A normal pregnancy lasts 37 to 42 weeks, calculated from the first day of the last menstrual cycle. Premature birth is defined as labor starting before 37 weeks, but after 20 weeks of gestation. Most premature births are triggered spontaneously. However, 1 of 4 premature births are induced by the physician, due to complications caused by pregnancy, such as preeclampsia or placental abruption or abruptio placentae (premature detachment of the placenta). These are absolute indications for labor onset. Triggered birth before 20 weeks of gestation, is called miscarriage.
Premature Labor Causes
Premature birth can be caused by fetus, mother or both mother and fetus problems. Most of the times premature labor is determined by a combination of several factors and in about 25-30% of cases no specific cause can be identified.
The causes of premature labour include:
- A history of multiple births is the cause of approximately 30% of premature labors:
- Twin pregnancies are generally at high risk for complications, both maternal and fetal – usually born after a premature labor
- Infections can trigger premature labor or premature rupture of membranes
- Placental abruption, premature separation of placenta from uterus
- Drugs, like cocaine or methamphetamine
- Uterus or cervix problems such as a short cervix, uterine fibroids or an abnormally shaped uterus.
- Some pregnancy complications endanger the mother and fetus, so it is necessary to trigger premature labor. These are indications for induction of premature birth and represent 15% to 20% of all preterm births. Whenever possible, in these cases, drugs will be used to trigger the natural birth. However, there are situations where natural childbirth is contraindicated, so Caesarean section remains the only option.
Premature Labor Symptoms
Premature labor is most common triggered without obvious symptoms. However, one or more of the following premature labor symptoms:
- Cramps like those during the menses, with or without diarrhea
- Feeling of pressure in the pelvis and lower abdomen
- Persistent pain in the back, pelvis, lower abdomen or thighs
- Changes in vaginal discharge, which may increase in volume or become pink or red
- Contractions are persistent, regular, 4 in 20 minutes or 8 per hour, these contractions may be painless, but make the abdomen firm to palpation.
- Uterus sensitivity
It is sometimes difficult to distinguish between Braxton – Hicks contractions and premature labor. These symptoms are not always equivalent with the onset of premature labor. However, if you notice any of these symptoms you should address your gynecologist.
Premature Labor Causes And Risk Factors
It is difficult to predict if a pregnant woman is at risk of premature birth. While in some women with risk factors for premature labor, pregnancy ends normally, others without premature labor risk factors give birth prematurely. In all pregnancy cases with premature labor (before 37 weeks and without membranes ruptured spontaneously), half will be born at term.
Labor and premature birth
In some cases, medical intervention is needed to induce birth as the mother and child are in danger. Premature birth is most likely triggered by a combination of risk factors. The most common causes and risk factors premature labor are listed below:
- Pregnancies with twins, triplets or more fetuses, (use of assisted reproductive techniques or superovulation increases the risk of multiple pregnancies and premature labor implicitly)
- History of premature labor
- Vaginal bleeding in the second trimester
- Urinary tract infections or sexually transmitted diseases
- Age under 18
- Low-weight or height of the mother
- Smoking during pregnancy
- Frequent contractions.
Other factors that increase the risk of premature labor are:
- Cocaine or methamphetamine
- Excess amniotic fluid (polyhydramnios)
- A significantly shortened cervix, viewed during ultrasonography exam.
Less common premature labor risk factors are:
- Unclosed cervix (incompetent cervix)
- History of two or more abortions on demand in history, the risk increases with each additional abortion
- New pregnancy – 3 months after birth
- Uterus disorders, such as an abnormally shaped uterus (the presence of twins can break the uterus and the amniotic sac)
- Previous surgery on the cervix, cervical conization
- Exposure to DES (diethylstilbestrol – U.S. drug used in the ’40s until the ’70s to treat impending abortion)
- Insufficient weight gain during pregnancy
- Jobs physically or mentally exhausting , for example a job that requires standing for long periods of time (in factories, sales or nursing)
- Consumption of large amounts of licorice, more than 230 g of licorice per week may increase the risk for premature labor
- Severe emotional stress during pregnancy
- Unbalanced diet.
Triggering premature labor when needed
Approximately 1 in 4 births are induced early by doctors due to different complications. These are called pregnancies with indication for premature labor.
- Fetal suffering
- Insufficient growth of the fetus, threatening its survival
- Placental abruption (premature separation of the placenta from the uterine wall).