Premature Births and Associated Complications

Lesson Transcript
Instructor: Heather Adewale

Heather has taught reproductive biology and has researched neuro, repro and endocrinology. She has a PhD in Zoology/Biology.

What classifies a baby as premature? If they are born premature, how likely is it that they will survive? Learn about this and more in this lesson on the risks and complications of premature birth.

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.

Blood loss or restriction due to a placental abruption is one possible factor of premature labor.
Risk factor of premature birth

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
  • Stress
  • Smoking, drinking or drug use
  • Poor nutrition

These are just some of the lifestyle choices that can be changed to help prevent premature births.

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  • 0:06 Causes of Premature Labor
  • 2:59 Immature vs. Premature Babies
  • 7:04 Common Problems in Preemies
  • 10:09 Lesson Summary
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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 less a baby weighs at birth, the more likely it is to have health problems.
Lower weight and premature birth

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

Babies born at less than 27 weeks have a decreased chance of survival.
Early births

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:

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