Preterm Labor: Signs, Causes, and How It's Managed

In short: Preterm labour is regular contractions that open the cervix before 37 completed weeks of pregnancy. Risk factors include a previous preterm birth, twins, smoking, urinary infections and abnormal weight. Signs include low back pain, cramps, pressure in the pelvis, a change in discharge and leaking fluid. Prevention includes measuring the length of the cervix and progesterone, and steroids are given to mature the baby’s lungs.

What is preterm labor?

Preterm labor happens when the uterus begins having regular contractions that cause the cervix to change — including effacement (thinning) and dilation (opening) — before 37 weeks of pregnancy. If you notice these signs, it’s important to contact your doctor promptly so your pregnancy can be assessed.

What is preterm birth?

Preterm birth refers to a baby being born between 20 and 37 weeks of pregnancy.

What is premature rupture of membranes?

• Rupture of membranes (PROM) that occur at term before onset of delivery
• Preterm PROM if occur less than 37 weeks
• Prolonged preterm PROM before viability (at < 24 wk)
• The interval between PROM and onset of spontaneous labor (latent period) and delivery varies inversely with gestational age.
• At term, more than 90% of women with PROM labor starts within 24 hours
• At 32 to 34 wk, mean latency period around 4 days.

Risk factors, which increase the incidence of preterm labor

• Infection
• Smoking or substance abuse during pregnancy
• History of PROM or preterm delivery in previous pregnancies
• Polyhydramnios: large volume of amniotic fluid
• Multiple gestation: being pregnant with two or more fetuses at one time
• Having had episodes of bleeding anytime during the pregnancy
• Amniocentesis
• Cervical incompetence: having a short or prematurely dilated cervix during pregnancy

Mechanism of rupture of membranes

Intrauterine infection is thought to be one cause of preterm premature rupture of the membranes (PPROM).

A prospective study of the vaginal flora in pregnancy shows that the presence of these vaginal floras increases the risk of premature rupture of membranes:

• Trichomonas vaginalis
• Bacteroides sp
• Ureaplasma urealyticum

What are the signs and symptoms of preterm labor?

• Change in character of vaginal discharge (watery, mucus, or bloody)
• Increase in amount of discharge
• Pelvic or lower abdominal pressure
• Constant low, dull backache
• Abdominal cramps, with or without diarrhea
• Regular or frequent contractions or uterine tightening

Rupture of membranes and leakage of liquor

Diagnosis of premature rupture of membranes

• History: sudden gush of fluid or continued leakage of fluid
• Physical exam: check pooling of amniotic fluid
• Sterile speculum exam: The presence of amniotic fluid pooling in the posterior fornix of the vagina
• Dilatation of cervix
• If no fluid is seen on speculum examination, a bedside test that detects amniotic fluid proteins (IGFBP-1 or PAMG-1, e.g. AmniSure) is recommended. Older tests such as nitrazine paper (amniotic fluid is alkaline, pH 7.0–7.5, and turns the paper dark blue) are less reliable, because blood, semen or infection can give false-positive results.
• Using slides looking for ferning
• Avoid digital exam unless presence of labor
• Endocervical samples may be considered for gonorrhea and chlamydia testing if clinically indicated. Group B streptococcus cultures are obtained.
• Ultrasound: amniotic fluid index

Complication of premature rupture of membranes

• Chorioamnionitis: may occur, it is a medical emergency. The mother will complain of fever, foul-smelling vaginal discharge, and abdominal pain.
• Abruption: premature separation of placenta
• Cord compression
• Preterm delivery & its complications
• Limb deformity and lung hypoplasia

Differential diagnosis of premature rupture of membranes

• Urinary incontinence.
• Normal vaginal secretions of pregnancy
• Increased sweat or moisture around the perineum
• Increased cervical discharge: this can happen when there is a genital tract infection
• Semen
• Douching
• Vesicovaginal fistula: an abnormal connection between the bladder and the vagina
• Loss of the mucus plug

Management of preterm labor

• The main goal is to safely delay delivery as long as possible without putting the mother or baby at risk.
• Use tocolytic if no contraindications
• Corticosteroid
• Magnesium sulfate
• In utero transfer to tertiary center

Prevention in high-risk women: those with a previous preterm birth or late miscarriage are offered cervical length scans, and if the cervix is short (25 mm or less), vaginal progesterone or a cervical stitch (cerclage) can reduce the risk of preterm birth

Management of premature rupture of membranes

Corticosteroid: * Betamethasone 12 mg, 24 hours apart, in 2 doses.

• Dexamethasone 6 mg, 12 hours apart, in 4 doses.

Antibiotic: All women with preterm rupture of membranes are given antibiotics (usually erythromycin 250 mg four times a day for 10 days, or until labor starts). This prolongs the pregnancy and reduces infection in the mother and the baby. Co-amoxiclav (Augmentin) is avoided because it has been linked to a serious bowel condition in premature babies (necrotizing enterocolitis).

Delivery

Tocolytics

Tocolytics are medications used to help calm and suppress uterine contractions. They work within hours and aim to delay birth for about 48 hours, which buys valuable time for corticosteroids to help mature the baby’s lungs, or to allow safe transfer to a hospital with a neonatal unit. The medicines most often used are nifedipine or atosiban. Both mother and baby are typically monitored closely during this time.

Contraindication to tocolytics

• Gestational age more than 34 weeks gestation
• Estimated fetal weight more than 2500 grams, or intrauterine growth restriction
• Placental insufficiency
• Lethal congenital or chromosomal abnormalities
• Advanced cervical changes, dilatation is greater than 4 centimeters
• Chorioamnionitis
• Mother has cardiac disease, pre-eclampsia
• Fetal distress or fetal death

What is magnesium sulfate?

Magnesium sulfate is a medication that is given when gestational age is less than 30 weeks, and may also be considered up to 33 weeks and 6 days, when the mother is in established preterm labor or delivery is planned within the next 24 hours.

It offers neuroprotection, helping reduce the risk of cerebral palsy associated with early preterm birth.

What are corticosteroids?

Betamethasone and dexamethasone are corticosteroids given before birth to help accelerate a preterm baby’s lung development. They are used when a mother is in preterm labor to help prevent respiratory distress syndrome (RDS) and other complications of premature birth.

Antenatal steroids can decrease rates of:

• Breathing problems (respiratory distress syndrome) after birth.
• Bleeding in the brain (intraventricular hemorrhage).
• Intestinal infection (necrotizing enterocolitis).
• Death.

Types of corticosteroids?

If there is a possibility of preterm delivery, two types of corticosteroids may be recommended to help your baby. Corticosteroids are given by injection into the muscle.

Betamethasone and dexamethasone help the fetal lungs produce surfactant, so babies are more able to breathe on their own — or need less treatment with surfactant — after birth.

Both dexamethasone and betamethasone are effective and are recommended by the World Health Organization; the choice depends on availability and local practice.

Treatment consists of 12 mg of betamethasone in 2 doses given 24 hours apart, or 6 mg of dexamethasone in 4 doses given 12 hours apart.

At what stage of pregnancy should corticosteroids be given?

A single course of corticosteroids is offered to women between 24 and 33 weeks and 6 days of gestation who are at risk of preterm birth, and may be considered from 22 weeks and up to 35 weeks and 6 days after discussion. For a planned caesarean section at 37 to 38 weeks and 6 days, corticosteroids are not given routinely; they may be discussed individually, as they slightly reduce breathing problems but can cause low blood sugar in the newborn and their long-term effects are uncertain. If delivery does not occur within 7 days of treatment, the injections are not repeated routinely, as multiple courses may affect the baby’s growth; a single repeat course may be considered if a high risk of preterm birth returns.

How long are they effective for?

Corticosteroids are most effective if the last dose is given between 24 hours and 1 week before delivery.

Corticosteroids can also help reduce the risk of neonatal death within the first 24 hours, so they may still be given close to delivery.

Side Effects of Corticosteroid

Corticosteroids can cause fluid retention and increased blood pressure, but these effects are usually short-term and less likely during such a brief course of treatment.

Blood sugar control may be more difficult in pregnant women with diabetes when corticosteroids are used. Your doctor may recommend an adjusted insulin dose during this time.

Who should be given corticosteroids in pregnancy?

• Premature labor
• Premature rupture of membranes
• Intrauterine growth restriction
• Antepartum hemorrhage

Caution should be taken when giving corticosteroid therapy to women with systemic infection, tuberculosis, or sepsis.

If you’re experiencing signs of preterm labor or have concerns about your pregnancy, Dr. Najeeb Layyous and his team are here to guide you through personalized monitoring and care. Please reach out to the clinic to discuss your situation.

Dr Najeeb Layyous F.R.C.O.G

Consultant Obstetrician, Gynecologist and Infertility Specialist