References:
- Maternal & Child Health Nursing: Care of the childbearing & childrearing family, 8th Edition, ISBN 978-1-4963-4813-5, by JoAnne Silbert-Flagg and Adele Pillitteri (Ch. 21, Postterm Pregnancy)
- Maternal & Child Health Nursing: Care of the childbearing & childrearing family, 8th Edition, ISBN 978-1-4963-4813-5, by JoAnne Silbert-Flagg and Adele Pillitteri (Ch. 26, The Postterm Infant)
Term infants are those born after the beginning of week 38 and before week 42 of pregnancy (calculated from the first day of the last menstrual period). Approximately 90% of all live births fall into this category. Infants born before term (before the beginning of the 38th week of pregnancy) are classified as preterm infants regardless of their birth weight. Infants born after the end of week 41 of pregnancy are classified as postterm infants or postmature.
Preterm Pregnancy
A preterm infant is traditionally defined as a live-born infant born before the end of week 37 of gestation. In terms of the degree of care needed, they are further divided into late preterm (born between 34 and 37 weeks) and early preterm (born between 24 and 34 weeks). Preterm birth occurs in approximately 11% of live births worldwide, with the United States having one of the highest rates of preterm births. While many examples of possible causes have been documented, the exact cause of premature labor and early birth is rarely exactly known. Altogether, preterm births make up for at least 50% of all neonatal deaths.
Critical Care
Most preterm infants need intensive care from the moment of birth to give them their best chance of survival without neurologic aftereffects because they are more prone than others to hypoglycemia and intracranial hemorrhage. Lack of lung surfactant, because this does not form until about the 34th week of pregnancy, makes them extremely vulnerable to respiratory distress syndrome.
| Characteristic | Small-for-Gestational-Age Infant | Preterm Infant |
|---|---|---|
| Gestational Age | 24–44 weeks | <37 weeks |
| Birth Weight | <10th percentile | Normal for age |
| Congenital Malformations | Strong possibility | Possibility |
| Pulmonary Affectation | Meconium aspiration, pulmonary hemorrhage, pneumothorax | Respiratory distress syndrome |
| Hyperbilirubinemia | Possibility | Very strong possibility |
| Hypoglycemia | Very strong possibility | Possibility |
| Intracranial hemorrhage | Strong possibility | Possibility |
| Apnea episodes | Possibility | Very strong possibility |
| Feeding problems | Most likely because of accompanying problem such as hypoglycemia | Small stomach capacity; immature sucking reflex |
| Weight gain in nursery | Rapid | Slow |
| Future restricted growth | Possibly always be <10th percentile because of poor organ development | Not likely to be restricted in growth because “catch-up” growth occurs |
Assessment
The history of a pregnant woman is often normal up until the beginning of labor. If the woman’s history does involve potential risk factors for preterm pregnancy, the nurse should take not to prevent inducing guilt over what could have been. An accurate but comforting answer to a direct inquiry about why preterm birth occurs is, “No one really knows what causes prematurity.”
- The head appears disproportionately large (≥3 cm greater than chest size)
- The skin appears unusually ruddy because there is so little subcutaneous fat beneath it, making veins easily noticeable.
- A high degree of acrocyanosis may be present.
- Newborns delivered at 28 weeks are typically covered with vernix caseosa. In very preterm newborns (<28 weeks of gestation), however, the vernix will be lacking.
- Lanugo is usually scant the same way in very preterm newborns but will be extensive, covering the back, forearms, forehead, and sides of the face in late preterm babies.
- Both anterior and posterior fontanelles will be small.
- There are few or no creases on the soles of the feet.
- The eyes of most preterm infants appear small in relation to term infants. Although difficult to elicit, a pupillary reaction is present.
- The ears appear large in relation to the head. The cartilage of the ear is immature and allows the pinna to fall forward. The level of the ears should be carefully inspected to rule out chromosomal abnormalities.
- Neurologic function in the preterm infant is often difficult to evaluate because the neurologic system is still immature. Observing the infant make spontaneous or provoked muscle movements can be as important as formal reflex testing. If they are tested, reflexes such as sucking with coordinated swallowing and breathing will be absent if an infant’s age is below 33 weeks; deep tendon reflexes such as the Achilles tendon reflex will also be markedly diminished.
Postterm Pregnancy
A term pregnancy is 38 to 42 weeks long. A pregnancy that exceeds these limits is prolonged (i.e., postterm pregnancy, postmature, or postdate). The infant of such a pregnancy is considered postmature, or dysmature, if there is evidence that placental insufficiency has occurred and interfered with fetal growth. Postterm pregnancy occurs in 3% to 12% of all pregnancies.
Faulty due dates, such as in women with long menstrual cycles, may become considered "late"
In other instances, the pregnancy is truly overdue. For some reason, the trigger that initiates labor did not turn on. This includes (a) women receiving a high dose of salicylates that interferes with the synthesis of prostaglandins, which are theorized to be responsible for the initiation of labor; (b) myometrial quiescence, or a uterus that (for unknown reasons) does not respond to normal labor stimulation.
Remaining in utero for longer than 2 weeks beyond term creates a danger to the fetus for several reasons.
- Meconium aspiration and staining become more common as the fetal intestinal contents are more likely to reach the rectum.
- Macrosomia may occur if the fetus continues to grow, creating a growth problem.
- Inadequate growth or weight loss (postterm syndrome) occurs more often than macrosomia due to the stoppage of growth and withdrawal of nutrients by the 40th to 42nd week, the average limit of a placenta’s functioning ability. After this time, the placenta acquires calcium deposits that exposes a fetus to decreased blood perfusion and a lack of oxygen, fluid, and nutrients.
- Oligohydramnios can occur as decreased placental functioning decreases the fetal fluid supply. This can lead to variable decelerations in the FHR from cord compression.
Assessment
Postterm infants may be small for their gestational age (SGA) due to weight loss from placental insufficiency.
- They have dry, cracked, almost leatherlike skin from lack of fluid and an absence of vernix, like in SGA infants.
- Fingernails will have grown well beyond the end of the fingertips.
- They may demonstrate an alertness much more like a 2-week-old baby than a newborn.
- At birth, the postterm baby is likely to have difficulty establishing respirations, especially if meconium aspiration has occurred.
- Polycythemia may have developed from decreased oxygenation in the final weeks in utero. Hematocrit may be elevated because polycythemia and dehydration have lowered the circulating plasma level.
- In the first hours of life, hypoglycemia may develop because the fetus had to use stores of glycogen for nourishment in the last weeks of intrauterine life. Subcutaneous fat levels may also be low for the same reason. This loss of fat can make temperature regulation difficult, making it important to prevent a postterm infant from being chilled at birth or during transport.
Therapeutic Management
If labor has not begun by 41 weeks, a nonstress test, and/or a biophysical profile may be done to document the state of placental perfusion and the amount of amniotic fluid present. If these are normal, it suggests the due date was miscalculated. If the test results are abnormal or the physical examination or biparietal diameter measured on ultrasound suggests the fetus is term size, labor will be induced.
- Prostaglandin gel or misoprostol (Cytotec) applied to the vagina to initiate cervical ripening followed by an oxytocin infusion are common methods to begin labor.
- If oxytocin is ineffective, cesarean birth may be necessary.
Monitor the FHR closely during labor to be certain placental insufficiency is not occurring from aging of the placenta.