Preterm Birth versus Low Birth Weight

• Preterm birth or prematurity and low birth weight were often interchanged in the past. Preterm birth describes length of gestation (i.e., less than 37 weeks 0 days regardless of the weight of the infant), whereas low birth weight describes only weight at the time of birth.

• Preterm birth is a more dangerous health condition for an infant because less time in the uterus correlates with immaturity of body systems. Low-birth-weight babies can be, but are not necessarily, preterm.

• Low birth weight can be caused by conditions other than preterm birth, such as intrauterine growth restriction (IUGR), a condition of inadequate fetal growth not necessarily correlated with initiation of labor. Pregnant women who have various complications of pregnancy that interfere with uteroplacental perfusion, such as gestational hypertension or poor nutrition, may give birth to a baby at term who is low birth weight because of IUGR. Infants born at a preterm gestation can weigh more than 2500 g at birth.

• Birth weight as a substitute for gestational age in developed countries is no longer considered acceptable.

Predicting Spontaneous Preterm Labor and Birth

Risk Factors

In addition to the risk factors already listed:

• Social determinants, such as living in a disadvantaged neighborhood, state, or region

• Lack of access to prenatal care

• Risk for preterm birth also appears to be genetically related

Diagnosis

The following should be considered when diagnosing preterm labor:

• Gestational age between 20 weeks 0 days and 36 weeks 6 days

• Regular uterine activity, accompanied by a change in cervical effacement, dilation, or both

• Initial presentation with regular contractions and cervical dilation of at least 2 cm

• Presence of fFN may be used as another diagnostic criterion

• A pregnant woman at 30 weeks of gestation with an irritable uterus but no documented cervical change is not in preterm labor.

• Cervical Length:  One possible predictor of preterm labor is endocervical length. Cervical measurement can identify women in whom the labor process has begun. Women whose cervical length as measured by transvaginal ultrasound is greater than 30 mm in the second and third trimesters of pregnancy are unlikely to give birth prematurely even if they have symptoms of preterm labor.

• Fetal Fibronectin Test:  Fetal fibronectin (fFN) is the glycoprotein “glue” found in plasma and produced during fetal life. It normally appears in cervical and vaginal secretions early in pregnancy and then again in late pregnancy. The fFN test is performed by collecting fluid from the woman’s vagina using a swab during a speculum examination. The presence of fFN during the late second and early third trimesters of pregnancy may be related to placental inflammation, which is thought to be one cause of spontaneous preterm labor.

Client Education

Onset of preterm labor is often insidious and can be easily mistaken for normal discomforts of pregnancy, thus client education is crucial.

All pregnant women should be taught the symptoms of preterm labor:

• Symptoms of uterine contractions

• Pain

• Vaginal discharge occurring between 20 weeks 0 days and 36 weeks 6 days of gestation

Prevention

Prevention methods include:

• Programs aimed at health promotion and disease prevention

• Preconception counseling

• Smoking cessation

• Prevention can be achieved in some women by administering prophylactic progesterone supplementation: Supplementation begins at 16 weeks and continues until 36 weeks of gestation; it does not affect the rate of preterm birth in women with multiple gestations.

Early Recognition

Preterm birth is often not preventable. Early recognition of preterm labor is essential to implement interventions that have been demonstrated to reduce neonatal and infant morbidity and mortality.

Signs and Symptoms

Signs and symptoms of preterm labor include:

• Change in type of vaginal discharge (watery, mucus, or bloody)

• Increase in amount of vaginal discharge

• Pelvic or lower abdominal pressure

• Constant low, dull backache

• Mild abdominal cramps, with or without diarrhea

• Regular or frequent contractions or uterine tightening, often painless

• Ruptured membranes

Interventions

Interventions include:

• Transferring the mother before birth to a hospital equipped to care for her preterm infant

• Administering antibiotics during labor to prevent neonatal group B streptococci infection

• Administering antenatal glucocorticoids (e.g., betamethasone, dexamethasone) to women at risk for preterm birth to prevent or reduce neonatal and infant morbidity and mortality from health problems, which include respiratory distress syndrome, intraventricular hemorrhage, and necrotizing enterocolitis

• Administering magnesium sulfate to women giving birth before 32 weeks of gestation to reduce the incidence of cerebral palsy in their infants

• Transporting pregnant women in preterm labor to a tertiary or quaternary care facility

• Lifestyle Modifications:  The following lifestyle modifications should be considered:

• Activity restriction: bedrest, hydration, and limited work

• Restriction of sexual activity: pelvic rest

Promotion of Fetal Lung Maturity

• Antenatal glucocorticoids

  • • 1. Betamethasone: 12 mg intramuscular (IM) for two doses 24 hours apart

      2. Dexamethasone: 6 mg IM for four doses 12 hours apart

  • Given as IM injections to the mother to accelerate fetal lung maturity by stimulating fetal surfactant production

  • Significantly reduce the incidence of:

    • Respiratory distress syndrome

    • Intraventricular hemorrhage

    • Necrotizing enterocolitis

    • Death in neonates

• All women between 24 and 34 weeks of gestation who are at risk for preterm birth should receive treatment with a single course of antenatal glucocorticoids.

• 48 hours from the time of the first injection are required for the fetus to receive optimal benefit.

Management of Inevitable Preterm Birth

When preterm birth appears inevitable (i.e., is expected to occur within the next 24 hours), magnesium sulfate may be administered to reduce or prevent neonatal neurologic morbidity (e.g., cerebral palsy).

Magnesium sulfate for neuroprotection should be given to women who are at least 24 but less than 32 weeks of gestation at the time birth is expected to occur.