Preterm birth refers to delivery at 28 weeks of gestation but less than 37 weeks. Newborns born at this time are called premature babies. Developed countries such as the United States have defined the lower limit of premature birth as 24 or 20 weeks of gestation.
During premature delivery, patients will feel uterine contractions ("uterine contractions") such as lower abdomen swelling and pain, and some may have a small amount of vaginal bleeding or fluid flow out.
The earlier the premature baby is born, the lighter the weight, the more serious the immaturity of various organs, and the greater the chance of serious problems in their short-term and long-term health.
Epidemiology
Preterm birth is a common pregnancy complication. The worldwide incidence of premature birth is about 11%. Currently, the global premature birth rate is on the rise year by year.
According to data from the United States, about 5% of premature births occur at 20-28 weeks of gestation, 12% at 28-31 weeks of gestation, 13% at 32-33 weeks of gestation, and 70% at 34-36 weeks of gestation.
Disease type
Classification by gestational age
In order to facilitate the expression of the severity of preterm birth and compare the treatment characteristics of preterm infants at different gestational weeks, preterm birth is currently divided into early preterm birth and late preterm birth according to gestational age.
Early preterm birth: 28 weeks ≤ gestational age < 34 weeks.
Late preterm birth: 34 weeks ≤ gestational age < 37 weeks.
Classification according to etiology
Spontaneous premature birth
Refers to the natural occurrence of premature birth, which is divided into premature birth with intact membranes and premature rupture of membranes. Preterm birth with intact membranes is the most common type, accounting for about 45%.
Iatrogenic premature birth
Refers to the termination of pregnancy by induction of labor or cesarean section before the 37th week of pregnancy is not allowed due to maternal or fetal health reasons.
The etiology of premature birth is still not very clear, and it may be related to infection, decidual hemorrhage, excessive dilatation of the uterine cavity, and maternal-fetal stress response. History of premature birth, history of cervical surgery, multiple gestation, maternal age too old or too young are high risk factors for premature birth.
Basic cause
Infect
Including intrauterine infection, systemic or pelvic infection.
Multiple studies have demonstrated that infection is an important factor in preterm birth. Infection can activate a variety of inflammatory pathways, promote the release of inflammatory factors, increase the synthesis of prostaglandins and other substances in the body, and lead to premature delivery.
Intrauterine infection
Pathogens in the lower genital tract can ascend through the cervix, and the common cause is chorioamnionitis.
Systemic or pelvic infection
The pathogens of maternal systemic infection can invade the fetus through the placenta, or the pathogens of pelvic infection can enter the uterine cavity through the fallopian tubes.
Decidual hemorrhage
Studies have shown that premature birth is closely related to hemorrhage due to maternal decidual spiral artery injury.
Overdilation of the uterine cavity
The excessive expansion of the uterine cavity caused by multiple pregnancy, polyhydramnios, and other factors can cause excessive stretching of the myometrium, induce the production of inflammatory cytokines, prostaglandins, etc., induce uterine contractions and cause premature delivery.
Maternal fetal stress response
Excessive mental and psychological stress of pregnant women can prematurely ripen the cervix and induce uterine contractions through endocrine pathways, increasing the risk of spontaneous premature birth.
Predisposing factors
The following reasons may increase the risk of preterm birth.
History of late miscarriage and/or preterm birth
Pregnant women with a history of preterm birth have twice the risk of preterm birth when they are pregnant again, and the younger the gestational week of the previous preterm birth, the higher the risk of preterm birth again.
Reproductive tract infection
Vaginal infections such as bacterial vaginosis can increase the risk of preterm birth.
Abnormal placenta
These include placenta previa (where the placenta attaches to the lower portion of the uterus, even reaching or covering the internal os of the cervix) and placental abruption (where the placenta separates from the uterus prematurely).
Shortened cervix
Pregnant women with cervical length (CL) < 25 mm detected by vaginal ultrasonography in the second trimester have an increased risk of preterm birth.
history of cervical surgery
Such as cervical conization, ring electrode excision (LEEP) treatment, repeated induced abortion to dilate the cervix, etc., can increase the risk of preterm birth.
Abnormal uterus
Abnormal uterine development and cervical deformity increase the risk of preterm birth.
Pregnant women who are too young or too old
Pregnant women ≤17 years old or >35 years old.
short intervals between pregnancies
If the interval between 2 pregnancies is less than 24 months, the risk of preterm birth increases.
Excessive emaciation
Pregnant women whose body mass index is less than 19kg/m 2 , or whose pre-pregnancy weight is less than 50kg, have poor nutritional status and are prone to premature delivery.
Multiple pregnancy
The premature birth rate is nearly 50% for twins and as high as 90% for triplets.
Assisted reproductive technology
Pregnancy using assisted reproductive technology is at higher risk of preterm birth.
Abnormal amniotic fluid volume
Too much or too little amniotic fluid increases the risk of preterm birth.
Pregnancy Complications or Comorbidities
If complicated with severe preeclampsia, eclampsia, antepartum hemorrhage, intrahepatic cholestasis of pregnancy, gestational diabetes mellitus, thyroid disease, severe cardiopulmonary disease, acute infectious disease, etc., the risk of premature delivery increases.
Abnormal hobby
Pregnant women who smoke, drink alcohol, or use drugs during pregnancy have an increased risk of preterm birth.
Pregnant women may have a history of late miscarriage, premature delivery, and birth trauma. Uterine contractions may occur after 28 weeks to 37 weeks of pregnancy, and some patients may be accompanied by a small amount of vaginal bleeding or vaginal fluid.
Typical symptoms
Maternal symptoms
The uterus contracts and the abdomen feels tight. Irregular uterine contractions at the beginning can develop into regular uterine contractions later, with 4 or more uterine contractions every 20 minutes, or 8 or more uterine contractions within 60 minutes.
Light vaginal bleeding.
A watery discharge or gush of fluid (amniotic fluid) from the vagina due to rupture of the membranes of the preterm membranes.
Persistent low back pain.
Pregnant women with a history of premature birth or cervical surgery have regular contractions of the uterus before 28 to 37 weeks of pregnancy, and have a feeling of swelling in the lower abdomen or pelvis;
If there is fluid outflow or a large amount of vaginal discharge, you need to be alert to the possibility of rupture of the membranes;
The doctor will ask the patient's medical history, evaluate its risk factors, and make a diagnosis based on symptoms, signs, ultrasound examination, vaginal discharge examination, etc. Clinically, premature labor can be divided into two stages: threatened premature labor and premature labor, which can only be diagnosed when the following conditions are met:
Threatened premature labor: 28 weeks to less than 37 weeks of pregnancy, regular uterine contractions (4 or more times per 20 minutes or 8 or more times every 60 minutes), the cervix has not yet dilated, and the cervical length measured by transvaginal ultrasound is ≤25mm.
Premature labor: in accordance with the gestational age of premature birth, with the above-mentioned regular uterine contractions, accompanied by continuous shortening of the cervical canal (cervical canal regression ≥ 80%), and dilation of the cervix.
The doctor may ask the following questions to understand the medical history, and the mother or family members can prepare in advance:
when symptoms were first noticed;
Have you had contractions, and if so, how many times per hour;
Whether there is vaginal bleeding or discharge;
Whether you have had an infection during pregnancy and whether you have a fever;
Whether there has been a history of pregnancy, miscarriage, cervical or uterine surgery, etc. in the past;
Whether smoking, drinking.
Doctor's checkup
The doctor checks the firmness of the uterus, as well as the size and position of the fetus; checks to see if the amniotic fluid has broken and the cervix has begun to dilate.
Film degree exam
Transvaginal ultrasonography can measure the length of the cervix. Before 24 weeks of gestation, the cervical length is less than 25 mm, or the funnel formation of the internal os of the cervix is accompanied by shortening of the cervix, suggesting an increased risk of preterm birth. Especially the positive and negative predictive value of cervical length <15mm and >30mm is greater.
Ultrasound can also help examine the condition of the fetus or placenta, confirm fetal position, estimate fetal weight, and assess amniotic fluid volume.
Special inspection
Doctors may use electronic fetal heart rate monitoring to watch the duration and interval of contractions.
Differential diagnosis
This disease will have similarities with the physiological uterine contraction that occurs in the third trimester of pregnancy, and the doctor will conduct detailed examinations from multiple aspects to judge.
Physiological uterine contractions are generally irregular, painless, and not accompanied by changes such as shortening of the cervical canal and dilation of the cervix. The uterine contractions may disappear by walking, resting, or changing postures, which is also called false premature labor.
Really premature contractions will not disappear through the above behaviors, but will continue.
TreatmentIf the fetus is alive, there is no obvious deformity, no chorioamnionitis and fetal distress, no serious pregnancy complications and complications, the dilation of the cervix is less than 2cm, and the preterm birth prediction is positive, the doctor will try to prolong the gestational period to prevent premature delivery.
Treatment for preterm labor needs to be discontinued in due course in the following situations:
The pregnant woman's uterine contractions are constantly increasing and cannot be controlled after treatment;
Intrauterine infection;
The doctor weighs the pros and cons, and the harm to the mother and fetus of continuing pregnancy outweighs the benefits of fetal lung maturation to the fetus;
Pregnancy ≥ 34 weeks, if there are no maternal-fetal complications, the doctor will stop the tocolytic, and let it go, while monitoring the maternal-fetal situation.
The doctor will choose the appropriate delivery method for the mother according to the specific situation.
After the fetus is delivered, especially if the birth weight is less than 2000g, the doctor will put it in the incubator, and adjust the temperature and humidity of the incubator according to its gestational age, birth weight, postnatal age and condition to maintain a constant temperature. sexual temperature.
General treatment
Those with frequent uterine contractions but no changes in the cervix do not need to stay in bed or be hospitalized. It is enough to appropriately reduce the intensity of activities and avoid standing for a long time.
Threatened premature birth with shortened cervix can be hospitalized and pay attention to rest.
She was born prematurely and required hospital treatment and bed rest
Medical treatment
Due to large individual differences, there is no absolute best, fastest, or most effective medication. Except for commonly used over-the-counter drugs, you should choose the most appropriate drug based on your personal situation under the guidance of a doctor.
Patients can use the following drugs for treatment under the guidance of doctors.
If the fetus is alive, there is no obvious deformity, no chorioamnionitis and fetal distress, no serious pregnancy complications and complications, the dilation of the cervix is less than 2cm, and the preterm birth prediction is positive, the doctor will try to prolong the gestational period to prevent premature delivery.
Treatment for preterm labor needs to be discontinued in due course in the following situations:
The pregnant woman's uterine contractions are constantly increasing and cannot be controlled after treatment;
Intrauterine infection;
The doctor weighs the pros and cons, and the harm to the mother and fetus of continuing pregnancy outweighs the benefits of fetal lung maturation to the fetus;
Pregnancy ≥ 34 weeks, if there are no maternal-fetal complications, the doctor will stop the tocolytic, and let it go, while monitoring the maternal-fetal situation.
The doctor will choose the appropriate delivery method for the mother according to the specific situation.
After the fetus is delivered, especially if the birth weight is less than 2000g, the doctor will put it in the incubator, and adjust the temperature and humidity of the incubator according to its gestational age, birth weight, postnatal age and condition to maintain a constant temperature. sexual temperature.
General treatment
Those with frequent uterine contractions but no changes in the cervix do not need to stay in bed or be hospitalized. It is enough to appropriately reduce the intensity of activities and avoid standing for a long time.
Threatened premature birth with shortened cervix can be hospitalized and pay attention to rest.
She was born prematurely and required hospital treatment and bed rest
Medical treatment
Due to large individual differences, there is no absolute best, fastest, or most effective medication. Except for commonly used over-the-counter drugs, you should choose the most appropriate drug based on your personal situation under the guidance of a doctor.
Patients can use the following drugs for treatment under the guidance of doctors.
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