What Is an Anembryonic Pregnancy (Blighted Ovum)?

An anembryonic pregnancy occurs when a fertilized egg implants in the uterus and forms a gestational sac, but an embryo never develops inside it. The American Pregnancy Association estimates this accounts for roughly half of all first-trimester miscarriages, making it one of the most common types of early pregnancy loss. The condition was long called a “blighted ovum,” a term still in wide use but increasingly replaced by “anembryonic pregnancy” because it more accurately describes what is happening and avoids language that many patients and clinicians find unnecessarily harsh.

What Actually Happens Inside the Uterus

After fertilization, the dividing ball of cells normally differentiates into two components: the trophoblast, which becomes the placenta and supporting membranes, and the inner cell mass, which becomes the embryo. In an anembryonic pregnancy, the trophoblast does its job. It burrows into the uterine lining, triggers the formation of a gestational sac, and begins producing hormones. But the inner cell mass either fails to form or stops developing so early that it is reabsorbed before it can be detected. The result is a hollow sac that looks, on early ultrasound, much like a normal early pregnancy.

Tissue analysis reveals concrete differences between these pregnancies and viable ones. In anembryonic pregnancies, the blood vessel networks inside the chorionic villi are far less developed than in pregnancies with a living embryo. Instead of the branching vascular tree you would expect, the vessels appear as primitive cord-like structures, and the protein markers associated with blood vessel development are significantly reduced. The trophoblast cells themselves show microscopic changes, including abnormal expression of alpha-fetoprotein compared to embryonic pregnancies.¹ These findings make biological sense: without an embryo sending signals to drive vascular development, the placental tissue forms but never matures properly.

Why the Embryo Fails to Develop

The single biggest driver is chromosomal abnormality in the fertilized egg. Studies examining the tissue from anembryonic pregnancies consistently find that a substantial share carry the wrong number of chromosomes. One analysis using a high-resolution genetic technique found that half of anembryonic pregnancy samples had a normal chromosome count, while the other half carried abnormalities. The most common was trisomy 16 (an extra copy of chromosome 16), found in about 15% of cases, followed by trisomies of chromosomes 22, 15, and 19. Advanced maternal age was linked to a higher rate of these chromosomal errors.²

The picture gets more complex when you look across different studies. Some research has found much higher rates of abnormal chromosomes, with one large study of 1,500 women with anembryonic pregnancy reporting abnormal karyotypes in about 61% of cases, most commonly autosomal trisomies, triploidy, and monosomy X. Conversely, other work has found the opposite pattern, with over 80% of samples showing normal chromosomes, suggesting that something other than a gross chromosomal problem can derail embryo formation. Researchers have proposed that single-gene defects or submicroscopic genetic changes below the resolution of standard chromosome testing may play a significant role in cases where the karyotype looks normal.³

This discrepancy matters because it changes how you think about the condition. When the cause is a random chromosomal error during cell division, the pregnancy was essentially never viable. It is a biological accident rather than a sign that something is wrong with either parent. But when chromosomes look normal, it opens the door to other explanations, including structural chromosome variations that do not show up on standard testing. Chromosome 9, for instance, carries natural structural variations in 1–2% of the general population, and some evidence links these variations to recurrent anembryonic pregnancy, possibly by disrupting the orderly division of cells during the earliest stages after fertilization.⁴

Why You Can Still “Feel Pregnant”

One of the cruelest aspects of anembryonic pregnancy is that it can produce all the hallmarks of a viable pregnancy for weeks. The trophoblast tissue produces human chorionic gonadotropin (hCG), the hormone detected by pregnancy tests, and it can do so at entirely normal levels well into the first trimester. Research has shown that in cases of anembryonic pregnancy and missed abortion, both hCG levels and gestational sac size often track within the normal range through the sixth to eighth week. It is only after the ninth week that the sac typically falls behind in size, while hCG can occasionally remain in the normal range as late as the fourteenth week.⁵

This means nausea, breast tenderness, fatigue, and a positive (even strongly positive) pregnancy test do not guarantee an embryo is growing. In one study, about a third of patients with a confirmed anembryonic pregnancy had their first hCG measurement in the normal range.⁶ Even more striking, research studying women 16 days after conception found that those who turned out to have an anembryonic pregnancy had hCG concentrations that were not only normal but rising at an apparently normal rate at that early stage.⁷ Over time, hormone levels in anembryonic pregnancies tend to drift to the low end of normal or below, with some studies documenting clearly abnormal values by around the tenth week.⁸ But by then, ultrasound usually makes the diagnosis plain.

How the Diagnosis Is Made

Ultrasound is the definitive diagnostic tool, but a single scan early in pregnancy is not always enough to be certain. Early guidelines identified a gestational sac measuring 25 mm or more in mean diameter without a visible embryo as a major criterion for diagnosing anembryonic pregnancy. A distorted sac shape, a thin or irregular lining reaction, and the absence of a double-layered decidual ring were considered supporting signs.⁹ Modern guidelines have generally moved toward even more conservative thresholds to avoid misdiagnosis, though the core principle remains the same: if the sac is large enough that an embryo should be visible and none is seen, the pregnancy is anembryonic.

One complication is that a viable early pregnancy can look like an empty sac simply because it is too early. A sac under about 20 mm may be too small to show an embryo even when one is developing normally. This is why clinicians will often schedule a follow-up scan a week or two later rather than making the call on a single visit. A well-defined, continuous trophoblastic ring around the sac is considered a good sign for ongoing viability, while a sac larger than 20 mm with no embryonic echoes is concerning.¹⁰ The anxiety of waiting for a repeat scan is considerable, but the alternative, acting on an uncertain diagnosis, carries risks of ending what might turn out to be a healthy pregnancy.

The Ectopic Pregnancy Trap

A dangerous mimicry can occur when an ectopic pregnancy (one implanted outside the uterus, usually in a fallopian tube) produces a fluid collection inside the uterus called a pseudogestational sac. On ultrasound, this can look like the empty gestational sac of an anembryonic pregnancy. If a clinician sees what appears to be an intrauterine sac and stops investigating, the ectopic pregnancy goes undiagnosed, potentially leading to a life-threatening rupture.

The key distinguishing feature is the double-layered decidual-chorionic sac sign. In a true intrauterine pregnancy, even an anembryonic one, the sac is surrounded by both decidual tissue and a chorionic layer, creating a distinctive two-ring appearance. Research found this sign present in all confirmed intrauterine pregnancies studied but absent in every case of proven ectopic pregnancy.¹¹ When the ultrasound image is ambiguous, follow-up with repeat scanning, serial hCG measurements, and sometimes tissue analysis after passage is necessary to confidently distinguish between these two very different conditions.¹²

Common Symptoms and How They Vary

Many people with an anembryonic pregnancy have no symptoms at all until a routine ultrasound reveals the empty sac. Others experience the same signs as any early miscarriage: vaginal bleeding, cramping, or a gradual fading of pregnancy symptoms. In one cross-sectional analysis, the most frequently identified finding was low hCG on bloodwork (about 41% of cases), followed by abdominal discomfort (roughly 23%) and vaginal bleeding (about 18%).¹³ The fact that low hCG was the most common presentation rather than bleeding or pain underscores that many cases are caught on lab work or ultrasound before the body shows outward signs of trouble.

Management Options

Once an anembryonic pregnancy is confirmed, there are three approaches, and no single one is universally best. The choice depends on how far along the pregnancy is, the patient’s preferences, access to follow-up care, and medical history.

Expectant Management

This means waiting for the body to recognize the failed pregnancy and pass the tissue on its own. It works: success rates for expectant management of early miscarriage range from about 66% to 91%, depending on the type of pregnancy loss. The main risk is heavy bleeding, which requires a blood transfusion in about 1–2% of cases. If the tissue does not pass within a set window, usually a few weeks, medication or surgery becomes the next step.¹⁴ The appeal of this approach is that it avoids medications and procedures; the downside is unpredictability. Some people find the waiting emotionally unbearable.

Medical Management With Misoprostol

Misoprostol, a medication that causes the uterus to contract and expel its contents, is the most common drug used. When given vaginally, it produces complete passage of tissue in roughly 81–95% of early miscarriages overall, with around 5–20% of patients eventually needing a surgical procedure to complete the process.¹⁵ In a trial focused specifically on anembryonic pregnancy, vaginal misoprostol achieved complete abortion in 63% of women, compared to about 19% in a placebo group. Side effects included lower abdominal pain in roughly three-quarters of patients and fever in about 15%.¹⁶ Vaginal administration tends to be more effective with fewer side effects than oral dosing. For many patients, this offers a middle ground: more predictable timing than waiting it out, less invasive than surgery.

Surgical Options

Surgical management typically involves vacuum aspiration, either manual or electric, or traditional dilation and curettage. A randomized trial comparing these approaches in early pregnancy loss found very low complication rates across the board. Heavy bleeding occurred in about 2% of traditional curettage patients and under 1% of vacuum aspiration patients, with incomplete evacuation rates similarly low. No severe complications were observed in any group.¹⁷ Newer approaches include operative hysteroscopy, where a camera is inserted into the uterus to visualize and remove tissue directly. A recent randomized trial comparing hysteroscopy to vacuum aspiration found that while suspected retained tissue was somewhat more common after hysteroscopy, confirmed retained tissue rates were not significantly different between the two methods.¹⁸ Surgery offers the fastest resolution and the most certainty that the tissue has been removed, which is why some patients prefer it despite the procedural risks.

The Emotional Toll

Losing a pregnancy that you believed was progressing normally is a significant psychological event, and research confirms that the emotional aftermath of anembryonic pregnancy is not meaningfully different from other types of early pregnancy loss. A study screening women diagnosed with missed abortion, anembryonic pregnancy, and spontaneous abortion found moderate anxiety levels across all three groups before treatment. In the week after discharge, depression screening scores were above the threshold for clinical concern in all groups, and grief scores were similarly elevated. There was no statistically significant difference between the groups, meaning that the absence of an embryo does not make the loss feel any less real to the person experiencing it.¹⁹

This matters practically because well-meaning friends or family sometimes minimize anembryonic pregnancy with comments like “there was never really a baby” or “at least it was early.” The clinical data does not support the notion that this type of loss is easier. Grief, anxiety, and depression follow the loss of the pregnancy as a hoped-for future, not the loss of a specific embryo at a specific developmental stage. Clinicians increasingly recognize the need for psychological follow-up after any early pregnancy loss, not just those where an embryo was visualized.

Anembryonic Pregnancy and Assisted Reproduction

People who conceive through IVF or similar techniques sometimes worry that the process itself increases the risk of anembryonic pregnancy. There is some basis for this concern. A retrospective study examining IVF outcomes found that both blastocyst-stage embryo transfer and advanced maternal age were independent risk factors for anembryonic pregnancy.²⁰ The finding about blastocyst transfer is particularly interesting because it suggests that extending embryo culture in the lab may allow embryos that would have arrested earlier to reach a stage where they can implant but not sustain embryonic development. This is an active area of research, and it does not mean IVF patients should avoid blastocyst transfers; the overall live birth rates with blastocyst transfer remain higher than with earlier-stage transfers. But it does mean that an empty sac on the first ultrasound after IVF, while devastating, is a recognized possibility with a plausible biological explanation.

Why the Term “Blighted Ovum” Is Fading

For decades, the standard medical term was “blighted ovum.” It appears throughout older research papers, textbooks, and patient handouts. The shift toward “anembryonic pregnancy” reflects two things. First, the older term is clinically misleading: the ovum (egg) is not “blighted” in the sense of being cursed or damaged in a way visible at fertilization. The problem is that an embryo fails to develop after the pregnancy has already begun establishing itself, which is a different thing entirely. Second, the language carries an emotional weight that many patients find unnecessarily painful. Being told your pregnancy is “blighted” sounds like a judgment, while “anembryonic” is descriptive: it simply means without an embryo. Medical communication research increasingly emphasizes that the words clinicians use in delivering bad news affect how patients process and cope with loss, and the shift in terminology reflects that awareness.

Future Fertility After an Anembryonic Pregnancy

For most people, a single anembryonic pregnancy does not signal a fertility problem. Because the majority of cases stem from random chromosomal errors in one particular egg, the next egg is statistically likely to be normal. Clinicians generally advise that trying again after one or two normal menstrual cycles is reasonable, though the exact timing depends on physical recovery and emotional readiness.

The picture shifts if anembryonic pregnancies recur. Two or more may prompt investigation into parental chromosomes, uterine anatomy, hormonal function, and immune factors. The chromosome 9 structural variations mentioned earlier, for instance, are the kind of finding that would typically only surface during workup for recurrent loss rather than after a single event. For the vast majority of people, though, a single anembryonic pregnancy is a common and usually non-recurring misfortune. The statistical odds of a subsequent healthy pregnancy remain firmly in your favor.

Histopathology and What the Tissue Reveals

When tissue from an anembryonic pregnancy is examined under a microscope, the findings are not always what you might expect. In one study, the placental villi looked histologically normal in about a third of cases of anembryonic pregnancy and missed abortion.²¹ The placenta was doing its job at the cellular level even though no embryo existed. This disconnect helps explain why hormone levels and early ultrasound findings can look reassuring: the tissue producing those signals is healthy tissue. The problem is not in the placenta but in the absent inner cell mass that should have become the embryo.

More detailed analysis shows that the vascular architecture of the villi tells a different story than their surface appearance. The blood vessels inside the villi of anembryonic pregnancies are far fewer and more primitive than in viable pregnancies, appearing as simple cords rather than the branching capillary networks needed to support an embryo.²² This makes intuitive sense: vascular development in the placenta is partly driven by signals from the embryo itself. Without those signals, the placenta grows a shell but never develops the internal plumbing. It is a pregnancy that built the house but never moved anyone in.