What is Preterm Labor?
Preterm labor refers to childbirth that happens between the 20th and nearly the 37th week of pregnancy. This situation can be further divided into two categories: Early preterm is when the baby is born before the 33rd week, and late preterm is when the baby is born between the 34th and 36th weeks of pregnancy.
What Causes Preterm Labor?
Preterm labor, or giving birth before 37 weeks of pregnancy, can be caused by a variety of factors. These include stress, infections, complications with the placenta (like placental abruption or placenta previa), substance use, a prior preterm birth or abortion, insufficient prenatal care, smoking, maternal age under 18 or over 40, poor nutrition, low body weight, abnormalities in the baby’s development, restricted or excessive growth of the baby, low or excessive amniotic fluid, vaginal bleeding, premature rupture of membranes, and environmental factors. This is not an exhaustive list, but it does cover the most common reasons people might experience preterm labor.
One condition to be aware of is the premature preterm rupture of membranes (PPROM), which is when the water breaks before 37 weeks of pregnancy. This affects about 3% of all pregnancies in the United States. Such ruptures can be normal or problematic. Infections within the amniotic sac contribute the most to PPROM, especially earlier in the pregnancy. Other causes include a short cervix, bleeding in the second or third trimester, low body weight, low socioeconomic status, and the use of cigarettes or illegal drugs. Once the water breaks, about half of people with PPROM give birth within a week.
PPROM’s main risk is prematurity. The most common problem early birth can cause is respiratory distress, or difficulty breathing, in the newborn. Other risks include sepsis (a severe infection), intraventricular hemorrhage (bleeding in the brain), and necrotizing enterocolitis (serious intestinal damage). If PPROM leads to inflammation within the uterus, it can cause neurodevelopmental impairment, or harm to the baby’s brain development, and if the water breaks early in the pregnancy, it increases the risk of damage to the baby’s white brain matter. There’s also a 1-2% chance that the baby could die before birth from an infection or problems with the umbilical cord after PPROM.
Risk Factors and Frequency for Preterm Labor
In 2005, the World Health Organization reported that preterm births made up nearly 9.5% of all the births around the world. This translates to nearly 13 million babies born prematurely. In the United States, as of 2013, the rate of preterm births was about 11.4%. The highest rate of preterm births was recorded in 2006 at 12.8%, partly because of earlier dating of pregnancy through ultrasound, the use of assistive reproductive technologies, and induced preterm labor. Since then, the rate has dipped due to improved fertility practices. The prevalence of preterm labor varies from state to state in the U.S., with African Americans having almost double the rate compared to other racial and ethnic groups.
Signs and Symptoms of Preterm Labor
Preterm labor, referring to labor that occurs before the full term of pregnancy, is typically identified through a combination of patient history, symptoms, and physical examinations. Information about any past or present pregnancy-related issues is particularly useful. If there isn’t an early gestational age ultrasound available, a fetal biometry – a type of ultrasound that measures the size of the fetus – can be performed.
Other important aspects to check in a pregnant woman suspected of preterm labor include maternal vital signs such as blood pressure, heart rate and body temperature, the fetal heart rate and the pattern, duration and intensity of uterine contractions.
A physical evaluation is also carried out to assess the firmness of the abdomen, any discomfort in the abdominal area, and the size and position of the fetus. An examination of the cervix can reveal cervix dilation and thinning. Signs and symptoms of preterm labor include:
- Regular contractions before full-term pregnancy, accompanied by changes in the cervix
- Feeling of pelvic pressure
- Cramps similar to menstrual cramps
- A watery vaginal discharge
- Lower back pain (although this can also be normal in pregnancy, if it happens before full term, it could be a sign of imminent preterm labor)
If a pregnant woman’s cervix has opened (dilated) at least 2 or 3 cm before 34 weeks of pregnancy, it is highly likely that she will give birth prematurely. Another sign of preterm labor is a ‘short cervix’, which can be evaluated using a transvaginal ultrasound. Generally, a normal cervix length is between 35-48 mm. If the cervical length is less than 25mm between the 16th and 24th weeks of pregnancy, this is considered a ‘short cervix’. Importantly, a transvaginal ultrasound can help differentiate between a thinning cervix due to cervical insufficiency and active labor.
Testing for Preterm Labor
When a doctor suspects that a patient might have preterm premature rupture of membranes (PPROM), which is a condition in which the amniotic sac that holds the baby breaks before the baby is ready to be born, several checks are done. One of these is a speculum examination. This involves the doctor using a device that allows them to see inside the vagina, where they can check if any fluid is coming out of the cervix and pooling in the vagina.
Afterward, the doctor may run two tests on the fluid: the fern test and pH test. The fern test checks if the fluid forms a fern-like pattern when it dries, which is a sign of amniotic fluid. The pH test checks the acidity of the fluid; amniotic fluid usually has a pH between 7.1 and 7.3, which is less acidic than typical vaginal secretions.
Sometimes, a protein called fetal fibronectin is released when the substance that holds together the tissues of the cervix begins to break down. The presence of this protein can also indicate preterm labor. However, while a negative result is normally a good sign that the membrane hasn’t ruptured, a positive result doesn’t always mean that it has.
In addition to these tests, lab work can help figure out what’s causing the preterm labor and guide treatment. This could include a test for group B streptococcus, a type of bacteria, in the rectum and vagina. If this hasn’t been done in the past five weeks, then antibiotics may be needed to prevent the infection from spreading to the baby. A urine culture may also be done, since silent (asymptomatic) urinary tract infections have been linked to a higher risk of preterm labor and birth.
In patients who use drugs, a urine drug screen may be done. This is because using certain drugs, like cocaine, can lead to problems with the placenta that can cause preterm labor. Finally, if a woman is less than 34 weeks into her pregnancy, the opening of her cervix is less than 3 cm wide, and her cervix is only 20-30 mm long when checked with a transvaginal ultrasound, a fetal fibronectin test might be done. Tests for sexually transmitted infections may also be run, as they can sometimes contribute to preterm labor.
Treatment Options for Preterm Labor
When a mother comes to the hospital earlier than 34 weeks into her pregnancy with signs of early labor, severity dictates the process. Mothers who are showing less severe signs are often allowed to go home after 4-6 hours of observation and given instructions on when to return. Any indications of complications or worsening labor will result in more immediate care.
Mothers presenting at the hospital before 34 weeks into their pregnancy with clear signs of early labor are admitted for treatment. Medications designed to stop or slow down labor, called tocolytics, are given to these mothers to buy more time for baby’s development. These are typically considered for use between weeks 22 and 34 of pregnancy, as long as there are no other health reasons that would make their usage unsafe.
The tocolytics used include a variety of drugs each doing the job slightly differently:
– Calcium channel blockers like Nifedipine prevent contractions by helping to keep calcium out of muscle cells in the uterus.
– Beta-2 agonist drugs, like terbutaline, help to relax the muscles of the uterus.
– COX inhibitors, like indomethacin, which reduce the production of hormones that trigger uterine contractions.
– Certain other weaker drugs are used in specific situations to slow down contractions.
When a mother’s amniotic sac breaks (her water breaks) early, the pregnancy generally can’t continue for much longer. But doctors can still take steps to reduce risks to the baby. This can involve sending the mother to a hospital with advanced resources, giving the mother antibiotics and steroids to protect both mother and baby, and using magnesium sulfate to protect the baby’s brain if labor is happening before 32 weeks.
Sometimes, despite taking drugs to slow down labor, contractions may still continue. In these cases, doctors will reevaluate the mother for any signs of infection or other changes.
In some cases, inducing early labor may be necessary. This happens in serious situations like infections, lack of amniotic fluid, high blood pressure conditions like preeclampsia, or if the baby isn’t growing properly. In these cases, just like with full-term babies, doctors will keep a constant eye on the baby’s heart rate and other vital signs.
Finally, it’s good to know that delayed cord clamping (waiting longer to cut the umbilical cord) can be beneficial for babies born early. This can lead to better blood counts, higher blood pressure, and less need for resuscitation amongst other benefits.
What else can Preterm Labor be?
These are some conditions related to pregnancy that may need medical attention:
- Abruptio placentae (when the placenta peels away from the inner wall of the uterus before delivery)
- Fetal growth restriction (when a baby doesn’t grow at a normal rate inside the womb)
- Multifetal pregnancy (having more than one baby at a time, such as twins or triplets)
- Preeclampsia (a pregnancy complication characterised by high blood pressure and signs of damage to liver or kidneys)
- Premature rupture of membranes (early breaking of the amniotic sac)
- Preterm labor (labor that begins before 37th week of pregnancy)
Possible Complications When Diagnosed with Preterm Labor
Mothers who have experienced preterm labor are at a higher risk of heart disease and conditions that affect the heart’s function. The reasons for this increased risk are not fully understood and usually appear years after the child is born.
Furthermore, infants born prematurely may face several developmental issues. These include problems with cognitive abilities like thinking and learning, issues with motor skills, and conditions like cerebral palsy, and vision and hearing loss. The likelihood of these problems rises the earlier the baby is born. Additionally, behavioral concerns like anxiety, depression, autism spectrum disorders, and ADHD have been linked to babies born prematurely.
In terms of newborn complications, preterm birth could result in a variety of health problems. These might involve a severe intestinal disease called necrotizing enterocolitis, bleeding inside the brain, a lung condition named bronchopulmonary dysplasia, an eye condition affecting premature babies known as retinopathy of immaturity, slow growth, and the presence of birth defects.
Despite these concerns, there is good news. Thanks to advancements in medical care for pregnant women and newborns, the rate of complications in preterm births has gone down. Plus, through personalized education and consistent follow-up, the long term consequences and disabilities caused by preterm births have significantly improved.
Complications:
- Mother: Higher risk of heart disease
- Infant: Developmental and behavioral issues
- Newborn: variety of health problems, including intestinal diseases, brain bleeding, and eye conditions affecting premature babies
- With ongoing medical advances, the rate of these complications is decreasing
