Pregnancies last a long time in my family.
My mother had four babies, each born two or more weeks after the expected 40 week duration.
The first of my two children were born at 41 and 42 weeks respectively. Number three arrived at 39 weeks.
Under ideal conditions, the end-point of pregnancy occurs when the fetus has reached its optimal size and is mature enough for life outside the womb. In uncomplicated pregnancies, this usually means the longer inside the better.
In twin pregnancies, where two babies compete for resources in the womb, the situation is not so simple. If a pregnancy manages to last beyond about 38 weeks, weight gain in babies can slow or even go backwards due to limitations of physical space and the diminishing capacity of the placenta (or placentas) to deliver nutrients.
A 2012 study from Adelaide obstetrician and researcher Jodie Dodd suggests that delivery of twins at 37 weeks – before they reach this ‘going backwards’ point in pregnancy – may offer health benefits to the babies.
Here’s a Science Story I wrote for the Robinson Institute on Jodie’s research.
[image thanks to miss pupik on flickr]