Premature birth

Premature birth (also known as preterm birth) is the birth of a baby before the standard period of pregnancy is completed. In most systems of human pregnancy, prematurity is considered to occur when the baby is born sooner than 37 weeks after the beginning of the last menstrual period (LMP). The opposite condition, postmature birth, is defined as birth more than 42 weeks after the LMP.

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Overview

The standard length of a human gestation is 266 days. However, for convenience most timing is based on the LMP, with conception being assumed to occur approximately 14 days after the LMP, making a standard term pregnancy 280 days or 40 weeks. Premature or preterm birth is defined medically as childbirth occurring earlier than 37 completed weeks of pregnancy. Approximately 12 percent of babies in the United States — or 1 in 8 — are born prematurely each year.^[1] In 2003, more than 490,000 babies in the U.S. were born prematurely. Worldwide rates of prematurity are more difficult to obtain as the lack of widespread professional obstetric care in developing regions makes determination of gestational age less reliable. The World Health Organization instead tracks rates of low birth weight, which occurred in 16.5 percent of births in less developed regions in 2000.^[2] It is estimated that one-third of these low birth weight deliveries are due to premature delivery.

The shorter the term of pregnancy, the greater the risks of complications. Infants born prematurely have an increased risk of death in the first year of life (infant mortality), with most of that occurring in the first month of life (neonatal mortality). Worldwide, prematurity accounts for 10% of neonatal mortality, or around 500,000 deaths per year.^[3] In the U.S. where many infections and other causes of neonatal death have been markedly reduced, prematurity is the leading cause of neonatal mortality at 25%.^[4] Prematurely born infants are also at greater risk for developing serious health problems such as cerebral palsy, chronic lung disease, gastrointestinal problems, mental retardation, vision or hearing loss^[5] and are more susceptible to developing depression as teenagers.^[6]

Although there are several known risk factors for prematurity (see below), nearly half of all premature births have no known cause. When conditions permit, doctors may attempt to stop premature labor, so that the pregnancy can have a chance to continue to full term, thereby increasing the baby's chances of health and survival. However, there is currently no reliable means to stop or prevent preterm labor in all cases. In fact, the rate of preterm births in the United States has increased 30% in the past two decades.^[7]

In developed countries premature infants are usually cared for in a Neonatal Intensive Care Unit (NICU). The physicians who specialize in the care of very sick or premature babies are known as neonatologists. In the NICU, premature babies are kept under radiant warmers or in incubators (also called isolettes), which are bassinets enclosed in plastic with climate control equipment designed to keep them warm and limit their exposure to germs. Modern neonatal intensive care involves sophisticated measurement of temperature, respiration, cardiac function, oxygenation, and brain activity. Treatments may include fluids and nutrition through intravenous catheters, oxygen supplementation, mechanical ventilation support, and medications. In developing countries where advanced equipment and even electricity may not be available or reliable, simple measures such as kangaroo care (skin to skin warming), encouraging breastfeeding, and basic infection control measures can significantly reduce preterm morbidity and mortality.

Factors

There are many different factors which may contribute to a preterm birth.

Factors related to maternal disease or condition that have been shown to increase the risk of preterm birth, with associated odds ratio (OR) when known include:

• high blood pressure (OR = 4.06)^[8]

• pre-eclampsia (OR = 4.0)^[9]

• age > 35 (OR = 1.8) ^[10]

• age < 18 (OR = 3.4) ^[10]

• short cervix ^[8] (the strongest predictor of premature birth)^[11][12][13]

• maternal diabetes ^[14]

• anxiety ^[15]

• periodontal disease (OR = 4.45%)^[16]

Whether or not urinary tract infections directly cause preterm birth is uncertain, however, it is known that urinary tract infections increase pre-eclampsia which as stated above increases the risk of preterm birth. Sexually transmitted disease STD, Beta Strep, kidney disease, and uterine infections are also suspected of increasing the risk of preterm birth.

Adequate maternal nutrition is important to fetal development and a diet low in saturated fat and cholesterol may help reduce the risk of a preterm delivery. ^[17]

Factors related to pregnancy history that have been shown to increase the risk of preterm birth include:

• prior preterm delivery (OR = 2.79)
• prior induced abortion (OR = 1.6)
• antepartum hemorrhage / vaginal bleeding during labor
• prior miscarriage ^[8]

Multiple pregnancies (twins, triplets, etc.) are another significant factor in preterm birth. The March of Dimes Multicenter Prematurity and Prevention Study found that 54% of twins were delivered preterm vs. 9.6% of singleton births. ^[18]

Women who have tried to conceive for more than a year before getting pregnant are at a higher risk for premature birth. A recent study done by Dr. Olga Basso of the University of Aarhus in Denmark and Dr. Donna Baird of the U.S. National Institute of Environmental Health Sciences suggests that women who had difficulty conceiving were about 40 percent higher risk of preterm birth than those who had conceived easily.

Finally, the use of tobacco and alcohol during pregnancy also increases the chance of preterm delivery. Tobacco is the most commonly abused drug during pregnancy and also contributes significantly to low birth weight delivery.^{[19] [20]}

Prevention of preterm birth

Recent research has identified possible methods to prevent preterm birth, pre-eclampsia/eclampsia, premature rupture of membranes, and preterm labor.

These include self-care methods to reduce infections, nutritional and psychological interventions, and the control of preterm birth risk factors (e.g. working long hours while standing on feet, carbon monoxide exposure, domestic abuse, and other factors). Injection with a form of progesterone (17 alpha-hydroxyprogesterone caproate) although the safety of this treatment for the fetus has been questioned by the FDA and its expert panel due to an associated increase in miscarriage and fetal death^[21], the use of vaginal progesterone^[22][23] ,taking fish oil supplements, and self-monitoring vaginal PH followed by yogurt treatment or Clindamycin treatment if the PH was too high all seem to be effective at reducing the risk of preterm birth.^[24][25]

This research is quite new; however, doctors using these newer strategies have obtained preterm birth rates as low as 1 to 2%, compared to the 11 to 16% currently in the US.^{[citation needed]}

Symptoms and indications

The symptoms of an imminent premature birth include:

• Four or more uterine contractions in one hour, before 37 weeks' gestation.
• A watery discharge from the vagina which may indicate premature rupture of the membranes surrounding the baby.
• Pressure in the pelvis or the sensation that the baby has "dropped".
• Menstrual cramps or abdominal pain.
• Pain or rhythmic tightening in lower abdomen or back.
• Vaginal spotting or bleeding.

Maternal treatments

There are two tactics that can be used to deal with a potential premature birth: delay the arrival of birth as much as possible, or prepare the prospectively premature fetus for arrival. Both of these tactics may be used simultaneously.

Delaying the premature birth from occurring is typically the most favored option. This gives the fetus or fetuses as much time as possible to mature in the womb. There are a number of techniques that can be used to try to accomplish this. The first resort is usually complete bed rest. Maintaining a horizontal position reduces pressure on the cervix, which may allow it to stay lengthened longer, and avoiding unnecessary movement may reduce uterine irritation, which can lead to contractions. Likewise, proper nutrition and especially hydration are important: dehydration can lead to premature uterine contractions. In a hospital setting, a drug-free IV drip may be used to try to stop premature labor simply by improving the mother's hydration. Lastly, there are anti-contraction medications (tocolytics), such as ritodrine, fenoterol, nifedipine and atosiban, although these do not appear to have more than a short-term effect on delaying delivery.

Premature birth can not always be prevented. Severely premature infants may have underdeveloped lungs, because they are not yet producing their own surfactant. This can lead directly to Respiratory Distress Syndrome, also called hyaline membrane disease, in the neonate. To try to reduce the risk of this outcome, pregnant mothers with threatened premature delivery prior to 34 weeks are often administered at least one course of glucocorticoids, a steroid that crosses the placental barrier and stimulates growth in the lungs of the fetus. Typical glucocorticoids that would be administered in this context are betamethasone or dexamethasone, often when the fetus has reached viability at 23 weeks. In cases where premature birth is imminent, a second "rescue" course of steroids may be administered 12 to 24 hours before the anticipated birth. There is no research consensus on the efficacy and side-effects of a second course of steroids, but the consequences of RDS are so severe that a second course is often viewed as worth the risk.

Newborn complications

Premature infants show physical signs of their prematurity and may develop other problems as well. These include, but are not limited to, the following:

Neurologic

• Apnea of prematurity
• Hypoxic-ischemic encephalopathy (HIE)
• Intracranial hemorrhage
• Retinopathy of prematurity (ROP)
• Developmental disability

Cardiovascular

• Patent ductus arteriosus (PDA)

Respiratory

• Respiratory distress syndrome (RDS or IRDS)
• Chronic lung disease (previously called bronchopulmonary dysplasia or BPD)

Gastrointestinal / metabolic

• Hypoglycemia
• Feeding difficulties
• Rickets of prematurity
• Hypocalcemia
• Inguinal hernia
• Necrotizing enterocolitis (NEC)

Hematologic

• Anemia of prematurity
• Thrombocytopenia
• Hyperbilirubinemia (jaundice)

Infectious

• Sepsis
• Urinary tract infection ^[5]

The earliest gestational age at which the infant has at least a 50% chance of survival is referred to as the limit of viability^[6]. As NICU care has improved over the last 40 years, viability has reduced to approximately 24 weeks, although rare survivors have been documented as early as 21 weeks.[7] As risk of brain damage and developmental delay is significant at that threshold even if the infant survives, there are ethical controversies over the aggressiveness of the care rendered to such infants. The limit of viability has also become a factor in the abortion debate.

Some of the complications related to prematurity are not apparent until years after the birth. For example, children who were born prematurely (especially if born less than 1,500 grams) have a higher likelihood of having behavioral problems, delays in motor development, and difficulties in school. Specifically these problems can be described as being within the executive domain and have been speculated to arise due to decreased myelinization of the frontal lobes.^[26] Throughout life they are more likely to require services provided by physical therapists, occupational therapists, or speech therapists.

Treatment measures for a premature infant

The required care for premature infants differs greatly depending on the child's gestational age, birth weight, and overall maturity. Measures common among extremely premature infants include:

• Placing the infant in a warmer or isolette. Premature infants are easily susceptible to cold-stress or hypothermia and infection, and preventing these is a key priority.
• Infants under 32 weeks typically do not produce enough surfactant in their lungs to enable them to breathe on their own. In these cases, surfactant will be administered to assist them.
• A breathing tube may be inserted in the infant's trachea, and a ventilator and supplemental oxygen may be used.
• Adequate nutrition, via a feeding tube or, in extremely premature infants, intravenously. If a feeding tube is used, expressed breast milk from the mother or a breastmilk bank can be used, which lowers the risk of infections such as necrotizing enterocolitis.

Records

James Elgin Gill (born on 20 May 1987 in Ottawa, Canada) was the earliest premature baby in the world. He was 128 days premature (21 weeks and 5 days gestation) and weighed 1 lb. 6 oz. (624 g). He survived and is quite healthy.^[27][28]

Amillia Taylor is also often cited as the most-premature baby.^[29] She was born on 24 October 2006 in Miami, Florida, at 21 weeks and 6 days gestation.^[30] At birth she was 9 inches (23 cm) long and weighed 10 ounces (283 grams).^[29] She suffered digestive and respiratory problems, together with a brain hemorrhage. She was discharged from the Baptist Children's Hospital on 20 February 2007.^[29]

The record for the smallest premature baby to survive was held for some time by Madeline Mann, who was born at 26 weeks weighing 9.9 oz (280 g) and 9.5 inches (24 cm) long.^[31] This record was broken in September 2004 by Rumaisa Rahman, who was born in the same hospital^[32] at 25 weeks gestation. At birth she was eight inches (20 cm) long and weighed 244 grams (8.6 ounces). Her twin sister was also a small baby, weighing 563 grams (1 pound 4 ounces) at birth. During pregnancy their mother had suffered from pre-eclampsia, which causes dangerously high blood pressure putting the baby into distress and leading to birth by caesarean section. The larger twin left the hospital at the end of December, while the smaller remained there until 10 February, 2005 by which time her weight had increased to 1.18 kg (2 pounds 10 ounces).^[33] Generally healthy, the twins had to undergo laser eye surgery to correct visual problems, a common occurrence among premature babies.

Historical figures who were born prematurely include Johannes Kepler (born in 1571 at 7 months gestation), Isaac Newton (born in 1643, small enough to fit into a quart mug, according to his mother), Winston Churchill (born in 1874 at 7 months gestation), and Anna Pavlova (born in 1885 at 7 months gestation).^[34]

See also

• Macrophage-activation syndrome
• WalkAmerica an annual walking-for-charity event that has raised more than $1.7 billion since 1970 to prevent premature birth

References