An ectopic pregnancy happens when a fertilized egg implants and starts growing outside the uterus, most often in a fallopian tube. It occurs in roughly 1 to 2 percent of all pregnancies. Because the fallopian tube cannot stretch or sustain a growing pregnancy the way the uterus can, an ectopic pregnancy is never viable and can become a medical emergency if it ruptures.
Where Ectopic Pregnancies Implant
About 95 percent of ectopic pregnancies occur somewhere along the fallopian tube. The most common spot is the ampullary section, the wider middle portion of the tube closest to the ovary, which accounts for roughly 70 to 80 percent of all cases. The isthmic section, a narrower stretch closer to the uterus, makes up about 12 percent. The fimbrial end (the finger-like opening near the ovary) accounts for around 5 to 11 percent, and the interstitial segment, where the tube passes through the uterine wall, represents about 2 percent.
In rare cases, implantation happens outside the tubes entirely: on an ovary, in the abdominal cavity, at the cervix, or within a scar from a previous cesarean delivery. Together these account for fewer than 5 percent of ectopic pregnancies.
Why It Happens
After fertilization, the egg normally travels down the fallopian tube toward the uterus, propelled by tiny hair-like structures called cilia that line the tube’s interior. Anything that damages these cilia or narrows the tube can trap the embryo before it reaches the uterus. Inflammation from a pelvic infection is one of the most common culprits. Chlamydia and gonorrhea can scar the tube’s lining and destroy the cilia, slowing or blocking the embryo’s passage.
Smoking also plays a significant role. Chemicals in cigarette smoke impair the cilia’s rhythmic beating and affect the tube’s ability to contract, both of which are needed to move the egg along. Previous tubal surgery, endometriosis, and structural abnormalities can have a similar effect by distorting the tube’s shape or creating adhesions that obstruct it. Assisted reproductive technologies like IVF modestly increase the risk as well, partly because the women using them often have underlying tubal issues.
Sometimes there is no identifiable risk factor. About half of women diagnosed with an ectopic pregnancy have none of the known risk factors.
Symptoms and When They Appear
Early on, an ectopic pregnancy can feel just like a normal pregnancy: a missed period, breast tenderness, nausea. The first warning signs that something is wrong are typically light vaginal bleeding and one-sided pelvic pain, which often show up between the sixth and eighth week of pregnancy.
As the pregnancy grows, the pain usually intensifies. If the fallopian tube begins to stretch or leak blood, you may feel sharp, stabbing pain in the pelvis or lower abdomen. Shoulder pain is a particularly important red flag. It happens when blood from a leaking or ruptured tube pools in the abdomen and irritates the diaphragm, which shares nerve pathways with the shoulder. An urge to have a bowel movement can accompany this for similar reasons.
A ruptured ectopic pregnancy is a surgical emergency. Signs include sudden, severe abdominal pain, extreme lightheadedness, fainting, and signs of shock such as a rapid pulse and pale, clammy skin. Rupture can cause life-threatening internal bleeding within minutes.
How It Is Diagnosed
Diagnosis relies on two tools used together: blood tests measuring a pregnancy hormone called beta-hCG and transvaginal ultrasound.
In a healthy pregnancy, beta-hCG levels rise predictably. When the starting level is below 1,500 mIU/mL, you’d expect at least a 49 percent increase over 48 hours. At levels between 1,500 and 3,000, at least a 40 percent rise is normal, and above 3,000, at least 33 percent. When the rise is abnormally slow, or the level plateaus, ectopic pregnancy becomes a strong possibility. A drop of at least 21 percent over 48 hours typically points to a failing intrauterine pregnancy instead, but a smaller, ambiguous decrease raises concern for an ectopic.
Ultrasound comes into play once beta-hCG levels are high enough that a normal pregnancy should be visible inside the uterus. Most pregnancies can be seen by the time the level reaches about 1,500 mIU/mL, though clinicians often use a threshold of 3,500 mIU/mL to avoid mistakenly intervening on a very early but normal pregnancy. If the uterus is empty at that level, an ectopic pregnancy is likely. Sometimes the ectopic mass itself can be spotted on the ultrasound, but not always.
Treatment With Medication
When an ectopic pregnancy is caught early and hasn’t ruptured, medication can be an option. The treatment uses a drug that stops the pregnancy’s cells from dividing, allowing the body to reabsorb the tissue over several weeks. It works best when the ectopic mass is small (under 3.5 cm), there is no fetal heartbeat detected, and hormone levels are not extremely high.
Overall success rates are around 87 percent, meaning most women treated this way avoid surgery. Success depends heavily on how high beta-hCG levels are at the time of treatment. At moderate levels, the success rate is roughly 75 percent; at higher levels (above 4,500 mIU/mL), it drops to about 65 percent. After receiving the medication, you’ll need repeated blood draws over several weeks to confirm that hormone levels are falling back to zero. This monitoring period can take a month or more and requires patience.
This treatment is not an option if there are signs of internal bleeding, if the ectopic pregnancy has a detectable heartbeat, or if hormone levels are very high (typically above 5,000 to 10,000 mIU/mL depending on the institution). In those cases, surgery is necessary.
Surgical Options
Surgery for an ectopic pregnancy is almost always done laparoscopically, through small incisions in the abdomen. There are two main approaches.
Salpingectomy removes the affected fallopian tube entirely. It is the standard choice when the tube is badly damaged, heavily distended, or has already ruptured. It is also preferred when the other tube is healthy and fertility is not the primary concern, because it eliminates any chance of a recurrent ectopic in that same tube.
Salpingostomy makes a small incision in the tube to remove the ectopic tissue while leaving the tube in place. This may be considered when preserving the tube matters for future fertility, particularly if the other tube is damaged or absent. It works best when the tube is only mildly swollen, has thin walls, and the inner lining is still intact. After salpingostomy, follow-up blood tests are needed to make sure no residual pregnancy tissue remains, since there is a small chance of incomplete removal.
Recovery from laparoscopic surgery typically takes one to two weeks before you can return to normal activities, though full internal healing takes longer.
Fertility After an Ectopic Pregnancy
One of the first questions many women have is whether they can get pregnant again. The answer for most people is yes. Having one functioning fallopian tube is sufficient for natural conception, and many women go on to have successful pregnancies after treatment.
The risk of having another ectopic pregnancy does increase, however. Estimates vary, but the recurrence rate is generally around 10 to 15 percent. The risk is higher if the underlying cause, such as tubal damage from infection, affects both tubes. Women who had a salpingostomy (tube-sparing surgery) retain two tubes but also retain whatever damage led to the first ectopic, which is why close monitoring in early subsequent pregnancies is important. An early ultrasound to confirm the pregnancy is inside the uterus is standard after a previous ectopic.
For women with significant tubal damage on both sides, IVF bypasses the fallopian tubes entirely and is often the most effective path to pregnancy.