Tuesday, June 7, 2011

Preterm birth

In humans preterm birth refers to the birth of a baby of less than 37 weeks gestational age. The cause for preterm birth is in many situations elusive and unknown; many factors appear to be associated with the development of preterm birth, making the reduction of preterm birth a challenging proposition.
Premature infants are at greater risk for short and long term complications, including disabilities and impediments in growth and mental development.
In humans whereas the usual definition of preterm birth is birth before 37 weeks gestation, a "premature" infant is one that has not yet reached the level of fetal development that generally allows life outside the womb. In the normal human fetus, several organ systems mature between 34 and 37 weeks, and the fetus reaches adequate maturity by the end of this period. One of the main organs greatly affected by premature birth is the lungs. The lungs are one of the last organs to develop in the womb; because of this, premature babies typically spend the first days/weeks of their life on a ventilator. Prematurity can be reduced to a small extent by using drugs to accelerate maturation of the fetus, and to a greater extent by preventing preterm birth.
Symptoms of imminent spontaneous preterm birth, are signs of premature labor; one sign is four or more uterine contractions in one hour, accompanied by cervical dilatation and effacement. Also, vaginal bleeding in the third trimester, heavy pressure in the pelvis, or abdominal or back pain could be indicators that a preterm birth is about to occur. A watery discharge from the vagina may indicate premature rupture of the membranes that surround the baby.
Preterm-premature babies ("preemies" or "premmies") 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). Prematurely born infants are also at greater risk for having subsequent serious chronic health problems. A large study on children born between 22 and 25 weeks who were currently at school age found that 46 percent had severe or moderate disabilities such as cerebral palsy, vision or hearing loss and learning problems. 34 percent were mildly disabled and 20 percent had no disabilities, while 12 percent had disabling cerebral palsy.
A number of factors have been identified that are linked to a higher risk of a preterm birth: age at the upper and lower end of the reproductive years, be it more than 35 or less than 18 years of age. Maternal height and weight can also play a role. Pregnancy interval makes a difference as women with a 6 months span or less between pregnancies have a two-fold increase in preterm birth. Studies on type of work and physical activity have given conflicting results, but it is opined that stressful conditions, hard labor, and long hours are probably linked to preterm birth. Women who have undergone previous surgically induced abortions have been shown to have a higher risk of preterm birth. Adequate maternal nutrition is important. Women with a low BMI are at increased risk for preterm birth. Further, women with poor nutritional status may also be deficient in vitamins and minerals. Adequate nutrition is critical for fetal development and a diet low in saturated fat and cholesterol may help reduce the risk of a preterm delivery. Obesity does not directly lead to preterm birth; however, it is associated with diabetes and hypertension which are risk factors by themselves. Women with vaginal bleeding during pregnancy are at higher risk for preterm birth. While bleeding in the third trimester may be a sign of placenta previa or placental abruption – conditions that occur frequently preterm – even earlier bleeding that is not caused by these two conditions is linked to a higher preterm birth rate. Women with abnormal amounts of amniotic fluid, too much (polyhydramnios) or too little (oligohydramnios) are also at risk. The mental status of the women is of significance. Anxiety and depression have been linked to preterm birth. Finally, the use of tobacco, cocaine, and excessive alcohol during pregnancy also increases the chance of preterm delivery. Babies with birth defects are at higher risk of being born preterm.
Obstetric ultrasound has become useful in the assessment of the cervix in women at risk for premature delivery. A short cervix preterm is undesirable: At 24 weeks gestation a cervix length of less than 25 mm defines a risk group for preterm birth. Further, the shorter the cervix the greater the risk. It also has been helpful to use ultrasonography in women with preterm contractions, as those whose cervix length exceeds 30 mm are unlikely to deliver within the next week.
Interventions that should have been initiated prior to pregnancy, can still be instituted during pregnancy including nutritional adjustments, use of vitamin supplements, and smoking cessation. Calcium supplementation as well as supplemental intake of C and E vitamins could not be shown to reduce preterm birth rates. Self-care methods to reduce the risk of preterm birth include proper nutrition, avoiding stress, seeking appropriate medical care, avoiding infections, 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).
Anti-contraction medications (tocolytics), such as Beta2-agonist drugs (ritodrine, terbutaline, fenoterol), calcium-channel blockers nifedipine and oxytocin antagonists (atosiban) appear only to have a temporary effect in delaying delivery. However, just gaining 48 hours is sufficient to allow the pregnant women to be transferred to a center specialized for management of preterm deliveries and give administered corticosteroids the possibility to reduce neonatal organ immaturity.
Neonatal care
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. Bili lights may also be used to treat newborn jaundice (hyperbilirubinemia).
Many children will adjust well during childhood and adolescence, although a large study that followed children born between 22 and 25 weeks found some alarming results. As survival has improved, the focus of interventions directed at the newborn has shifted to reduce long-term disabilities, particularly those related to brain injury. Some of the complications related to prematurity may not be apparent until years after the birth. A long-term study demonstrated that the risks of medical and social disabilities extend into adulthood and are higher with decreasing gestational age at birth and include cerebral palsy, mental retardation, disorders of psychological development, behavior, and emotion, disabilities of vision and hearing, and epilepsy. People born prematurely may be more susceptible to developing depression as teenagers.
Notable preterm births
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 pound 6 ounces (624 g). He survived and is quite healthy.
Amillia Taylor is also often cited as the most-premature baby. She was born on 24 October 2006 in Miami, Florida, at 21 weeks and6 days gestation. This report has created some confusion as her gestation was measured from the date of conception (through in-vitro fertilization) rather than the date of her mother's last menstrual period making her appear 2 weeks younger than if gestation was calculated by the more common method. At birth, she was 9 inches (22.86 cm) long and weighed 10 ounces (283 grams). She suffered digestive and respiratory problems, together with a brain hemorrhage.
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 (24.13 cm) long. This record was broken in September 2004 by Rumaisa Rahman, who was born in the same hospital 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 requiring 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 to1.18 kg (2.6 lb). Generally healthy, the twins had to undergo laser eye surgery to correct vision problems, a common occurrence among premature babies.
The autistic savant Derek Paravicini was born at 25 weeks. The oxygen therapy given during his time in a neonatal intensive care unit rendered him blind and affected his developing brain, resulting in his severe learning disability. Furthermore Paravicini developed autism. However, he also has absolute pitch and his musical abilities developed to genius levels.
The world's smallest premature boy to survive was born in February 2009 at Children's Hospitals and Clinics of Minnesota in Minneapolis, Minnesota. Jonathon Whitehill was born at 25 weeks gestation with a weight of 310 grams (10.9 ounces). He was hospitalized in the Neonatal Intensive Care Unit for five months, and then discharged.
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).
The most difficult decisions are about whether or not to resuscitate a newborn baby or admit him or her to neonatal intensive care. And then whether or not to withdraw intensive care and give the child palliative care. The gestational age at which a child is born plays a key part in these decisions.
22 weeks: in the UK and France babies are not normally resuscitated.
23 weeks: in Holland babies are not normally resuscitated at this age or below.
24 weeks: in most countries babies at this gestation are resuscitated.