Threatened Miscarriage: Why It Happens & How To Stop It

A threatened miscarriage is defined as any vaginal bleeding that happens during the first 20 weeks of pregnancy, while the cervix remains closed. Despite the anxiety that it causes, this occurrence is very common, especially in the first trimester and less so in the second. As many as 20% of all expecting women will have some type of vaginal bleeding and about half of these will still carry to term successfully. 

A threatened miscarriage can raise the risk of miscarriage by 2.6 times. Moreover, 17% of women who suffered a threatened abortion but did not miscarry may go on to have further complications within the same pregnancy. This is why it’s critical to carefully investigate, monitor and treat any expecting woman who presents with vaginal bleeding.

Threatened miscarriage doesn't necessarily mean pregnancy loss

Threatened miscarriage doesn't necessarily mean pregnancy loss


A threatened miscarriage presents with vaginal bleeding. The bleeding can range from mild spotting to heavy bleeding, sometimes with clots. The color of the blood can also range from soft brown to bright red (the latter indicating a fresh bleeding). The vaginal bleeding is sometimes accompanied by lower abdominal or back pain, which may resemble period pain or feel different. The cervix remains closed at all times. If the cervix opens, the threatened miscarriage becomes an imminent miscarriage and it can no longer be prevented from happening.

If bleeding and pain occur, but the pregnancy cannot be located on a transvaginal ultrasound, ectopic pregnancy or a chemical miscarriage (a miscarriage that happens before the pregnancy reaches a clinically visible size) are the most common explanations.

What Causes a Threatened Miscarriage

There is a wide variety of possible causes and favoring factors for a (threatened) miscarriage.

Often, a problem with the pregnancy itself is what causes a miscarriage and all its accompanying symptoms. A chromosomal abnormality in the embryo, an embryo that has stopped developing, a blighted ovum (a pregnancy that is missing an embryo altogether) or very rarely even a molar pregnancy (a very abnormal development of the placenta) will all trigger the woman’s body to eliminate the pregnancy that is no longer viable.

Another very common reason for a threatened abortion is a progesterone deficiency, which may result from a more general Luteal Phase Defect syndrome or from an isolated inability to produce sufficient amounts of progesterone for that particular pregnancy. Whatever the underlying cause, it can be easily treated with progesterone supplements or HCG (Human Chorionic Gonadotropin) injections, which both increase progesterone levels.

A bacterial infection in the proximity of the uterus (such as a vaginal infection that has reached the cervix and uterus), or one that has spread to the blood (bacteremia) from another part of the body, can often induce a miscarriage. It’s unfortunately very difficult to salvage a pregnancy that has been exposed to bacterial infection, even with prompt use of antibiotics.

Certain types of viral and parasitic infections can also trigger a miscarriage. Toxoplasmosis, Rubella, Cytomegalovirus, HIV, Syphilis, even Influenza, have been all been associated with failed pregnancies in various studies.

Occasionally, an anatomic abnormality of the uterus could hinder the pregnancy from developing normally. For example, certain uterine malformations (arcuate uterus, septate uterus, unicornuate uterus, etc.) or uterine growths like fibroids, polyps and adhesions may create an unfavorable environment for the pregnancy and set off various complications, including a threatened miscarriage. 

A threatened abortion can have multiple causes, many of which can be treated

A threatened abortion can have multiple causes, many of which can be treated

Untreated chronic diseases such as thyroid conditions (particularly hypothyroidism and hyperthyroidism), diabetes or chronic high blood pressure have long been linked to miscarriage and pregnancy complications. Similarly, systemic autoimmune disorders (lupus, antiphospholipid syndrome) and clotting abnormalities (thrombophilia) can lead to an unfavorable pregnancy outcome if they are not properly managed. 

Sometimes, an Rh incompatibility between the mother and fetus is what activates the rejection response from the mother’s body, in cases when the mother is Rh negative. Rh is a type of blood antigen and is easily tested for with a quick blood test. Normally this rejection almost never happens with a first pregnancy, but an immune response could develop with subsequent pregnancies.

Exposure to certain medications and chemical substances during early pregnancy has also been shown to increase the likelihood of a miscarriage. Alcohol, drug use, smoking and even high caffeine intake (over 200mg per day) are associated with various negative pregnancy outcomes.

A traumatism of any kind to the abdomen may also conceivably trigger a pregnancy loss.

When no obvious cause can be identified for a threatened miscarriage, it is called unexplained (or idiopathic). More subtle underlying mechanisms may be at work, some that we cannot yet clinically study or test for, or that we have just begun investigating. Possibilities include: an irritable uterus (a uterus that doesn’t relax as it should during the pregnancy and keeps cramping and contracting), advanced maternal age (age over 35), emotional stress, excessive physical exercise, sexual intercourse.

Tests and diagnosis

If you are dealing with a threatened miscarriage, your doctor will probably order a few medical tests to better understand the source of the problem and make the best decision for you and your pregnancy.

A transvaginal ultrasound is typically the first investigation performed, since it can offer a quick and clear picture of the pregnancy, its location and whether or not the cervix is still closed. It will help indicate if the pregnancy has stopped developing, is ectopic or is still developing normally. As a general rule, if a normally developed embryo with a good heartbeat is discovered in the uterus and the cervix is still closed, then there is a very good chance that the pregnancy will continue successfully, in spite of the vaginal bleeding (in some studies, over 90% odds).

First trimester ultrasound, showing a healthy pregnancy and embryo

First trimester ultrasound, showing a healthy pregnancy and embryo

The doctor may also perform a pelvic exam to look at the cervix and vagina and determine if the source of the bleeding may be the cervix instead. A high vaginal or cervical swab and a Pap test will usually be taken with this occasion to look for any possible infections.

A series of blood tests is also recommended. 

HCG (Human Chorionic Gonadotropin) blood levels will normally correlate with the gestational age, so a large discrepancy may point to a pregnancy that is not developing normally. A series of HCG tests taken every 48h will often show whether the pregnancy is advancing or failing, since HCG titers are expected to double every 48-72h. 

A progesterone blood test is very relevant in determining whether the pregnancy may benefit from progesterone supplements.

Other blood tests may include: a Complete Blood Count, TSH (Thyroid Stimulating Hormone) levels to check for thyroid dysfunction, Blood group and Rh.

In cases where there is a history of recurrent miscarriage - especially if consecutive, screening panels for Thrombophilia and APS (Antiphospholipid Syndrome), as well as ANA (Antinuclear Antibodies) titers will probably be additionally recommended.

A urine test (urinalysis) is indicated as well, to screen for a UTI (urinary tract infection).

Treatment options

If the pregnancy is non-viable for whatever reason (abnormal embryo, embryo that has stopped developing, no heartbeat, blighted ovum, etc.) usually the course of action is either a watchful wait (for a natural miscarriage to take place) or a pregnancy termination procedure (an abortion). Various factors may influence this decision, depending on the risks involved and the woman’s personal choice. An ectopic pregnancy will always need to be treated promptly, either with medication or surgically.

If however, the pregnancy is progressing normally despite the bleeding and there is a good fetal heartbeat present, pregnancy support and tocolytic therapy (medications that relax the uterus) may be initiated, especially when there is pain involved and/or a history of multiple miscarriages.

Needless to say, treatment of any underlying conditions affecting fertility, like infections, autoimmune diseases, thyroid dysfunction, diabetes, thrombophilia etc. needs to be initiated as soon as possible and is essential for the favorable progression of the pregnancy.

Certain medications may be helpful when dealing with threatened miscarriage or repeated pregnancy loss

Certain medications may be helpful when dealing with threatened miscarriage or repeated pregnancy loss

I have compiled a comprehensive list of pregnancy supporting medications that have been studied, used and proven to be largely safe and effective for both mother and baby in cases of threatened miscarriage. Some of them are widely known and available and some are only used in certain parts of the world.

As an important note, the medications listed here may or may not be recommended during pregnancy in all countries and/or by all doctors. Depending on each country’s medical system regulations and each doctor's professional views, some of these drugs may be discouraged to use during pregnancy or unavailable.

First trimester treatment options for threatened abortion (weeks 2 to 12)

The first trimester is the most sensitive part of embryo development, a time when any minor mistake or interference could possibly result in a birth defect. This is why most medications are restricted or discouraged during this time, unless the benefits of taking them outweigh the risks involved. Still, there are a few relatively safe treatment options if you are dealing with a threatened miscarriage at this stage:

Acetaminophen (Paracetamol) is likely the safest painkiller to take during pregnancy. It is classified as a mild analgesic, so it may be of help if the vaginal bleeding is accompanied by mild to moderate pain. Don’t take it for more than 3 days in a row without speaking to a doctor, though. Trade names also include Tylenol, Panadol.

Drotaverine is an antispasmodic drug that helps calm smooth muscle contractions (including those of the uterus). It is considered completely safe during pregnancy and is available in Asian and Eastern European countries. According to medical studies however, it is only effective to relieve uterine cramps in a little less than 50% of patients. Trade names include No-Spa, Droverin.

Micronized progesterone supplements are often recommended when dealing with a threatened abortion and even preventively during the first trimester, when there is a history of recurrent pregnancy loss. Progesterone is an essential hormone during pregnancy, which relaxes the uterus and makes the uterine lining more receptive. Micronized progesterone supplements are safe to take and come in a variety of forms: oral pills, vaginal suppositories and vaginal gel, of which the vaginal route of administration seems to be the most effective on the uterus. Another very efficient supplement form is progesterone in oil, however it needs to be administered by intramuscular injection.

HCG (Human Chorionic Gonadotropin) injectable supplements are an extracted form of the natural hormone that is released by the placenta after implantation. HCG keeps the corpus luteum from disintegrating and stimulates progesterone production, both essential for the continuation of the pregnancy. HCG intramuscular injections during the first trimester have been proven to reduce the odds of miscarriage and boost progesterone levels. However, certain brands of HCG should be avoided when the patient suffers from thrombophilia or certain other medical conditions. Trade names include Pregnyl, Novarel, Pubergen, Choragon and Ovidrel.

Sildenafil citrate (more widely known as Viagra) is a medicine that has shown promising results in certain studies where it was administered vaginally during pregnancy. It increased pregnancy retention and lowered miscarriage rates during the first trimester and it improved outcomes in cases of Fetal Growth Restriction and pre-eclampsia in later trimesters. Acting as a vasodilator, it improves blood circulation to and within the uterus when administered locally. 

Low dose aspirin (or ‘baby aspirin’, meaning an aspirin dose of less than 100mg) is sometimes prescribed during pregnancy to improve blood flow when a minor blood clotting dysfunction is suspected. It is also useful in preventing miscarriage in cases with a history of recurrent pregnancy loss. It is however debatable whether taking it will improve or rather worsen an active bleeding within the uterus (since aspirin is a blood-thinner that delays coagulation).

Prednisolone is occasionally recommended by some doctors during the first trimester, to encourage pregnancy retention, usually when there is a history of recurrent pregnancy loss. Prednisolone is a corticosteroid that downregulates the immune system. A low dose of it may make it less likely for the mother’s body to interpret the pregnancy as a foreign body and reject it. Its use is, however, still controversial and depends on each doctor’s professional views.

Second trimester treatment options for threatened abortion (weeks 13 to 27)

A (threatened) miscarriage, by definition, can only happen within the first 20 weeks of pregnancy. After this period, it will be called preterm labor. However, most medications that work for preventing a threatened miscarriage during the first part of the second trimester will also work for preventing preterm labor later on.

The second trimester is a somewhat safer time to receive medical treatment, since organogenesis, the most sensitive part of development in the embryo, is now complete.

Metamizole (dipyrone) is used in certain countries (sometimes in combination with other medications) to reduce uterine contractions and lessen the pain sometimes associated with the bleeding. Metamizole is a painkiller, antispasmodic and fever reliever, with anti-inflammatory properties. It is not recommended during the third trimester, but it is considered generally safe when taken before 25 weeks of pregnancy. Mode of administration is usually oral or injectable (intramuscular). 

Diazepam is a less popular choice now than it was a couple of decades ago, but in some countries it is still viewed as an efficient aid in stopping a threatened miscarriage during the second trimester. Diazepam is a benzodiazepine with tocolytic features, inhibiting uterine contractions by acting as an alpha1 adrenergic antagonist. Usually delivered at low doses by intravenous drip or by intramuscular injection, it can also be taken orally and has proven a potent uterine muscle relaxant. Because of its sedative properties however, Diazepam is often frowned upon as a solution during pregnancy and it is only used during the second trimester, in certain parts of the world (such as Europe and Asia). This medication should not be taken during the first or third trimester, unless your doctor recommends it. Trade names include Valium, Vazepam.

Beta2 adrenergic agonists are typically a popular choice worldwide for treatment of both threatened miscarriage and preterm labor. They are vasodilators and uterine muscle relaxants that suppress uterine contractions very efficiently, however they are not as effective before at least 17-18 weeks of pregnancy, so they are a better choice for the second half of the second trimester (and until term). Medications in this category include: terbutaline, hexoprenaline, ritodrine, salbutamol/albuterol, etc. and are usually administered by intravenous drip in a hospital setting and sometimes as oral tablets. Side effects include headaches and an increased heart rate.

Nifedipine is a calcium channel blocker typically used to treat high blood pressure. It is also very efficient at suppressing uterine contractions, which is why some doctors use it to prevent a premature birth. Nifedipine is both available as oral tablets and injection. Its most frequent side-effect is an increased heart rate.

Atosiban is an oxytocin receptor agonist which acts as a successful tocolytic (inhibits uterine contractions). It is typically given intravenously to prevent a threatened miscarriage and stop premature labor, in a hospital setting.

Nitroglycerine is a vasodilator commonly used for treating heart conditions. It can also be used as a local transdermal patch, to relax the uterus and improve blood flow to the pregnancy.

Magnesium sulphate used to be a more popular choice for treating a threatened miscarriage, as well as premature labor, however its use is now reduced to just a few countries. Due to its risks to both the mother and the baby and the lack of sufficient evidence supporting its efficiency, it is usually replaced by other therapeutic options nowadays.

Possible Complications

A threatened miscarriage can sometimes bring on additional complications. 

The most common complication are subchorionic hematomas, which are blood clots or blood collections that form between the uterine wall and the gestational membranes of the pregnancy. They are a rather common finding on first and second trimester ultrasound, but it does suggest a bleeding from behind the placenta so they need to be monitored carefully. When a retroplacental hematoma forms right behind the placenta, it could cause a placental abruption (which is when a part of the placenta detaches from the uterus). This is a serious complication that needs medical attention.

Ultrasound shows a large subchorionic hematoma (SCH) next to the gestational sac

Ultrasound shows a large subchorionic hematoma (SCH) next to the gestational sac

In around half of the cases of threatened miscarriage, the bleeding and cramping unfortunately progress to a complete or partial miscarriage. This is more often the case in the first trimester, if the pregnancy has stopped developing and the embryo presents with no heartbeat on the ultrasound.

Occasionally during the second or third trimester, prolonged bleeding, uterine contractions or a local infection causing the threatened miscarriage might lead to PPROM (preterm premature rupture of membranes). This is when the ‘water’ breaks much too early in the pregnancy. The rupture of membranes may or may not be followed by a miscarriage or premature delivery. If the pregnancy remains in the uterus and no infection complicates it, there might still be hope for its continuation, even when the PPROM happens before the pregnancy is viable (before 24 weeks).

Other conditions sometimes associated with a threatened miscarriage are premature birth, intrauterine growth restriction of the fetus and low birth weight.

Natural remedies for Threatened Miscarriage

Although it’s not recommended by all fertility specialists, bed rest can be helpful in some cases. There are women (including myself) who have spend the majority of their pregnancies in full bed rest, at home or in the hospital. So if you are dealing with vaginal bleeding and cramping during pregnancy and bed rest seems to help, listen to what your body is telling you and lie down for as long as you need. Physical activity can stimulate the muscles in the whole body and therefore increase uterine cramping and contractions as well. Also, standing or sitting can further increase the pressure on the cervix.

  • Increase your daily water intake. More water in the blood will help dilute the hormones that sustain uterine contractions, such as oxytocin. Reversely, dehydration can increase oxytocin concentrations in the blood and trigger more contractions.

  • You may benefit from over-the-counter Magnesium supplements, since Magnesium is a natural muscle relaxant. In one study, expecting women who took Magnesium supplements had overall fewer pregnancy complications. Many forms of supplements are available, which include Magnesium citrate, Magnesium malate and Magnesium gluconate. Magnesium oxide, despite being the most popular form, is very poorly absorbed. 

  • Prenatal multivitamin supplements were found to reduce the number of early and late miscarriages in certain medical studies. In these studies, multivitamins were statistically more efficient at lowering miscarriage rate than any isolated vitamin supplement.

  • More recent medical research has pointed to a link between low blood Vitamin D levels and first trimester miscarriage risk. A Vitamin D supplement could help prevent or at least lower the risk of pregnancy loss.