What is a premature birth?
On average, a pregnancy lasts 40-weeks. A preterm or premature birth is a birth that occurs more than three weeks before the estimated due date.
That is, it occurs before the start of the 37th week of pregnancy.
When a premature birth occurs without medical interventions it’s known as spontaneous premature birth. Sometimes, a provider may need to induce birth before a mother’s due date if the pregnancy is causing health complications. For example, preeclampsia, a pregnancy complication characterized by high blood pressure and organ damage .
In 2019, the total rate of premature birth in the US was 10.23% . This rate varies when looking at specific races, being the highest for Black women (14.39%) and the lowest for Asian women (8.72%).
What causes a premature birth?
Most premature births occur spontaneously. The exact cause is often unclear .
But there are some things that may increase your risk of going into labor before your due date. This includes:
- Carrying twins, triplets, or other multiples
- A history of premature birth
- Getting pregnant through in vitro fertilization (IVF)
- Physical trauma and stressful life events
- Chronic conditions like diabetes, obesity, high blood pressure , 
Another known risk factor for premature birth are sexually transmitted infections (STIs).
For example, a vaginal infection with Trichomonas vaginalis bacteria during pregnancy increases the risk of premature birth. What’s more, babies born to infected mothers are more likely to have low birth weight .
Other STIs that increase the risk of premature birth include:
- Gonorrhea, an infection caused by Neisseria gonorrhoeae bacteria. This STI has been associated with premature birth, premature water breaking, low birth weight, and other pregnancy complications , .
- Chlamydia, caused by Chlamydia trachomatis bacteria. Untreated, this infection during pregnancy has been associated with premature birth –.
- Syphilis. Depending on how long a pregnant woman has had syphilis (an infection caused by Treponema pallidum subsp. pallidum bacteria), she may have an increased risk of premature birth. Syphilis can also lead to other serious consequences for a mother’s baby , .
And still, sometimes early labor and delivery happens without any risk factors involved.
Premature birth symptoms
There are certain symptoms that may indicate premature labor:
- Regular contractions
- A constant and dull backache
- Mild abdominal cramps
- A sensation of pelvic or lower abdominal pressure
- Vaginal spotting or light bleeding
- Water breaking
- Changes in vaginal discharge 
If you are far from your due date and suspect you have premature birth symptoms, contact your provider right away.
It could be a false alarm, but it’s always better to ask. Your provider may run a series of tests including a pelvic exam, an ultrasound, uterine monitoring, and other lab tests to identify if you’re in preterm labor.
Premature birth and its associated complications for mom and baby
Unfortunately, premature birth can mean a variety of short and long-term health complications for your baby.
After birth, there may be problems with breathing, heart or brain function, temperature regulation, blood disorders like anemia or jaundice, gastrointestinal function, metabolism, or issues involving your baby’s immune system.
Over time, babies born prematurely have an increased risk for sudden infant death syndrome (SIDS), cerebral palsy, developmental disabilities, issues with vision and hearing, and dental problems .
One study found that premature babies have a slightly higher risk of developing type 1 diabetes in the future .
Moms that experience preterm labor are also superheroes - and this takes its toll.
A premature birth is hard on the whole family and it’s been found that mothers are more likely to experience issues like anxiety, postpartum depression, post-traumatic stress disorder, and problems connecting with their baby .
How a healthy vaginal microbiome protects against premature birth
At this point, we know that bacteria that cause STIs can increase the risk of premature birth. But what about other bacteria, like those that can cause bacterial vaginosis?
Scientists have tried to identify if certain bacterial species of the vaginal microbiome, often associated with dysbiosis, can directly increase the risk of premature birth.
Some bacteria that have been associated with premature birth are Sneathia sanguinegens, Megasphaera, and Gardnerella , . But, some studies haven’t found such direct associations –.
Looking at all the studies performed up to this day, there are two main things we can conclude:
- High levels of Lactobacillus species (except for L. iners) have a protective effect and reduce the risk of premature birth. This is great!
- On the other hand, women with lower levels of non-iners Lactobacillus species or with a Community State Type (CST) 4 are at higher risk of premature labor , , –.
For example, one study found that pregnant women with CST 4 were roughly 7 - 8 times more likely to give birth prematurely compared to women with a non-iners Lactobacillus-dominated vaginal community . Another study found that pregnant women with CST 4 were over 3 more likely to have recurrent spontaneous premature birth than women with a Lactobacillus-dominated vaginal community .
About one third of preterm births happen after the preterm pre-labor rupture of membranes (PPROM), also known as water breaking. This gives an opportunity for microbes in the vagina to go up into the amniotic sac, where they may cause infection.
What’s noteworthy here is that scientists have found that a high number of women who experience water breaking also have a vaginal microbiome with low or moderate numbers of Lactobacillus.
Remember, Lactobacillus are friendly and keep the vaginal microbiome healthy.
For example, the risk of water breaking among pregnant women with a vaginal community with less than 75% Lactobacillus was 2.34-2.54 times higher than the risk for women with a Lactobacillus-dominated vaginal community , .
But why do low levels of Lactobacillus increase the risk of premature birth? Scientists have just begun to unravel this.
A study found that compared to women who delivered at term, women who delivered preterm had low levels of non-iners Lactobacillus and this correlated with higher levels of certain immune molecules that recognize and bind microbes. This led to increased levels of inflammation .
So the proposed mechanism is that a vaginal microbiome low in non-iners Lactobacillus can’t properly contain an inflammatory response.
The microbes that live in your mouth may also have something to do with preterm birth
Pregnant women are more prone to suffer from periodontal disease. Scientists have two theories on how this may be connected to premature labor:
- The microbes that cause periodontitis may travel through the bloodstream into the placenta and cause infection that leads to premature birth.
- Pro-inflammatory molecules produced in the mouth can go into the bloodstream and into the placenta, causing inflammation that leads to premature birth.
One study found that the risk of spontaneous premature birth in pregnant women with moderate to severe periodontitis was twice the risk of spontaneous premature birth among healthy pregnant women .
Then comes the obvious question: Does treating periodontitis decrease the risk of premature birth?
Well, scientists are not convinced.
One study found that pregnant women who didn’t receive periodontal treatment during pregnancy were 13.5 times more likely to have premature birth than women that received the treatment . That’s a pretty high risk, right?
However, a major pitfall of that study was not accounting for other variables that may have influenced the risk. That is, confounding factors. Besides, other studies have found that the risk of premature birth doesn’t decrease when periodontal disease is treated –.
Clearly more studies are needed on this matter.
The gut microbiome and premature birth
The connection between the gut microbiome and premature birth is a recent area of research. Just a few studies have looked at the possible associations.
Related to the possible role of oral microbes in premature birth, a small study found that women who had premature labor had increased numbers of oral bacteria in the gut, like Streptococcus, Porphyromonas, and Prevotella . Another study found that women who had premature labor had lower numbers of Clostridium and Bacteroides species, which are common gut bacteria .
5 tips to protect against premature birth
Although the cause of premature birth is often unknown and there are many factors involved, there are some things that may help reduce the risk.
- Consider taking folic acid while trying to conceive. If you aren't pregnant yet but plan to be soon, the intake of folic acid several months before conception may help reduce the risk of premature birth. Studies have reported a risk reduction of 8-14% –.
- Make sure you are taking adequate amounts of calcium during pregnancy. Getting enough calcium during pregnancy can help to reduce the risk of premature birth –. This may come from diet and/or supplements, so it’s a good idea to check whether you are receiving enough calcium with your provider.
- Check your vaginal microbiome. Several studies show that women with a CST 4 or bacterial vaginosis have a higher rate of premature birth , –. Unfortunately, there are no well-designed clinical trials evaluating if a shift in vaginal microbial composition reduces the risk of preterm labor. Some clinical trials have looked at the effect of treating bacterial vaginosis with antibiotics, and have found no reduction in the risk –.
- Wash only with water. One study found that women who used a vaginal gel before or during pregnancy had 2.3-3.4 times higher risk of premature birth . Here are some tips for vaginal health that will help you take good care of your vaginal microbiome.
- Probiotics may help delay birth after water breaking. If water breaks before week 34, birth may need to be delayed. This is accomplished by corticoid and antibiotic treatment. Two studies found that women who also received vaginal probiotics (inserted in the vagina) had a larger latency period, which resulted in increased gestational age at birth , . A third study didn’t find that probiotics had any effects in gestational age, but the babies from moms who received probiotics had better health outcomes than those from moms who only received conventional treatment . Despite these encouraging results, research on vaginal probiotics and premature birth is still in progress. Not all vaginal probiotics may have the same effect as those that were studied, and right now we can’t recommend one for this particular situation. If you find yourself in this scenario, always ask your provider before using any vaginal probiotics.
Want to know what your vaginal microbiome looks like? Our Tiny Health vaginal test can give you the full picture.