Preterm Labor
Preterm Birth:Definition. Labour which occur from viability of the fetus ( currently defined as 24 completed weeks of gestational age) until the completion of the 37th weeks of gestation.
Preterm birth is a major contributor to developmental delay, visual and hearing impairment, chronic lung disease, and cerebral palsy. More than 50% of these condition result from preterm births especially before 34 weeks' gestation.
Epidemiology. The incidence is between ( 6 - 10%). Recently, rates have increased slightly, largely caused by the increase in multifetal gestations. Complications from prematurity account for more than 70%of neonatal and infant deaths in infants without anomalies.
"Spontaneous" preterm birth. Seventy-five percent of preterm births occur spontaneously after preterm labor and premature rupture of membranes (PROM).
"Indicated" preterm birth. Twenty to thirty percent of all preterm births occur because of a medical or obstetric disorder that places the mother of fetus at significant risk for serious morbidity or mortality.
Neonatal morbidity and mortality increase as the gestational age at delivery decreases.
Risk Factors and causes for Preterm Delivery:
Sociodemographic factors.
Low socioeconomic status. Low income, low level of education, and poor nutrition are associated with preterm delivery.
Ethnicity. Contributes to the difference in the incidence.
Age. Maternal age of 18 years or less or of 40 years or more increases the risk of preterm delivery.
Previous premature birth. The risk in the subsequent pregnancy after one premature birth is 17 to 37%.
Strenuous work.
Tobacco smoking. Due to decrease anti-proteus activity (which is protective mechanism).
Cocaine use.
Complicated obstetric history. Women with one or more spontaneous second-trimester abortions have an increased risk of premature birth.
Acute emotional disturbances.
Low weight, small stature.
Coitus by increase risk of infection.
Maternal medical and obstetrical conditions.
Uterine conditions.
Mullerian malformations. Women with unicornuate or bicornuate uteri are at increased risk of preterm delivery.
Cervical incompetence. This painless cervical dilation in the second trimester is associated with pregnancy loss. It can be caused by trauma during an obstetric or gynecologic procedure, diethylstilbestrol exposure in utero, or unknown etiology. Congenital abnormalities of the uterus and cervix account for 1-3% of all causes of peterm labour.
Leiomayoma of the uterus.
Uterine overdistention.
Polyhydramnios (amniotic fluid index of more than 25 cm).
Multiple gestation. Twin intrauterine pregnancies have a preterm labor rate of approximately 40%. Triplet intrauterine has more incidence.
Obstetric conditions.
Preeclampsia-eclampsia.
Placenta abruption.
Placenta previa.
Fetal growth restriction.
Premature rupture of membranes.
3- Other maternal conditions. These disorders include chronic hypertension, diabetes mellitus type 1, renal disease, osteogenesis imperfecta, and collagen vascular disease, sickle cell disease, congenital heart disease and severe asthma
Infection. A correlation exists between individual infectious causes of preterm birth and low socioeconomic status. Significant maternal infections that may cause preterm labor and delivery include:
Chorioamnionitis: its the cause in 20-30 % of all cases of preterm labour. The mechanism is that the body react to bacterial invasion by production of intermediate substances e.g. interleukin I causing activation of PG production by decidua and amniotic membranes which initiate labour.
Pyelonephritis.
Pneumonia.Asymptomatic bacteriuria.
Bacterial vaginosis.
Sexually transmitted diseases (STDs) (ill-defined relationship with preterm labor).
Fetal causes: Neural tube defects, or error of metabolism.
Truama: External cephalic version or accidents.
Maternal and fetal consequences of preterm labour:
Maternal effect:Psychological trauma.
Postpartum endometritis.
Fetal effect:
Increase perinatal mortality.
Increase perinatal morbidity. Due to RDS, Intracranial haemorrhage, feeding problems, hypothermia, hyperbilirubinemia, infection, iron deficiency anaemia, hypoglycemia, hypocalcemia, long term disability.
Evaluation of Patients in Preterm Labor:
History. Symptoms of preterm labor include:Uterine cramping or contractions.
Rhythmic low back pain.
Pelvic pressure.
Increased vaginal discharge.
Vaginal bleeding (bloody show), which may result from cervical dilation.
Physical examination.
A sterile speculum examination is a significant part of the physical examination. The evaluation of fetal membrane status and presence of cervicovaginal infection is determined at this time. If vaginal bleeding is present, an ultrasound must be performed to rule out placenta previa before a digital examination is performed.
Endocervical samples are obtained for gonorrhea and Chlamydia testing.
Group B Streptococcus cultures are obtained.
Premature rupture of membranes (PROM) is ruled out by doing fern and Nitrazine tests.
If there is no evidence of PROM, a baseline digital cervical examination is performed, and follow-up examinations are done with continued uterine contractions.
A urine specimen is sent for culture.
Fetal heart rate and uterine activity monitoring are used to assess fetal well-being and patterns of uterine contraction. Uterine contractions without cervical change do not constitute preterm labor and may represent uterine irritability.
Intravenous normal saline infusion is started during the initial evaluation.
Parenteral fluids can treat dehydration, which is a cause of uterine irritability.
Diagnosis.
Regular uterine contractions associated with progressive cervical change (i.e., cervical dilation of 2 cm or more or cervical effacement of 80% or more) must be present.
The goal is early identification of pregnant women who develop preterm labor and are at risk for delivery. In women who present with the symptoms of preterm labor, there are certain techniques. Which are also used to reduce the overdiagnosis of preterm labor, these are:
Cervical length. This value can be measured accurately by a transvaginal ultrasound. A cervical length of less than 3 cm has a positive predictive value (30 to 50%).
Fetal fibronection. This extracellular matrix glycoprotein found in fetal membranes plays an active role in intercellular adhesion. Fibronection found in the cervicovaginal fluid in the late second and early third trimester has been associated with preterm birth.
Management of Preterm Labor:
Admission to hospital and Bed rest.
Tocolysis. Treatment with tocolytic medications may not reduce the rate of preterm birth, but it may delay delivery for 48 hours and reduce the associated complications. The time gained allows for transfer to a tertiary center or corticosteroid administration.
Magnesium sulfat, it delays delivery by at least 48 hours.
The mechanism of action is unclear. Acts by competitive inhibition of calcium at the motor end plate or the cell membrane, thereby decreasing calcium influx into the cell. It is cleared from the maternal circulation by the kidneys.
Administration involves infusing 2 to 4 g per hour to elevate serum levels to above the normal range. The loading dose is 4 to 6 g given over 30 minutes. Once contractions cease, the infusion is reduced to the lowest possible dose to maintain uterine quiescence.
Precautions:
Intravenous fluid is limited to 125 mL per hour, and fluid status is observed closely. An indwelling Foley catheter can be used to monitor urine output accurately.
Deep tendon reflexes and vital signs should be checked hourly.
A pulmonary examination should be performed every 2 to 4 hours.
If signs of magnesium toxicity occur, the infusion should be discontinued and calcium gluconate administered as needed.
Complications:
Nausea and vomiting.
Flushing and headache.
Muscle weakness.
Pulmonary edema.
Cardiopulmonary arrest.
Contraindications to magnesium therapy include renal failure, myasthenia gravis, and hypocalcemia.
β-Mimetics.
These agents stimulate β receptors, leading to smooth muscle relaxation and decreased uterine contractions.Ritodrine, but may cause maternal side effects.
Terbutaline is the other β-mimetic tocolytic agent, which may be given subcutaneously, parenterally, or orally.
Salbutamol ( ventoline) is the most widely use in Iraq
Administration in a dose of 2.5 mg in 500 ml dextrose solution, start with 6 drops / min. up to 60 drops /min. but if uterine activity cease before that or the pulse rate increase to 140/min. so no more increament in the dose. The treatment continue for up to 12 hours after stopping contractions then change it to 2 - 4 mg orally /6-8 hours
Side effects include tachycardia, palpitations, tremer hypotension, shortness of breath, pulmonary edema ( in twins, those received generous amount of IV fluid, chorioamnionitis, or using glucocorticoids ), hyperglycemia, hypokalemia, flushing and tachyphylaxis.
Contraindications: heart disease, hyperdynamic circulation ( hyperthyroidism, sickle cell disease ), uncontrolled insulin dependent diabetes mellitus, chorioamnionitis, eclampsia or severe PET, multiple pregnancy, severe obstetrical bleeding, severe anaemia.
Prostaglandines synthetase inhibitors: as Indomethacin. This nonsteroidal anti-inflammatory medication inhibits the synthesis of prostaglandins, which are involved in the biochemical process of labor.
Indomethacin, 50 to 100 mg, is initially given rectally. Remaining doses are given orally, 25 to 50 mg every 6 hours. This agent is usually given for no longer than 48 hours.
Maternal side effects include nausea, vomiting, and gastrointestinal bleeding.
A main neonatal side effect is constriction of the ductus arteriosus.
Such constriction in a fetus causes tricuspid regurgitation and eventual right heart failure. Ductal constriction is usually transient and responds to discontinuation of the drug.
Because of this significant side effect, indomethacin is uncommonly used as a tocolytic after 32 weeks' gestation.
Other significant neonatal complications include oligohydramnios, pulmonary hypertension, and (possibly) necrotizing enterocolitis.
Calcium channel blocker: as Nifedipine. This decreases smooth muscle contractions.
Nifedipine is administered orally, 10 to 20 mg every 8 hours.
Maternal side effects include a decrease in blood pressure and tachycardia.
Oxytocine agonist.
Diazoxide.
Ethyl alcohol.
Allow labor to continue in when we have the followings:
If establish labor ( fully effaced cervix and mor than 2 cm dilate
cervix because of high failure rate).
If gestational age more than 34 weeks ( in Iraq more than 36
weeks).
Preeclampsia-eclampsia.
Antepartum hemorrhage.
Maternal cardiac disease.
Chorioamnionitis.
Lethal fetal anomaly.
In utero fetal compromise.
Nonreassuring fetal heart rate.
Significant fetal growth restriction.
Refractory preterm labor. This condition is defined as persistent uterine contractions and cervical change despite maximal tocolytic therapy. Management may include amniocentesis, which can be performed to rule out an intra-amniotic infection.
A Gram stain is positive for intra-amniotic infection if bacteria are present.
A glucose level of less than 14 mg/dL may be a sign of intra-amniotic infection.
A positive amniotic fluid culture signals intra-amniotic infection.
Adjunctive therapy.
Corticosteroids.
Corticosteroids are given to women in preterm labor at 24 to 34 weeks' gestation with intact membranes. The dose 12 mg intramuscular / 24 hours for 2 doses.
This medication includes fetal lung maturity, and optimal benefit begins 24 hours after initiation of therapy. Corticosteroids accelerate pulmonary maturity by stimulating the synthesis and release of surfactant from type II pneumocytes.
Corticosteroids decrease mortality, respiratory distress syndrome, and intraventricular hemorrhage.
Side effects: increase risk of infection in PROM, makes diabetes mellitus control rather difficult, increase severity of hypertension and increase wound healing of caesarean section.
Antibiotics. These agents are given as prophylaxis for neonatal group B streptococcal infection.
Antibiotics are started on admission and continued if the group B Streptococcus culture is positive. Affected women are treated for 7 days and then retreated during labor and delivery if the latency period is longer than 7 days.
Antibiotics are discontinued if the group B Streptococcus culture is negative.
Fetal assessment.
Ultrasound.An ultrasound is performed on admission to assess the estimated fetal weight and fetal presentation.
The estimated fetal weight can indicate whether the fetal has grown appropriately.
The fetal presentation is important when making a delivery plan. A fetus in breech presentation usually requires a cesarean section.
Fetal well-being. The fetal heart rate testing should be reassuring before starting tocolytic therapy. If the fetal heart rate is a concern, a biophysical profile should be performed before starting tocolytic therapy.
Episiotomy is a must, forceps is needed and paediatrician must be available.
Prevention of preterm labour:
Recognition of signs of impending preterm labour.
Antibiotics for infection.
Treatment of medical problems.
Good management of multiple pregnancy
Cervical cerclage for indicated cases.
Treatment of polyhydraminous, uterine fibroid by myomectomy, and metroplasty for congenital abnormalities of the uterus.
Coitus abstinence for patient at risk.
Limitation of working activities.
Test for assessment for fetal lung maturity:
LS ratio ( lystheine/sphingomyline ratio) in amniotic fluid. Value ≥ 2.3 means mature lung.Phosphotidylglycerol ( PG) in amniotic fluid, this substance usually appear after 36 weeks.
Shake test
Foam stability index.