Heather has taught reproductive biology and has researched neuro, repro and endocrinology. She has a PhD in Zoology/Biology.
Causes of Premature Labor
Well, by now I'm sure many, if not all, of you know that under normal conditions, it takes 9 months for a baby to develop inside its mother's uterus. At the end of 9 months, when the baby is fully developed, it triggers the process known as labor.
Now, true labor is when contractions of the uterus begin at the top of the mother's uterus and sweep down toward the cervix, forcing the baby out of the uterus and through the birth canal, resulting in delivery of the baby. This is not to be confused with false labor - when the uterus contracts but the contractions aren't regular and don't propel the baby towards the birth canal.
But, what happens if labor is triggered before the 9 months is up? Is the baby fully developed? Does it survive if it leaves the mother's womb before it is fully developed? What might trigger this process of early labor, and what are some of the consequences?
The answers to these questions often depend on how early the baby is born. So first, let's take a look at what might trigger early labor.
Causes of premature labor vary widely and oftentimes cannot be pinpointed. However, there are many factors during pregnancy that are known to increase the chances of premature labor. Some of the more common factors include:
- Twins or multiple births: This increases the risk of premature labor because of growth restrictions within the uterus and the strain multiple births can place on the mother's body.
- Problems with the uterus or the cervix: These can be anatomical problems leading to an abnormal shape of the uterus or cervix that may prevent a woman from carrying her baby to full-term.
- Placental problems: If the placenta is not formed correctly, is not in the right place or comes detached from the uterine wall, it may cause blood loss and restrict the delivery of blood and nutrients to the baby, resulting in a premature birth.
- Previous premature births or having had a baby within the last 6 months can also increase the chances, as can previous miscarriages or abortions.
While the above factors may not be preventable, some risk factors are, such as:
- Being under- or overweight
- Smoking, drinking or drug use
- Poor nutrition
These are just some of the lifestyle choices that can be changed to help prevent premature births.
Immature vs. Premature Babies
But, even though some premature births can be prevented, others cannot. So, let's take a look at the two different types of early births. What separates early, or premature, labor from really early, or immature, labor?
Premature labor is when true labor occurs before the fetus has completed normal development. Any baby born more than three weeks before his or her due date can be considered a premature baby. However, this definition seems kind of general, doesn't it? It can encompass labor that occurs at any time during pregnancy, right?
So, doctors came up with another term, one that separates babies born prematurely and that are likely to survive from those that are born really, really early and are not likely to survive. These babies are considered to be immature babies, and they have a very low chance of survival.
The earlier a baby is born, the less it will weigh and the more likely it is to have severe health problems. Since the chances of a premature baby surviving can be linked directly to its weight at the time of birth, the dividing line between premature birth and immature birth is based on the weight of the baby.
So, let's break it down by weight vs. chances of survival.
Babies that are born at 8.5-9 months of development usually weigh between 6-8lbs (or between 3-4kg). These babies have the highest chance of survival, almost 100%, if development proceeded normally. This is because all of their tissue and organ systems have developed and are ready to function in the world outside the mother's womb.
Now, on the other end of the spectrum. If the newborn weighs under 400g (or 14oz) at the time of birth, there is almost zero chance that they will survive. This is because most of the organ systems needed for survival have not yet completed development and therefore cannot function normally outside the mother.
Okay, so what about all the spaces in between?
Well, let's look at babies that weigh around 600g (or 21.1oz) when born. These babies straddle the line of survival. Some survive, but most will not, and so in general, they tend to have a low chance of survival. While the tissues and organ systems at this stage are not as underdeveloped as a baby born at 400g or less, they are still not yet fully developed, and many babies will have difficulty surviving outside the mother - even with intensive neonatal care.
Those that do survive often show signs of long-term developmental abnormalities, such as breathing and respiratory issues; visual, hearing and digestive problems; and bleeding in the brain, as well as a higher chance of intellectual disabilities and cerebral palsy (a disorder of muscle movement).
However, because babies around this stage do have a chance of survival, doctors have placed the dividing line between premature births and immature births (which are also called spontaneous abortions) at 500g of body weight.
So, what babies have a good chance of survival, then? Well, any baby born between 28 and 36 weeks, while still considered to be premature, actually has a good chance of survival. These babies usually weigh in somewhere between 1-2.5kg, depending on how early they are born.
Common Problems in Preemies
Once they pass that 27-week mark, they have about an 80% chance of survival! But, that doesn't mean complications can't occur. Remember, the earlier the baby is born, the higher the chance of health problems. So, even though a baby born at 27 weeks and a baby born at 36 weeks both have a good chance of survival, the baby born at 27 weeks does have a higher chance of health problems.
Most of the time, complications associated with this stage of premature birth are short-term and go away as the baby gets older. These might include:
- Breathing problems (as the lungs adjust to air): During normal development, the last trimester includes the production of a substance called surfactant. Surfactant allows the lungs to expand and fill with air easily. Premature babies that lack surfactant can show signs of respiratory distress syndrome. This is characterized by difficulty breathing because the lungs can't take in enough oxygen. With time, however, the baby's lungs will begin to make surfactant on their own and the breathing problems will disappear.
- Heart problems: Most often this includes low blood pressure - and sometimes a hole between two of the major vessels leaving the heart. If not watched, this can cause heart failure; however, given enough time, the problem usually corrects itself as the baby continues to develop.
- Premature babies will also exhibit difficulty controlling their temperature due to their low weight and lack of fat tissue.
- They often show signs of digestion or metabolism problems, such as a weakened intestinal wall and hypoglycemia because they cannot store sugar as well as a full-term baby would.
- Other problems can be due to their blood, such as infant anemia (a low red blood cell count) or infant jaundice (another problem associated with the blood).
- Their underdeveloped immune systems can lead to an increased chance of infection.
While most of these complications of premature babies are short-term, there is always the chance for long-term health problems, such as asthma due to immature lung development at the time of birth or learning and behavioral problems. The brain continues to develop throughout childhood, and premature babies may show signs of slower language, coordination or abstract thinking problem skills. The behavioral issues associated with premature babies may be due to their early birth, but it may also be due to the environment in which they are raised. Mothers are often more overprotective of preemies, and this can lead to less discipline. Over time, this may result in a need for attention, difficulty following rules or instructions, temper or emotional issues and other problems.
Remember, not all premature babies will have problems, but they do have a higher chance of health problems compared to full-term babies. About 12-13% of all babies in the United States are born prematurely. That may sound like a low number to you, but it actually amounts to around half a million premature babies in the U.S. each year!
Let's take a quick moment to review what we learned today. First, any birth occurring before the fetus has completed normal development can be termed a premature birth. However, if this birth occurs before the baby has reached the weight of 500g, it is then called an immature birth, and the baby often has little or no chance of survival.
Some of the risk factors that can increase chances of premature or immature births cannot be controlled, such as multiple births, abnormalities of the uterus or cervix or placental problems.
However, there are many risk factors that mothers can actively try to decrease or prevent. These include:
- Smoking, drinking and drug use during pregnancy
- Poor diet and nutrition
- Being overweight prior to and during pregnancy
- Excessive stress during pregnancy
One of the biggest factors determining if a premature or immature baby will live is its weight at the time of delivery. The older the baby, the more it will weigh and the higher its chances are for survival are.
Babies born before week 19 of gestation usually weigh 400g or less. Unfortunately, these babies have little or no chance of survival. Those born after the dividing line of 500g have higher chances of survival.
If they're born around 600g, they still have a low chance of survival, but they do have a chance. Babies who survive at this weight, though, often have a higher risk of long-term health issues.
If the baby is born later, around 6-7 months, they usually weigh between 1-2.5kg and have a good chance of survival, and most complications are usually short-term.
And remember, any baby born before week 36 of gestation is considered to be premature - or immature, depending on how early they are born - while those born after week 36 are considered full-term. These babies have the highest chance of survival with little to no complications.
Following this lesson, you will be able to:
- Distinguish between true labor and false labor
- Describe both preventable and non-preventable factors that can lead to premature births
- Differentiate between immature births and premature births and explain why there is a difference
- Explain some of the common health problems found in babies born prematurely
- Understand the relationship between birth weight and how likely it is that a premature baby will survive
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