Preterm birth
Preterm birth, also known as premature birth, is the birth of a baby at fewer than 37 weeks gestational age, as opposed to full-term delivery at approximately 40 weeks. Extreme preterm is less than 28 weeks, very early preterm birth is between 28 and 32 weeks, early preterm birth occurs between 32 and 34 weeks, late preterm birth is between 34 and 36 weeks' gestation. These babies are also known as premature babies or colloquially preemies or premmies. Symptoms of preterm labor include uterine contractions which occur more often than every ten minutes and/or the leaking of fluid from the vagina before 37 weeks. Premature infants are at greater risk for cerebral palsy, delays in development, hearing problems and problems with their vision. The earlier a baby is born, the greater these risks will be.
The cause of spontaneous preterm birth is often not known. Risk factors include diabetes, high blood pressure, multiple gestation, being either obese or underweight, vaginal infections, air pollution exposure, tobacco smoking, and psychological stress. For a healthy pregnancy, medical induction of labor or cesarean section are not recommended before 39 weeks unless required for other medical reasons. There may be certain medical reasons for early delivery such as preeclampsia.
Preterm birth may be prevented in those at risk if the hormone progesterone is taken during pregnancy. Evidence does not support the usefulness of bed rest to prevent preterm labor. Of the approximately 900,000 preterm deaths globally in 2019, it is estimated that at least 75% of these preterm infants would have survived with appropriate cost-effective treatment, and the survival rate is highest among the infants born the latest in gestation. In women who might deliver between 24 and 37 weeks, corticosteroid treatment may improve outcomes. A number of medications, including nifedipine, may delay delivery so that a mother can be moved to where more medical care is available and the corticosteroids have a greater chance to work. Once the baby is born, care includes keeping the baby warm through skin-to-skin contact or incubation, supporting breastfeeding and/or formula feeding, treating infections, and supporting breathing. Preterm babies sometimes require intubation.
Preterm birth is the most common cause of death among infants worldwide. About 15 million babies are preterm each year. Late preterm birth accounts for 75% of all preterm births. This rate is inconsistent across countries. In the United Kingdom 7.9% of babies are born pre-term and in the United States 12.3% of all births are before 37 weeks gestation. Approximately 0.5% of births are extremely early periviable births, and these account for most of the deaths. In many countries, rates of premature births have increased between the 1990s and 2010s. Complications from preterm births resulted globally in 0.81 million deaths in 2015, down from 1.57 million in 1990. The chance of survival at 22 weeks is about 6%, while at 23 weeks it is 26%, 24 weeks 55% and 25 weeks about 72%. The chances of survival without any long-term difficulties are lower.
Signs and symptoms
Signs and symptoms of preterm labor include four or more uterine contractions in one hour. In contrast to false labour, true labor is accompanied by cervical dilation 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. While the rupture of the membranes may not be followed by labor, usually delivery is indicated as infection is a serious threat to both fetus and mother. In some cases, the cervix dilates prematurely without pain or perceived contractions, so that the mother may not have warning signs until very late in the birthing process.Causes
Preterm labor can be caused by medical conditions including infections, environmental or drug exposures, cervix insufficiency, uterine abnormalities, or amniotic fluid problems. Some women require preterm labor induction for medical conditions. Other preterm births are spontaneous. In some cases, preterm labor occurs spontaneously and there is no identifiable cause. There are maternal and pregnancy-related risk factors that increase the risk of a woman experiencing preterm labor.Risk factors of preterm labor
The exact cause of spontaneous preterm birth is difficult to determine and it may be caused by many different factors at the same time as labor is a complex process. The research available is limited with regard to the cervix and therefore is limited in discerning what is or is not normal. Four different pathways have been identified that can result in preterm birth and have considerable evidence: precocious fetal endocrine activation, uterine overdistension, decidual bleeding, and intrauterine inflammation or infection.Identifying women at high risk of giving birth early would enable the health services to provide specialized care for these women and their babies, for example a hospital with a special care baby unit such as a neonatal intensive care unit. In some instances, it may be possible to delay the birth. Risk scoring systems have been suggested as an approach to identify those at higher risk; however, there is no strong research in this area so it is unclear whether the use of risk scoring systems for identifying mothers would prolong pregnancy and reduce the numbers of preterm births or not.
Maternal factors
Risk factors in the mother have been identified that are linked to a higher risk of a preterm birth. These include age, high or low body mass index, length of time between pregnancies, endometriosis, previous spontaneous or surgical abortions, unintended pregnancies, untreated or undiagnosed celiac disease, fertility difficulties, heat exposure, and genetic variables.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. Obesity does not directly lead to preterm birth; however, it is associated with diabetes and hypertension which are risk factors by themselves. To some degree those individuals may have underlying conditions that persist. Couples who have tried more than one year versus those who have tried less than one year before achieving a spontaneous conception have an adjusted odds ratio of 1.35 of preterm birth. Pregnancies after IVF confers a greater risk of preterm birth than spontaneous conceptions after more than one year of trying, with an adjusted odds ratio of 1.55.
Certain ethnicities may have a higher risk as well. For example, in the U.S. and the UK, Black women have preterm birth rates of 15–18%, more than double than that of the white population. Many Black women have higher preterm birth rates due to multiple factors but the most common is high amounts of chronic stress, which can eventually lead to premature birth. Adult chronic disease is not always the case with premature birth in Black women, which makes the main factor of premature birth challenging to identify. Filipinos are also at high risk of premature birth, and it is believed that nearly 11–15% of Filipinos born in the U.S. are premature. Filipinos being a big risk factor is evidenced with the Philippines being the eighth-highest ranking in the world for preterm births, the only non-African country in the top 10. This discrepancy is not seen in comparison to other Asian groups or Hispanic immigrants and remains unexplained. Genetic make-up is a factor in the causality of preterm birth. Genetics has been a big factor into why Filipinos have a high risk of premature birth as the Filipinos have a large prevalence of mutations that help them be predisposed to premature births. An intra- and transgenerational increase in the risk of preterm delivery has been demonstrated. No single gene has been identified.
Marital status has long been associated with risks for preterm birth. A 2005 study of 25,373 pregnancies in Finland revealed that unmarried mothers had more preterm deliveries than married mothers. Pregnancy outside of marriage was associated overall with a 20% increase in total adverse outcomes, even at a time when Finland provided free maternity care. A study in Quebec of 720,586 births from 1990 to 1997 revealed less risk of preterm birth for infants with legally married mothers compared with those with common-law wed or unwed parents. A study conducted in Malaysia in 2015 showed a similar trend, with marital status being significantly associated with preterm birth. However, the result of a study conducted in the US showed that between 1989 and 2006, marriage became less protective of preterm births which was attributed to the changing social norms and behaviors surrounding marriage.
Factors during pregnancy
Medications during pregnancy, living conditions, air pollution, smoking, illicit drugs or alcohol, infection, or physical trauma may also cause a preterm birth.Air pollution: Living in an area with a high concentration of air pollution is a major risk factor for preterm labor, including living near major roadways or highways where vehicle emissions are high from traffic congestion or are a route for diesel trucks that tend to emit more pollution.
The use of fertility medication that stimulates the ovary to release multiple eggs and of IVF with embryo transfer of multiple embryos has been implicated as a risk factor for preterm birth. Often labor has to be induced for medical reasons; such conditions include high blood pressure, pre-eclampsia, maternal diabetes, asthma, thyroid disease, and heart disease.
Certain medical conditions in the pregnant mother may also increase the risk of preterm birth. Some women have anatomical problems that prevent the baby from being carried to term. These include a weak or short cervix. 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 conditions is linked to a higher preterm birth rate. Women with abnormal amounts of amniotic fluid, whether too much or too little, are also at risk. Anxiety and depression have been linked as risk factors for preterm birth.
The use of tobacco, cocaine, and excessive alcohol during pregnancy increases the chance of preterm delivery. Tobacco is the most commonly used drug during pregnancy and contributes significantly to low birth weight delivery. Babies with birth defects are at higher risk of being born preterm.
Passive smoking and/or smoking before the pregnancy influences the probability of a preterm birth. The World Health Organization published an international study in March 2014.
Presence of anti-thyroid antibodies is associated with an increased risk preterm birth with an odds ratio of 1.9 and 95% confidence interval of 1.1–3.5.
Intimate violence against the mother is another risk factor for preterm birth.
Physical trauma may case a preterm birth. The Nigerian cultural method of abdominal massage has been shown to result in 19% preterm birth among women in Nigeria, plus many other adverse outcomes for the mother and baby. This ought not be confused with massage therapy conducted by a fully trained and certified/licensed massage therapist or by significant others trained to provide massage during pregnancy, which—in a study involving pregnant females with prenatal depression—has been shown to have numerous positive results during pregnancy, including the reduction of preterm birth, less depression, lower cortisol, and reduced anxiety. In healthy women, however, no effects have been demonstrated in a controlled study.