A positive pregnancy test, an empty uterus on the scan, and an embryo growing where it can never survive. Learn the discriminatory zone, the serial beta-hCG trend, and the one call that decides between a shot and the operating room.
The Setup
An Embryo in the Wrong Room
Everything dangerous about an ectopic comes from one fact: the embryo implanted somewhere with no room to grow and a rich blood supply waiting to bleed. Walk the chain once and the whole disease falls into place.
A 29-year-old woman with a history of chlamydia two years ago has not had a period in 7 weeks. A home pregnancy test was positive. Today she has crampy left-sided lower belly pain and some light vaginal spotting. She is not dizzy and her vitals are normal.
What single fact best explains why she is at high risk for this pain being an ectopic?
Start with the journey. After fertilization in the fallopian tube, the embryo is supposed to ride tiny hair-like cilia down the tube and into the uterus to implant. Anything that scars or slows the tube can strand the embryo partway. It implants where it lands, usually in the ampulla (the wide middle of the tube, the most common ectopic site). That tube has no room to stretch and a thin wall full of vessels, so as the pregnancy grows it stretches the tube, then tears it → brisk internal bleeding.
Now the risk factors. They are all variations on one theme: anything that damages or slows the tube. Prior pelvic inflammatory diseaseInfection of the upper genital tract, classically from chlamydia or gonorrhea, that scars the fallopian tubes. The single biggest risk factor for ectopic pregnancy., a prior ectopic, prior tubal surgery or ligation, and assisted reproduction (IVF) all raise the odds. Flip each card for the high-yield nuances.
Scarred tubesTap to flip
PID is number onePrior chlamydia or gonorrhea infection scars the tube and is the leading risk factor. A prior ectopic and prior tubal surgery (including a ligation that fails) carry the same scarring logic.
The IUD twistTap to flip
Lower absolute risk, higher proportionAn intrauterine device makes pregnancy rare overall, so it lowers the absolute number of ectopics. But if a patient does conceive with an IUD in place, that pregnancy is more likely to be ectopic. Both facts are true.
IVF and heterotopicTap to flip
Two pregnancies at onceAssisted reproduction raises the risk of a heterotopic pregnancy: a normal uterine pregnancy AND a tubal ectopic at the same time. Seeing a sac in the uterus does not fully rule out an ectopic in an IVF patient.
Most ectopics implant in the ampulla. An isthmic ectopic sits in the narrow part of the tube and tends to rupture earliest. The uterine cavity is the only place a pregnancy can safely grow.
Clinical Images
Laparoscopy: a swollen, pregnant fallopian tube · tap
Ultrasound: adnexal mass, empty uterus · tap
At the Bedside
The Triad and the Crash
An unruptured ectopic whispers a classic triad. A ruptured one screams. Learn both faces, because the second one is a surgical emergency.
The classic triad. A reproductive-age woman with a missed period (amenorrhea), unilateral lower abdominal pain, and vaginal bleeding has an ectopic until proven otherwise. The bleeding is often light and dark, because the uterine lining is being shed without a healthy pregnancy to support it. Many ectopics are caught before any of this is dramatic, which is exactly why the pregnancy test and the scan matter so much.
The crash. When the tube ruptures, the picture flips to internal hemorrhage: sudden severe pain, lightheadedness or fainting, a fast heart rate, and falling blood pressure. Tap each finding for what it tells you.
Shoulder tip pain (Kehr sign)
Tap to reveal
Blood pooling under the diaphragm irritates it, and the diaphragm refers pain to the shoulder. In a woman who could be pregnant, shoulder pain plus belly pain means hemoperitoneum until proven otherwise.
Cervical motion tenderness
Tap to reveal
Moving the cervix on exam tugs the inflamed, bleeding tube and hurts. It is not specific (also seen in pelvic infection) but supports a tubal source of pain.
Adnexal tenderness or mass
Tap to reveal
A tender fullness to one side of the uterus is the ectopic itself. Do not poke hard at a suspected ectopic, because pressure can help it rupture.
Hypotension and tachycardia
Tap to reveal
Signs of blood loss. A young woman compensates well, then drops fast. Orthostatic dizziness or a near-faint in early pregnancy is a red flag for a leaking ectopic.
From the Attending
Any woman of reproductive age with abdominal pain gets a pregnancy test before you anchor on anything else. A positive test plus one-sided pain is an ectopic until the scan proves otherwise. The patient who faints at home and arrives pale with a soft belly and shoulder pain is bleeding into her abdomen right now. Pregnant, painful, and unstable means the operating room, not another hour of observation.
Confirming It
The hCG and the Scan
Two numbers run this workup: where the uterus should show a pregnancy (the discriminatory zone) and how the beta-hCG moves over 48 hours. Work the algorithm, then learn the look-alikes.
The discriminatory zone. Above a beta-hCG of about 1500 to 2000 mIU per mL, a normal pregnancy inside the uterus should be visible on a transvaginal ultrasound. So if the beta-hCG is above that line and the uterus is empty, you should worry hard about an ectopic. Below that line you cannot tell yet, and you follow the trend.
The serial trend. In a healthy early uterine pregnancy the beta-hCG climbs briskly, rising by at least about 35 to 53 percent every 48 hours (the old shorthand is that it nearly doubles). A beta-hCG that rises too slowly, plateaus, or falls only a little points to an abnormal pregnancy, either a failing intrauterine pregnancy or an ectopic. Work each fork before you reveal it.
A stable woman with a positive test and lower pelvic pain. What is the first paired workup?
A quantitative beta-hCG paired with a transvaginal ultrasound is the backbone. The number tells you whether a pregnancy should be visible; the scan tells you whether it is in the uterus. Number plus picture: beta-hCG and transvaginal ultrasound.
Beta-hCG is 2600 mIU per mL and the uterus is empty on transvaginal ultrasound. Best interpretation?
Above the discriminatory zone a normal intrauterine pregnancy should be visible. An empty uterus with this number means an ectopic until proven otherwise (or a very early miscarriage). High hCG plus empty uterus equals ectopic until disproven.
Beta-hCG is only 900 and the uterus is empty. She is stable and pain-free. Next step?
Below the discriminatory zone the scan cannot localize the pregnancy yet, so you follow the 48-hour trend. A brisk rise favors a normal pregnancy; a slow or flat rise points to an ectopic or a failing pregnancy. Below the zone and stable: serial beta-hCG, do not treat blindly.
The mimics. One-sided pelvic pain in a young woman has a crowded differential. The table sorts the usual suspects.
Look-alike
What separates it
Threatened or missed miscarriage
Positive beta-hCG but the pregnancy is inside the uterus on ultrasound. Bleeding and cramping with a closed or open cervix.
Ruptured ovarian cyst
Sudden pain, often mid-cycle, free fluid on ultrasound, and the beta-hCG is negative.
Ovarian torsion
Sudden severe unilateral pain with an enlarged ovary and absent Doppler flow. A surgical emergency for the ovary.
Pelvic inflammatory disease
Fever, discharge, bilateral pain, cervical motion tenderness, and a negative pregnancy test.
Appendicitis
Periumbilical pain that migrates to the right lower quadrant with anorexia. Check the pregnancy test first.
Heterotopic pregnancy
A uterine pregnancy AND an adnexal ectopic together. Suspect it after IVF when pain persists despite a uterine sac.
The Plan
A Shot or the Operating Room
The whole management question is one fork: is she stable and a good candidate for medicine, or does she need surgery now? The board points live in the criteria.
Methotrexate, the medical route. Methotrexate is a folate antagonist that stops the fast-dividing pregnancy tissue from growing, and the body reabsorbs it. It is reserved for a patient who is stable, unruptured, reliable for follow-up, with a small mass, low beta-hCG, and no fetal cardiac activity. After treatment you check the beta-hCG on day 4 and day 7 and expect at least a 15 percent fall between day 4 and day 7; if it does not drop, you redose or operate.
When methotrexate is off the table. Do not give it if she is unstable or ruptured, if the beta-hCG is high or the mass is large, if there is fetal cardiac activity, or if she has a reason she cannot take the drug: liver or kidney disease, a blood count problem, immunodeficiency, active peptic ulcer disease, or breastfeeding. A patient who cannot reliably return for follow-up labs is also a poor candidate.
Surgery. A ruptured or unstable ectopic goes to the operating room for a salpingectomy (removing the tube) to stop the bleeding fast. A stable patient who needs surgery but wants to preserve fertility may get a salpingostomy (opening the tube and removing the pregnancy while leaving the tube), though that tube needs beta-hCG follow-up to be sure no tissue is left behind.
From the Attending
Do not forget the blood type. An Rh-negative woman with an ectopic or any early-pregnancy bleeding gets anti-D immunoglobulin to prevent her from making antibodies that would attack a future pregnancy. Rh-negative plus pregnancy bleeding equals anti-D immunoglobulin. Make it reflex.
Board Trap
After IVF, suspect a heterotopic pregnancy: a normal pregnancy in the uterus AND an ectopic in the tube. You cannot give methotrexate, because it would poison the wanted uterine pregnancy. The heterotopic ectopic is managed surgically so the intrauterine pregnancy can continue. Seeing a sac in the uterus does not let you exhale in an IVF patient with ongoing pain.
Prove It
Board Walkthrough
Original clinical vignettes, 5 dealt per round, answer choices shuffled, never repeating within a round. Tap a wrong answer first to see why it almost works, then read the glowing clues.
Medically reviewed by Kaitlyn Cocuzzo, MD and Fatima Ali, DO · Last reviewed June 2026
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