Incidence of Pelvic Inflammatory Disease in Pregnant Women
Pelvic inflammatory disease is exceedingly rare during pregnancy, with only 49 documented cases reported in the medical literature through 2022, making it an exceptional rather than expected occurrence. 1
Epidemiological Context
The rarity of PID during pregnancy stands in stark contrast to the general population incidence:
In non-pregnant women of reproductive age: Approximately 1 million women in the United States experience symptomatic PID annually, with hospitalization rates of 2.2 per 1,000 women. 2
In pregnant women: A systematic review spanning decades of medical literature identified only 49 cases of PID occurring after conception, indicating this is an extraordinarily uncommon event. 1
Sexually active women under age 25: PID is diagnosed in 1-2% annually in the general population, with the highest rates among 15-19 year olds. 2, 3
Why Pregnancy Protects Against PID
The protective effect of pregnancy against PID relates to fundamental pathophysiologic mechanisms:
Cervical mucus barrier: The thick cervical mucus plug that forms during pregnancy creates a mechanical barrier preventing canalicular ascent of organisms from the endocervix to the upper genital tract. 4
Altered hormonal milieu: Pregnancy hormones fundamentally change the cervical environment, unlike the menstrual cycle changes that facilitate bacterial ascent in non-pregnant women. 4
Obliteration of the endometrial cavity: As pregnancy progresses, the developing gestational sac and decidua physically prevent the typical ascending infection pathway. 4
Clinical Characteristics When PID Does Occur in Pregnancy
When this rare event happens, specific patterns emerge:
Mean gestational age at diagnosis: 19.0 ± 10.3 weeks, indicating most cases occur in the second trimester when reported. 1
Mean maternal age: 25 ± 6.3 years. 1
Parity: 67.6% of affected patients were multiparous. 1
Risk Factors for the Rare Pregnancy-Associated PID
Specific circumstances increase vulnerability:
Recent pelvic procedures: In vitro fertilization, oocyte retrieval, or recent pelvic surgery create pathways for infection. 1
Maternal pelvic structural anomalies: Pre-existing anatomic abnormalities may compromise protective barriers. 1
History of sexually transmitted infections: Prior STI history increases baseline risk. 1
Severe Outcomes When PID Occurs in Pregnancy
The consequences are disproportionately severe compared to non-pregnant PID:
Nonviable births: 39.5% of pregnancies resulted in fetal loss. 1
Preterm delivery: Among viable births, mean gestational age was only 33.8 ± 5.1 weeks. 1
Surgical intervention: 62.8% required exploratory laparotomy, 32.6% underwent unilateral salpingo-oophorectomy, and 7.7% required cesarean hysterectomy. 1
Neonatal sepsis and death: Sepsis complicated 7.0% of cases and caused 3 neonatal deaths. 1
Critical Clinical Pitfall
The extreme rarity of PID during pregnancy means clinicians must maintain high suspicion for alternative diagnoses (appendicitis, ovarian torsion, ectopic pregnancy, placental abruption) when evaluating pregnant women with pelvic pain and fever. 1 The protective mechanisms of pregnancy make true ascending PID highly unlikely unless specific risk factors (recent instrumentation, structural anomalies) are present. 1