‘Term’ and dates
Prolonged pregnancy means a pregnancy that has extended beyond 42 weeks of gestation. This is counting from the onset of her last menstrual period, unless adjustment has been made following an ultrasound scan within the first 20 weeks of pregnancy.
Prolonged pregnancy, ‘post-term’ and ‘post-mature’ mean exactly the same thing.
‘Post-dates’ has a different meaning and is less significant.
If ‘post-term’ refers to the period beyond forty-two weeks of gestation, what is ‘Term’?
It is very important to be clear that ‘Term’ does not refer to a fixed point on the calendar. In fact, ‘term’ refers to the five week period from thirty-seven weeks to forty-two completed weeks of gestation.
Over 80 per cent of women deliver within this period and their babies are physiologically mature. The date that is given as the "Expected Date of Delivery" (EDD) is a 40 week mark which is within this period. It has no sanctity of any kind.
Frankly speaking, this is only a reference point within the ‘Term’ period. It is a point to focus on for both the mother and the attending midwife or doctor. The baby can arrive any day around the EDD. It could be three weeks before or two weeks after, and this will be of no consequence. It will still be term.
Only a tiny minority of babies arrive spontaneously on the calculated EDD. When. someone last bothered to check what proportion of women actually deliver on the so-called expected date, they came up with a figure of 6%; that is, less than one in sixteen. This study actually included those induced and those who had elective Caesarean sections. Most studies have actually shown much lower figures (in the region of 1%) representing only those going into spontaneous labour.
Is there any reason to panic if pregnancy continues beyond the EDD: that is, the 40 weeks mark?
Absolutely not. If the pregnancy is categorised as low-risk or minimal risk, there is absolutely no reason to panic. Of course, a midwife or doctor will have followed up the progress of the pregnancy to ensure that it remains low-risk. If there have been any factors or developments which move the pregnancy out of that category to moderate- or high-risk status, then advice will be given accordingly. This could take the form of early delivery.
What proportion of pregnancies become prolonged, i.e. continue beyond 42 weeks?
Without intervention, about 3-10% of all pregnancies will reach the 42 weeks mark.
Causes of prolonged pregnancy: Next Page