The length of pregnancy is very important which is why so much attention is given to the due date and accurate dating of pregnancy. 

Pregnancy usually lasts about 280 days from the date of a woman’s last menstrual period.  This time gives the baby the best chances to grow and mature and be ready to survive outside of the mother’s womb.  We often talk about pregnancy as lasting 9 calendar months, but it is actually a little longer, about 40 weeks.  However, since babies can be born at any time, there are different terms used to describe the timing of deliveries.   

• Term means that the baby is born between 37 and 42 weeks, and unless there are medical reasons to deliver earlier, the best time for a baby to be born is about 40 weeks

Preterm means the baby is delivered after 20 weeks but before 37 weeks of gestation (3 or more weeks before the due date).  Premature which means the baby is born before it has had time to fully develop or mature, is often used interchangeably with preterm birth even though they are slightly different.  The earlier a baby is born, the greater the chance that they will have serious health problems or not survive.

• Preterm means that the baby is born after 20 weeks but before 37 weeks

Late preterm birth happens when a baby is born between 34 and 36 weeks.  Even a few weeks before term, the baby’s major organs including the brain have usually not had enough time to mature, which can put the newborn at risk for serious health problems.

• Late preterm means that the baby is born between 34 and 36 weeks, which is still too early unless there are medical complications

Sometimes pregnancy can last too long; this is referred to as post term. A post term pregnancy can cause serious problems for both the baby and mother.  When this happens it may be necessary to help the baby be born by trying to start (induce) labor.  Some physicians become concerned if a pregnancy lasts more than 41 weeks and will begin antepartum testing or induce labor at that point.

• Post term means that the baby is born after 42 weeks

For more information on this topic, download:
The Facts About Preterm Birth    
The Problem with Late Preterm Birth   
The Costs of Preterm Birth

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