Preterm Labor and Delivery

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Definition

Preterm labor is the occurrence of uterine contractions that is enough in frequency and intensity to lead to the progressive effacement and dilation of the cervix before a pregnancy reaches term (that is between 28-37 weeks of gestation).

Decidual hemorrhage such as abruption
Mechanical factors such as uterine overdistention from multiple gestation or polyhydramnios
Cervical incompetence (e.g., trauma, cone biopsy)
Uterine distortion (e.g., müllerian duct abnormalities, fibroid uterus)
Cervical inflammation as a result of, for example, bacterial vaginosis (BV) or trichomonas
Maternal inflammation/fever (e.g., urinary tract infection)
Hormonal changes (e.g., mediated by maternal or fetal stress)
Uteroplacental insufficiency (e.g., hypertension, insulin-dependent diabetes, drug abuse, smoking, alcohol consumption)

History

Risk factors for preterm birth include:

Demographic characteristics
Behavioral factors
Past obstetric history such as previous preterm birth.

Demographic/Risk factors for preterm labor include:

Non-white race
Extremes of maternal age (< 17 y or >35 y)
Low socioeconomic status
Low pre-pregnancy weight.
Preterm labor and birth can be associated with stressful life situations (e.g., domestic violence; close family death; insecurity over food, home, or partner; work and home environment) either indirectly by associated risk behaviors or directly by mechanisms not completely understood.
Many risk factors may manifest in the same gravida.
The presence of asymptomatic bacteriuria.
Sexually transmitted disease (STD)
Symptomatic BV may be investigated

A genome-wide association study that included 43,568 European women identified six genes (BF1, EEFSEC, AGTR2, WNT4, ADCY5, and RAP2C) that were associated with gestational duration, of which, three genes were associated with preterm birth (EBF1, EEFSEC, and AGTR2).

Physical assessment

The integrity of the cervix and the extent of any prior injury to the cervix may be assessed by speculum and digital examination.

Cervical length

A short cervical length in the early or late second trimester has been associated with a markedly increased risk of preterm labor and delivery. In a study, a cervical length of 25 mm or less at 28 weeks had a 49% sensitivity for prediction of preterm delivery at less than 35 weeks.

Investigations

In patients with a history of mid-trimester loss, laboratory tests for risk assessment include the following:

Rapid plasma reagin test
Gonorrheal and chlamydial screening
Vaginal pH/wet smear/whiff test
Anticardiolipin antibody (e.g., anticardiolipin immunoglobulin [Ig] G and IgM, anti-beta2 microglobulin)
Lupus anticoagulant antibody
Activated partial thromboplastin time
One-hour glucose challenge test

In addition, one should consider TORCH (toxoplasmosis, other infections, rubella, cytomegalovirus infection, herpes simplex), immunoglobulin G, and immunoglobulin M screening whenever the historical or clinical suspicion is present.

Diagnosis

Contractions of sufficient frequency and intensity to effect progressive effacement and dilation of the cervix at 28-37 weeks’ gestation are indicative of active preterm labor.

If the diagnosis of preterm labor is suspected, but not confirmed, it may be prudent to first obtain a vaginal fetal fibronectin (FFN) sample before pelvic cervical examination.

If the diagnosis remains in doubt after the exam, the FFN specimen can be sent to the lab for analysis.

Prediction of Preterm Labor

Methods used for predicting preterm birth include:

Home uterine activity monitoring (HUAM)
Assessments of salivary estriol, fetal fibronectin (FFN),
The presence of BV,
Cervical length assessment.

Saliva Estriol is now being discarded because of diurnal variation and its suppression by Betamethasone.

Treatment

Goals of obstetric patient management of preterm labor should include:

Early identification of risk factors associated with preterm birth,
Timely diagnosis of preterm labor,
Identifying the etiology of preterm labor,
Evaluating fetal well-being,
Providing prophylactic pharmacologic therapy to prolong gestation and reduce the incidence of respiratory distress syndrome (RDS) and intra-amniotic infection (IAI),
Initiating tocolytic therapy when indicated,
Establishing a plan of maternal and fetal surveillance with patient/provider education to improve neonatal outcome.

Preconceptual evaluation

While the risk for preterm birth in nulliparous patients is hard to determine, past obstetric experience and personal behavior may provide significant insight into future pregnancy outcome in multiparous women.

Identifying at-risk patients pre-conceptually may allow additional treatment options.

Women who seek birth control have a 30% chance of becoming pregnant in the next 2 years, suggesting that these women represent one potential opportunity for intervention and the presence of any of the risk factors should be addressed prior to pregnancy.

Progesterone

Studies support the use of progesterone supplementation to reduce preterm birth in patients at high risk for recurrent preterm delivery.

Tocolytic agents

Criteria that indicate consideration of tocolytic therapy include more than 6 contractions per hour resulting in a demonstrated cervical change or presumed prior cervical change (transvaginal cervical length < 25 mm, >50% cervical effacement, or cervical dilation ≥20 mm).

If contractions are present without cervical change, management options include continued observation or therapeutic sleep for the patient (e.g., morphine sulphate 10-15 mg subcutaneous).

Types of Tocolytic Agents:

Magnesium sulfate (MgSO4): Widely used as the primary tocolytic agent because it has similar efficacy to terbutaline (one of the previous agents of choice), with far better tolerance
Indomethacin: An appropriate first line tocolytic for early preterm labor (< 30 wks.) or preterm labor associated with polyhydramnios
Nifedipine: Despite its unlabelled status, several randomized studies have found nifedipine to be associated with a more frequent successful prolongation of pregnancy than other tocolytics

Glucocorticoids

The administration of glucocorticoids is recommended in the absence of clinical infection whenever the gestational age is between 24 and 34 weeks.

An attempt should be made to delay delivery for a minimum of 12 hours to obtain clinical benefits of antenatal steroids.

The recommended dosage of betamethasone consists of two 12 mg doses 24 hours apart while four doses of 6 mg of dexamethasone should be administered at 6-hour intervals.

Delivery of the preterm infant involves several unique issues:

Avoidance of excessive trauma, caution in the use of vacuum prior to 34 weeks’ gestation, risk of breech head entrapment, etc.) to optimize new-born well-being.
The American College of Obstetricians and Gynecologists has endorsed a policy of delayed cord clamping in both term and preterm new-borns as this practice increases new-born hemoglobin and, in preterm infants reduces rates of intraventricular hemorrhage, necrotizing enterocolitis and required transfusions.
Specifically, ACOG recommends a delay in umbilical cord clamping in vigorous term and preterm infants for at least 30–60 seconds after birth, though care must be individualized and provided only to infants not requiring immediate resuscitation.

Mid-trimester loss (es) due cervical incompetence:

A history of prior mid-trimester losses is carefully reviewed at the initial visit to distinguish incompetent cervix from other causes (e.g., abruption, infection, intrauterine death, ruptured membranes) with review of the pathology or autopsy reports if available.

Parental karyotypes are generally not helpful unless more than one mid-trimester loss has occurred, or a mid-trimester loss has occurred in which the fetus was structurally or genetically abnormal.

A preconceptual hysterosalpingogram may be of benefit in patients with a history of 2 or more mid-trimester losses. One can also attempt to pass a No. 8 Hegar’s dilator into the nonpregnant cervix; easy passage may be a sign of cervical incompetence. During pregnancy, whenever the suspicion of incompetent cervix exists, one should consider performing baseline transvaginal ultrasonography to assess cervical length, especially at 13-17 weeks’ gestation; abnormal findings include a length less than 2.5 cm, funnelling greater than 5 mm, or dynamic changes.

A cerclage may be indicated after 2 or more mid-trimester losses consistent with incompetent cervix or in which the etiology is unknown, and the transvaginal ultrasonography of the cervix is abnormal. A cerclage is usually performed electively at 13-17 weeks’ gestation.

Respiratory Distress Syndrome

Intraventricular Hemorrhage

Sepsis

Necrotizing Enterocolitis

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