Preterm Infants and Gestational Age

Babies born alive before 37 weeks of pregnancy are completed.

A full-term pregnancy typically lasts 40 weeks, but it's considered within the normal range between 37 to 42 weeks.

A preterm infant is typically defined as a baby born before the completion of the 37th week of gestation.

Gestational age assessment helps determine how far along a pregnancy was when the baby was born. It helps identify whether it was preterm, full-term, or post-term.

Ballard scoring, sole creases, skull firmness, ear cartilage, neurologic development, mother's last menstrual period, and sonographic estimation are all used to determine gestational age.

Newborns undergo an evaluation at birth to determine their weight, height, head circumference, and gestational age. This helps identify immediate healthcare needs and possible future problems.

Preterm birth occurs in about 11% of births globally, with the US having one of the highest rates.

Preterm infants require intensive care from birth due to their vulnerability to hypoglycemia, intracranial hemorrhage, and Respiratory Distress Syndrome (RDS).

Preterm infants have limited glycogen and fat stores, making them more prone to hypoglycemia.

Preterm infants have underdeveloped blood vessels, making them fragile.

Preterm infants lack lung surfactant, which is usually developed by the 34th week of pregnancy.

Approximately 90% of all live births fall within the normal growth category.

Term neonates are babies born after the beginning of week 38 and before week 42 of pregnancy.

Preterm births are categorized as either early preterm (24-34 weeks) or late preterm (34-37 weeks).

Preterm infants are further categorized into sub-categories based on their gestational age: moderate premature (<37 weeks), extremely premature (<32 weeks), very premature (<28 weeks), and late preterm.

Non-preterm infants are categorized as: early term (37-38 6/7 weeks), full term (39-40 6/7 weeks), late term (41-41 6/7 weeks), and post-term (≥42 weeks).

The exact cause of premature labor and early birth is often unknown.

Premature rupture of membranes can precede premature labor and delivery, but the underlying cause is often unknown.

Gestational age is a significant factor in determining neonatal death rates. Premature babies are more vulnerable to complications.

Preterm infant death accounts for 80-90% of infant mortality within the first year of life.

Reducing preterm birth rates would significantly decrease infant mortality.

Even though there are possible causes of preterm birth, the exact reason is often unknown.

Elective preterm delivery is recommended by the American College of Obstetricians and Gynecologists (ACOG) in cases of multiple gestation with complications, preeclampsia, placenta previa, placenta accreta, or premature rupture of membranes.

ACOG recommends elective preterm delivery as early as 32 weeks in multiple gestation cases with complications. Quasi-elective delivery (almost but it depends) before 32 weeks is evaluated on a case-by-case basis to handle severe maternal or fetal complications.

Spontaneous preterm delivery can occur with or without an obvious immediate trigger, such as infections like intra-amniotic infection, infectious disease during pregnancy, or placental abruption.

Toxoplasmosis is a parasitic infection that can cause miscarriage and stillbirth.

Chorioamnionitis is an infection of the placenta and amniotic fluid.

Prior premature births, prior multiple pregnancies, and prior multiple abortions are all considered risk factors for preterm birth.

Pregnancy achieved through artificial insemination or in-vitro fertilization, younger or older maternal age, cigarette smoking, poor nutrition during gestation, untreated infections, and limited or no prenatal care are all considered risk factors for preterm birth.

Race (people of color have a higher incidence than white people), order of birth (highest in first pregnancy and those fourth and beyond), closely spaced pregnancies, abnormalities of the birthing parent's reproductive system like intrauterine septum, pregnancy complications like PROM, early induction of labor, elective cesarean section, cervical insufficiency, preeclampsia, certain congenital defects, placental abruption, and certain congenital defects such as acyanotic or cyanotic heart defects are all considered risk factors for preterm birth.

Low socioeconomic status and mothers with less education are associated with a higher risk of preterm birth, but it's unclear how much these factors contribute independently or alongside other factors.

The skin may appear unusually ruddy and translucent, with thin, pink skin and easily visible veins. There may be little subcutaneous fat and a high degree of acrocyanosis.

The head may appear disproportionately large, with a circumference 3 cm greater than the chest size.

Preterm infants at 28 weeks of gestation may have extensive lanugo covering the back, forearms, forehead, and sides of the face, and may have vernix caseosa covering their bodies.

The extremities of a preterm infant may not be held in a flexed position. The fontanelles, especially the posterior fontanelle, may be small in late preterm infants.

A preterm infant at 28 weeks gestation may have a small amount of ear cartilage or a flattened pinna, while a term infant has well-developed cartilage with instant recoil.

The ears of a preterm infant may appear large in relation to the head, and the cartilage is immature, causing the pinna to fall forward. The level of the ears should be inspected for chromosomal abnormalities.

A preterm infant at 28 weeks gestational age may have a flat sole, while at 33 weeks, there may be an anterior crease, and a term infant has multiple creases.

The scrotum of a preterm infant may have few rugae (ridges). Undescended testes may need repair to prevent sterility (ORCHIOPEXY) if still present until 6 years old.

Preterm infants may have a weak pupillary reaction, making ophthalmoscopic examinations difficult. They may have varying degrees of myopia due to lack of eye globe depth.

Muscle movements, sucking with coordinated swallowing and breathing, and deep tendon reflexes may be diminished in preterm infants.

Preterm infants may be less active than term neonates and cry less frequently, with weak and high-pitched cries.

Anemia of prematurity can occur in infants born less than 32 weeks, due to immaturity of the hematopoietic system, destruction of red blood cells (low vitamin E), and excessive blood drawing for tests.

Acute bilirubin encephalopathy can occur in preterm infants due to excessive breakdown of red blood cells, lower levels of serum albumin, and acidosis from poor respiratory exchange.

Persistent patent ductus arteriosus can occur in preterm infants due to lack of surfactant, which leads to difficulty moving blood from the pulmonary artery into the lungs.

Periventricular/intraventricular hemorrhage can occur in preterm infants due to fragile capillaries and immature cerebral vascular development, rapid changes in cerebral blood pressure, and capillary rupture.

Intraventricular hemorrhage (IVH) is classified into four grades based on the severity of the bleeding. Grade 1 is bleeding in the periventricular germinal matrix, Grade 2 is bleeding within the lateral ventricle, Grade 3 is bleeding causing dilatation of the ventricle, and Grade 4 is bleeding causing enlargement of the ventricles.

IVH occurs most often in very low birth weight (less than 1500 grams) infants. The germinal matrix, a transient, highly vascularized region in the fetal brain, matures at 32-34 weeks and becomes a watershed area after 34 weeks, making it more susceptible to IVH.

Ultrasonography is used to detect IVH in preterm infants. Cranial ultrasounds are usually scheduled 7 to 10 days after birth for babies born less than 32 weeks or weighing less than 1,500 gm, 3 days after birth for high-risk preterm infants.

The timing of cranial ultrasound for premature infants varies depending on their gestational age and risk factors. For babies born at less than 32 weeks or weighing less than 1,500 gm, ultrasounds are typically performed 7 to 10 days after birth. High-risk preterm infants may have ultrasounds done 3 days after birth.

Baby Nathan, born at 30 weeks AOG weighing 1200gm and considered high-risk preterm, should have a cranial ultrasound within the first three days after birth.

Delaying cord clamping at birth allows more blood from the placenta to enter the newborn, helping to prevent anemia of prematurity.

Coordinating blood draws to minimize the amount drawn and keeping a record of blood loss can help prevent anemia of prematurity.

Phototherapy can be used to help break down bilirubin levels in the bloodstream, preventing acute bilirubin encephalopathy.

Exchange transfusion can be used to remove bilirubin from the blood and replace it with fresh blood, preventing acute bilirubin encephalopathy.

Administer intravenous therapy cautiously to preterm infants to prevent increasing blood pressure, which could worsen patent ductus arteriosus.

Monitor urine output and observe for bleeding, especially at injection sites, when administering medications like indomethacin or ibuprofen to preterm infants to manage patent ductus arteriosus.

Cranial ultrasounds are performed routinely in preterm infants to detect IVH. Regular monitoring based on gestational age helps track the progression of IVH.