What are the potential causes of vaginal spotting in a pregnant female of childbearing age with a history of previous pregnancies, miscarriages, or gynecological conditions?

Causes of Vaginal Spotting in Pregnancy

Vaginal spotting in pregnancy has distinct causes that vary by trimester, with ectopic pregnancy being the most critical diagnosis to exclude immediately in early pregnancy, followed by threatened abortion, placenta previa in later pregnancy, and placental abruption—though approximately 50% of cases have no identifiable cause. 1, 2

First Trimester Causes (0-13 weeks)

Life-Threatening Conditions Requiring Immediate Exclusion

• Ectopic pregnancy must be ruled out first, as 7-20% of pregnancies of unknown location will ultimately be diagnosed as ectopic 1, 2
• Ectopic pregnancy can be missed on initial ultrasound in up to 74% of cases, making serial beta-hCG monitoring critical when imaging is non-diagnostic 1

Common Benign Causes

• Threatened abortion with viable intrauterine pregnancy is diagnosed when fetal cardiac activity is confirmed on ultrasound—this occurs in approximately 25% of early pregnancies and is usually benign 2, 3
• Subchorionic hemorrhage can cause spotting when blood collects between the uterine wall and gestational sac, requiring follow-up ultrasound in 1-2 weeks 1
• Spontaneous abortion (miscarriage) represents a spectrum of presentations depending on cervical os integrity and hemodynamic status 4, 5

Other First Trimester Causes

• Gestational trophoblastic disease (molar pregnancy) presents with bleeding and abnormally elevated beta-hCG levels 2
• Cervical lesions, polyps, or cervicitis can cause spotting and are typically identified during speculum examination 1
• Implantation bleeding may occur as the embryo attaches to the uterine lining 4

Second Trimester Causes (14-27 weeks)

• Incompetent cervix is the most common cause of second-trimester bleeding, with cervical insufficiency leading to painless cervical dilation 3
• Cervical change with preterm labor can cause bleeding as the cervix begins to efface and dilate 1
• Vaginal and cervical lesions remain possible causes throughout pregnancy 4

Third Trimester Causes (28+ weeks)

Placental Abnormalities (Most Common)

• Placenta previa is the most common diagnosis in late pregnancy bleeding, affecting approximately 1 in 200 pregnancies at delivery, and classically presents as painless bleeding 1, 2, 4
• Placental abruption affects approximately 1% of pregnancies and may present with abdominal pain and bleeding, though ultrasound misses up to 50% of cases initially 1, 2, 4
• Vasa previa involves fetal vessels overlying the internal cervical os and carries risk of fetal exsanguination 1

Normal Physiologic Bleeding

• "Bloody show" with term labor is normal physiologic bleeding characterized as pink or brown-tinged mucus, minimal in volume, occurring as the cervix begins to dilate 1

Non-Pregnancy-Specific Causes (Any Trimester)

• Cervical or vaginal lesions including polyps, inflammation, or malignancy can cause spotting at any gestational age 1, 4
• Hormonal contraceptive effects (if inadvertently continued) or progesterone supplementation can cause irregular bleeding patterns 2
• Underlying bleeding disorders may manifest with increased obstetric bleeding complications, including miscarriage risk and postpartum hemorrhage 6

Idiopathic Bleeding

• No identifiable cause is found in approximately 50% of women with vaginal bleeding in pregnancy, though these patients still require thorough evaluation to exclude dangerous conditions 1

Critical Clinical Pitfalls

• Never perform digital pelvic examination before ultrasound in pregnant women with bleeding, as this can precipitate catastrophic hemorrhage with undiagnosed placenta previa or vasa previa 1, 2, 7
• Transvaginal ultrasound is the primary diagnostic tool and is safe even with placenta previa, providing superior resolution compared to transabdominal approach 1, 7
• Serial beta-hCG measurements (every 48 hours) are mandatory for pregnancy of unknown location until diagnosis is established, as ectopic pregnancy cannot be excluded on single measurements 1, 7
• Normal vital signs do not exclude significant placental pathology—placental abruption can present with normal hemodynamics initially but rapidly deteriorate 1

Long-Term Implications

• First trimester bleeding is associated with increased risk of preterm delivery, placental abruption later in pregnancy, and small for gestational age infants 1
• Short cervix identified on transvaginal ultrasound with bleeding significantly increases preterm delivery risk 1