 5 mg/kg IV once daily (or 1.5 mg/kg IV every 8 hours). This is the gold standard regimen
If no improvement in 24 to 48 hours	Add Ampicillin	Ampicillin 2 g IV every 6 hours added to cover Enterococcus (inherently resistant to clindamycin and cephalosporins)
Alternative regimen	Ampicillin-sulbactam	3 g IV every 6 hours. Covers most aerobic and anaerobic organisms. Used when gentamicin is contraindicated or in settings preferring monotherapy
Alternative regimen	Piperacillin-tazobactam	3.375 g IV every 6 hours. Broad-spectrum option
Duration endpoint	Clinical improvement	Continue IV antibiotics until the patient has been afebrile for 24 to 48 hours and clinically improved. No oral antibiotics are needed after IV therapy is discontinued
Septic pelvic thrombophlebitis	Anticoagulation + antibiotics	Heparin (unfractionated or LMWH) added to the antibiotic regimen. Dramatic defervescence within 48 hours of starting heparin is both diagnostic and therapeutic

The cornerstone of treatment is IV clindamycin plus gentamicin, and this combination is one of the most commonly tested regimens in obstetric infectious disease. Clindamycin provides excellent anaerobic coverage (including Bacteroides fragilis, which produces beta-lactamase) and also covers gram-positive aerobes. Gentamicin provides gram-negative aerobic coverage, particularly against E. coli and Klebsiella. Together, they address the polymicrobial nature of the infection.

Once antibiotics are started, most patients improve within 48 to 72 hours. The endpoint for IV therapy is not a fixed number of days but rather a clinical milestone: the patient must be afebrile and symptomatically improved for 24 to 48 hours. After this point, IV antibiotics are stopped and no oral antibiotics are prescribed for outpatient continuation. This is a high-yield pearl because it contradicts the instinct to "step down" to oral therapy, which is standard practice for many other infections.

If the patient fails to defervesce within 48 hours on clindamycin plus gentamicin, the next best step is to add ampicillin. The rationale is that Enterococcus faecalis is a common genital tract organism that is intrinsically resistant to both clindamycin and gentamicin (though gentamicin has synergistic activity when combined with a cell-wall-active agent like ampicillin). This "triple regimen" of clindamycin, gentamicin, and ampicillin covers essentially all organisms responsible for postpartum endometritis.

If the patient remains febrile despite the triple regimen for an additional 48 to 72 hours, the differential expands beyond simple endometritis:

Wound infection at the cesarean incision or episiotomy site (examine the wound)
Pelvic abscess (order CT with contrast)
Septic pelvic thrombophlebitis (order CT venography or MRI; empiric heparin trial)
Retained products of conception (pelvic ultrasound)
Drug fever (diagnosis of exclusion)

Septic pelvic thrombophlebitis deserves emphasis. It should be suspected when a postpartum patient has persistent spiking fevers ("picket fence" pattern) despite broad-spectrum antibiotics, appears otherwise well between fever spikes, and has no localizing source on examination. The classic teaching is that adding heparin to the antibiotic regimen leads to rapid defervescence within 48 hours, and this response essentially confirms the diagnosis.

Contraindications and considerations: Gentamicin requires dose adjustment in renal insufficiency, and trough levels should be monitored with extended use to avoid nephrotoxicity and ototoxicity. In patients with renal impairment, ampicillin-sulbactam or a carbapenem may be substituted. For patients with a true penicillin allergy who require Enterococcal coverage, vancomycin can be used in place of ampicillin.

5. Differential Diagnosis and Distractors

Differential Diagnosis	Why It Is Similar	Key Discriminator
Urinary tract infection / Pyelonephritis	Postpartum fever, may have lower abdominal discomfort	Costovertebral angle tenderness, dysuria, urinary frequency. Urine culture is positive. Uterine tenderness is absent
Wound infection (cesarean or episiotomy)	Postpartum fever after surgical delivery	Erythema, induration, or purulent drainage at the incision site. Uterine tenderness is not the dominant finding. Wound dehiscence may be present
Mastitis / Breast abscess	Postpartum fever, commonly within the first few weeks	Focal breast erythema, warmth, and tenderness. Often associated with breastfeeding difficulties. Unilateral. No uterine tenderness
Septic pelvic thrombophlebitis	Persistent postpartum fever despite antibiotics	Failure to defervesce on appropriate antibiotics for endometritis. "Picket fence" fever pattern. Responds to heparin. CT venography shows ovarian vein thrombosis
Retained products of conception	Postpartum fever, uterine tenderness, bleeding	Heavy or persistent vaginal bleeding is more prominent than in endometritis. Ultrasound shows echogenic material within the uterine cavity
Chorioamnionitis	Fever, uterine tenderness, polymicrobial infection	Occurs during labor before delivery, not postpartum. Associated with fetal tachycardia and maternal fever in the intrapartum period. Chorioamnionitis can progress to postpartum endometritis if not adequately treated
Atelectasis	Postpartum low-grade fever, especially after cesarean (general anesthesia)	Occurs within the first 24 hours, which is excluded from the puerperal fever definition. Clears with incentive spirometry. No uterine tenderness
Drug fever	Persistent fever despite antibiotics	Diagnosis of exclusion. Patient appears relatively well despite fever. No localizing signs. Fever resolves after discontinuing the offending drug

6. Traps and High-Yield Pearls

The most common way students get questions on postpartum endometritis wrong is by overcomplicating the diagnosis. When a vignette describes a postpartum patient (especially post-cesarean) with fever and uterine tenderness, students sometimes hesitate because there is no definitive lab confirmation. The trap is selecting "obtain endometrial cultures" or "order pelvic ultrasound" as the next best step, when the correct answer is to start empiric IV antibiotics immediately. Endometritis is a clinical diagnosis, and delaying treatment to pursue additional workup is penalized.

A second common error involves the antibiotic regimen. Students may default to broad-spectrum beta-lactam monotherapy (such as ceftriaxone or piperacillin-tazobactam) because these are common answers in other infectious disease questions. The tested answer for postpartum endometritis is clindamycin plus gentamicin, and this pairing must be memorized as first-line. The reasoning is that clindamycin covers anaerobes (including beta-lactamase-producing Bacteroides, which resists many cephalosporins) while gentamicin covers gram-negative aerobes.

A third trap is the concept of "step-down" oral therapy. In most infectious disease scenarios, the pattern is IV-to-oral transition. In postpartum endometritis, no oral antibiotics are needed after clinical improvement. The correct endpoint is 24 to 48 hours afebrile on IV therapy, followed by discontinuation. Selecting "discharge with oral antibiotics" is a distractor.

Finally, the "enigma of persistent fever" vignette is a classic setup for septic pelvic thrombophlebitis. If a patient with endometritis has been on clindamycin, gentamicin, and ampicillin for more than 72 hours and still has spiking fevers with no other localizing source, the next best step is imaging followed by heparin therapy, not switching or escalating antibiotics further. The dramatic fever resolution after heparin is both diagnostic and therapeutic, and recognizing this pattern is the core competency being tested.

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